Mahadevappa Mahesh, MS, PhD, FAAPM, FACR, is the Associate Professor of Radiology and Associate Professor of Medicine in the Division of Cardiology at the Johns Hopkins University School of Medicine, Baltimore, MD. He is also the Chief Physicist at the Johns Hopkins Hospital, Baltimore, MD. Dr Mahesh is board certified from the American Board of Radiology in diagnostic radiological physics and is a member of the Radiation Control Advisory Board for the State of Maryland. His research interests are in medical imaging, particularly in areas of multiple-row detector computed tomography (MDCT), interventional fluoroscopy and digital mammography. Prior joining Hopkins, Dr Mahesh obtained his Ph.D. in Medical Physics from Medical College of Wisconsin, Milwaukee, WI.
Dr Mahesh is the editor of the Physics Columns (Technology Talk and Medical Physics Consult) for the Journal of American College of Radiology (JACR) since 2007 and editor for the American Association of Physicists in Medicine (AAPM) Newsletter since 2007, and is the Contributing Editor for RadioGraphics. He chairs or serves on various committees in the AAPM, RSNA and ACR.
Dr Mahesh is a fellow of the American Association of Physicists in Medicine (2007) and fellow of the American College of Radiology (2009). Dr Mahesh is the author of the textbook titled ‘MDCT Physics: The Basics – Technology, Image Quality and Radiation Dose’ published in June 2009 by Lippincott Williams and Wilkins.
Abstract: It is the responsibility of the medical Speech-Language Pathologist (SLP) who performs video-assisted fluoroscopy of swallowing (VFSS) to be aware of guidelines, recommendations, and preventive measures to reduce radiation to oneself and the patient. Established parameters to reduce radiation during videofluoroscopy include keeping the exposure time brief, using lead aprons and other shielding, and maximizing the distance from the source of radiation. The purpose of this study was to measure radiation exposure to SLPs in the clinical setting and to provide practical recommendations to keep radiation exposure as low as reasonably achievable. Our study measured radiation exposure to six SLPs practicing in an acute-care university hospital. We monitored the radiation received during 130 examinations, 102 of which were of the pharynx only and the other 28 included pharynx and intrathoracic viscera. Individual times were documented, and average doses per exam were calculated from dosimetry badges worn on the lead apron of the SLP doing inpatient exams. Average fluoroscopy time per procedure was 165 s. Average radiation to the dosimeter worn on the front of the lead apron at chest level was 0.15 mR (0.0015 mGy) per procedure. SLPs stood behind the lead shield during fluoroscopy when feasible. Our measurements document the practical importance of reducing radiation exposure to health-care personnel by increasing the distance from the source of radiation and by shielding. While recommendations are not new, details of the findings may help guide and reinforce good radiation safety practice.
Abstract: Prior reports regarding the association between physical activity and subclinical cardiovascular disease have not been consistent. The authors assessed physical activity and walking pace via questionnaire among 6,482 US adults aged 45-84 years without prior clinical cardiovascular disease participating in the Multi-Ethnic Study of Atherosclerosis from 2000 to 2002. Ankle-brachial index (ABI), coronary artery calcification, and internal and common carotid intima-media thickness (IMT) were measured. Metabolic equivalent-hours/week of physical activity were calculated. These data were analyzed by using multivariable linear or relative prevalence regression in gender-specific strata. After adjustment for age, race/ethnicity, clinic site, education, income, and smoking (model 1), increasing total, moderate + vigorous, and intentional-exercise physical activity were not associated with IMT or coronary artery calcification in either gender. These factors were associated with increased ABI (P<0.05) in women only. Walking pace was associated favorably with common carotid IMT, ABI, and coronary artery calcification in men and with common carotid IMT and ABI in women (all P<0.05) after adjustment for model 1 variables. These associations were attenuated and, for common carotid IMT, no longer significant when lipids, hypertension, diabetes, and body mass index were added to the model. These data suggest that walking pace is associated with less subclinical atherosclerosis; these associations may be mediated by cardiovascular disease risk factors.
Abstract: BACKGROUND: Use of computed tomography (CT) for diagnostic evaluation has increased dramatically over the past 2 decades. Even though CT is associated with substantially higher radiation exposure than conventional radiography, typical doses are not known. We sought to estimate the radiation dose associated with common CT studies in clinical practice and quantify the potential cancer risk associated with these examinations. METHODS: We conducted a retrospective cross-sectional study describing radiation dose associated with the 11 most common types of diagnostic CT studies performed on 1119 consecutive adult patients at 4 San Francisco Bay Area institutions in California between January 1 and May 30, 2008. We estimated lifetime attributable risks of cancer by study type from these measured doses. RESULTS: Radiation doses varied significantly between the different types of CT studies. The overall median effective doses ranged from 2 millisieverts (mSv) for a routine head CT scan to 31 mSv for a multiphase abdomen and pelvis CT scan. Within each type of CT study, effective dose varied significantly within and across institutions, with a mean 13-fold variation between the highest and lowest dose for each study type. The estimated number of CT scans that will lead to the development of a cancer varied widely depending on the specific type of CT examination and the patient's age and sex. An estimated 1 in 270 women who underwent CT coronary angiography at age 40 years will develop cancer from that CT scan (1 in 600 men), compared with an estimated 1 in 8100 women who had a routine head CT scan at the same age (1 in 11 080 men). For 20-year-old patients, the risks were approximately doubled, and for 60-year-old patients, they were approximately 50% lower. CONCLUSION: Radiation doses from commonly performed diagnostic CT examinations are higher and more variable than generally quoted, highlighting the need for greater standardization across institutions.
Abstract: BACKGROUND: The use of computed tomographic (CT) scans in the United States (US) has increased more than 3-fold since 1993 to approximately 70 million scans annually. Despite the great medical benefits, there is concern about the potential radiation-related cancer risk. We conducted detailed estimates of the future cancer risks from current CT scan use in the US according to age, sex, and scan type. METHODS: Risk models based on the National Research Council's "Biological Effects of Ionizing Radiation" report and organ-specific radiation doses derived from a national survey were used to estimate age-specific cancer risks for each scan type. These models were combined with age- and sex-specific scan frequencies for the US in 2007 obtained from survey and insurance claims data. We estimated the mean number of radiation-related incident cancers with 95% uncertainty limits (UL) using Monte Carlo simulations. RESULTS: Overall, we estimated that approximately 29 000 (95% UL, 15 000-45 000) future cancers could be related to CT scans performed in the US in 2007. The largest contributions were from scans of the abdomen and pelvis (n = 14 000) (95% UL, 6900-25 000), chest (n = 4100) (95% UL, 1900-8100), and head (n = 4000) (95% UL, 1100-8700), as well as from chest CT angiography (n = 2700) (95% UL, 1300-5000). One-third of the projected cancers were due to scans performed at the ages of 35 to 54 years compared with 15% due to scans performed at ages younger than 18 years, and 66% were in females. CONCLUSIONS: These detailed estimates highlight several areas of CT scan use that make large contributions to the total cancer risk, including several scan types and age groups with a high frequency of use or scans involving relatively high doses, in which risk-reduction efforts may be warranted.
Abstract: The U.S. National Council on Radiation Protection and Measurements and United Nations Scientific Committee on Effects of Atomic Radiation each conducted respective assessments of all radiation sources in the United States and worldwide. The goal of this article is to summarize and combine the results of these two publicly available surveys and to compare the results with historical information. In the United States in 2006, about 377 million diagnostic and interventional radiologic examinations and 18 million nuclear medicine examinations were performed. The United States accounts for about 12% of radiologic procedures and about one-half of nuclear medicine procedures performed worldwide. In the United States, the frequency of diagnostic radiologic examinations has increased almost 10-fold (1950-2006). The U.S. per-capita annual effective dose from medical procedures has increased about sixfold (0.5 mSv [1980] to 3.0 mSv [2006]). Worldwide estimates for 2000-2007 indicate that 3.6 billion medical procedures with ionizing radiation (3.1 billion diagnostic radiologic, 0.5 billion dental, and 37 million nuclear medicine examinations) are performed annually. Worldwide, the average annual per-capita effective dose from medicine (about 0.6 mSv of the total 3.0 mSv received from all sources) has approximately doubled in the past 10-15 years.
Abstract: Medical uses of radiation have grown very rapidly over the past decade, and, as of 2007, medical uses represent the largest source of exposure to the U.S. population. Most physicians have difficulty assessing the magnitude of exposure or potential risk. Effective dose provides an approximate indicator of potential detriment from ionizing radiation and should be used as one parameter in evaluating the appropriateness of examinations involving ionizing radiation. The purpose of this review is to provide a compilation of effective doses for radiologic and nuclear medicine procedures. Standard radiographic examinations have average effective doses that vary by over a factor of 1000 (0.01-10 mSv). Computed tomographic examinations tend to be in a more narrow range but have relatively high average effective doses (approximately 2-20 mSv), and average effective doses for interventional procedures usually range from 5-70 mSv. Average effective dose for most nuclear medicine procedures varies between 0.3 and 20 mSv. These doses can be compared with the average annual effective dose from background radiation of about 3 mSv.
Abstract: Medical radiation exposure of the U.S. population has not been systematically evaluated for almost 25 years. In 1982, the per-capita dose was estimated to be 0.54 mSv and the collective dose 124,000 person-Sv. The preliminary estimates of the National Council on Radiation Protection and Measurements Scientific Committee 6-2 medical subgroup are that, in 2006, the per-capita dose from all medical exposure (not including radiotherapy) had increased almost 600% to 3.0 mSv and the collective dose had increased more than 700% to approximately 900,000 person-Sv. >Nuclear medicine accounted for only about 2% of all procedures but 26% of the total collective dose from diagnostic studies in medicine. In 1982, the estimated number of nuclear medicine procedures was about 7.5 million. The per-capita effective dose from nuclear medicine was 0.14 mSv and the collective dose was 32,000 person Sv. By 2005, the estimated number of procedures had increased to about 19.6 million. The per-caput effective dose increased to about 0.75 mSv and the collective dose to about 220,000 person Sv. There also has been a marked shift in the type of procedures being performed with cardiac scanning accounting for about 70% of procedures.
Abstract: Medical radiation exposure of the U.S. population has not been systematically evaluated for almost 25 y. In 1982, the per capita dose was estimated to be 0.54 mSv and the collective dose 124,000 person-Sv. The preliminary estimates of the NCRP Scientific Committee 6-2 medical subgroup are that, in 2006, the per capita dose from medical exposure (not including dental or radiotherapy) had increased almost 600% to about 3.0 mSv and the collective dose had increased over 700% to about 900,000 person-Sv. The largest contributions and increases have come primarily from CT scanning and nuclear medicine. The 62 million CT procedures accounted for 15% of the total number procedures (excluding dental) and over half of the collective dose. Nuclear medicine accounted for about 4% of all procedures but 26% of the total collective dose. Medical radiation exposure is now approximately equal to natural background radiation.
Abstract: The authors develop a unique CT simulation tool based on the 4D extended cardiac-torso (XCAT) phantom, a whole-body computer model of the human anatomy and physiology based on NURBS surfaces. Unlike current phantoms in CT based on simple mathematical primitives, the 4D XCAT provides an accurate representation of the complex human anatomy and has the advantage, due to its design, that its organ shapes can be changed to realistically model anatomical variations and patient motion. A disadvantage to the NURBS basis of the XCAT, however, is that the mathematical complexity of the surfaces makes the calculation of line integrals through the phantom difficult. They have to be calculated using iterative procedures; therefore, the calculation of CT projections is much slower than for simpler mathematical phantoms. To overcome this limitation, the authors used efficient ray tracing techniques from computer graphics, to develop a fast analytic projection algorithm to accurately calculate CT projections directly from the surface definition of the XCAT phantom given parameters defining the CT scanner and geometry. Using this tool, realistic high-resolution 3D and 4D projection images can be simulated and reconstructed from the XCAT within a reasonable amount of time. In comparison with other simulators with geometrically defined organs, the XCAT-based algorithm was found to be only three times slower in generating a projection data set of the same anatomical structures using a single 3.2 GHz processor. To overcome this decrease in speed would, therefore, only require running the projection algorithm in parallel over three processors. With the ever decreasing cost of computers and the rise of faster processors and multi-processor systems and clusters, this slowdown is basically inconsequential, especially given the vast improvement the XCAT offers in terms of realism and the ability to generate 3D and 4D data from anatomically diverse patients. As such, the authors conclude that the efficient XCAT-based CT simulator developed in this work will have applications in a broad range of CT imaging research.
Abstract: BACKGROUND: Reduction of radiation exposure from computed tomography coronary angiography (CTA) will be a key factor for more liberal use in cardiac hybrid positron emission tomography (PET)-computed tomography (CT). We report our initial experience with a new algorithm for low-dose CTA based on a prospectively gated step-and-shoot technique. This limits acquisition to the diastolic phase and minimizes exposure time versus the previous standard of retrospectively gated helical acquisitions. METHODS AND RESULTS: In 15 consecutive patients referred for integrated functional and morphologic workup by rubidium 82 perfusion PET-CTA, step-and-shoot CTA (SnapShot Pulse; GE Medical Systems) (120 kV, 600-800 mA) was acquired on a 64-slice GE Discovery Rx VCT PET-CT scanner and compared with a group of patients with conventional helical CTA (120 kV, with modulation of the milliampere level) who were matched with regard to clinical variables. Effective dose was estimated from dose-length product. The American Heart Association 15-segment coronary tree model was used to determine study interpretability. Potential for fusion with Rb-82 perfusion PET was tested by use of commercial software. In addition, direct dose measurements were conducted by use of an anthropomorphic phantom for more accurate dosimetry. The dose-length product-derived effective patient dose for step-and-shoot and helical CTA was 5.5 +/- 0.1 mSv versus 20.5 +/- 3.5 mSv (P < .0001). The mean number of evaluable segments per patient for the best phase of helical CTA was 12.5 +/- 2.8 (83.3% +/- 18.7%) versus 13.3 +/- 2.2 (88.7% +/- 14.7%) (P = not significant vs helical) for step-and-shoot CTA. Review of multiple phases increased the number for helical CTA to 13.7 +/- 1.7 (91.3% +/- 11.3%; P = not significant vs step-and-shoot CTA, for which this was not an option). Semiautomated fusion with corresponding PET was feasible for all studies. Phantom data confirm effective doses of 5.4 mSv for step-and-shoot CTA and 19.6 mSv for helical acquisition. CONCLUSIONS: Low-dose prospectively gated CTA reduces radiation exposure by nearly 70% versus the previous standard of helical acquisition, without significant loss in interpretability and integrative potential with Rb-82 perfusion PET. This represents a step toward a broader, routine integration of CTA and perfusion PET for assessment of coronary morphology and physiology by cardiac PET-CT.
Abstract: Cardiac computed tomography (CT) is emerging as an important tool for the diagnosis and monitoring of heart disease. The prevalence of heart disease in the United States is already quite high and is expected to increase as the "baby boomer" segment of the population ages. To use complex multiple-row detector CT scanners most efficiently for cardiac examinations, it is important to understand many of the technical components. New developments in CT technology provide the ability to examine the structure of the heart with a level of detail that was not previously possible. In general, detector configurations have improved, the number of channels has increased, and rotation speed has increased, resulting in better quality of cardiac images. However, radiation dose for cardiac CT is fairly high and demands constant vigilance. Several steps can be taken to reduce the dose, including lowering the tube current as the x-ray beam crosses over certain areas of the body, decreasing the tube current during certain phases of the cardiac cycle, and using a higher pitch. Cardiac CT examination dose (for a coronary artery study) is approximately equivalent to that of an abdominal-pelvic CT examination or a dual-phase chest CT examination.
Abstract: Cardiac imaging with multiple-row detector computed tomography (CT) has become possible due to rapid advances in CT technologies. Images with high temporal and spatial resolution can be obtained with multiple-row detector CT scanners; however, the radiation dose associated with cardiac imaging is high. Understanding the physics of cardiac imaging with multiple-row detector CT scanners allows optimization of cardiac CT protocols in terms of image quality and radiation dose. Knowledge of the trade-offs between various scan parameters that affect image quality--such as temporal resolution, spatial resolution, and pitch--is the key to optimized cardiac CT protocols, which can minimize the radiation risks associated with these studies. Factors affecting temporal resolution include gantry rotation time, acquisition mode, and reconstruction method; factors affecting spatial resolution include detector size and reconstruction interval. Cardiac CT has the potential to become a reliable tool for noninvasive diagnosis and prevention of cardiac and coronary artery disease.
Abstract: The Digital Mammography Imaging Screening Trial, conducted by the American College of Radiology Imaging Network, is a clinical trial designed to compare the accuracy of full-field digital mammography (FFDM) versus screen-film mammography in a screening population. Five FFDM systems from four manufacturers (Fischer, Fuji, General Electric, and Lorad) were employed in the study at 35 clinical sites. A core physics team devised and implemented tests to evaluate these systems. A detailed description of physics and quality control tests is presented, including estimates of: mean glandular dose, modulation transfer function (MTF), 2D noise power spectra, and signal-to-noise ratio (SNR). The mean glandular doses for the standard breast ranged from 0.79 to 2.98 mGy, with 1.62 mGy being the average across all units and machine types. For the five systems evaluated, the MTF dropped to 50% at markedly different percentages (22% to 87%) of the Nyquist limit, indicating that factors other than detector element (del) size have an important effect on spatial resolution. Noise power spectra and SNR were measured; however, we found that it was difficult to standardize and compare these between units. For each machine type, the performance as measured by the tests was very consistent, and no predictive benefit was seen for many of the tests during the 2-year period of the trial. It was found that, after verification of proper operation during acceptance testing, if systems failed they generally did so suddenly rather than through gradual deterioration of performance. Because of the relatively short duration of this study further, investigation of the long-term failure characteristics of these systems is advisable.
Abstract: The Digital Mammography Imaging Screening Trial (DMIST), conducted under the auspices of the American College of Radiology Imaging Network (ACRIN), is a clinical trial designed to compare the accuracy of digital versus screen-film mammography in a screening population [E. Pisano et al., ACRIN 6652-Digital vs. Screen-Film Mammography, ACRIN (2001)]. Part I of this work described the Quality Control program developed to ensure consistency and optimal operation of the digital equipment. For many of the tests, there were no failures during the 24 months imaging was performed in DMIST. When systems failed, they generally did so suddenly rather than through gradual deterioration of performance. In this part, the utility and effectiveness of those tests are considered. This suggests that after verification of proper operation, routine extensive testing would be of minimal value. A recommended set of tests is presented including additional and improved tests, which we believe meet the intent and spirit of the Mammography Quality Standards Act regulations to ensure that full-field digital mammography systems are functioning correctly, and consistently producing mammograms of excellent image quality.
Abstract: PURPOSE: To determine acquisition protocol parameters currently used by different institutions for appendiceal multidetector computed tomography (MDCT). MATERIALS AND METHODS: A survey inquiring about multiple MDCT protocols was mailed to 99 fellows of the Society of Computed Body Tomography in August of 2004, with a second mailing sent in May 2005. A total of 46 institutions or hospitals are represented by these Society of Computed Body Tomography fellows. Details pertaining to protocols for the most advanced MDCT scanner in the department were requested. RESULTS: The overall survey response rate was 17 of 46 or 37%. Fifteen protocols using 16-MDCT for suspected appendicitis were collected and tabulated. Parameters that are similar across institutions include a nonfocused acquisition using oral and intravenous contrast. Detector configuration is even divided between submillimeter and greater than 1 mm, and the most common reconstruction section thickness is 5 mm. CONCLUSIONS: Contrast administration and anatomical coverage are quite consistent across this set of protocols. However, future appendiceal MDCT research will need to address the most efficacious detector row collimation, reconstruction section thickness and interval, and the diagnostic capacity of protocols implementing dose reduction measures.
Abstract: BACKGROUND: The purpose of this study was to determine the radiation exposure during catheter ablation of atrial fibrillation (AF) using the pulmonary vein (PV) approach. METHODS AND RESULTS: The study included 15 patients with AF and 5 patients each with atrial flutter and atrioventricular nodal reentrant tachycardia (AVNRT) who underwent fluoroscopically guided procedures on a biplane x-ray system operated at a low-frame pulsed fluoroscopy (7.5 frames per second). Radiation exposure was measured directly with 50 to 60 thermoluminescent dosimeters (TLDs). Peak skin doses (PSDs), effective radiation doses, and risk of fatal malignancies were all computed. Mean fluoroscopy durations for AF procedures were 67.8+/-21 minutes in the right anterior oblique (RAO) and 61.9+/-16.6 minutes in the left anterior oblique (LAO) projection, significantly different from that required for atrial flutter and AVNRT. The mean PSDs measured with the TLDs were 1.0+/-0.5 Gy in the RAO and 1.5+/-0.4 Gy in the LAO projection. The lifetime risk of excess fatal malignancies normalized to 60 minutes of fluoroscopy was 0.07% for women and 0.1% for men. CONCLUSIONS: The relatively small amounts of the patient's radiation exposure in this study, despite the prolonged fluoroscopy durations, can be attributed to the use of very-low-frame pulsed fluoroscopy, the avoidance of magnification, and optimal adjustments of the fluoroscopy exposure rates. The resulting lifetime risk of fatal malignancy is within the range previously reported for standard supraventricular arrhythmias.
Abstract: Recent advances in digital detector technology have paved the way to full-field digital mammography (FFDM) systems. The performance of these systems has evolved to the point where replacement of screen-film mammography (SFM) systems is becoming realistic. Despite some commonality between the two techniques, there are fundamental differences in how images are recorded, displayed, and stored. These differences necessitate an understanding of the principles of detection and the characteristics of digital images. Several approaches have been taken in the development of FFDM systems: (a) slot scanning with a scintillator and a charge-coupled device (CCD) array, (b) a flat-panel scintillator and an amorphous silicon diode array, (c) a flat-panel amorphous selenium array, (d) a tiled scintillator with fiberoptic tapers and a CCD array, and (e) photostimulable phosphor plates (computed radiography). Although the initial cost of an FFDM system is high compared with that of an SFM system, digital mammography has inherent advantages, such as wide dynamic range, reduction in recall rates, potential for reduction in radiation dose, increased patient throughput, postprocessing capability, and digital acquisition. These advantages and the rapidly occurring technologic developments will help establish FFDM as a mainstay of breast evaluation.
Abstract: BACKGROUND: Traditional risk factors for coronary artery disease predict the development of atherosclerosis; however, their ability to identify individual patients at risk of events is limited. METHODS: Coronary artery calcium (CAC) is a specific marker of atherosclerosis. It can be visualized and measured noninvasively by various imaging techniques, which may add incremental prognostic value to conventional coronary factors. RESULTS: The field of atherosclerosis imaging has expanded rapidly in the last decade, and technologies such as electron-beam computed tomography (EBCT) have contributed to our understanding of the prevalence of occult coronary artery disease and its consequences. Other modalities have been previously limited by the decreased temporal and spatial resolution and slower acquisition. Recent advances in helical CT (HCT) imaging with the development of multiple row detectors CT (MDCT) and improvements in the temporal resolution have renewed clinicians' interests in using this modality to evaluate CAC, although the scores obtained with MDCT may differ somewhat from those obtained with the EBCT technology. This study critically analyzes the literature comparing the utility of EBCT and HCT in detecting coronary calcium to identify individuals at increased risk for future coronary events. CONCLUSIONS: MDCT is a promising tool for coronary calcium scoring; however, more studies are needed comparing EBCT and MDCT, especially at lower CAC levels.
Abstract: Computed tomography (CT) is a method of acquiring and reconstructing the image of a thin cross section on the basis of measurements of attenuation. In comparison with conventional radiographs, CT images are free of superimposing tissues and are capable of much higher contrast due to elimination of scatter. Most of the developments in CT since its introduction can be considered as attempts to provide faster acquisition times, better spatial resolution, and shorter computer reconstruction times. From the early designs, the technology progressed with faster scanning times and higher scanning plane resolution, but true three-dimensional (3D) imaging became practical only with helical scanning capabilities. The recent advent of multiple-row detector helical scanners has the capability to produce 3D images that approach the ideal of a true "3D radiograph." Current multiple-row detector scanners can scan 40-cm volume lengths in less than 30 seconds with near-isotropic resolution and image quality that could not be envisioned at the time of Hounsfield's invention.
Abstract: Fluoroscopic procedures (particularly prolonged interventional procedures) may involve high patient radiation doses. The radiation dose depends on the type of examination, the patient size, the equipment, the technique, and many other factors. The performance of the fluoroscopy system with respect to radiation dose is best characterized by the receptor entrance exposure and skin entrance exposure rates, which should be assessed at regular intervals. Management of patient exposure involves not only measurement of these rates but also clinical monitoring of patient doses. Direct monitoring of patient skin doses during procedures is highly desirable, but current methods still have serious limitations. Skin doses may be reduced by using intermittent exposures, grid removal, last image hold, dose spreading, beam filtration, pulsed fluoroscopy, and other dose reduction techniques. Proper training of fluoroscopic operators, understanding the factors that influence radiation dose, and use of various dose reduction techniques may allow effective management of patient dose.
Abstract: OBJECTIVE: With single-slice helical CT, an increased pitch can decrease the radiation dose to the patient if all other parameters are constant. The purpose of this study was to determine whether the same relationship holds for a particular multislice helical CT system (Somatom Plus 4 VZ multislice helical CT scanner, version A11A) in our department. CONCLUSION: The measured radiation dose to the phantom was identical for all pitch selections on the multislice helical CT system we tested. This unexpected result was because of an automatic proportionate increase in the tube current when the pitch selection was increased. Radiologists and physicists should exercise caution when extrapolating dose reduction strategies from single-slice to multislice helical CT systems, and they must acquire a detailed understanding of the multislice helical CT scanner of their chosen manufacturer.
Abstract: The objective of this study was to identify factors that predict fluoroscopy duration and radiation exposure during catheter ablation procedures. The patient population included 859 patients who participated in the Atakr Ablation System clinical trial at 1 of 9 centers (398 male and 461 female patients, aged 36 +/- 21 years). Each patient underwent catheter ablation of an accessory pathway, the atrioventricular junction, or atrioventricular nodal reentrant tachycardia using standard techniques. The duration of fluoroscopy was 53 +/- 50 minutes. Factors identified as independent predictors of fluoroscopy duration included patient age and sex, the success or failure of the ablation procedure, and the institution at which the ablation was performed. Catheter ablation in adults required longer fluoroscopy exposure than it did in children. Men required longer durations of fluoroscopy exposure than did women. The mean estimated "entrance" radiation dose was 1.3 +/- 1.3 Sv. The dose needed to cause radiation skin injury was exceeded during 22% of procedures. The overall mean effective absorbed dose from catheter ablation procedures was 0.025 Sv for female patients and 0.017 Sv for male patients. This degree of radiation exposure would result in an estimated 1,400 excess fatal malignancies in female patients and 2,600 excess fatal malignancies in male patients per 1 million patients.
Abstract: Radiation exposure during fluoroscopic imaging poses potential risks to patients and physicians, especially during protracted cardiovascular or radiological interventional procedures. We describe a woman with refractory paroxysmal supraventricular tachycardia who underwent radiofrequency catheter ablation of the slow pathway involved in atrioventricular nodal reentrant tachycardia. The patient subsequently returned 4 weeks later with acute radiation dermatitis that was retrospectively attributed to a malfunction in the fluoroscopy unit that lacked a maximum current output cut-off switch. Using dose reconstruction studies and her estimated biological response, we determined that she received between 15 and 20 Gy (1 Gy = 100 rads) to the skin on her back during the procedure. The exposure will result in an increase in her lifelong risk of skin and lung cancer. This article underscores the potential for radiation-induced injury during lengthy therapeutic procedures using x-ray equipment.
Abstract: 31P nuclear magnetic resonance spectroscopy (NMRS) measurements were made on human T2 and T3 vertebral bodies. The bone mineral content (BMC) of isolated vertebral bodies minus the posterior elements and disks was measured using (1) NMRS on a 3.5 T, 85 mm bore GE Medical Systems NT-150 superconducting spectrometer, (2) a Lunar Corporation DPX-L dual-energy X-ray absorptiometry (DXA) scanner in an anterior-posterior (AP) orientation, (3) a Norland Corporation XR26 DXA scanner, also in an AP direction, and (4) a Norland Corporation model 2600 dual-photon absorptiometry (DPA) densitometer in both the AP and superior-inferior (SI) directions. Vertebral body volumes were measured using a water displacement technique to determine volume bone mineral densities (VBMD). They were then compressed to failure using an electrohydraulic testing device, followed by ashing in a muffle furnace at 700 degrees C for 18 h. Correlations of BMC between NMRS and DPA, DXA and ashing were excellent (0.96 < or = r < or = 0.99); in a one-way analysis of variance (ANOVA) test, means were not statistically different at a p level of 0.757. The correlations of VBMD between NMRS and the other methods were not as good (0.83 < or = r < or = 0.95); in a one-way ANOVA test, means were not statistically different at a p level of 0.089. BMC was a better predictor of ultimate compressive failure than VBMD for all six methods. For NMRS, the regression coefficient for BMC was r2 = 0.806, compared with r2 = 0.505 for VBMD. NMRS may prove an alternative to present methods of determining bone mineral.
Abstract: Alterations of posterior spinal elements including the facet joints are commonly associated with a variety of lumbar operative procedures. Under continuous physiologic compression-flexion load application L2-L3 and L4-L5 functional units were tested as intact preparations and then sequentially altered with unilateral facetectomy, bilateral facetectomy, posterior ligament transection, and partial discectomy. Using a method of continuous motion analysis, the movement of the individual spinal components (disc, facet joint, interspinous process distance) were statistically compared between the various surgical alterations. Higher physiologic loads produced significant increases in overall deflection from BF to BFL alterations indicating a preference to preserve the posterior ligaments for this surgical approach. Although insignificant changes in the force-deflection response from one surgical alteration to the next sequential alteration were noted, statistically significant increases in localized facet joint motion may suggest the potential for acceleration of segmental degenerative changes.
