Joel E. Gray

Radiologic and Nuclear Medicine Studies in the United States and Worldwide: Frequency, Radiation Dose, and Comparison with Other Radiation Sources—1950–2007

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.

MEDICAL RADIATION EXPOSURE IN THE U.S. IN 2006 : PRELIMINARY RESULTS

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.

The effects of nuclear magnetic resonance imagers on external and implantable pulse generators.

This study evaluates the effect of nuclear magnetic resonance (NMR) scanning on pacemaker function. it must be emphasized that each manufacturers pulse generators and each pacing modality may behave differently and, therefore, require individual evaluation. According to our results, patients with pacemakers should have their pacing activity monitored continuously during scanning with the NMR 1500 gauss imaging system. External pulse generators should he net to the asynchronous mode and placed outside the NMR image volume but within the radiofrequency [RF] shield. Implanted pacemakers should be verified for type and mode of operation. Ail implantable pulse generators evaluated reverted from the demand to the asynchronous mode within the magnetic field of the scanner. There was no observable damage to the discrete pacemaker components that were tested.

Effect of pulsed progressive fluoroscopy on reduction of radiation dose in the cardiac catheterization laboratory

The increased application of therapeutic interventional cardiology procedures is associated with increased radiation exposure to physicians, patients and technical personnel. New advances in imaging techniques have the potential for reducing radiation exposure. A progressive scanning video system with a standard vascular phantom has been shown to decrease entrance radiation exposure. The effect of this system on reducing actual radiation exposure to physicians and technicians was assessed from 1984 through 1987. During this time, progressive fluoroscopy was added sequentially to all four adult catheterization laboratories; no changes in shielding procedures were made. During this time, the case load per physician increased by 63% and the number of percutaneous transluminal coronary angioplasty procedures (a high radiation procedure) increased by 244%. Despite these increases in both case load and higher radiation procedures, the average radiation exposure per physician declined by 37%. During the same time, the radiation exposure for technicians decreased by 35%. Pulsed progressive fluoroscopy is effective for reducing radiation exposure to catheterization laboratory physicians and technical staff.

The effects of magnetic resonance imaging on implantable pulse generators.

The efects of magnetic resonance imaging were assessed on four dual chamber and two single chamber pulse generators. The tests were performed with a resistive, water‐cooled magnet operating at 0.15 T. The 6.4‐MHz radiofrequency (RF) field was operated at a maximum power of 1,000 watts with a period adjusted from 130 to 500 ms. Reed switch closure occurred in all six pulse generators tested when placed near the entrance of the magnetic resonance imaging scanner, and the generators reverted to asynchronous operation unless programmed to the “magnet of” mode. None of the pulse generators exhibited any alterations in programmed parameters or in the ability to be reprogrammed after RF pulsing. When the HF field was turned on, there was no change in the asynchronous paced cycle length in four pulse generators; however, during RF scanning there was rapid cardiac stimulation at the RF pulse period in one single chamber and one dual chamber pulse generator.

Proton MR chemical shift imaging using double and triple phase contrast acquisition methods

Conventional chemical shift magnetic resonance (MR) imaging with the phase contrast technique has a number of limitations with respect to quantitative accuracy. The hypothesis of this study is that the accuracy of phase contrast chemical shift MR may be improved by increasing the number of basis images from two to three. Water and fat images were obtained from phantoms and volunteers with a 1.5 T MR system using double and triple acquisition phase contrast chemical shift methods. Longitudinal relaxation time and relative water and fat content were calculated from these basis images. The T1 relaxation times of the aqueous component of composite phantoms were determined more accurately using the triple acquisition method than with the double acquisition method. In vivo studies demonstrate that the triple acquisition method separated fat and water signals more accurately and showed less field inhomogeneity dependence than the modified double acquisition method. The new method also provided a map of static field magnetic inhomogeneity and tissue magnetic susceptibility. The triple acquisition phase contrast chemical shift imaging technique should improve the prospect for quantitative tissue characterization in clinical MR.

ASA Monitoring Standards and Magnetic Resonance Imaging

Some patients, often because of age or altered mental state, require general anesthesia or monitored anesthesia care and sedation if adequate magnetic resonance imaging (MRI) is to be accomplished. This study evaluated whether patients can be monitored during MRI with 1.5-tesla scanners in a manner which complies with ASA monitoring standards without causing degradation of image quality. Ten volunteers were scanned in the MRI without sedation. Monitors meeting ASA standards were placed and electronic artifact produced by the magnetic resonance (MR) scanner was evaluated, after which two scans of the head and two of the chest were performed. One of each pair of scans was obtained with the monitors functioning and one with them turned off. Four radiologists, blinded as to whether the monitors were turned on or off, independently evaluated the 20 pairs of scans. Differences in diagnostic quality and image degradation between the scans were evaluated and scores assigned. All monitors functioned appropriately during the scans, with the exception of the electrocardiogram (ECG) which was grossly distorted to the extent that only ventricular rate could be evaluated. None of the head or body scans was nondiagnostic; however, images with the monitors off were of better quality overall than with them on. Two types of noise were generated and are described. During the head scans, three of seven monitoring combinations caused degradation of the images, while four were judged clinically adequate. During the body scans, two of six monitoring combinations created noticeable noise, while four introduced no significant noise. Ungated cardiac scans were nondiagnostic. With the exception of the described limits of ECG interpretation, monitoring configurations can be designed to meet the ASA standards during MRI with 1.5-tesla scanners. To minimize electronic noise generated by monitors, monitoring equipment should be tested in the MR setting where it is to be used. (Anesth Analg 1994;79:1141–7)

Field strength in neuro-MR imaging : a comparison of 0.5 T and 1.5 T

A study was undertaken comparing neurological magnetic resonance imaging at high (1.5 T) and mid (0.5 T) field strengths. Twenty-eight patients (20 head and 8 spine) from our routine case load volunteered to undergo two consecutive and identical MR studies on the two systems. The two MR systems were built by the same manufacturer and were equipped with essentially identical hardware and software. Individual patient studies were performed consecutively in adjacent MR suites, and pulse sequence parameters were replicated exactly at the two field strengths. One exception to this rule was that the second echo of the long TR sequence in the head was acquired with a narrow receiver bandwidth on the 0.5 T system. The resulting axial double echo long repetition time (TR) and sagittal short TR head images and sagittal short and double echo long TR spine images were graded by two blinded observers (senior staff neuroradiologists) on two levels. First, the images were graded for image quality, i.e., conspicuousness of artifacts and clarity in depiction of normal and pathologic anatomy. Second, diagnostic accuracy of MR was assessed relative to the clinical-pathologic diagnosis in each case. The image quality of the 1.5 T system was rated superior in both the head and spine for most specific items assessed. This observer preference for 1.5 T images did not, however, translate into greater diagnostic accuracy for the 1.5 T system in the head. Although the 1.5 T system did have a slight advantage in diagnostic accuracy in the spine, a significant difference was not found.

Video X-ray progressive scanning: new technique for decreasing X-ray exposure without decreasing image quality during cardiac catheterization

A newly developed video x-ray progressive scanning system improves image quality, decreases radiation exposure, and can be added to any pulsed fluoroscopic x-ray system using a video display without major system modifications. With use of progressive video scanning, the radiation entrance exposure rate measured with a vascular phantom was decreased by 32 to 53% in comparison with a conventional fluoroscopic x-ray system. In addition to this substantial decrease in radiation exposure, the quality of the image was improved because of less motion blur and artifact. Progressive video scanning has the potential for widespread application to all pulsed fluoroscopic x-ray systems. Use of this technique should make cardiac catheterization procedures and all other fluoroscopic procedures safer for the patient and the involved medical and paramedical staff.

Optimal resources for the examination and endovascular treatment of the peripheral and visceral vascular systems. AHA Intercouncil Report on Peripheral and Visceral Angiographic and Interventional Laboratories.

In 1969 the Intersociety Commission for Heart Disease Resources was established through a contract with the American Heart Association under Public Law 89-239. Its responsibility was to produce guidelines defining optimal medical resources and care for the prevention and treatment of cardiovascular disease, including guidelines for radiologic facilities (1). This resource guideline was revised in 1976 (2) and again in 1983 (3). The Intersociety Commission was disbanded shortly thereafter, but a joint ad hoc task force of the American Heart Association and the American College of Cardiology continued this work with “Guidelines for Cardiac Catheterization and Cardiac Catheterization Laboratories” (4), published in 1991. The task force concluded that “. . . while noncardiac diagnostic and therapeutic procedures are growing in number . . . guidelines for these services are beyond the scope of this document.” These documents have charted the evolution of cardiac catheterization from a procedure performed in a few highly specialized laboratories for cardiovascular research to one performed in a number of interventional cardiac laboratories. The documents also have provided useful optimal resource guidelines. In the 1983 report similar standards for angiographic facilities were implied but never specifically stated, with the emphasis always on the heart. Nevertheless, the report mentioned angiographic facilities and considerable involvement by radiologists. Just as cardiac catheterization has evolved, so too have peripheral and visceral angiography. Diagnostic angiography proliferated in the 1960s and the 1970s, and interventional radiology emerged in the 1980s. Nevertheless, optimal resource standards have never been promulgated except in an abbreviated form (5). In 1989 the Council Affairs Committee of the AHA approved the formation of a committee on peripheral vascular disease under the auspices of the Council on Cardiovascular Radiology. In 1992 an ad hoc task force was created, with members from the Councils on Cardiovascular Radiology, Cardio-Thoracic and Vascular Surgery, Clinical Cardiology, and Kidney in Cardiovascular Disease, to develop guidelines for peripheral and visceral angiographic and interventional laboratories. Task force members are Eric C. Martin, MD, chair; William J. Casarella, MD (Council on Cardiovascular Radiology); Barry T. Katzen, MD (Council on Cardiovascular Radiology); Gerald M. Dorros, MD (Council on Clinical Cardiology); Gary S. Roubin, MD (Council on Clinical Cardiology); James A. DeWeese, MD (Council on Cardio-Thoracic and Vascular Surgery); and John H. Laragh, MD (Council on Kidney in Cardiovascular Disease). The task force is grateful for the contributions of the following consultants: John F. Cardella, MD; Joel E. Gray, PhD; Victoria M. Marx, MD; Edward L. Nickoloff, ScD; Michael J. Pentecost, MD; and David C. Levin, MD.