A survey of clinical factors and patient dose in mammography.

A survey was conducted to estimate the mean glandular dose (MGD) for women undergoing mammography and to report the distribution of doses, compressed breast thickness, glandular tissue content, and mammographic technique factors used. From 24,471 mammograms, of 6,006 women, clinical data were collected. The survey data included mammograms from seven modern units using a molybdenum (Mo) anode and either Mo or rhodium (Rh) filter. Exposure factors for each mammogram were recorded automatically onto a floppy disk on each unit. All mammography units were calibrated individually using breast tissue equivalent attenuation slabs of varying glandular content, so the breast glandular content could be estimated on the basis of exposure factors and compressed breast thickness. The MGD was estimated for each mammogram based on the normalized glandular dose and calculated entrance exposure in air. The survey found a median MGD of 2.6 mGy. The median breast glandular tissue content was 28% and the median compressed breast thickness was 5.1 cm. Also, patient attenuation data were converted to equivalent BR-12 and acrylic thickness to help determine appropriate phantom thicknesses required for mammography unit automatic exposure control performance assessment.

Determining the sharpness of electronic image displays: an evaluation of three methods.

The authors evaluated 3 methods developed to assess the level of monitor cathode ray tube (CRT) sharpness. Results include a comparison of 2 observer-based methods to a charged coupled device (CCD) digital camera-based method for the purposes of CRT equipment comparison, acceptance testing, and routine CRT quality control. Three methods designed to measure a monitor's sharpness were evaluated on a single 20-inch CRT monitor. We defined signal-to-noise ratio (SNR) to be the overall signal difference measured by each method from the highest to lowest values divided by the average standard deviation of the measurements. Comparing the results of the 3 methods, the authors found that the digital CCD camera-based method provided a much higher SNR than the 2 observer-based methods and, therefore, is the preferred of the 3 methods for measuring the sharpness of CRT displays. The SNR values for the CCD, Cx and line target methods were 151.5, 4.9, and 4.3, respectively. The Cx target observer-based method (a novel target and scoring routine dubbed the "Cx" target because of its appearance) had a higher SNR than the line target observer-based method. The average time and standard deviation required to score the Cx and the line targets were 5.45 +/- 2.15 minutes and 8.34 +/- 2.95 minutes, respectively. The observer-based method results (and variability) versus the camera-based method results (and variability) indicate strong linear relationships. Exploring this finding and the optimization of the camera-based method are the subjects of future research.

A comparison of the uniformity requirements for SPECT image reconstruction using FBP and OSEM techniques.

OBJECTIVE: Gamma camera nonuniformity can result in the presence of ring artifacts in reconstructed SPECT images. The objective of this study is to compare the relationship between ring artifact magnitude and image noise in tomographic images reconstructed using FBP and OSEM. METHODS: A cylindrical phantom was filled with water and (99m)TC: Seven tomographic acquisitions were performed, with total counts per acquisition ranging from 1.5 Mcts to 100 MCTS: All acquisitions were reconstructed using both FBP and OSEM. Ring artifacts were generated in the transaxial data by introducing defects at a given location in each planar image. The modified acquisitions were again reconstructed using both FBP and OSEM. The ring artifacts were isolated by the subtraction of the uncorrupted datasets from the corrupted datasets. The magnitude of the ring artifacts in the corrupted reconstructions was measured and compared to the mean counts and noise level in the uncorrupted data. RESULTS: Ring magnitude in OSEM-reconstructed images is approximately one third that of FBP images. However, there is a corresponding reduction in image noise with OSEM and the ratio of ring magnitude-to-image noise was relatively similar for both OSEM and FBP. Rings generated with OSEM fell off more rapidly with distance from the image center, and reached a plateau at a higher magnitude at large distances. The visibility of rings with OSEM relative to FBP will depend on the location of the causative defect in the planar data and the number of iterations performed with OSEM. Differences between the 2 algorithms are subtle. CONCLUSION: Our results would indicate that the uniformity requirements for SPECT are similar for FBP and OSEM reconstruction algorithms.

Measurement of half-value layer in x-ray CT: a comparison of two noninvasive techniques.

The purpose of this paper is to determine the accuracy and reproducibility of two noninvasive methods of measuring half-value layer (HVL), ring and localization, compared with an invasive technique (suspending tube rotation). The ring method uses concentric aluminum rings about a CTDI ionization chamber at isocenter. Data were acquired using axial CT protocols (rotating x-ray tube, stationary patient table). The localization technique uses square aluminum sheets secured to the gantry shroud to filter the radiation beam, and a CTDI chamber suspended externally at isocenter. Data were acquired using localization image protocols (stationary x-ray tube, moving patient table). The invasive technique was similar to the localization technique except that the ion chamber was placed on the patient table and the tube rotation disabled using service software. Data for all techniques were collected on the same CT system. Independent data sets were collected to determine reproducibility. Sensitivity to ionization chamber lateral displacement from isocenter was investigated. Measured HVLs (mm aluminum, mean+/-std, n=4) were 7.19+/-0.03 (ring); 7.17+/-0.04 (localization); and 7.24+/-0.02 (service mode), which were not significantly different (p = 0.05). Displacing the chamber from isocenter changes the HVL, depending on the bow-tie filter, by as much as 5 mm aluminum. Aluminum filter to ion chamber distances of 25-35 cm provided accurate results. Both noninvasive techniques were accurate and reproducible at isocenter. However, the measured HVL was dependent upon the bow-tie filter and the lateral displacement of the ionization chamber with respect to isocenter. Greater than 2 cm off of isocenter, the ring technique did not provide accurate HVL measurements.

Papillary lymphoid hyperplasia of the terminal ileum: an unusual cause of intussusception and gastrointestinal bleeding in childhood.

Papillary lymphoid hyperplasia of the terminal ileum is a benign condition associated with abdominal pain, intussusception, and gastrointestinal hemorrhage. It appears to represent a distinct clinicopathologic entity, separate from the usual idiopathic intussusception of infancy and childhood. The lesions are reasonably well circumscribed, localized in the submucosa of the terminal ileum, and composed of lymphoid tissue with prominent germinal follicles. Management by ileocolectomy resulted in complete cure with no postoperative complications in our six cases. However, many authors recommend conservative therapy. The cause is not known but there may be some relationship between these cases and intestinal adenovirus infection.