Philip H. Heintz

CT scanning: a major source of radiation exposure.

CT scanning is a relatively high dose procedure that is becoming much more common worldwide. In the mid-1990s, CT scanning accounted for about 4% of procedures and about 40% of the collective dose in diagnostic radiology. With the advent of helical, fluoroscopic, and multi-slice techniques the dose per procedure has not diminished and the use of CT has increased even more. In large hospitals, CT scanning now accounts for about 15% of procedures and 75% of the diagnostic radiation dose received by patients. When multiple CT scans are conducted on the same patient, the absorbed doses are in the range at which small but statistically significant increases in cancer have been found in the atomic bomb survivors.

Ongoing quality control in digital radiography: Report of AAPM Imaging Physics Committee Task Group 151.

Quality control (QC) in medical imaging is an ongoing process and not just a series of infrequent evaluations of medical imaging equipment. The QC process involves designing and implementing a QC program, collecting and analyzing data, investigating results that are outside the acceptance levels for the QC program, and taking corrective action to bring these results back to an acceptable level. The QC process involves key personnel in the imaging department, including the radiologist, radiologic technologist, and the qualified medical physicist (QMP). The QMP performs detailed equipment evaluations and helps with oversight of the QC program, the radiologic technologist is responsible for the day-to-day operation of the QC program. The continued need for ongoing QC in digital radiography has been highlighted in the scientific literature. The charge of this task group was to recommend consistency tests designed to be performed by a medical physicist or a radiologic technologist under the direction of a medical physicist to identify problems with an imaging system that need further evaluation by a medical physicist, including a fault tree to define actions that need to be taken when certain fault conditions are identified. The focus of this final report is the ongoing QC process, including rejected image analysis, exposure analysis, and artifact identification. These QC tasks are vital for the optimal operation of a department performing digital radiography.

Physics Instruction for Radiology Residents in the Era of the New ABR Examination Process

t o b 4 o m t w q p n ajor changes in the ABR certifiation process are being impleented, starting with the class of edical residents who began their adiology residencies in July 2010. he former 3-examination certifiation process (physics, clinical ritten, and oral) is being elimiated over the next few years and ill be replaced by a new 2-examiation computer-based certificaion process [1,2]. Oral examinaions will no longer occur. The first of hese 2 computer-based examinaions will be administered during the esidency, and the second will be adinistered 15 months after graduaion from the residency program. oth examinations will include asessments of physics knowledge esential to practicing radiologists, as ell the ABR’s Maintenance of ertification cognitive examinaions radiologists will take to demnstrate their competency throughut their careers.

High-resolution imaging with a real-time synthetic aperture ultrasound system: a phantom study

It is difficult for ultrasound to image small targets such as breast microcalcifications. Synthetic aperture ultrasound imaging has recently developed as a promising tool to improve the capabilities of medical ultrasound. We use two different tissueequivalent phantoms to study the imaging capabilities of a real-time synthetic aperture ultrasound system for imaging small targets. The InnerVision ultrasound system DAS009 is an investigational system for real-time synthetic aperture ultrasound imaging. We use the system to image the two phantoms, and compare the images with those obtained from clinical scanners Acuson Sequoia 512 and Siemens S2000. Our results show that synthetic aperture ultrasound imaging produces images with higher resolution and less image artifacts than Acuson Sequoia 512 and Siemens S2000. In addition, we study the effects of sound speed on synthetic aperture ultrasound imaging and demonstrate that an accurate sound speed is very important for imaging small targets.

Solid-state dosimeters: A new approach for mammography measurements

PURPOSE To compare responses of modern commercially available solid-state dosimeters (SStDs) used in mammography medical physics surveys for two major vendors of current digital mammography units. To compare differences in dose estimates among SStD responses with ionization chamber (IC) measurements for several target/filter (TF) combinations and report their characteristics. To review scientific bases for measurements of quantities required for mammography for traditional measurement procedures and SStDs. METHODS SStDs designed for use with modern digital mammography units were acquired for evaluation from four manufacturers. Each instrument was evaluated under similar conditions with the available mammography beams provided by two modern full-field digital mammography units in clinical use: a GE Healthcare Senographe Essential (Essential) and a Hologic Selenia Dimensions 5000 (Dimensions), with TFs of Mo/Mo, Mo/Rh; and Rh/Rh and W/Rh, W/Ag, and W/Al, respectively. Measurements were compared among the instruments for the TFs over their respective clinical ranges of peak tube potentials for kVp and half-value layer (HVL) measurements. Comparisons for air kerma (AK) and their associated relative calculated average glandular doses (AGDs), i.e., using fixed mAs, were evaluated over the limited range of 28-30 kVp. Measurements were compared with reference IC measurements for AK, reference HVLs and calculated AGD, for two compression paddle heights for AK, to evaluate scatter effects from compression paddles. SStDs may require different positioning from current mammography measurement protocols. RESULTS Measurements of kVp were accurate in general for the SStDs (within -1.2 and +1.1 kVp) for all instruments over a wide range of set kVps and TFs and most accurate for Mo/Mo and W/Rh. Discrepancies between measurements and reference values were greater for HVL and AK. Measured HVL values differed from reference values by -6.5% to +3.5% depending on the SStD and TF. AK measurements over limited (28-30) kVps ranged from -6% to +7% for SStDs, compared with IC reference values. Relative AGDs for each SStD using its associated measurements of kVp, HVL and AK underestimated AGD in nearly all cases, compared with reference IC values, with discrepancies of <-1% to ∼-10%. Some differences in AGD were related to differences in contributions of compression paddle scatter to AK measurements made by ICs. Applying measured factors for scatter effects in AK measurements for three SStDs reduced discrepancies between -6.2% and +1.3%, shifting AGDs from SStDs closer to IC AGDs. CONCLUSIONS This study revealed that SStD measurements yielded good agreement with set kVp, poor agreement with standard HVL determinations, and AK measurements that were substantially different from IC measurements. Discrepancies are partly related to the scattered radiation measured by ICs in determining AK. As a result, IC measurements required for AGD, using currently accepted methodology, typically result in higher AGDs than SStDs, because current methodologies do not account for differing instrument responses to scatter. HVLs reported by SStDs contribute to discrepancies in calculated AGD that depend on kVp and TF. Medical physicists are encouraged to compare their results for SStD instruments using a similar methodology for potential discrepancies with their traditional instruments.

SU-E-I-86: Evaluation of the New RaySafe Unfors X2 Dosimetry System

PURPOSE To evaluate the new RaySafe Unfors X2 (X2) dosimetry system and compare it to the operation of the RaySafe Unfors Xi (Xi) and Radcal Accugold (RCAG) dosimetry systems. The comparison was done for the radiographic/fluoroscopic detectors, mammography detectors and the CT ionization chambers. METHODS This study used several R/F rooms, GE AMX4 portable x-ray unit, Siemens Biograph 16 slice CT scanner and a Hologic Dimensions mammography unit to evaluate the dosimetry systems. The three X2 detectors were compared to similar detectors of the older Xi and RCAG detectors under clinical conditions used for diagnostic medical physics testing. Measurements of kVp, HVL and exposure were made under identical conditions. RESULTS For radiography and fluoroscopy the three systems agreed to within +2 kVp in the 60 to 140 kVp range, HVL measurements agreed to within +2 mm Al and the exposures agreed to within +5%. The RCAG 6 cc ionization chamber measured at least 3% higher than the diode systems. The X2 R/F detector appeared to be transparent to the fluoroscopy AEC system. For exposures made using both the CT ACR dose phantoms, the X2 agreed to within +3% of the other two systems. For mammography measurements, the three systems agreed to within +0.4kVp (25-49 kVp range), HVL measurements agreed to within +0.05 mm Al and the exposures agreed to within +1% of the ionization chamber. CONCLUSION The X2 system is a new version of the older Xi system. The system is faster, more robust, very easy to use, has a larger dynamic range, produced less errors and stores 1000 exposures. The measurements showed that the system performs well in the clinical environment and the X2 is within + 5% agreement of the other two calibrated systems.

Effects of La0.2Ce0.6Eu0.2F3 nanocrystals capped with polyethylene glycol on human pancreatic cancer cells in vitro

Lanthanide fluoride colloidal nanocrystals offer a way to improve the diagnosis and treatment of cancer through the enhanced absorption of ionizing radiation, in addition to providing visible luminescence. In order to explore this possibility, tests with a kilovoltage therapy unit manufactured by the Universal X-Ray Company were performed to estimate the energy sensitivity of this technique. La0.2Ce0.6Eu0.2F3 nanocrystals capped with polyethylene glycol of molecular weight 6000 were synthesized, suspended in deionized water, and made tolerant to biological ionic pressures by incubation with fetal bovine serum. These nanocrystals were characterized by dynamic light scattering, muffle furnace ashing, and photoluminescence spectroscopy. Clonogenic assays were performed on the cells to assay the cytotoxicity and radiotoxicity of the nanocrystals on the human pancreatic cancer cell line PANC-1, purchased from ATCC.

Segmentation of knee joints in x-ray images using decomposition-based sweeping and graph search

Plain radiography (i.e., X-ray imaging) provides an effective and economical imaging modality for diagnosing knee illnesses and injuries. Automatically segmenting and analyzing knee radiographs is a challenging problem. In this paper, we present a new approach for accurately segmenting the knee joint in X-ray images. We first use the Gaussian high-pass filter to remove homogeneous regions which are unlikely to appear on bone contours. We then presegment the bones and develop a novel decomposition-based sweeping algorithm for extracting bone contour topology from the filtered skeletonized images. Our sweeping algorithm decomposes the bone structures into several relatively simple components and deals with each component separately based on its geometric characteristics using a sweeping strategy. Utilizing the presegmentation, we construct a graph to model the bone topology and apply an optimal graph search algorithm to optimize the segmentation results (with respect to our cost function defined on the bone boundaries). Our segmented results match well with the manual tracing results by radiologists. Our segmentation approach can be a valuable tool for assisting radiologists and X-ray technologists in clinical practice and training.

Meaningful Data or Just Measurements? Differences Between Ionization Chamber and Solid-State Detectors

One of the principal responsibilities of a clinical diagnostic medical physicist is to ensure good image quality at an appropriate dose. To determine dose, three quantities must be known for the x-ray beam: peak tube potential, half-value layer (HVL) and air kerma (AK), formerly known as exposure. Instrument and equipment setup (ie, geometric factors) are also important in finding the desired value. The gold standard for clinical exposure or AK measurements uses a calibrated air ionization chamber (IC), which is used with aluminum filters to determine HVL from additional measurements. A separate instrument is required to find the peak tube potential. Solidstate detectors (SStDs) are now available for use in diagnostic physics measurements in mammography, general radiography, and fluoroscopy. The advantage of these alternative instruments is that they can acquire measurements for multiple quantities simultaneously and record them directly into a computer database. The question is, how reliable are these measurements compared with the gold standard? Consider the following situation: You perform an image quality and dose assessment as part of your annual mammography medical physics survey. You have your trusted gold-standard instruments and a new

SU-C-116-03: Comparisons and Limitations of Physics Instrumentation in Mammography

PURPOSE To evaluate discrepancies in measurements for two major vendors of mammography equipment with a few models of physics instruments, and to make known potential errors in best use of these instruments for ACR and MQSA/FDA documentation. We show variability in responses under different beam conditions and report problems encountered. A separate study shows effects on calculated mean glandular dose. METHODS Recent mammography equipment evaluations for new installations show discrepancies in measurements of kVp and HVL with different instrumentation. This study tested well-behaved GE Essential and Hologic Dimensions units (6 target-filter combinations) with 3 vendors and 4 instruments (3 with solid-state detectors, SStDs) using recommended techniques, which sometime conflict. HVLs were measured two ways: (a) single-point measurements for the SStDs, and for some instruments, (b) with standardized mammography-grade aluminum filtration. Particular attention was paid to HVLs near values required for mammography phantom mean glandular dose calculations (28-30 kVp). Ionization chamber measurements with Al filtration, according to ACR recommendations, were used as reference HVLs for 28, 29 and 30 kVp. RESULTS Measurements of kVp with SStD instruments were most consistent with Mo/Mo, with a 0.18 kV average discrepancy for all instruments (discrepancy range (-0.3,+0.4). For Mo/Mo, one vendor was consistently high and 2 low, but this trend was inconsistent among other combinations. The range of discrepancies was within 1 kV for all except Mo/Rh for one instrument and W/Ag for another. Unlike kVp, HVL measurements showed large variations. Over 28-30 kVp, discrepancies of single-point HVLs ranged from approximately zero to nearly 15% from reference values. It was impossible to follow manufacturers or ACR HVL measurement recommendations with aluminum for 2 of the 3 SStDs. CONCLUSION All instruments appear to function well, but data show biases which affect accuracy. Users must be careful how they interpret their data, particularly for HVL.