Samuel Patz | Harvard Medical School (original) (raw)

Papers by Samuel Patz

Echoplanar images of rat head with and without blocking of external ear canals revealed large vox... more Echoplanar images of rat head with and without blocking of external ear canals revealed large voxel intensity changes outside as well as inside the cranium. These are probably mechanical effects of vibrational energy originating in the tympanic membrane and coupled to other tissue compartments of the head through the auditory ossicles, basilar membrane, and cochlear round window. They are so large that even slight variations in them may distort magnetic resonance imaging measurements of neural activity and water diffusion. Awareness of that possibility may inform measures to remove or compensate for it.

Magnetic Resonance Imaging, Apr 1, 2001

We have extended the utility of NMR as a technique to probe porous media structure over length sc... more We have extended the utility of NMR as a technique to probe porous media structure over length scales of ~ 100-2000 µm by using the spin 1/2 noble gas 129 Xe imbibed into the system's pore space. Such length scales are much greater than can be probed with NMR diffusion studies of water-saturated porous media. We utilized Pulsed Gradient Spin Echo NMR measurements of the time-dependent diffusion coefficient, D(t) of the xenon gas filling the pore space to study further the measurements of both the surface area-pore volume ratio, S/V p , and the tortuosity (pore connectivity) of the medium. In uniform-size glass bead packs, we observed D(t) decreasing with increasing t, reaching an observed asymptote of ~ 0.62-0.65D 0 , that could be measured over diffusion distances extending over multiple bead diameters. Measurements of D(t)/D 0 at differing gas pressures showed this tortuosity limit was not affected by changing the characteristic diffusion length of the spins during the diffusion encoding gradient pulse. This was not the case at the short time limit, where D(t)/D 0 was noticeably affected by the gas pressure in the sample. Increasing the gas pressure, and hence reducing D 0 and the diffusion during the gradient pulse served to reduce the previously observed deviation of D(t)/D 0 from the S/V p relation. The Pade approximation is used to interpolate between the long and short time limits in D(t). While the short time D(t) point lay above the interpolation line in the case of small beads, due to diffusion during the gradient pulse on the order of the pore size, it was also noted that the experimental D(t) data fell below the Pade line in the case of large beads, most likely due to finite size effects.

Journal of Neuroimaging, Apr 5, 2022

Background and Purpose:Biomechanical changes in the brain have not been fully elucidated in Alzhe... more Background and Purpose:Biomechanical changes in the brain have not been fully elucidated in Alzheimer’s disease (AD). We aimed to investigate the effect of β-amyloid accumulation on mouse brain viscoelasticity.Methods:Magnetic Resonance Elastography was used to calculate magnitude of the viscoelastic modulus (|G*|), elasticity (Gd), and viscosity (Gl) in the whole brain parenchyma (WB) and bilateral hippocampi of 9 transgenic J20 (AD) mice (5 males/4 females) and 10 wild-type (WT) C57BL/6 mice (5 males/5 females) at 11 and 14 months of age.Results:Cross-sectional analyses showed no significant difference between AD and WT mice at either time-points. No sex-specific differences were observed at 11 months of age, but AD females showed significantly higher hippocampal |G*| and Gl and WB |G*|, Gd and Gl compared to both AD and WT males at 14 months of age. Similar trending differences were found between female AD and female WT animals but did not reach significance. Longitudinal analyses showed significant increases in hippocampal |G*|, Gd, and Gl, and significant decreases in WB |G*|, Gd, and Gl between 11 and 14 months in both AD and WT mice. Each subgroup showed significant increases in all hippocampal and significant decreases in all WB measures, with the exception of AD females, which showed no significant changes in WB |G*|, Gd, or Gl.Conclusion:Aging had region-specific effects on cerebral viscoelasticity, namely WB softening and hippocampal stiffening. Amyloid plaque deposition may have sex-specific effects, which require further scrutiny.

Nuclear Instruments and Methods in Physics Research, 2002

A position-sensitive, superheated emulsion chamber (SEC) is introduced for three-dimensional (3D)... more A position-sensitive, superheated emulsion chamber (SEC) is introduced for three-dimensional (3D) spectrometry and dosimetry of fast neutrons. The detector is based on a fine suspension of octafluorocyclobutane droplets emulsified in a tissue-equivalent gel. This gel is highly viscous and immobilizes the bubbles at the location of their formation. At an operating temperature of 35°C, the droplets are moderately superheated and

Physical Review Letters, Oct 18, 1999

We show that gas diffusion nuclear magnetic resonance (GD-NMR) provides a powerful technique for ... more We show that gas diffusion nuclear magnetic resonance (GD-NMR) provides a powerful technique for probing the structure of porous media. In random packs of glass beads, using both laser-polarized and thermally polarized xenon gas, we find that GD-NMR can accurately measure the pore space surfacearea-to-volume ratio, S͞V p , and the tortuosity, a (the latter quantity being directly related to the system's transport properties). We also show that GD-NMR provides a good measure of the tortuosity of sandstone and complex carbonate rocks.

arXiv (Cornell University), Jul 23, 2007

The human lung and its functions are extremely sensitive to orientation and posture, and debate c... more The human lung and its functions are extremely sensitive to orientation and posture, and debate continues as to the role of gravity and the surrounding anatomy in determining lung function and heterogeneity of perfusion and ventilation. However, study of these effects is difficult. The conventional high-field magnets used for most hyperpolarized 3He MRI of the human lung, and most other common radiological imaging modalities including PET and CT, restrict subjects to lying horizontally, minimizing most gravitational effects. In this paper, we briefly review the motivation for posture-dependent studies of human lung function, and present initial imaging results of human lungs in the supine and vertical body orientations using inhaled hyperpolarized 3He gas and an open-access MRI instrument. The open geometry of this MRI system features a "walk-in" capability that permits subjects to be imaged in vertical and horizontal positions, and potentially allows for complete rotation of the orientation of the imaging subject in a two-dimensional plane. Initial results include two-dimensional lung images acquired with ~ 4 mm in-plane resolution and three-dimensional images with ~ 1.5 cm slice thickness. Effects of posture variation are observed.

Neurology, Nov 25, 2009

Background: Vitamin D deficiency has potential adverse effects on neurocognitive health and subco... more Background: Vitamin D deficiency has potential adverse effects on neurocognitive health and subcortical function. However, no studies have examined the association between vitamin D status, dementia, and cranial MRI indicators of cerebrovascular disease (CVD). Methods: Cross-sectional investigation of 25-hydroxyvitamin D [25(OH)D], dementia, and MRI measures of CVD in elders receiving home care (aged 65-99 years) from 2003 to 2007. Results: Among 318 participants, the mean age was 73.5 Ϯ 8.1 years, 231 (72.6%) were women, and 109 (34.3%) were black. 25(OH)D concentrations were deficient (Ͻ10 ng/mL) in 14.5% and insufficient (10-20 ng/mL) in 44.3% of participants. There were 76 participants (23.9%) with dementia, 41 of which were classified as probable AD. Mean 25(OH)D concentrations were lower in subjects with dementia (16.8 vs 20.0 ng/mL, p Ͻ 0.01). There was a higher prevalence of dementia among participants with 25(OH)D insufficiency (Յ20 ng/mL) (30.5% vs 14.5%, p Ͻ 0.01). 25(OH)D deficiency was associated with increased white matter hyperintensity volume (4.9 vs 2.9 mL, p Ͻ 0.01), grade (3.0 vs 2.2, p ϭ 0.04), and prevalence of large vessel infarcts (10.1% vs 6.9%, p Ͻ 0.01). After adjustment for age, race, sex, body mass index, and education, 25(OH)D insufficiency (Յ20 ng/mL) was associated with more than twice the odds of all-cause dementia (odds ratio [OR] ϭ 2.3, 95% confidence interval [CI] 1.2-4.2), Alzheimer disease (OR ϭ 2.5, 95% CI 1.1-6.1), and stroke (with and without dementia symptoms) (OR ϭ 2.0, 95% CI 1.0-4.0). Conclusions: Vitamin D insufficiency and deficiency was associated with all-cause dementia, Alzheimer disease, stroke (with and without dementia symptoms), and MRI indicators of cerebrovascular disease. These findings suggest a potential vasculoprotective role of vitamin D.

Magnetic Resonance Imaging, Jul 1, 1988

A retrospective analysis of clinical imaging using 2DFT SSFP at 0.14 T is presented. The techniqu... more A retrospective analysis of clinical imaging using 2DFT SSFP at 0.14 T is presented. The technique's potential for tissue characterization and its utility for clinical diagnosis were tested by both in vitro measurements of various tissues and in vivo clinical images. Different pulse angles not only influenced image contrast, but also helped characterize lesions, particularly those containing fat. In addition, the pulse angle changed the signal from venous flow perpendicular to the imaged slice. The slow flow sensitivity of the 2DFT SSFP technique was demonstrated in the detection of CSF motion. Rapid SSFP offers flow sensitivity and adequate lesion detecting ability, along with high patient throughput.

The human lung and its functions are extremely sensitive to gravity, however the conventional hig... more The human lung and its functions are extremely sensitive to gravity, however the conventional high-field magnets used for most laser-polarized 3He MRI of the human lung restrict subjects to lying horizontally. Imaging of human lungs using inhaled laser-polarized 3He gas is demonstrated in an open-access very-low-magnetic-field (< 5 mT) MRI instrument. This prototype device employs a simple, low-cost electromagnet, with an open geometry that allows variation of the orientation of the imaging subject in a two-dimensional plane. As a demonstration, two-dimensional lung images were acquired with 4 mm in-plane resolution from a subject in two orientations: lying supine, and sitting in a vertical position with one arm raised. Experience with this prototype device will guide optimization of a second-generation very-low-field imager to enable studies of human pulmonary physiology as a function of subject orientation.

Investigative Ophthalmology & Visual Science, 2005

The Journal of the Acoustical Society of America, 2017

Evaluate changes in the shear modulus of brain tissue as a new measure of localized brain functio... more Evaluate changes in the shear modulus of brain tissue as a new measure of localized brain function. A spin-echo magnetic resonance elastography (MRE) sequence was modified to allow two interleaved paradigms: stimulus ON/OFF. To avoid neuronal habituation, a paradigm was active for 9s before switching to the other paradigm. After each paradigm switch, a period of 1.8 s was allowed for hemodynamic equilibrium. Seven healthy black mice were studied. An electrical current to the hind limb, ~1 mA, 3 Hz, pulse width ~250 ms, was used as the functional stimulus. A separate control scan was also performed where no stimulus was applied for either paradigm. Vibration frequency = 1kHz. In six of the seven animals, a localized increase in G’ was observed in the somatosensory and motor cortex areas, whereas no difference was observed in the control scan. The average increase of G’ = 14%. Two potential mechanisms were considered: (i) a vascular effect similar to BOLD in fMRI and (ii) calcium infl...

We demonstrate MRI at very-low-magnetic fields ( 40 gauss) for hyperpolarized 3He gas inhaled int... more We demonstrate MRI at very-low-magnetic fields ( 40 gauss) for hyperpolarized 3He gas inhaled into human lungs. The low magnetic field is created with an open-geometry electromagnet, which enables MRI of lung ventilation with freedom of orientation of the human body. The role of gravity on lung function is a topic of much current debate. We plan to use an

ISMRM Annual Meeting

A stimulus-interleaved magnetic resonance elastography (MRE) sequence was utilized to demonstrate... more A stimulus-interleaved magnetic resonance elastography (MRE) sequence was utilized to demonstrate fast functionally mediated localized changes in shear wavelength during a motor task. Four healthy adult subjects underwent a visual-cue mediated right-hand finger-tapping task, switching between tapping and no-tapping blocks every 2 seconds. Areas of greatest significance between the stimulus states were localized to the left primary motor cortex. A decreased stiffness of ~30% was observed during task performance compared to rest. Compared to traditional BOLD fMRI with a 20-second block, functional MRE areas of greatest statistical difference demonstrated greater percentage change and greater spatial localization.

American Journal of Ophthalmology, Nov 1, 2006

Rationale and Objectives. We studied preparatory strategies for high-resolution human eye in vivo... more Rationale and Objectives. We studied preparatory strategies for high-resolution human eye in vivo imaging with commercially available magnets and coils. Materials and Methods. We imaged normal volunteers on 1.5T systems by Philips, GE, and Siemens, using commercial ϳ9 cm temporomandibular joint receive coils. Subjects fixated the nonimaged eye on a target. We compared signal (S) to tissue noise (N t) and system noise (N s) between images acquired with the imaged eye: 1) open, 2) held closed, 3) taped closed, and 4) taped closed with overlying water-soaked gauze. We standardized technique 4 to compare studies between manufacturers using T1-weighted parameters (repetition time/echo time/flip angle/number of signal averages ϭ 400 ms/ 10-17ms/90°/4-6, in-plane resolution ϳ250 ϫ 250 m 2 ; 2-3 mm slices, image time ϭ 4.3-5.2 min). We obtained similar images of an enucleated human eye to estimate in vivo effects of microsaccades and ocular pulsations. Results. Measurements of S/N t and S/N s gave surprising results of N t Ͻ N s in some instances. N s /N t was Х 1, varying ϳ20%, when the eye was taped shut and covered with water-soaked gauze. T1-weighted spin echo sequences, using technique 4, produced high-quality images with good S/N t on all systems. Images from the three manufacturers were comparable when parameters were normalized for pulse repetition time, echo time, number of signal averages, bandwidth in Hz/pixel, and reconstruction matrix. Images of the enucleated eye produced S/N t ratios that were comparable to in vivo images in some structures. Conclusions. Our best preparatory technique produced images with in-plane resolution of ϳ250 m in 4-5 minutes with three commercial 1.5T systems. The in vivo S/N t was comparable to in vitro values in most solid tissues but decreased in most fluid compartments.

American Journal of Neuroradiology, 2018

BACKGROUND AND PURPOSE: Currently no quantitative objective test exists to determine disease seve... more BACKGROUND AND PURPOSE: Currently no quantitative objective test exists to determine disease severity in a patient with Chiari I malformation. Our aim was to correlate disease severity in symptomatic patients with Chiari I malformation with cough-associated changes in CSF flow as measured with real-time MR imaging. MATERIALS AND METHODS: Thirteen symptomatic patients with Chiari I malformation (tonsillar herniation of Ն5 mm) were prospectively studied. A real-time, flow-sensitized pencil-beam MR imaging scan was used to measure CSF stroke volume during rest and immediately following coughing and relaxation periods (total scan time, 90 seconds). Multiple posterior fossa and craniocervical anatomic measurements were also obtained. Patients were classified into 2 groups by neurosurgeons blinded to MR imaging measurements: 1) nonspecific Chiari I malformation (5/13)-Chiari I malformation with nonspecific symptoms like non-cough-related or mild occasional cough-related headache, neck pain, dizziness, paresthesias, and/or trouble swallowing; 2) specific Chiari I malformation (8/13)-patients with Chiari I malformation with specific symptoms and/or objective findings like severe cough-related headache, myelopathy, syringomyelia, and muscle atrophy. The Spearman correlation was used to determine correlations between MR imaging measurements and disease severity, and both groups were also compared using a Mann-Whitney U test. RESULTS: There was a significant negative correlation between the percentage change in CSF stroke volume (resting to postcoughing) and Chiari I malformation disease severity (R ϭ 0.59; P ϭ .03). Mann-Whitney comparisons showed the percentage change in CSF stroke volume (resting to postcoughing) to be significantly different between patient groups (P ϭ .04). No other CSF flow measurement or anatomic measure was significantly different between the groups. CONCLUSIONS: Our exploratory study suggests that assessment of CSF flow response to a coughing challenge has the potential to become a valuable objective noninvasive test for clinical assessment of disease severity in patients with Chiari I malformation. ABBREVIATIONS: CMI ϭ Chiari I malformation; NS-CMI ϭ Chiari I malformation with nonspecific symptoms; PBI ϭ pencil-beam imaging; S-CMI ϭ Chiari I malformation with specific symptoms; SV CSF ϭ CSF stroke volume

American Journal of Neuroradiology, 2015

BACKGROUND AND PURPOSE: Invasive pressure studies have suggested that CSF flow across the foramen... more BACKGROUND AND PURPOSE: Invasive pressure studies have suggested that CSF flow across the foramen magnum may transiently decrease after coughing in patients with symptomatic Chiari I malformation. The purpose of this exploratory study was to demonstrate this phenomenon noninvasively by assessing CSF flow response to coughing in symptomatic patients with Chiari I malformation by using MR pencil beam imaging and to compare the response with that in healthy participants. MATERIALS AND METHODS: Eight symptomatic patients with Chiari I malformation and 6 healthy participants were studied by using MR pencil beam imaging with a temporal resolution of ϳ50 ms. Patients and healthy participants were scanned for 90 seconds (without cardiac gating) to continuously record cardiac cycle-related CSF flow waveforms in real-time during resting, coughing, and postcoughing periods. CSF flow waveform amplitude, CSF stroke volume, and CSF flow rate (CSF Flow Rate ϭ CSF Stroke Volume ϫ Heart Rate) in the resting and immediate postcoughing periods were determined and compared between patients and healthy participants. RESULTS: There was no significant difference in CSF flow waveform amplitude, CSF stroke volume, and the CSF flow rate between patients with Chiari I malformation and healthy participants during rest. However, immediately after coughing, a significant decrease in CSF flow waveform amplitude (P Ͻ .001), CSF stroke volume (P ϭ .001), and CSF flow rate (P ϭ .001) was observed in patients with Chiari I malformation but not in the healthy participants.

Medical Radiology, 2017

Pulmonary imaging is the least evolved branch of proton MRI, primarily due to the low volume frac... more Pulmonary imaging is the least evolved branch of proton MRI, primarily due to the low volume fraction of tissue in the lung; only ~20% of the volume contains tissue or blood while the remainder is filled with air. By comparison, most of the volume in other organs is hydrogen. Another source of the inherently weak MR signal in the lungs is the extremely large area of the tissue-gas interface. The 3 ppm difference in magnetic susceptibility between tissue and air causes an alteration of the local magnetic field resulting in very short signal coherence times. Despite having limited SNR, several promising techniques have been developed (Edelman et al. 1996; Mai et al. 2001; Hatabu et al. 2001; Jakob et al. 2004; Detre et al. 1994; Hopkins and Prisk 2010; Deimling et al. 2008; Bauman et al. 2009). These techniques work better at low magnetic fields (such as 1.5 T) because of the air/tissue susceptibility issue. This may be problematic for the future as the overall drive for clinical imaging is in the direction of higher field strengths. In preclinical small animal imaging, Kuethe et al. (2007) used 1.89 T field strength system to produce lung images approaching the quality of CT.