Daniel Chernoff | Albany Medical College (original) (raw)

Papers by Daniel Chernoff

Research paper thumbnail of Evaluation of electron beam CT coronary angiography in healthy subjects

American Journal of Roentgenology, Jul 1, 1997

This study evaluated the performance characteristics of electrocardiographically triggered, contr... more This study evaluated the performance characteristics of electrocardiographically triggered, contrast-enhanced electron beam CT (EBCT) in defining the coronary artery lumen in healthy subjects. SUBJECTS AND METHODS. The coronary arteries of I I healthy young men (mean age, 24 years old) were evaluated by contrast-enhanced EBCT. Measured parameters included degree of luminal enhancement, intravascular contrast-to-noise ratio, apparent luminal diameter, and length of continuously visualized lumen (1(X)-H threshold for diameter and length measurements). RESULTS. Aortic blood pool attenuation was 44 ± 5 H (mean ± SD) before and 27) ± 35 H after IV injection of contrast material. Contrast-to-noise ratios ranged from a high of 10.0 ± 2.6 in the proximal right coronary artery to a low of 3.2 ± 2.7 in the distal left circumflex artery. decreasing from proximal to distal within each vessel. Apparent luminal diameters were as follows: left main coronary artery, 4.5 ± 0.6 mm: left anterior descending artery. 3.7 ± 0.5 mmli: left circumflex artery, 2.9 ± 0.6 mm; and right coronary artery, 3.5 ± 0.5 ii ni. The mean lengths of visualized lumina were as follows: left main coronary artery, 10 ± 4 mm: left anterior descending artery, 65 ± 26 mm; left circumflex artery. 45 ± 20 mm: and right coronary artery. 58 ± 24 mm. CONCLUSION. EBCT angiography can reveal the lumen of long segments of the major coronary arteries.

Research paper thumbnail of Pancreatic pseudocyst and obstructive jaundice associated with transcaval penetration by a Bird's Nest vena cava filter

American Journal of Roentgenology, Jul 1, 1998

Research paper thumbnail of Coronary Angiography by EB-CT

Springer eBooks, May 3, 2006

Due to its high temporal resolution, EB-CT is well suited for cardiac imaging. Although the major... more Due to its high temporal resolution, EB-CT is well suited for cardiac imaging. Although the major cardiac application of EB-CT to date has been detection and quantification of coronary calcifications, studies have demonstrated that cardiac EB-CT in combination with intravenous injection of contrast agent permits imaging of the coronary vessel lumen and detection of coronary artery stenoses and occlusions. Results obtained for the left main and LAD coronary artery, as well as for venous bypass grafts, correlate well with conventional angiography, whereas motion artifacts and anatomic difficulties currently reduce the diagnostic value for the right and especially left circumflex coronary arteries. Even though improvements in scanner design and in the investigation protocol are warranted, clinical applications of the method (e.g., in the followup after coronary revascularization) seem possible. In the year 2000, cardiac-gated multislice CT has emerged as a very serious competitor for both EB-CT and MRI/MRA. The jury is still out as to which imaging modality will ultimately prevail. This topic continues to be hotly debated at many cardiac imaging meetings.

Research paper thumbnail of Common Carotid Artery Bifurcation: Evaluation with Spiral CT

To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery steno... more To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery stenosis, spiral CT images of 20 patients were compared with images obtained with conventional angiography (20 patients), ultrasound (US) (15 patients), and magnetic resonance (MR) angiography (six patients). The category of stenosis was determined for each internal carotid artery on the basis of the percentage of narrowing: mild = less than 30%, moderate = 30%-69%, and severe = 70%-99%. Occlusions were also noted. The degree of carotid stenosis determined with spiral CT correlated with that determined with conventional angiography in 92% of cases, with that determined with US in 97% of cases, and with that determined with MR angiography in 100% of cases. Calcifications and large ulcers were also well delineated. Spiral CT provided an accurate anatomic depiction of the carotid bifurcation, which could be helpful in preoperative evaluation. The major disadvantage of the technique was the need to postprocess data to remove veins, calcifications, and bone structures from the images.

Research paper thumbnail of Comparative Inhibition of Voltage-Gated Cation Channels by Local Anesthetics

Annals of the New York Academy of Sciences, Jun 1, 1991

Research paper thumbnail of Kinetic analysis of phasic inhibition of neuronal sodium currents by lidocaine and bupivacaine

Biophysical Journal, Jul 1, 1990

Phasic ("use-dependent") inhibition of sodium currents by the tertiary amine local anesthetics, l... more Phasic ("use-dependent") inhibition of sodium currents by the tertiary amine local anesthetics, lidocaine and bupivacaine, was observed in voltage-clamped node of Ranvier of the toad, Bufo marinus. Local anesthetics were assumed to inhibit sodium channels through occupation of a binding site with 1:1 stoichiometry. A three-parameter empirical model for state-dependent anesthetic binding to the Na channel is presented: this model includes two discrete parameters that represent the time integrals of binding and unbinding reactions during a depolarizing pulse, and one continuous parameter that represents the rate of unbinding of drug between pulses. The change in magnitude of peak sodium current during a train of depolarizing pulses to 0 mV was used as an assay of the extent of anesthetic binding at discrete intervals; estimates of model parameters were made by applying a nonlinear least-squares algorithm to the inhibition of currents obtained at two or more depolarizing pulse rates. Increasing the concentration of drug increased the rate of binding but had little or no effect on unbinding, as expected for a simple bimolecular reaction. The dependence of the model parameters on pulse duration was assessed for both drugs: as the duration of depolarizing pulses was increased, the fraction of channels binding drug during each pulse became significantly larger, whereas the fraction of occupied channels unbinding drug remained relatively constant. The rate of recovery from block between pulses was unaffected by pulse duration or magnitude. The separate contributions of open (0) and inactivated (I) channel binding of drug to the net increase in block per pulse were assessed at 0 mV: for lidocaine, the forward binding rate ko was 1.4 * 105 M-ls-1, k, was 2.4 * 104 M-1s-1; for bupivacaine, ko was 2.5-105 M-ls-1, k, was 4.4 * 104 M-ls-1. These binding rates were similar to those derived from time-dependent block of maintained Na currents in nodes where inactivation was incomplete due to treatment with chloramine-T. The dependence of model parameters on the potential between pulses (holding potential) was examined. All three parameters were found to be nearly independent of holding potential from-70 to-100 mV. These results are discussed with respect to established models of dynamic local anesthetic-Na channel interactions.

Research paper thumbnail of Membrane potential determination in large unilamellar vesicles with hexakis(2-methoxyisobutylisonitrile)technetium(I)

Biochimica Et Biophysica Acta - Biomembranes, Apr 1, 1993

The accumulation of the lipophilic cation hexakis (2-methoxyisobutylisonitrile)technetium (99mTc-... more The accumulation of the lipophilic cation hexakis (2-methoxyisobutylisonitrile)technetium (99mTc-MIBI) within large unilamellar vesicles made from egg phosphatidylcholine was examined as a function of time and membrane potential (Em). Equilibrium distribution occurred within minutes at 30°C. The transmembrane distribution of Tc-MIBI was measured at E m = 0 mV and at a series of negative membrane potentials. The distribution of Tc-MIBI was in close agreement with the Nernst equation for passive distribution of a permeant ion across a bilayer, permitting the membrane potential to be predicted from Tc-MIBI distribution. In this respect, Tc-MIBI behaves similarly to other radioprobes of membrane potential, but with unique properties including high specific activity (109 Ci/mol), rapid kinetics of distribution, low potential-independent binding, and short half-life (6.02 h). The results indicate a mechanism for tissue accumulation of Tc-MIBI in vivo that may in part account for its utility in clinical imaging of ischemic myocardium.

Research paper thumbnail of Asymptomatic functional popliteal artery entrapment: demonstration at MR imaging

Radiology, Apr 1, 1995

To determine if functional popliteal entrapment can occur in healthy subjects and to define the m... more To determine if functional popliteal entrapment can occur in healthy subjects and to define the mechanism of vascular compression. The right lower extremities were examined in 13 subjects (nine men 27-34 years of age, mean age 31 years; four women 29-44 years of age, mean age 34 years) with no symptoms of popliteal artery entrapment. Magnetic resonance (MR) and Doppler ultrasound images were obtained while the subjects were at rest and while they performed plantar flexion against resistance. Blood flow during plantar flexion ceased in nine of 13 subjects (69%) and was impaired in three of 13 (23%). MR images showed muscular compression of the popliteal artery at two levels: between the plantaris muscle and the medial head of the gastrocnemius muscle and between the plantaris and popliteus muscles. Functional impairment of popliteal arterial flow during plantar flexion occurs in subjects who have no symptoms of popliteal entrapment syndrome.

Research paper thumbnail of Kinetics of local anesthetic inhibition of neuronal sodium currents. pH and hydrophobicity dependence

Biophysical Journal, Jul 1, 1990

This study assesses the importance of local anesthetic charge and hydrophobicity in determining t... more This study assesses the importance of local anesthetic charge and hydrophobicity in determining the rates of binding to and dissociation from neuronal Na channels. Five amide-linked local anesthetics, paired either by similar PKa or hydrophobicity, were chosen for study: lidocaine, two tertiary amine lidocaine homologs, a neutral lidocaine homolog, and bupivacaine. Voltage-clamped nodes of Ranvier from the sciatic nerve of Bufo marinus were exposed to anesthetic externally, and use-dependent ("phasic") block of Na current was observed. Kinetic analysis of binding (blocking) rates was performed using a three parameter, piecewise-exponential binding model. Changes in extracellular pH (pH.) were used to assess the role of drug protonation in determining the rate of onset of, and recovery from, phasic block. For those drugs with pKa's in the range of pHo tested (6.2-10.4), the forward binding rate during a depolarizing pulse increased at higher pH, consistent with an increase in either intracellular or intramembrane concentration of drug. The rate for unbinding during depolarization was independent of pHo. The dissociation rate between pulses also increased at higher pHo. The pHo dependence of the dissociation rate was not consistent with a model in which the cation is trapped relentlessly within a closed channel. Quantitative estimates of dissociation rates show that the cationic form of lidocaine dissociates at a rate of 0.1 s-1 (at 130C); for neutral lidocaine, the dissociation rate is 7.0 s-1. Furthermore, the apparent PKa of bound local anesthetic was found to be close to the PKa in aqueous solution, but different than the PKa for '"free" local anesthetic accessible to the depolarized channel.

Research paper thumbnail of Three-dimensional imaging and displayof renal tumors using spiral CT a potential aid to partial nephrectomy

Urology, 1994

Objective. A new technique for creating three-dimensional (3D) images of renal tumors using contr... more Objective. A new technique for creating three-dimensional (3D) images of renal tumors using contrast-enhanced spiral computed tomography (CT) is described and preliminarily investigated. Methods. 3D spiral CT was employed in 2 patients before radical nephrectomy and in 5 patients before partial nephrectomy. Preoperative and postoperative image analyses were conducted to evaluate the ability of the images to depict key anatomic relationships in planning partial nephrectomies. Results. 3D spiral CT defined the tumor's location and relationship to the kidney surface better than the tumor's proximity to renal hilar vessels and collecting system. Negative surgical margins were obtained in all 4 patients with renal cell carcinoma, and postoperative serum creatinine remained less than 2 mg/dL in all 5 patients after partial nephrectomy. Conclusions. This early experience suggests that 3D spiral CT can help in the planning of partial nephrectomy and in attaining complete resection of renal cell carcinoma while conserving normal renal tissue.

Research paper thumbnail of Detection of extracapsular extension of prostate carcinoma with endorectal and phased-array coil MR imaging: multivariate feature analysis

Radiology, Mar 1, 1997

To determine which magnetic resonance (MR) imaging features are most predictive of extracapsular ... more To determine which magnetic resonance (MR) imaging features are most predictive of extracapsular extension of prostate carcinoma. In 77 patients who had stage pT2 or pT3 prostate carcinoma, MR images were retrospectively reviewed by three readers with varying experience in interpretation of endorectal coil images of the prostate gland. MR imaging features assessed were broad tumor contact, smooth capsular bulge, irregular bulge, obliteration of the rectoprostatic angle, and asymmetry of the neurovascular bundle. Multivariate logistic regression analysis was performed to determine the relative value of each MR imaging feature. At multivariate analysis, obliteration of the rectoprostatic angle and asymmetry of the neurovascular bundle were most predictive of extracapsular extension, with a specificity of up to 95% and sensitivity of 38%. Poor-quality images reduced accuracy for all readers. The most experienced reader demonstrated overall accuracy of 77% in determination of extracapsular extension. Obliteration of the rectoprostatic angle and asymmetry of the neurovascular bundle were most indicative of extracapsular extension. Reader experience plays an important role in the ability to interpret prostate MR images and is an important contributor to interobserver variability.

Research paper thumbnail of Tonic and phasic block of neuronal sodium currents by 5-hydroxyhexano-2',6'-xylide, a neutral lidocaine homologue

The Journal of General Physiology, Jun 1, 1989

The effects of a neutral lidocaine homologue, 5-hydroxyhexano-2',6'xylidide (5-HHX), on the kinet... more The effects of a neutral lidocaine homologue, 5-hydroxyhexano-2',6'xylidide (5-HHX), on the kinetics and amplitude of sodium currents in voltageclamped amphibian nerve fibers are described. 5-HHX produced two types of sodium current inhibition: (a) tonic block, in resting fibers (ICs0 ~ 2 raM), and (b) phasic block, an additional, incremental inhibition, in repetitively depolarized fibers (frequency > 1 Hz). The kinetics of phasic block were characterized by a single-receptor, switcbed-affinity model, in which binding increases during a depolarizing pulse and decreases between pulses. In the presence of 4 mM 5-HHX, binding increased during pulses from-80 to 0 mV, with an apparent rate constant of 6.4 • 1.4 s-~. Binding decreased between pulses with an apparent rate constant of 1.1 + 0.3 s-~. There was little effect of extracellular pH on the kinetics of phasic block. These findings demonstrate that neither the presence of a terminal amine nor a net charge on a local anesthetic is required for phasic block of sodium channels.

Research paper thumbnail of Measurement of collateral blood flow in a porcine model of aortic coarctation by velocity-encoded cine MRI

Journal of Magnetic Resonance Imaging, May 1, 1997

The purpose of this study was to investigate the time course of development of collateral blood f... more The purpose of this study was to investigate the time course of development of collateral blood flow in an animal model of aortic coarctation. A juxtaductal aortic stenosis (model coarctation) was surgically created in five juvenile pigs. MRI was performed preoperatively, 1 to 2 days postoperatively, and 2 to 10 weeks postoperatively. Aortic blood flow was measured by velocity-encoded cine MR (VENC-MR). The percent change in aortic blood flow (delta BF) from proximal to distal descending thoracic aorta was calculated, and a multiple-comparison paired t test used to assess changes in delta BF over time. Invasive flow measurements were obtained in one animal before sacrifice using an ultrasonic probe. delta BF preoperatively was -2 +/- 8% (mean +/- SE). delta BF increased to 32 +/- 7% (mean +/- SE, P = .022) 2 days postoperatively and 55 +/- 19% (P = .032) 2 to 8 weeks postoperatively. Invasive measurements were in qualitative agreement with the VENC-MR data. VENC-MR is an accurate noninvasive method of measuring collateral blood flow in aortic coarctation. Recruitment and development of collateral flow pathways occur rapidly in an animal model.

Research paper thumbnail of Coronary artery stenoses: assessment with contrast-enhanced electron-beam CT and axial reconstructions

Radiology, Jul 1, 1998

To evaluate the usefulness of electron-beam computed tomography (CT) for identification of corona... more To evaluate the usefulness of electron-beam computed tomography (CT) for identification of coronary artery stenoses. Coronary angiography and contrast material-enhanced, electrocardiographically triggered electron-beam CT of the heart were performed in 23 patients. With axial CT images and axial maximum intensity projection reconstructions, the coronary arteries were assessed by two observers blinded to the results of angiography. Cardiac motion artifact (unsharpness) precluded evaluation of the right coronary artery (RCA) in six subjects and the left circumflex coronary artery (LCX) in one patient. With the vessels degraded by motion artifact eliminated from analysis, overall sensitivity of electron-beam CT for hemodynamically significant stenoses was 88%, and specificity was 79%. In the left anterior descending coronary artery (LAD), sensitivity was 93% and specificity was 63%; in the LCX, sensitivity was 100% and specificity was 67%; and in the RCA, sensitivity was 67% and specificity was 77%. The presence of coronary artery calcification did not have an effect on sensitivity for stenoses, but it did decrease specificity. Electron-beam CT angiography can depict hemodynamically significant stenoses in the LAD and LCX with a sensitivity of more than 90%. The presence of coronary artery calcification resulted in decreased specificity but no appreciable change in sensitivity.

Research paper thumbnail of Common carotid artery bifurcation: evaluation with spiral CT. Work in progress

Radiology, Nov 1, 1992

To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery steno... more To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery stenosis, spiral CT images of 20 patients were compared with images obtained with conventional angiography (20 patients), ultrasound (US) (15 patients), and magnetic resonance (MR) angiography (six patients). The category of stenosis was determined for each internal carotid artery on the basis of the percentage of narrowing: mild = less than 30%, moderate = 30%-69%, and severe = 70%-99%. Occlusions were also noted. The degree of carotid stenosis determined with spiral CT correlated with that determined with conventional angiography in 92% of cases, with that determined with US in 97% of cases, and with that determined with MR angiography in 100% of cases. Calcifications and large ulcers were also well delineated. Spiral CT provided an accurate anatomic depiction of the carotid bifurcation, which could be helpful in preoperative evaluation. The major disadvantage of the technique was the need to postprocess data to remove veins, calcifications, and bone structures from the images.

Research paper thumbnail of Frequency analysis of catheter systems used for invasive blood pressure monitoring

Departmental Committee on Graduate Stu ents S1DSIRARlIFB 1U ACKNOWLEDGEMENT I am grateful for the... more Departmental Committee on Graduate Stu ents S1DSIRARlIFB 1U ACKNOWLEDGEMENT I am grateful for the guidance, support and surplus of enthusiasm which Mr. David Ellis supplied during the research and writing of this thesis. His help and criticisms were truly invaluable. Dr. Roger Mark provided perspective on the problem and aided in directing the focus of the research. I wish to thank the many people at Hewlett-Packard's Waltham Division who supplied ideas and moral support throughout this project.

Research paper thumbnail of Coronary artery stenoses: assessment with contrast-enhanced electron-beam CT and axial reconstructions

Radiology, 1998

To evaluate the usefulness of electron-beam computed tomography (CT) for identification of corona... more To evaluate the usefulness of electron-beam computed tomography (CT) for identification of coronary artery stenoses. Coronary angiography and contrast material-enhanced, electrocardiographically triggered electron-beam CT of the heart were performed in 23 patients. With axial CT images and axial maximum intensity projection reconstructions, the coronary arteries were assessed by two observers blinded to the results of angiography. Cardiac motion artifact (unsharpness) precluded evaluation of the right coronary artery (RCA) in six subjects and the left circumflex coronary artery (LCX) in one patient. With the vessels degraded by motion artifact eliminated from analysis, overall sensitivity of electron-beam CT for hemodynamically significant stenoses was 88%, and specificity was 79%. In the left anterior descending coronary artery (LAD), sensitivity was 93% and specificity was 63%; in the LCX, sensitivity was 100% and specificity was 67%; and in the RCA, sensitivity was 67% and specificity was 77%. The presence of coronary artery calcification did not have an effect on sensitivity for stenoses, but it did decrease specificity. Electron-beam CT angiography can depict hemodynamically significant stenoses in the LAD and LCX with a sensitivity of more than 90%. The presence of coronary artery calcification resulted in decreased specificity but no appreciable change in sensitivity.

Research paper thumbnail of Common carotid artery bifurcation: evaluation with spiral CT. Work in progress

Radiology, 1992

To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery steno... more To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery stenosis, spiral CT images of 20 patients were compared with images obtained with conventional angiography (20 patients), ultrasound (US) (15 patients), and magnetic resonance (MR) angiography (six patients). The category of stenosis was determined for each internal carotid artery on the basis of the percentage of narrowing: mild = less than 30%, moderate = 30%-69%, and severe = 70%-99%. Occlusions were also noted. The degree of carotid stenosis determined with spiral CT correlated with that determined with conventional angiography in 92% of cases, with that determined with US in 97% of cases, and with that determined with MR angiography in 100% of cases. Calcifications and large ulcers were also well delineated. Spiral CT provided an accurate anatomic depiction of the carotid bifurcation, which could be helpful in preoperative evaluation. The major disadvantage of the technique was the need to postprocess data to remove veins, calcifications, and bone structures from the images.

Research paper thumbnail of Stereoselective effects of local anesthetics reveal two sites of action on neuronal sodium channels

Regional Anesthesia & Pain Medicine, 1989

Research paper thumbnail of Asymptomatic functional popliteal artery entrapment: demonstration at MR imaging

Radiology, 1995

To determine if functional popliteal entrapment can occur in healthy subjects and to define the m... more To determine if functional popliteal entrapment can occur in healthy subjects and to define the mechanism of vascular compression. The right lower extremities were examined in 13 subjects (nine men 27-34 years of age, mean age 31 years; four women 29-44 years of age, mean age 34 years) with no symptoms of popliteal artery entrapment. Magnetic resonance (MR) and Doppler ultrasound images were obtained while the subjects were at rest and while they performed plantar flexion against resistance. Blood flow during plantar flexion ceased in nine of 13 subjects (69%) and was impaired in three of 13 (23%). MR images showed muscular compression of the popliteal artery at two levels: between the plantaris muscle and the medial head of the gastrocnemius muscle and between the plantaris and popliteus muscles. Functional impairment of popliteal arterial flow during plantar flexion occurs in subjects who have no symptoms of popliteal entrapment syndrome.

Research paper thumbnail of Evaluation of electron beam CT coronary angiography in healthy subjects

American Journal of Roentgenology, Jul 1, 1997

This study evaluated the performance characteristics of electrocardiographically triggered, contr... more This study evaluated the performance characteristics of electrocardiographically triggered, contrast-enhanced electron beam CT (EBCT) in defining the coronary artery lumen in healthy subjects. SUBJECTS AND METHODS. The coronary arteries of I I healthy young men (mean age, 24 years old) were evaluated by contrast-enhanced EBCT. Measured parameters included degree of luminal enhancement, intravascular contrast-to-noise ratio, apparent luminal diameter, and length of continuously visualized lumen (1(X)-H threshold for diameter and length measurements). RESULTS. Aortic blood pool attenuation was 44 ± 5 H (mean ± SD) before and 27) ± 35 H after IV injection of contrast material. Contrast-to-noise ratios ranged from a high of 10.0 ± 2.6 in the proximal right coronary artery to a low of 3.2 ± 2.7 in the distal left circumflex artery. decreasing from proximal to distal within each vessel. Apparent luminal diameters were as follows: left main coronary artery, 4.5 ± 0.6 mm: left anterior descending artery. 3.7 ± 0.5 mmli: left circumflex artery, 2.9 ± 0.6 mm; and right coronary artery, 3.5 ± 0.5 ii ni. The mean lengths of visualized lumina were as follows: left main coronary artery, 10 ± 4 mm: left anterior descending artery, 65 ± 26 mm; left circumflex artery. 45 ± 20 mm: and right coronary artery. 58 ± 24 mm. CONCLUSION. EBCT angiography can reveal the lumen of long segments of the major coronary arteries.

Research paper thumbnail of Pancreatic pseudocyst and obstructive jaundice associated with transcaval penetration by a Bird's Nest vena cava filter

American Journal of Roentgenology, Jul 1, 1998

Research paper thumbnail of Coronary Angiography by EB-CT

Springer eBooks, May 3, 2006

Due to its high temporal resolution, EB-CT is well suited for cardiac imaging. Although the major... more Due to its high temporal resolution, EB-CT is well suited for cardiac imaging. Although the major cardiac application of EB-CT to date has been detection and quantification of coronary calcifications, studies have demonstrated that cardiac EB-CT in combination with intravenous injection of contrast agent permits imaging of the coronary vessel lumen and detection of coronary artery stenoses and occlusions. Results obtained for the left main and LAD coronary artery, as well as for venous bypass grafts, correlate well with conventional angiography, whereas motion artifacts and anatomic difficulties currently reduce the diagnostic value for the right and especially left circumflex coronary arteries. Even though improvements in scanner design and in the investigation protocol are warranted, clinical applications of the method (e.g., in the followup after coronary revascularization) seem possible. In the year 2000, cardiac-gated multislice CT has emerged as a very serious competitor for both EB-CT and MRI/MRA. The jury is still out as to which imaging modality will ultimately prevail. This topic continues to be hotly debated at many cardiac imaging meetings.

Research paper thumbnail of Common Carotid Artery Bifurcation: Evaluation with Spiral CT

To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery steno... more To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery stenosis, spiral CT images of 20 patients were compared with images obtained with conventional angiography (20 patients), ultrasound (US) (15 patients), and magnetic resonance (MR) angiography (six patients). The category of stenosis was determined for each internal carotid artery on the basis of the percentage of narrowing: mild = less than 30%, moderate = 30%-69%, and severe = 70%-99%. Occlusions were also noted. The degree of carotid stenosis determined with spiral CT correlated with that determined with conventional angiography in 92% of cases, with that determined with US in 97% of cases, and with that determined with MR angiography in 100% of cases. Calcifications and large ulcers were also well delineated. Spiral CT provided an accurate anatomic depiction of the carotid bifurcation, which could be helpful in preoperative evaluation. The major disadvantage of the technique was the need to postprocess data to remove veins, calcifications, and bone structures from the images.

Research paper thumbnail of Comparative Inhibition of Voltage-Gated Cation Channels by Local Anesthetics

Annals of the New York Academy of Sciences, Jun 1, 1991

Research paper thumbnail of Kinetic analysis of phasic inhibition of neuronal sodium currents by lidocaine and bupivacaine

Biophysical Journal, Jul 1, 1990

Phasic ("use-dependent") inhibition of sodium currents by the tertiary amine local anesthetics, l... more Phasic ("use-dependent") inhibition of sodium currents by the tertiary amine local anesthetics, lidocaine and bupivacaine, was observed in voltage-clamped node of Ranvier of the toad, Bufo marinus. Local anesthetics were assumed to inhibit sodium channels through occupation of a binding site with 1:1 stoichiometry. A three-parameter empirical model for state-dependent anesthetic binding to the Na channel is presented: this model includes two discrete parameters that represent the time integrals of binding and unbinding reactions during a depolarizing pulse, and one continuous parameter that represents the rate of unbinding of drug between pulses. The change in magnitude of peak sodium current during a train of depolarizing pulses to 0 mV was used as an assay of the extent of anesthetic binding at discrete intervals; estimates of model parameters were made by applying a nonlinear least-squares algorithm to the inhibition of currents obtained at two or more depolarizing pulse rates. Increasing the concentration of drug increased the rate of binding but had little or no effect on unbinding, as expected for a simple bimolecular reaction. The dependence of the model parameters on pulse duration was assessed for both drugs: as the duration of depolarizing pulses was increased, the fraction of channels binding drug during each pulse became significantly larger, whereas the fraction of occupied channels unbinding drug remained relatively constant. The rate of recovery from block between pulses was unaffected by pulse duration or magnitude. The separate contributions of open (0) and inactivated (I) channel binding of drug to the net increase in block per pulse were assessed at 0 mV: for lidocaine, the forward binding rate ko was 1.4 * 105 M-ls-1, k, was 2.4 * 104 M-1s-1; for bupivacaine, ko was 2.5-105 M-ls-1, k, was 4.4 * 104 M-ls-1. These binding rates were similar to those derived from time-dependent block of maintained Na currents in nodes where inactivation was incomplete due to treatment with chloramine-T. The dependence of model parameters on the potential between pulses (holding potential) was examined. All three parameters were found to be nearly independent of holding potential from-70 to-100 mV. These results are discussed with respect to established models of dynamic local anesthetic-Na channel interactions.

Research paper thumbnail of Membrane potential determination in large unilamellar vesicles with hexakis(2-methoxyisobutylisonitrile)technetium(I)

Biochimica Et Biophysica Acta - Biomembranes, Apr 1, 1993

The accumulation of the lipophilic cation hexakis (2-methoxyisobutylisonitrile)technetium (99mTc-... more The accumulation of the lipophilic cation hexakis (2-methoxyisobutylisonitrile)technetium (99mTc-MIBI) within large unilamellar vesicles made from egg phosphatidylcholine was examined as a function of time and membrane potential (Em). Equilibrium distribution occurred within minutes at 30°C. The transmembrane distribution of Tc-MIBI was measured at E m = 0 mV and at a series of negative membrane potentials. The distribution of Tc-MIBI was in close agreement with the Nernst equation for passive distribution of a permeant ion across a bilayer, permitting the membrane potential to be predicted from Tc-MIBI distribution. In this respect, Tc-MIBI behaves similarly to other radioprobes of membrane potential, but with unique properties including high specific activity (109 Ci/mol), rapid kinetics of distribution, low potential-independent binding, and short half-life (6.02 h). The results indicate a mechanism for tissue accumulation of Tc-MIBI in vivo that may in part account for its utility in clinical imaging of ischemic myocardium.

Research paper thumbnail of Asymptomatic functional popliteal artery entrapment: demonstration at MR imaging

Radiology, Apr 1, 1995

To determine if functional popliteal entrapment can occur in healthy subjects and to define the m... more To determine if functional popliteal entrapment can occur in healthy subjects and to define the mechanism of vascular compression. The right lower extremities were examined in 13 subjects (nine men 27-34 years of age, mean age 31 years; four women 29-44 years of age, mean age 34 years) with no symptoms of popliteal artery entrapment. Magnetic resonance (MR) and Doppler ultrasound images were obtained while the subjects were at rest and while they performed plantar flexion against resistance. Blood flow during plantar flexion ceased in nine of 13 subjects (69%) and was impaired in three of 13 (23%). MR images showed muscular compression of the popliteal artery at two levels: between the plantaris muscle and the medial head of the gastrocnemius muscle and between the plantaris and popliteus muscles. Functional impairment of popliteal arterial flow during plantar flexion occurs in subjects who have no symptoms of popliteal entrapment syndrome.

Research paper thumbnail of Kinetics of local anesthetic inhibition of neuronal sodium currents. pH and hydrophobicity dependence

Biophysical Journal, Jul 1, 1990

This study assesses the importance of local anesthetic charge and hydrophobicity in determining t... more This study assesses the importance of local anesthetic charge and hydrophobicity in determining the rates of binding to and dissociation from neuronal Na channels. Five amide-linked local anesthetics, paired either by similar PKa or hydrophobicity, were chosen for study: lidocaine, two tertiary amine lidocaine homologs, a neutral lidocaine homolog, and bupivacaine. Voltage-clamped nodes of Ranvier from the sciatic nerve of Bufo marinus were exposed to anesthetic externally, and use-dependent ("phasic") block of Na current was observed. Kinetic analysis of binding (blocking) rates was performed using a three parameter, piecewise-exponential binding model. Changes in extracellular pH (pH.) were used to assess the role of drug protonation in determining the rate of onset of, and recovery from, phasic block. For those drugs with pKa's in the range of pHo tested (6.2-10.4), the forward binding rate during a depolarizing pulse increased at higher pH, consistent with an increase in either intracellular or intramembrane concentration of drug. The rate for unbinding during depolarization was independent of pHo. The dissociation rate between pulses also increased at higher pHo. The pHo dependence of the dissociation rate was not consistent with a model in which the cation is trapped relentlessly within a closed channel. Quantitative estimates of dissociation rates show that the cationic form of lidocaine dissociates at a rate of 0.1 s-1 (at 130C); for neutral lidocaine, the dissociation rate is 7.0 s-1. Furthermore, the apparent PKa of bound local anesthetic was found to be close to the PKa in aqueous solution, but different than the PKa for '"free" local anesthetic accessible to the depolarized channel.

Research paper thumbnail of Three-dimensional imaging and displayof renal tumors using spiral CT a potential aid to partial nephrectomy

Urology, 1994

Objective. A new technique for creating three-dimensional (3D) images of renal tumors using contr... more Objective. A new technique for creating three-dimensional (3D) images of renal tumors using contrast-enhanced spiral computed tomography (CT) is described and preliminarily investigated. Methods. 3D spiral CT was employed in 2 patients before radical nephrectomy and in 5 patients before partial nephrectomy. Preoperative and postoperative image analyses were conducted to evaluate the ability of the images to depict key anatomic relationships in planning partial nephrectomies. Results. 3D spiral CT defined the tumor's location and relationship to the kidney surface better than the tumor's proximity to renal hilar vessels and collecting system. Negative surgical margins were obtained in all 4 patients with renal cell carcinoma, and postoperative serum creatinine remained less than 2 mg/dL in all 5 patients after partial nephrectomy. Conclusions. This early experience suggests that 3D spiral CT can help in the planning of partial nephrectomy and in attaining complete resection of renal cell carcinoma while conserving normal renal tissue.

Research paper thumbnail of Detection of extracapsular extension of prostate carcinoma with endorectal and phased-array coil MR imaging: multivariate feature analysis

Radiology, Mar 1, 1997

To determine which magnetic resonance (MR) imaging features are most predictive of extracapsular ... more To determine which magnetic resonance (MR) imaging features are most predictive of extracapsular extension of prostate carcinoma. In 77 patients who had stage pT2 or pT3 prostate carcinoma, MR images were retrospectively reviewed by three readers with varying experience in interpretation of endorectal coil images of the prostate gland. MR imaging features assessed were broad tumor contact, smooth capsular bulge, irregular bulge, obliteration of the rectoprostatic angle, and asymmetry of the neurovascular bundle. Multivariate logistic regression analysis was performed to determine the relative value of each MR imaging feature. At multivariate analysis, obliteration of the rectoprostatic angle and asymmetry of the neurovascular bundle were most predictive of extracapsular extension, with a specificity of up to 95% and sensitivity of 38%. Poor-quality images reduced accuracy for all readers. The most experienced reader demonstrated overall accuracy of 77% in determination of extracapsular extension. Obliteration of the rectoprostatic angle and asymmetry of the neurovascular bundle were most indicative of extracapsular extension. Reader experience plays an important role in the ability to interpret prostate MR images and is an important contributor to interobserver variability.

Research paper thumbnail of Tonic and phasic block of neuronal sodium currents by 5-hydroxyhexano-2',6'-xylide, a neutral lidocaine homologue

The Journal of General Physiology, Jun 1, 1989

The effects of a neutral lidocaine homologue, 5-hydroxyhexano-2',6'xylidide (5-HHX), on the kinet... more The effects of a neutral lidocaine homologue, 5-hydroxyhexano-2',6'xylidide (5-HHX), on the kinetics and amplitude of sodium currents in voltageclamped amphibian nerve fibers are described. 5-HHX produced two types of sodium current inhibition: (a) tonic block, in resting fibers (ICs0 ~ 2 raM), and (b) phasic block, an additional, incremental inhibition, in repetitively depolarized fibers (frequency > 1 Hz). The kinetics of phasic block were characterized by a single-receptor, switcbed-affinity model, in which binding increases during a depolarizing pulse and decreases between pulses. In the presence of 4 mM 5-HHX, binding increased during pulses from-80 to 0 mV, with an apparent rate constant of 6.4 • 1.4 s-~. Binding decreased between pulses with an apparent rate constant of 1.1 + 0.3 s-~. There was little effect of extracellular pH on the kinetics of phasic block. These findings demonstrate that neither the presence of a terminal amine nor a net charge on a local anesthetic is required for phasic block of sodium channels.

Research paper thumbnail of Measurement of collateral blood flow in a porcine model of aortic coarctation by velocity-encoded cine MRI

Journal of Magnetic Resonance Imaging, May 1, 1997

The purpose of this study was to investigate the time course of development of collateral blood f... more The purpose of this study was to investigate the time course of development of collateral blood flow in an animal model of aortic coarctation. A juxtaductal aortic stenosis (model coarctation) was surgically created in five juvenile pigs. MRI was performed preoperatively, 1 to 2 days postoperatively, and 2 to 10 weeks postoperatively. Aortic blood flow was measured by velocity-encoded cine MR (VENC-MR). The percent change in aortic blood flow (delta BF) from proximal to distal descending thoracic aorta was calculated, and a multiple-comparison paired t test used to assess changes in delta BF over time. Invasive flow measurements were obtained in one animal before sacrifice using an ultrasonic probe. delta BF preoperatively was -2 +/- 8% (mean +/- SE). delta BF increased to 32 +/- 7% (mean +/- SE, P = .022) 2 days postoperatively and 55 +/- 19% (P = .032) 2 to 8 weeks postoperatively. Invasive measurements were in qualitative agreement with the VENC-MR data. VENC-MR is an accurate noninvasive method of measuring collateral blood flow in aortic coarctation. Recruitment and development of collateral flow pathways occur rapidly in an animal model.

Research paper thumbnail of Coronary artery stenoses: assessment with contrast-enhanced electron-beam CT and axial reconstructions

Radiology, Jul 1, 1998

To evaluate the usefulness of electron-beam computed tomography (CT) for identification of corona... more To evaluate the usefulness of electron-beam computed tomography (CT) for identification of coronary artery stenoses. Coronary angiography and contrast material-enhanced, electrocardiographically triggered electron-beam CT of the heart were performed in 23 patients. With axial CT images and axial maximum intensity projection reconstructions, the coronary arteries were assessed by two observers blinded to the results of angiography. Cardiac motion artifact (unsharpness) precluded evaluation of the right coronary artery (RCA) in six subjects and the left circumflex coronary artery (LCX) in one patient. With the vessels degraded by motion artifact eliminated from analysis, overall sensitivity of electron-beam CT for hemodynamically significant stenoses was 88%, and specificity was 79%. In the left anterior descending coronary artery (LAD), sensitivity was 93% and specificity was 63%; in the LCX, sensitivity was 100% and specificity was 67%; and in the RCA, sensitivity was 67% and specificity was 77%. The presence of coronary artery calcification did not have an effect on sensitivity for stenoses, but it did decrease specificity. Electron-beam CT angiography can depict hemodynamically significant stenoses in the LAD and LCX with a sensitivity of more than 90%. The presence of coronary artery calcification resulted in decreased specificity but no appreciable change in sensitivity.

Research paper thumbnail of Common carotid artery bifurcation: evaluation with spiral CT. Work in progress

Radiology, Nov 1, 1992

To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery steno... more To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery stenosis, spiral CT images of 20 patients were compared with images obtained with conventional angiography (20 patients), ultrasound (US) (15 patients), and magnetic resonance (MR) angiography (six patients). The category of stenosis was determined for each internal carotid artery on the basis of the percentage of narrowing: mild = less than 30%, moderate = 30%-69%, and severe = 70%-99%. Occlusions were also noted. The degree of carotid stenosis determined with spiral CT correlated with that determined with conventional angiography in 92% of cases, with that determined with US in 97% of cases, and with that determined with MR angiography in 100% of cases. Calcifications and large ulcers were also well delineated. Spiral CT provided an accurate anatomic depiction of the carotid bifurcation, which could be helpful in preoperative evaluation. The major disadvantage of the technique was the need to postprocess data to remove veins, calcifications, and bone structures from the images.

Research paper thumbnail of Frequency analysis of catheter systems used for invasive blood pressure monitoring

Departmental Committee on Graduate Stu ents S1DSIRARlIFB 1U ACKNOWLEDGEMENT I am grateful for the... more Departmental Committee on Graduate Stu ents S1DSIRARlIFB 1U ACKNOWLEDGEMENT I am grateful for the guidance, support and surplus of enthusiasm which Mr. David Ellis supplied during the research and writing of this thesis. His help and criticisms were truly invaluable. Dr. Roger Mark provided perspective on the problem and aided in directing the focus of the research. I wish to thank the many people at Hewlett-Packard's Waltham Division who supplied ideas and moral support throughout this project.

Research paper thumbnail of Coronary artery stenoses: assessment with contrast-enhanced electron-beam CT and axial reconstructions

Radiology, 1998

To evaluate the usefulness of electron-beam computed tomography (CT) for identification of corona... more To evaluate the usefulness of electron-beam computed tomography (CT) for identification of coronary artery stenoses. Coronary angiography and contrast material-enhanced, electrocardiographically triggered electron-beam CT of the heart were performed in 23 patients. With axial CT images and axial maximum intensity projection reconstructions, the coronary arteries were assessed by two observers blinded to the results of angiography. Cardiac motion artifact (unsharpness) precluded evaluation of the right coronary artery (RCA) in six subjects and the left circumflex coronary artery (LCX) in one patient. With the vessels degraded by motion artifact eliminated from analysis, overall sensitivity of electron-beam CT for hemodynamically significant stenoses was 88%, and specificity was 79%. In the left anterior descending coronary artery (LAD), sensitivity was 93% and specificity was 63%; in the LCX, sensitivity was 100% and specificity was 67%; and in the RCA, sensitivity was 67% and specificity was 77%. The presence of coronary artery calcification did not have an effect on sensitivity for stenoses, but it did decrease specificity. Electron-beam CT angiography can depict hemodynamically significant stenoses in the LAD and LCX with a sensitivity of more than 90%. The presence of coronary artery calcification resulted in decreased specificity but no appreciable change in sensitivity.

Research paper thumbnail of Common carotid artery bifurcation: evaluation with spiral CT. Work in progress

Radiology, 1992

To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery steno... more To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery stenosis, spiral CT images of 20 patients were compared with images obtained with conventional angiography (20 patients), ultrasound (US) (15 patients), and magnetic resonance (MR) angiography (six patients). The category of stenosis was determined for each internal carotid artery on the basis of the percentage of narrowing: mild = less than 30%, moderate = 30%-69%, and severe = 70%-99%. Occlusions were also noted. The degree of carotid stenosis determined with spiral CT correlated with that determined with conventional angiography in 92% of cases, with that determined with US in 97% of cases, and with that determined with MR angiography in 100% of cases. Calcifications and large ulcers were also well delineated. Spiral CT provided an accurate anatomic depiction of the carotid bifurcation, which could be helpful in preoperative evaluation. The major disadvantage of the technique was the need to postprocess data to remove veins, calcifications, and bone structures from the images.

Research paper thumbnail of Stereoselective effects of local anesthetics reveal two sites of action on neuronal sodium channels

Regional Anesthesia & Pain Medicine, 1989

Research paper thumbnail of Asymptomatic functional popliteal artery entrapment: demonstration at MR imaging

Radiology, 1995

To determine if functional popliteal entrapment can occur in healthy subjects and to define the m... more To determine if functional popliteal entrapment can occur in healthy subjects and to define the mechanism of vascular compression. The right lower extremities were examined in 13 subjects (nine men 27-34 years of age, mean age 31 years; four women 29-44 years of age, mean age 34 years) with no symptoms of popliteal artery entrapment. Magnetic resonance (MR) and Doppler ultrasound images were obtained while the subjects were at rest and while they performed plantar flexion against resistance. Blood flow during plantar flexion ceased in nine of 13 subjects (69%) and was impaired in three of 13 (23%). MR images showed muscular compression of the popliteal artery at two levels: between the plantaris muscle and the medial head of the gastrocnemius muscle and between the plantaris and popliteus muscles. Functional impairment of popliteal arterial flow during plantar flexion occurs in subjects who have no symptoms of popliteal entrapment syndrome.