Recommendations on performance characteristics of diagnostic exposure meters: report of AAPM Diagnostic X-Ray Imaging Task Group No. 6.

Task Group 6 of the Diagnostic X-Ray Imaging Committee of the American Association of Physicists in Medicine (AAPM) was appointed to develop performance standards for diagnostic x-ray exposure meters. The recommendations as approved by the Diagnostic X-Ray Imaging Committee and the Science Council of the AAPM are delineated in this report and provide specifications on meter precision, calibration accuracy, calibration reference points, linearity, energy dependence, exposure rate dependence, leakage, amplification gain settings, directional dependence, the stem effect, constancy checks, and calibration intervals. The report summarizes recommendations for meters used in mammography, general purpose radiography including special procedures, computed tomography, and radiation safety surveys for x-ray radiography.     

Use of a Doppler guide wire for intravascular blood flow measurements: a validation study for potential neurologic endovascular applications.

PURPOSETo conduct a validation study of a Doppler guide wire for potential neuroendovascular applications.METHODSA 12-MHz, 0.018-inch Doppler guide wire was evaluated in eight swine under various blood flow conditions using two types of in vivo cerebrovascular models (physiologic and arteriovenous shunting). Flow conditions were mechanically and pharmacologically altered. Doppler average peak velocity was compared with volumetric blood flow, and flow profile corrections were calculated and analyzed. Qualitative aspects of the Doppler guide wire spectra were also assessed.RESULTSPlots of average peak velocity versus volumetric blood flow showed excellent linear relationships (r2 > 0.94), which were maintained at high flow conditions (average peak velocity, 99 to 236 cm/sec; volumetric blood flow, 392 to 889 mL/min). Values of flow profile correction varied from 0.43 to 0.94 and showed no consistent relationship to changes in volumetric blood flow.CONCLUSIONSThe excellent correlation between average peak velocity and volumetric blood flow over a wide range of blood flow conditions and the additional qualitative information of the Doppler guide wire spectra establish a foundation for clinical implementation. The unpredictable variations of flow profile corrections remain obstacles for calculating volumetric blood flow based on Doppler guide wire average peak velocity.     

Breast sonography: technique, equipment, and normal anatomy

In order to interpret breast sonograms successfully, it is necessary to understand the technical factors that affect the image. It is especially important to be aware of the effects of focal zone, power, time gain compensation, and gray scale selection on cyst/solid differentiation, the primary indication for breast sonography. Adequate breast examinations can be performed with either high-frequency automated whole-breast ultrasound units or hand-held instruments with a transducer operating at 5 MHz or greater frequency, and with a depth of focus of no more than 3 cm. Familiarity with the normal breast sonogram, including the variations in the relative amounts of parenchyma, connective tissue, and fat that occur with increasing age and parity, is essential for the identification, characterization, and localization of abnormalities.     

Renal stone shadowing: an investigation of contributing factors

A series of in vitro experiments evaluated the effects of intervening tissue, B-mode processing algorithms, stone chemical composition, stone size, and reverberation artifacts on the acoustic shadows of renal stones. Stone size was found to be the most important variable; intervening tissue and focal zone placement also affected imaging. Reverberation artifacts may fill in an acoustic shadow, but can still provide information. The survey algorithm produced slightly clearer shadows than the static storage algorithm. Gray-scale map changes, increased power, and chemical composition of calculi did not affect shadowing.     

High frequency breast ultrasound. Hand-held versus automated units; examination for palpable mass versus screening

Four hundred forty-five patients had one or more breast ultrasound examinations with equipment from six manufacturers, operating at 5, 7.5, or 10 MHz. Two hundred seven patients were examined by both automated and hand-held units. In revealing cysts and solid masses, the automated and hand-held units performed nearly identically. Of 198 patients who had screening mammograms, ultrasound evaluation revealed that 85 (43%) had cysts, while 32 (16%) had solid masses. Of the 207 patients who had diagnostic mammograms for a palpable mass, 63 (30.4%) had cysts, while an equal number had solid masses. Of 45 solid masses from both groups that were imaged and biopsied, all 15 that were malignant were palpable. No nonpalpable malignancies were found by ultrasound alone.     

A review of mammography test objects for the calibration of resolution, contrast, and exposure

Mandated and voluntary accreditation and quality control programs for mammography require the use of standardized mammography test objects. We evaluated eleven commercially available test objects and three prototype test objects, comparing them with respect to their resolution targets, contrast targets, and the dose they required when imaged by the same automatic exposure meter. Ion chamber and/or thermoluminescent dosimeter measurements of exposure were made with each test object, while attenuation was measured for seven. Measurements of dosage using acrylic (5 test objects) and tissue equivalent epoxy (9 test objects) showed as much as a 400% variation in the radiation supplied by the same automatic exposure device when differences in thicknesses of test objects were normalized. Speck visibility was as dependent on the composition of the specks and of the surrounding material as on the size of the specks. Contrast targets were adequate in only three test objects. Optical density differences between images of a 4-cm-thick breast and of different test object materials, also 4 cm in thickness, exposed to the same radiation, imply that untested acrylic or epoxy resin materials should not used in the calibration of automatic exposure controls.     

New and future developments in screen-film mammography equipment and techniques.

Two improvements in mammography equipment during the last 4 years will greatly affect the practice of mammography during the next decade: dose reduction and improved testing equipment for monitoring the quality of mammography. The increased use of digital radiography has stimulated studies comparing digital mammography with screen-film mammography. Some digital algorithms for detecting clusters of calcifications may have application in screening mammography within the next decade.     

Effect of poor control of film processors on mammographic image quality.

With the increasingly stringent standards of image quality in mammography, film processor quality control is especially important. Current methods are not sufficient for ensuring good processing. The authors used a sensitometer and densitometer system to evaluate the performance of 22 processors at 16 mammographic facilities. Standard sensitometric values of two films were established, and processor performance was assessed for variations from these standards. Developer chemistry of each processor was analyzed and correlated with its sensitometric values. Ten processors were retested, and nine were found to be out of calibration. The developer components of hydroquinone, sulfites, bromide, and alkalinity varied the most, and low concentrations of hydroquinone were associated with lower average gradients at two facilities. Use of the sensitometer and densitometer system helps identify out-of-calibration processors, but further study is needed to correlate sensitometric values with developer component values. The authors believe that present quality control would be improved if sensitometric or other tests could be used to identify developer components that are out of calibration.