G. Donald Frey

Embryo Dose Estimates in Body CT

OBJECTIVE The purpose of this article is to develop a method for estimating embryo doses in CT. MATERIALS AND METHODS Absorbed doses to the uterus (embryo) of a 70-kg woman were estimated using the ImPACT CT Patient Dosimetry Calculator. For a particular CT scan length, relative uterus doses and normalized plateau uterus doses were determined for a range of commercial CT scanners. Patient size characteristics were obtained from cross-sectional axial images of 100 consecutive patients (healthy women undergoing unenhanced pelvic CT examinations). For each patient, the diameter of a water cylinder with the same mass as the patients pelvis was computed. Relative dose values were generated for cylinder diameters ranging from 16 to 36 cm at x-ray tube voltages between 80 and 140 kV. RESULTS Values of relative uterus dose increased monotonically with increasing scan length, independently of scanner model, and reached a plateau for scan lengths greater than approximately 50 cm. The average normalized plateau uterus dose for all scanners was approximately 1.4 and showed interscanner differences of less than 10% for modern scanners operated at 120 kV. Normalized plateau doses show little dependence on the x-ray tube voltage used to perform the CT examination. Our results show that the uterus dose estimate in an abdominal or pelvis CT examination performed on a 70-kg patient is about 40% higher than the reported value of the volume CT dose index (CTDI(vol)). The pelvis of a 70-kg patient may be modeled as a water cylinder with a diameter of 28 cm and has an average anteroposterior dimension of 22 cm. For constant CT technique factors, embryo dose estimates for a 45-kg patient would be approximately 18% higher than those for a 70-kg patient, whereas the corresponding dose estimates in a 120-kg patient would be approximately 37% lower. CONCLUSION Embryo doses can be estimated using relative uterus doses, normalized plateau uterus doses, and CTDI(vol) data with correction factors for patient size.

Evaluation of a flat panel digital radiographic system for low-dose portable imaging of neonates.

The purpose of this study was to evaluate the clinical utility of an investigational flat-panel digital radiography system for low-dose portable neonatal imaging. Thirty image-pairs from neonatal intensive care unit patients were acquired with a commercial Computed Radiography system (Agfa, ADC 70), and with the investigational system (Varian, Paxscan 2520) at one-quarter of the exposure. The images were evaluated for conspicuity and localization of the endings of ancillary catheters and tubes in two observer performance experiments with three pediatric radiologists and three neonatologists serving as observers. The results indicated no statistically significant difference in diagnostic quality between the images from the investigational system and from CR. Given the investigational systems superior resolution and noise characteristics, observer results suggest that the high detective quantum efficiency of flat-panel digital radiography systems can be utilized to decrease the radiation dose/exposure to neonatal patients, although post-processing of the images remains to be optimized. The rapid availability of flat-panel images in portable imaging was found to be an added advantage for timely clinical decision-making.

Quantitative mammography contrast threshold test tool

Mammographic contrast is commonly evaluated by visualizing small objects of varying size or mass divided by projected area. These qualitative contrast determinations are commonly performed by imaging a phantom like the American College of Radiology accreditation phantom at clinical mammographic settings. However, this contrast assessment does not take into account the kVp of the machine. This work describes a quantitative mammography contrast threshold test tool which examines light object contrast on a uniform background for a contrast range of 0.32% to 1.38% at 25 kVp. For this mammography contrast threshold test tool, contrast is defined by delta I/I = loge (psi O/ psi b), where psi O is the target energy flux, and psi b is the background energy flux. Contrast threshold is defined as the lowest contrast value for which the objects are visible. Unlike traditional assessments of mammographic contrast, this measurement of contrast threshold is kVp corrected. The mammography contrast threshold test tool is constructed out of common plastics and provides a quantitative means of assessing contrast threshold for individual mammographic units and total mammographic systems.

Computed tomography evaluation of pheochromocytoma in pregnancy.

Two cases representative of the spectrum of the problem of pheochromocytoma in pregnancy are presented. One patient was typical of many cases of pheochromocytoma not diagnosed until delivery, with resultant maternal and fetal death. Computed tomography accurately preoperatively localized a pheochromocytoma involving the organ of Zuckerkandl in the second patient, with subsequent uncomplicated removal of the tumor during a cesarean delivery. A discussion of pheochromocytomas in pregnancy and the relative risk and benefits of preoperative localization with computed tomography are presented.

Control and management of the radiation environment.

867 quirements. A joint radiologist–physicist project would allow for additional benefits. Radiologists by training have always been masters of the radiation environment. With the recent concerns of colleagues, government regulators, and the public about the risks and possible misuses of radiation it is important for the profession to demonstrate that this training is reflected in the day-to-day control of the radiation environment so everyone can have confidence that studies are done effectively and safely. The AJR’s recent emphasis on medical physics and informatics reflects these concerns and can be of benefit to radiologists. G. Donald Frey AJR Section Editor, Medical Physics and Informatics Department of Radiation and Radiation Sciences Medical University of South Carolina Charleston, SC 29425 ajrsubmit@acr-arrs.org

Lung, liver and bone cancer mortality after plutonium exposure in beagle dogs and nuclear workers.

The Mayak Production Association (MPA) worker registry has shown evidence of plutonium-induced health effects. Workers were potentially exposed to plutonium nitrate [239Pu(NO3)4] and plutonium dioxide (239PuO2). Studies of plutonium-induced health effects in animal models can complement human studies by providing more specific data than is possible in human observational studies. Lung, liver, and bone cancer mortality rate ratios in the MPA worker cohort were compared to those seen in beagle dogs, and models of the excess relative risk of lung, liver, and bone cancer mortality from the MPA worker cohort were applied to data from life-span studies of beagle dogs. The lung cancer mortality rate ratios in beagle dogs are similar to those seen in the MPA worker cohort. At cumulative doses less than 3 Gy, the liver cancer mortality rate ratios in the MPA worker cohort are statistically similar to those in beagle dogs. Bone cancer mortality only occurred in MPA workers with doses over 10 Gy. In dogs given 239Pu, the adjusted excess relative risk of lung cancer mortality per Gy was 1.32 (95% CI 0.56–3.22). The liver cancer mortality adjusted excess relative risk per Gy was 55.3 (95% CI 23.0–133.1). The adjusted excess relative risk of bone cancer mortality per Gy2 was 1,482 (95% CI 566.0–5686). Models of lung cancer mortality based on MPA worker data with additional covariates adequately described the beagle dog data, while the liver and bone cancer models were less successful.

Medical Physics—Meeting the Needs of Radiologists: The Role of the American Journal of Roentgenology

AJR:192, April 2009 can Journal of Roentgenology (AJR) that address this need, including an article by Gunderman and Stephens [6] that discusses the need to teach medical students about imaging techniques. The American Roentgen Ray Society (ARRS) and the AJR are committed to providing medical physics articles, self-assessment modules, and other educational materials that can be used by radiologists to keep their knowledge of medical physics current. The AJR is striving to become the primary source of medical physics and informatics for practicing radiologists. Medical physics is one of the many components of radiology that allows the radiologist to provide optimal patient care and bring added value to the medical imaging process. Medical physics education is going through revitalization and societies like ARRS are and will be providing useful materials for radiologists. G. Donald Frey Section Editor, Medical Physics and Informatics Freyd@musc.edu

Teleradiology: technology and practice.

Teleradiology increases the ability of radiologists to provide service to remote and underserved locations as well as coverage at times when direct reading of images is not possible. Good practices for teleradiology are described in the American College of Radiology (ACR) teleradiology standard. Teleradiology equipment is converging with picture archiving and communications systems (PACS) equipment so that diagnostic interpretation from remote locations is possible. Image capture can be directly from digital modalities or by film scanner. Transmission speed is still an issue. High transmission speeds were difficult to achieve but recent improvements may increase speeds and decrease costs.

The American Board of Radiology Perspective on Maintenance of Certification: Part IV: Practice quality improvement in radiologic physics.

Recent initiatives of the American Board of Medical Specialties (ABMS) in the area of maintenance of certification (MOC) have been reflective of the response of the medical community to address public concerns regarding quality of care, medical error reduction, and patient safety. In March 2000, the 24 member boards of the ABMS representing all medical subspecialties in the USA agreed to initiate specialty-specific maintenance of certification (MOC) programs. The American Board of Radiology (ABR) MOC program for diagnostic radiology, radiation oncology, and radiologic physics has been developed, approved by the ABMS, and initiated with full implementation for all three disciplines beginning in 2007. The overriding objective of MOC is to improve the quality of health care through diplomate-initiated learning and quality improvement. The four component parts to the MOC process are: Part I: Professional standing, Part II: Evidence of life long learning and periodic self-assessment, Part III: Cognitive expertise, and Part IV: Evaluation of performance in practice (with the latter being the focus of this paper). The key components of Part IV require a physicist-based response to demonstrate commitment to practice quality improvement (PQI) and progress in continuing individual competence in practice. Diplomates of radiologic physics must select a project to be completed over the ten-year cycle that potentially can improve the quality of the diplomates individual or systems practice and enhance the quality of care. Five categories have been created from which an individual radiologic physics diplomate can select one required PQI project: (1) Safety for patients, employees, and the public, (2) accuracy of analyses and calculations, (3) report turnaround time and communication issues, (4) practice guidelines and technical standards, and (5) surveys (including peer review of self-assessment reports). Each diplomate may select a project appropriate for an individual, participate in a project within a clinical department, participate in a peer review of a self-assessment report, or choose a qualified national project sponsored by a society. Once a project has been selected, the steps are: (1) Collect baseline data relevant to the chosen project, (2) review and analyze the data, (3) create and implement an improvement plan, (4) remeasure and track, and (5) report participation to the ABR, using the template provided by the ABR. These steps begin in Year 2, following training in Year 1. Specific examples of individual PQI projects for each of the three disciplines of radiologic physics are provided. Now, through the MOC programs, the relationship between the radiologic physicist and the ABR will be continuous through the diplomates professional career. The ABR is committed to providing an effective infrastructure that will promote and assist the process of continuing professional development including the enhancement of practice quality improvement for radiologic physicists.

Radiation cataracts: new data and new recommendations.

OBJECTIVE This Minimodule discusses radiation cataracts and makes some basic suggestions for practicing radiologists. CONCLUSION For many years radiation-induced cataracts were considered unlikely by most radiologists. Recent data suggest that the likelihood is much higher than previously thought, and the International Commission on Radiological Protection has suggested lower exposure limits.