Yogesh Thakur - Academia.edu (original) (raw)

Papers by Yogesh Thakur

Research paper thumbnail of Continuing Professional Development / Perfectionnement Canadian Association of Radiologists Radiation Protection Working Group: Review of Radiation Units and the Use of Computed Tomography Dose Indicators in Canada

Research paper thumbnail of Health Policy and Practice / Sant : politique et pratique m Health Canada Safety Code 35: Awareness of the Impacts for Diagnostic Radiology in Canada

Research paper thumbnail of Orthopaedic Surgeon Brain Radiation During Fluoroscopy

Journal of Bone and Joint Surgery, 2020

Background: The aims of this study were to quantify exposure of the surgeon's brain to radiation ... more Background: The aims of this study were to quantify exposure of the surgeon's brain to radiation during short cephalomedullary (SC) nailing, to extrapolate lifetime dose, and to determine the effects of personal protective equipment (PPE) on brain dose. Methods: Two cadaveric specimens were used: (1) a whole cadaveric body representing the patient, with a left nail inserted to act as the scatter medium, and (2) an isolated head-and-neck cadaveric specimen representing a surgeon, with radiation dosimeters placed in specific locations in the brain. The "patient" cadaver's left hip was exposed in posteroanterior and lateral radiographic planes. Measurements were performed without shielding of the head-and-neck specimen and then repeated sequentially with different PPE configurations. An average surgeon career was estimated to be 40 years (ages 25 to 65 years) with the caseload obtained from the department's billing data. Results: The mean radiation dose to the surgeon brain without PPE was 3.35 mGy (95% confidence interval [CI]: 2.4 to 4.3) per nail procedure. This was significantly reduced with use of a thyroid collar (2.94 mGy [95% CI: 1.91 to 3.91], p = 0.04). Compared with use of the thyroid collar in isolation, there was no significant additional reduction in radiation when the collar was used with leaded glasses (2.96 mGy [95% CI: 2.15 to 3.76], p = 0.97), with a lead cap (3.22 mGy [95% CI: 2.31 to 4.13], p = 0.55), or with both (2.31 mGy [95% CI: 1.61 to 3.01], p = 0.15). The extrapolated lifetime dose over 40 working years for SC nailing without PPE was 2,146 mGy (95% CI: 1,539 to 2,753), with an effective dose of 21.5 mSv. Conclusions: The extrapolated cumulative lifetime radiation to a surgeon's brain from SC nailing based on our institution's workload and technology is low and comparable with radiation during a one-way flight from London to New York. Of note, we studied only one of many fluoroscopy-aided procedures and likely underestimated total lifetime exposure if exposures from other procedures are included. This study also demonstrates that thyroid collars significantly reduce brain dose for this procedure whereas other head/neck PPE such as lead caps appear to have minimal additional effect. This study provides a methodology for future studies to quantify brain dose for other common orthopaedic procedures. Clinical Relevance: This study, based on our institutional data, demonstrates that although the lifetime brain dose from SC nailing is low, thyroid collars significantly reduce this dose further. As such, in accordance with the "as low as reasonably achievable" radiation exposure principle, radiation safety programs and individual surgeons should consider use of thyroid collars in this setting. Disclosure: This research was supported by funding from AOTrauma North America. DePuy-Synthes Canada provided implants and instruments for insertion. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJS/G99).

Research paper thumbnail of A Radiographic Diagnostic Reference Level Survey Using Patient and Phantom Data

Radiation Protection Dosimetry, 2016

A diagnostic reference level (DRL) survey was conducted for seven common radiographic projections... more A diagnostic reference level (DRL) survey was conducted for seven common radiographic projections across an integrated health region, covering 27 hospitals and clinics. The projections surveyed were Chest Posterior-Anterior (PA) and Lateral, Abdomen Supine and Upright, L-spine Anterior-Posterior (AP) and Lateral, and Pelvis. Dose area product (DAP) values were collected from patient examinations in 43 digital radiography (DR) rooms and in 18 conventional rooms which use computed radiography (CR). In each room, data were collected for between 10 and 20 patient exposures for each surveyed projection. In addition, for each projection and room, a DAP value was measured for the exposure of a uniform acrylic phantom of standardized thickness. DAP values in DR rooms were found to be significantly lower than in CR rooms (p < 0.05). Therefore, DR and CR rooms were analyzed separately. Based on the survey results, separate DRLs are presented for DR and CR rooms, for both patient and phantom DAP values. DRLs have been set at the 75th percentile values; 25th percentile and median values are also presented to characterize the range of observed values. When identifying which rooms were above the DRLs, the patient and phantom data identified a partially different set of rooms. Possible reasons for these differences, including uncertainties in the patient data, are discussed.

Research paper thumbnail of Reply: To PMID 22623545

AJR. American journal of roentgenology, 2013

Research paper thumbnail of A Magnetic-Resonance-Imaging-Compatible Remote Catheter Navigation System

IEEE Transactions on Biomedical Engineering, 2013

A remote catheter navigation system compatible with magnetic resonance imaging has been developed... more A remote catheter navigation system compatible with magnetic resonance imaging has been developed to facilitate magnetic resonance image guided catheterization procedures. The interventionalist's conventional motions (axial motion and rotation) on an input catheter-acting as the master-are measured by a pair of optical encoders and a custom embedded system relays the motions to a pair of ultrasonic motors. The ultrasonic motors drive the patient catheter (slave) within the MRI scanner, replicating the motion of the input catheter. The performance of the remote catheter navigation system was evaluated in terms of accuracy and delay of motion replication outside and within the bore of the magnet. While inside the scanner bore, motion accuracy was characterized during the acquisition of frequently used imaging sequences, including realtime GRE acquisition. The effect of the catheter navigation system on image SNR was also evaluated. The results show that the master-slave system has a maximum time delay of 41±21 ms in replicating motion; an absolute value error of 2±2º was measured for radial catheter motion replication over 360º and 1.1 ± 0.8 mm in axial catheter motion replication over 100 mm of travel. The worst case SNR drop (in spin echo images) was observed to be 2.5%.

Research paper thumbnail of Canadian Association of Radiologists Radiation Protection Working Group: Review of Radiation Units and the Use of Computed Tomography Dose Indicators in Canada

Canadian Association of Radiologists Journal, 2013

Research paper thumbnail of Pulmonary CT Angiography as First-Line Imaging for PE: Image Quality and Radiation Dose Considerations

American Journal of Roentgenology, 2013

OBJECTIVE. This article reviews dose reduction techniques in pulmonary CT angiography (CTA) for i... more OBJECTIVE. This article reviews dose reduction techniques in pulmonary CT angiography (CTA) for imaging pulmonary embolism (PE). Dose reduction technologies covered include tube current modulation, kilovoltage modulation, scanning length modification, dynamic z-axis collimation, iterative reconstruction, and dual-energy CT. Age-and weight-specific imaging techniques are suggested. CONCLUSION. Pulmonary CTA plays a vital role in imaging PE. Using dose reduction technologies can provide high-quality diagnostic imaging with a significant reduction in patient dose.

Research paper thumbnail of Risk-Benefit Analysis of Pulmonary CT Angiography in Patients With Suspected Pulmonary Embolus

American Journal of Roentgenology, 2012

T examinations are the largest source of medical radiation exposure, accounting for 49% of collec... more T examinations are the largest source of medical radiation exposure, accounting for 49% of collective effective medical radiation dose in 2006 [1]. In comparison with radiography, CT examinations are intrinsically high dose [2] and the increased x-ray power of MDCT scanners is associated with an increased average dose per examination [3], making it likely that an even higher radiation dose is currently delivered in centers with limited radiation dose awareness. CT dose reduction efforts have two components: The first is optimizing acquisition and reconstruction parameters to ensure that dose is as low as reasonably achievable and the second is ensuring that CT examinations are appropriately requested with adequate clinical justification. Clinical justification requires that the outcome

Research paper thumbnail of Comparison of Rhenium and Iodine as Contrast Agents in X-Ray Imaging

Contrast Media & Molecular Imaging

Purpose. The majority of X-ray contrast agents (XCA) are made with iodine, but iodine-based XCA (... more Purpose. The majority of X-ray contrast agents (XCA) are made with iodine, but iodine-based XCA (I-XCA) exhibit low contrast in high kVp X-rays due to iodine’s low atomic number (Z = 53) and K-edge (33.1 keV). While rhenium is a transition metal with a high atomic number (Z = 75) and K-edge (71.7 keV), the utilization of rhenium-based XCA (Re-XCA) in X-ray imaging techniques has not been studied in depth. Our study had two objectives: (1) to compare both the image quality and the absorbed dose of I- and Re-XCA and (2) to prepare and image a rhenium-doped scaffold. Procedures. I- and Re-XCA were prepared and imaged from 50 to 120 kVp by Micro-computed tomography (µCT) and digital radiography and from 120 to 220 kVp by planar X-ray imaging. The scans were repeated using 0.1 to 1.6 mm thick copper filters to harden the X-ray beam. A rhenium-doped scaffold was prepared via electrospinning, used to coat catheters, and imaged at 90 kVp by µCT. Results. I-XCA have a greater contrast-to-noi...

Research paper thumbnail of Supplemental_Appendix_S1 - Peer Review Tool for General Radiography Technologists Improves Image Quality

Supplemental_Appendix_S1 for Peer Review Tool for General Radiography Technologists Improves Imag... more Supplemental_Appendix_S1 for Peer Review Tool for General Radiography Technologists Improves Image Quality by Andrew M. Hsiao, Annemarie Budau-Bymoen, Petar Seslija, Charlotte J. Yong-Hing and Yogesh Thakur in Canadian Association of Radiologists Journal

Research paper thumbnail of Supplemental Material, Appendix - Multidisciplinary Development of Mobile Radiography Guidelines Reduced the Number of Inappropriate Mobile Exams in Patients Receiving Chest Radiographs in British Columbia

Supplemental Material, Appendix for Multidisciplinary Development of Mobile Radiography Guideline... more Supplemental Material, Appendix for Multidisciplinary Development of Mobile Radiography Guidelines Reduced the Number of Inappropriate Mobile Exams in Patients Receiving Chest Radiographs in British Columbia by Kevin J. Kobes, Annemarie Budau-Bymoen, Yogesh Thakur and Charlotte J. Yong-Hing in Canadian Association of Radiologists Journal

Research paper thumbnail of Orthopaedic Surgeon Brain Radiation During Fluoroscopy A Cadaver Model

J Bone Joint Surg Am . 2020 Nov 18;102(22):e125. doi: 10.2106/JBJS.19.01053., 2020

Background: The aims of this study were to quantify exposure of the surgeon's brain to radiat... more Background: The aims of this study were to quantify exposure of the surgeon's brain to radiation during short cephalomedullary (SC) nailing, to extrapolate lifetime dose, and to determine the effects of personal protective equipment (PPE) on brain dose. Methods: Two cadaveric specimens were used: (1) a whole cadaveric body representing the patient, with a left nail inserted to act as the scatter medium, and (2) an isolated head-and-neck cadaveric specimen representing a surgeon, with radiation dosimeters placed in specific locations in the brain. The "patient" cadaver's left hip was exposed in posteroanterior and lateral radiographic planes. Measurements were performed without shielding of the head-and-neck specimen and then repeated sequentially with different PPE configurations. An average surgeon career was estimated to be 40 years (ages 25 to 65 years) with the caseload obtained from the department's billing data. Results: The mean radiation dose to the sur...

Research paper thumbnail of Remote MR-Compatible Catheter Navigation System

Mohammad Ali Tavallaei, Yogesh Thakur, Syed Haider, and Maria Drangova Imaging Research Laborator... more Mohammad Ali Tavallaei, Yogesh Thakur, Syed Haider, and Maria Drangova Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada, Biomedical Engineering Graduate Program, The University of Western Ontario, London, Ontario, Canada, Radiology, Vancouver Coastal Health Authority, Vancouver, British Columbia, Canada, Medical Biophysics, The University of Western Ontario, London, Ontario, Canada

Research paper thumbnail of Implications of Cone Beam CT Peripheral Edge Blurring and Signal Attenuation for Interventional Procedures

CardioVascular and Interventional Radiology

To the Editor, Cone beam CT (CBCT) has recently seen increased utilization in interventional proc... more To the Editor, Cone beam CT (CBCT) has recently seen increased utilization in interventional procedures [1]. However, CBCT has shortcomings, which include increased radiation scatter, decreased contrast-to-noise ratio, longer image acquisition, and HU values that are location dependent [2, 3]. The net effect is that peripheral tissues can become indistinct and even disappear, which poses a significant hazard to vital superficial structures during ablative procedures. We encountered this issue at our institution while performing CBCT-guided cryoablation. In some cases, cryoprobe entry points could not be visualized at all (Fig. 1a), even with an optimized window width and level (Fig. 1b). Fortunately, clear visualization of the skin can be achieved when a water-filled glove is applied over the region of interest, which we identified when using this technique for superficial thermal injury protection (Fig. 1c) [4, 5]. As a result, we routinely apply a glove during cryoprobe path planning such as when performing pelvic cryoablation via an anterior approach in order to avoid the spermatic cord, inferior epigastric and femoral vessels (Figure E1a and E1b). We investigated the underlying cause of the peripheral attenuation artifact in collaboration with the CBCT manufacturer (Philips), and a software solution is in development. The abdomen CBCT technique typically used for body intervention increases detector sensitivity compared to the head technique to compensate for the overall increased attenuation of the body. With a high sensitivity detector, scattered photons make a significant contribution to the overall detected signal, even resulting in detector saturation for primary ray paths with minimal attenuation through the periphery of a phantom/patient. Filtered backprojection of the saturated value results in a ‘hazy’ or washed-out appearance of the peripheral tissue, and the effect is more pronounced for large patients due to increased scatter. A water-filled glove on the patient’s surface prevents detector saturation by attenuating ray path photons around the area of interest, such that detector saturation does not occur, and thus prevents the artifact. To assess the impact of a glove on edge definition, we performed phantom studies using the ACR 464 CT phantom with and without tissue equivalent expansion rings as well as with and without the presence of a water-filled nitrile glove. CBCT was performed on a Philips Allura Clarity FD20/20 biplane unit. Image acquisitions were performed using the XperCT Abdomen Low Dose technique (120kVp, 230 mA) and XperCT Head Low Dose technique (120kVp, 250 mA) at 30fps for 10.4 s. & R. Davis Holmes davisholmes@gmail.com

Research paper thumbnail of Discontinuing Gonadal and Fetal Shielding in X-Ray

Canadian Association of Radiologists Journal

Research paper thumbnail of Unsuspected Pregnancies in Hysterosalpingography: Implementation and Review of a Multi-Institutional Pre-Procedural Pregnancy Screening Protocol

Canadian Association of Radiologists Journal

Purpose: Owing to the increasing average age of first-time mothers, as well as advances in assist... more Purpose: Owing to the increasing average age of first-time mothers, as well as advances in assistive reproductive technology, the number of hysterosalpingography (HSG) requests has continued to rise. This increases the likelihood of patients presenting with unsuspected early pregnancies prior to HSG. Currently, there is no standard of practice for the pre-procedural screening of pregnancy prior to HSG, with most institutions using patient-reported pregnancy status and unreliable menstrual cycle dating methods. We implemented a multi-institutional pre-procedural pregnancy screening protocol in order to determine the rate of unsuspected pregnancies prior to HSG and improve the quality and safety of these procedures. Methods: Following multi-institutional and multidisciplinary input, a consensus protocol was formulated and implemented across 9 institutions in the Lower Mainland of British Columbia, Canada. Subsequent tracking of pregnancy testing was then performed over a period of 3 y...

Research paper thumbnail of Peer Review Tool for General Radiography Technologists Improves Image Quality

Canadian Association of Radiologists Journal

Purpose: Quality improvement is vital to ensure health-care providers meet optimal patient care s... more Purpose: Quality improvement is vital to ensure health-care providers meet optimal patient care standards. Within our jurisdiction, accreditation requires image peer review as part of the quality assurance program. We propose a method to improve quality assurance in radiography by implementing a novel software-based peer review system for radiography technologists. Methods: This is a retrospective study. A peer review tool was developed in Microsoft Excel and Visual Basic. The tool has 14 image quality criteria, which were selected based on national and international criteria, each containing standardized answers ensuring a common scoring regime. The tool provides data analysis and storage of all peer reviews performed. Radiography supervisors utilized the tool to evaluate image quality of various body parts at 28 hospitals. The tool enabled each Medical Imaging Department to objectively score images at their own hospital. Approximately 2% of all radiographs were randomly chosen for...

Research paper thumbnail of Multidisciplinary Development of Mobile Radiography Guidelines Reduced the Number of Inappropriate Mobile Exams in Patients Receiving Chest Radiographs in British Columbia

Canadian Association of Radiologists Journal

Aim: To decrease the number of mobile chest radiograph requests for inpatients in British Columbi... more Aim: To decrease the number of mobile chest radiograph requests for inpatients in British Columbia who are medically able to tolerate transport to the main department by introducing and implementing request criteria. Method: Concerns regarding inappropriate mobile exam requests in patients receiving chest radiography were surveyed at 28 medical imaging sites. In response, a multidisciplinary team composed a set of mobile radiography request guidelines incorporating feedback from all sites. These were successfully implemented along with in-person education to 21 sites. The number of adult annual mobile chest radiographs was tracked from 2014 to 2018, and informal feedback was obtained from participating sites. Results: The percentage of mobile chest radiographs of all chest radiographs performed between 2014 and 2018 decreased by 3.2%, while the total number of all chest radiographs performed during this time, including both departmental and mobile, increased by 1.9%. Sites reported ...

Research paper thumbnail of Comparison of the CTDI and AAPM report No. 111 methodology in adult, adolescent, and child head phantoms for MSCT and dental CBCT scanners

Journal of Medical Imaging

This study investigates the dosimetry methodology proposed by the American Association of Physici... more This study investigates the dosimetry methodology proposed by the American Association of Physicists in Medicine (AAPM) task group 111 and compares with the computed tomography dose index (CTDI) method and the SEDENTEXCT DI method on one clinical multislice CT and two dental cone beam CT (CBCT) scanners using adult, adolescent, and child head phantoms. Following the AAPM method, the normalized (100 mAs) equilibrium doses (D eq) for Toshiba Aquilion One MSCT computed using dose measurements from the central hole of the phantom (D eq;c), the peripheral hole of the phantom, (D eq;p), and by the CTDI w equation (D eq;w) are in the range from 20 to 25 mGy. For i-CAT Next Generation dental CBCT, the normalized D eq;c , D eq;p , D eq;w , and D 0 eq s by the two SEDENTEXCT DI methods are in the range from 12 to 15 mGy. Fitting the AAPM equation is not possible for the limited scan lengths available on the CS 9300 dental CBCT. This study offers a simple CTDI-like measurement that can approximate the AAPM D eq in clinical CBCT scanners capable of providing four or more scan lengths. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Research paper thumbnail of Continuing Professional Development / Perfectionnement Canadian Association of Radiologists Radiation Protection Working Group: Review of Radiation Units and the Use of Computed Tomography Dose Indicators in Canada

Research paper thumbnail of Health Policy and Practice / Sant : politique et pratique m Health Canada Safety Code 35: Awareness of the Impacts for Diagnostic Radiology in Canada

Research paper thumbnail of Orthopaedic Surgeon Brain Radiation During Fluoroscopy

Journal of Bone and Joint Surgery, 2020

Background: The aims of this study were to quantify exposure of the surgeon's brain to radiation ... more Background: The aims of this study were to quantify exposure of the surgeon's brain to radiation during short cephalomedullary (SC) nailing, to extrapolate lifetime dose, and to determine the effects of personal protective equipment (PPE) on brain dose. Methods: Two cadaveric specimens were used: (1) a whole cadaveric body representing the patient, with a left nail inserted to act as the scatter medium, and (2) an isolated head-and-neck cadaveric specimen representing a surgeon, with radiation dosimeters placed in specific locations in the brain. The "patient" cadaver's left hip was exposed in posteroanterior and lateral radiographic planes. Measurements were performed without shielding of the head-and-neck specimen and then repeated sequentially with different PPE configurations. An average surgeon career was estimated to be 40 years (ages 25 to 65 years) with the caseload obtained from the department's billing data. Results: The mean radiation dose to the surgeon brain without PPE was 3.35 mGy (95% confidence interval [CI]: 2.4 to 4.3) per nail procedure. This was significantly reduced with use of a thyroid collar (2.94 mGy [95% CI: 1.91 to 3.91], p = 0.04). Compared with use of the thyroid collar in isolation, there was no significant additional reduction in radiation when the collar was used with leaded glasses (2.96 mGy [95% CI: 2.15 to 3.76], p = 0.97), with a lead cap (3.22 mGy [95% CI: 2.31 to 4.13], p = 0.55), or with both (2.31 mGy [95% CI: 1.61 to 3.01], p = 0.15). The extrapolated lifetime dose over 40 working years for SC nailing without PPE was 2,146 mGy (95% CI: 1,539 to 2,753), with an effective dose of 21.5 mSv. Conclusions: The extrapolated cumulative lifetime radiation to a surgeon's brain from SC nailing based on our institution's workload and technology is low and comparable with radiation during a one-way flight from London to New York. Of note, we studied only one of many fluoroscopy-aided procedures and likely underestimated total lifetime exposure if exposures from other procedures are included. This study also demonstrates that thyroid collars significantly reduce brain dose for this procedure whereas other head/neck PPE such as lead caps appear to have minimal additional effect. This study provides a methodology for future studies to quantify brain dose for other common orthopaedic procedures. Clinical Relevance: This study, based on our institutional data, demonstrates that although the lifetime brain dose from SC nailing is low, thyroid collars significantly reduce this dose further. As such, in accordance with the "as low as reasonably achievable" radiation exposure principle, radiation safety programs and individual surgeons should consider use of thyroid collars in this setting. Disclosure: This research was supported by funding from AOTrauma North America. DePuy-Synthes Canada provided implants and instruments for insertion. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJS/G99).

Research paper thumbnail of A Radiographic Diagnostic Reference Level Survey Using Patient and Phantom Data

Radiation Protection Dosimetry, 2016

A diagnostic reference level (DRL) survey was conducted for seven common radiographic projections... more A diagnostic reference level (DRL) survey was conducted for seven common radiographic projections across an integrated health region, covering 27 hospitals and clinics. The projections surveyed were Chest Posterior-Anterior (PA) and Lateral, Abdomen Supine and Upright, L-spine Anterior-Posterior (AP) and Lateral, and Pelvis. Dose area product (DAP) values were collected from patient examinations in 43 digital radiography (DR) rooms and in 18 conventional rooms which use computed radiography (CR). In each room, data were collected for between 10 and 20 patient exposures for each surveyed projection. In addition, for each projection and room, a DAP value was measured for the exposure of a uniform acrylic phantom of standardized thickness. DAP values in DR rooms were found to be significantly lower than in CR rooms (p < 0.05). Therefore, DR and CR rooms were analyzed separately. Based on the survey results, separate DRLs are presented for DR and CR rooms, for both patient and phantom DAP values. DRLs have been set at the 75th percentile values; 25th percentile and median values are also presented to characterize the range of observed values. When identifying which rooms were above the DRLs, the patient and phantom data identified a partially different set of rooms. Possible reasons for these differences, including uncertainties in the patient data, are discussed.

Research paper thumbnail of Reply: To PMID 22623545

AJR. American journal of roentgenology, 2013

Research paper thumbnail of A Magnetic-Resonance-Imaging-Compatible Remote Catheter Navigation System

IEEE Transactions on Biomedical Engineering, 2013

A remote catheter navigation system compatible with magnetic resonance imaging has been developed... more A remote catheter navigation system compatible with magnetic resonance imaging has been developed to facilitate magnetic resonance image guided catheterization procedures. The interventionalist's conventional motions (axial motion and rotation) on an input catheter-acting as the master-are measured by a pair of optical encoders and a custom embedded system relays the motions to a pair of ultrasonic motors. The ultrasonic motors drive the patient catheter (slave) within the MRI scanner, replicating the motion of the input catheter. The performance of the remote catheter navigation system was evaluated in terms of accuracy and delay of motion replication outside and within the bore of the magnet. While inside the scanner bore, motion accuracy was characterized during the acquisition of frequently used imaging sequences, including realtime GRE acquisition. The effect of the catheter navigation system on image SNR was also evaluated. The results show that the master-slave system has a maximum time delay of 41±21 ms in replicating motion; an absolute value error of 2±2º was measured for radial catheter motion replication over 360º and 1.1 ± 0.8 mm in axial catheter motion replication over 100 mm of travel. The worst case SNR drop (in spin echo images) was observed to be 2.5%.

Research paper thumbnail of Canadian Association of Radiologists Radiation Protection Working Group: Review of Radiation Units and the Use of Computed Tomography Dose Indicators in Canada

Canadian Association of Radiologists Journal, 2013

Research paper thumbnail of Pulmonary CT Angiography as First-Line Imaging for PE: Image Quality and Radiation Dose Considerations

American Journal of Roentgenology, 2013

OBJECTIVE. This article reviews dose reduction techniques in pulmonary CT angiography (CTA) for i... more OBJECTIVE. This article reviews dose reduction techniques in pulmonary CT angiography (CTA) for imaging pulmonary embolism (PE). Dose reduction technologies covered include tube current modulation, kilovoltage modulation, scanning length modification, dynamic z-axis collimation, iterative reconstruction, and dual-energy CT. Age-and weight-specific imaging techniques are suggested. CONCLUSION. Pulmonary CTA plays a vital role in imaging PE. Using dose reduction technologies can provide high-quality diagnostic imaging with a significant reduction in patient dose.

Research paper thumbnail of Risk-Benefit Analysis of Pulmonary CT Angiography in Patients With Suspected Pulmonary Embolus

American Journal of Roentgenology, 2012

T examinations are the largest source of medical radiation exposure, accounting for 49% of collec... more T examinations are the largest source of medical radiation exposure, accounting for 49% of collective effective medical radiation dose in 2006 [1]. In comparison with radiography, CT examinations are intrinsically high dose [2] and the increased x-ray power of MDCT scanners is associated with an increased average dose per examination [3], making it likely that an even higher radiation dose is currently delivered in centers with limited radiation dose awareness. CT dose reduction efforts have two components: The first is optimizing acquisition and reconstruction parameters to ensure that dose is as low as reasonably achievable and the second is ensuring that CT examinations are appropriately requested with adequate clinical justification. Clinical justification requires that the outcome

Research paper thumbnail of Comparison of Rhenium and Iodine as Contrast Agents in X-Ray Imaging

Contrast Media & Molecular Imaging

Purpose. The majority of X-ray contrast agents (XCA) are made with iodine, but iodine-based XCA (... more Purpose. The majority of X-ray contrast agents (XCA) are made with iodine, but iodine-based XCA (I-XCA) exhibit low contrast in high kVp X-rays due to iodine’s low atomic number (Z = 53) and K-edge (33.1 keV). While rhenium is a transition metal with a high atomic number (Z = 75) and K-edge (71.7 keV), the utilization of rhenium-based XCA (Re-XCA) in X-ray imaging techniques has not been studied in depth. Our study had two objectives: (1) to compare both the image quality and the absorbed dose of I- and Re-XCA and (2) to prepare and image a rhenium-doped scaffold. Procedures. I- and Re-XCA were prepared and imaged from 50 to 120 kVp by Micro-computed tomography (µCT) and digital radiography and from 120 to 220 kVp by planar X-ray imaging. The scans were repeated using 0.1 to 1.6 mm thick copper filters to harden the X-ray beam. A rhenium-doped scaffold was prepared via electrospinning, used to coat catheters, and imaged at 90 kVp by µCT. Results. I-XCA have a greater contrast-to-noi...

Research paper thumbnail of Supplemental_Appendix_S1 - Peer Review Tool for General Radiography Technologists Improves Image Quality

Supplemental_Appendix_S1 for Peer Review Tool for General Radiography Technologists Improves Imag... more Supplemental_Appendix_S1 for Peer Review Tool for General Radiography Technologists Improves Image Quality by Andrew M. Hsiao, Annemarie Budau-Bymoen, Petar Seslija, Charlotte J. Yong-Hing and Yogesh Thakur in Canadian Association of Radiologists Journal

Research paper thumbnail of Supplemental Material, Appendix - Multidisciplinary Development of Mobile Radiography Guidelines Reduced the Number of Inappropriate Mobile Exams in Patients Receiving Chest Radiographs in British Columbia

Supplemental Material, Appendix for Multidisciplinary Development of Mobile Radiography Guideline... more Supplemental Material, Appendix for Multidisciplinary Development of Mobile Radiography Guidelines Reduced the Number of Inappropriate Mobile Exams in Patients Receiving Chest Radiographs in British Columbia by Kevin J. Kobes, Annemarie Budau-Bymoen, Yogesh Thakur and Charlotte J. Yong-Hing in Canadian Association of Radiologists Journal

Research paper thumbnail of Orthopaedic Surgeon Brain Radiation During Fluoroscopy A Cadaver Model

J Bone Joint Surg Am . 2020 Nov 18;102(22):e125. doi: 10.2106/JBJS.19.01053., 2020

Background: The aims of this study were to quantify exposure of the surgeon's brain to radiat... more Background: The aims of this study were to quantify exposure of the surgeon's brain to radiation during short cephalomedullary (SC) nailing, to extrapolate lifetime dose, and to determine the effects of personal protective equipment (PPE) on brain dose. Methods: Two cadaveric specimens were used: (1) a whole cadaveric body representing the patient, with a left nail inserted to act as the scatter medium, and (2) an isolated head-and-neck cadaveric specimen representing a surgeon, with radiation dosimeters placed in specific locations in the brain. The "patient" cadaver's left hip was exposed in posteroanterior and lateral radiographic planes. Measurements were performed without shielding of the head-and-neck specimen and then repeated sequentially with different PPE configurations. An average surgeon career was estimated to be 40 years (ages 25 to 65 years) with the caseload obtained from the department's billing data. Results: The mean radiation dose to the sur...

Research paper thumbnail of Remote MR-Compatible Catheter Navigation System

Mohammad Ali Tavallaei, Yogesh Thakur, Syed Haider, and Maria Drangova Imaging Research Laborator... more Mohammad Ali Tavallaei, Yogesh Thakur, Syed Haider, and Maria Drangova Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada, Biomedical Engineering Graduate Program, The University of Western Ontario, London, Ontario, Canada, Radiology, Vancouver Coastal Health Authority, Vancouver, British Columbia, Canada, Medical Biophysics, The University of Western Ontario, London, Ontario, Canada

Research paper thumbnail of Implications of Cone Beam CT Peripheral Edge Blurring and Signal Attenuation for Interventional Procedures

CardioVascular and Interventional Radiology

To the Editor, Cone beam CT (CBCT) has recently seen increased utilization in interventional proc... more To the Editor, Cone beam CT (CBCT) has recently seen increased utilization in interventional procedures [1]. However, CBCT has shortcomings, which include increased radiation scatter, decreased contrast-to-noise ratio, longer image acquisition, and HU values that are location dependent [2, 3]. The net effect is that peripheral tissues can become indistinct and even disappear, which poses a significant hazard to vital superficial structures during ablative procedures. We encountered this issue at our institution while performing CBCT-guided cryoablation. In some cases, cryoprobe entry points could not be visualized at all (Fig. 1a), even with an optimized window width and level (Fig. 1b). Fortunately, clear visualization of the skin can be achieved when a water-filled glove is applied over the region of interest, which we identified when using this technique for superficial thermal injury protection (Fig. 1c) [4, 5]. As a result, we routinely apply a glove during cryoprobe path planning such as when performing pelvic cryoablation via an anterior approach in order to avoid the spermatic cord, inferior epigastric and femoral vessels (Figure E1a and E1b). We investigated the underlying cause of the peripheral attenuation artifact in collaboration with the CBCT manufacturer (Philips), and a software solution is in development. The abdomen CBCT technique typically used for body intervention increases detector sensitivity compared to the head technique to compensate for the overall increased attenuation of the body. With a high sensitivity detector, scattered photons make a significant contribution to the overall detected signal, even resulting in detector saturation for primary ray paths with minimal attenuation through the periphery of a phantom/patient. Filtered backprojection of the saturated value results in a ‘hazy’ or washed-out appearance of the peripheral tissue, and the effect is more pronounced for large patients due to increased scatter. A water-filled glove on the patient’s surface prevents detector saturation by attenuating ray path photons around the area of interest, such that detector saturation does not occur, and thus prevents the artifact. To assess the impact of a glove on edge definition, we performed phantom studies using the ACR 464 CT phantom with and without tissue equivalent expansion rings as well as with and without the presence of a water-filled nitrile glove. CBCT was performed on a Philips Allura Clarity FD20/20 biplane unit. Image acquisitions were performed using the XperCT Abdomen Low Dose technique (120kVp, 230 mA) and XperCT Head Low Dose technique (120kVp, 250 mA) at 30fps for 10.4 s. & R. Davis Holmes davisholmes@gmail.com

Research paper thumbnail of Discontinuing Gonadal and Fetal Shielding in X-Ray

Canadian Association of Radiologists Journal

Research paper thumbnail of Unsuspected Pregnancies in Hysterosalpingography: Implementation and Review of a Multi-Institutional Pre-Procedural Pregnancy Screening Protocol

Canadian Association of Radiologists Journal

Purpose: Owing to the increasing average age of first-time mothers, as well as advances in assist... more Purpose: Owing to the increasing average age of first-time mothers, as well as advances in assistive reproductive technology, the number of hysterosalpingography (HSG) requests has continued to rise. This increases the likelihood of patients presenting with unsuspected early pregnancies prior to HSG. Currently, there is no standard of practice for the pre-procedural screening of pregnancy prior to HSG, with most institutions using patient-reported pregnancy status and unreliable menstrual cycle dating methods. We implemented a multi-institutional pre-procedural pregnancy screening protocol in order to determine the rate of unsuspected pregnancies prior to HSG and improve the quality and safety of these procedures. Methods: Following multi-institutional and multidisciplinary input, a consensus protocol was formulated and implemented across 9 institutions in the Lower Mainland of British Columbia, Canada. Subsequent tracking of pregnancy testing was then performed over a period of 3 y...

Research paper thumbnail of Peer Review Tool for General Radiography Technologists Improves Image Quality

Canadian Association of Radiologists Journal

Purpose: Quality improvement is vital to ensure health-care providers meet optimal patient care s... more Purpose: Quality improvement is vital to ensure health-care providers meet optimal patient care standards. Within our jurisdiction, accreditation requires image peer review as part of the quality assurance program. We propose a method to improve quality assurance in radiography by implementing a novel software-based peer review system for radiography technologists. Methods: This is a retrospective study. A peer review tool was developed in Microsoft Excel and Visual Basic. The tool has 14 image quality criteria, which were selected based on national and international criteria, each containing standardized answers ensuring a common scoring regime. The tool provides data analysis and storage of all peer reviews performed. Radiography supervisors utilized the tool to evaluate image quality of various body parts at 28 hospitals. The tool enabled each Medical Imaging Department to objectively score images at their own hospital. Approximately 2% of all radiographs were randomly chosen for...

Research paper thumbnail of Multidisciplinary Development of Mobile Radiography Guidelines Reduced the Number of Inappropriate Mobile Exams in Patients Receiving Chest Radiographs in British Columbia

Canadian Association of Radiologists Journal

Aim: To decrease the number of mobile chest radiograph requests for inpatients in British Columbi... more Aim: To decrease the number of mobile chest radiograph requests for inpatients in British Columbia who are medically able to tolerate transport to the main department by introducing and implementing request criteria. Method: Concerns regarding inappropriate mobile exam requests in patients receiving chest radiography were surveyed at 28 medical imaging sites. In response, a multidisciplinary team composed a set of mobile radiography request guidelines incorporating feedback from all sites. These were successfully implemented along with in-person education to 21 sites. The number of adult annual mobile chest radiographs was tracked from 2014 to 2018, and informal feedback was obtained from participating sites. Results: The percentage of mobile chest radiographs of all chest radiographs performed between 2014 and 2018 decreased by 3.2%, while the total number of all chest radiographs performed during this time, including both departmental and mobile, increased by 1.9%. Sites reported ...

Research paper thumbnail of Comparison of the CTDI and AAPM report No. 111 methodology in adult, adolescent, and child head phantoms for MSCT and dental CBCT scanners

Journal of Medical Imaging

This study investigates the dosimetry methodology proposed by the American Association of Physici... more This study investigates the dosimetry methodology proposed by the American Association of Physicists in Medicine (AAPM) task group 111 and compares with the computed tomography dose index (CTDI) method and the SEDENTEXCT DI method on one clinical multislice CT and two dental cone beam CT (CBCT) scanners using adult, adolescent, and child head phantoms. Following the AAPM method, the normalized (100 mAs) equilibrium doses (D eq) for Toshiba Aquilion One MSCT computed using dose measurements from the central hole of the phantom (D eq;c), the peripheral hole of the phantom, (D eq;p), and by the CTDI w equation (D eq;w) are in the range from 20 to 25 mGy. For i-CAT Next Generation dental CBCT, the normalized D eq;c , D eq;p , D eq;w , and D 0 eq s by the two SEDENTEXCT DI methods are in the range from 12 to 15 mGy. Fitting the AAPM equation is not possible for the limited scan lengths available on the CS 9300 dental CBCT. This study offers a simple CTDI-like measurement that can approximate the AAPM D eq in clinical CBCT scanners capable of providing four or more scan lengths. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.