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Biomedical subjects

A J Alter

Publications and source records attributed to A J Alter.

At least 19 recordsLinked to original sources
PubMed2005

Microcontrolled pyro-electric instrument for measuring X-ray intensity in mammography.

A novel instrument for measurement of X-ray intensity from mammography consists of a sensitive pyro-electric detector, a high-sensitivity, low-noise current-to-voltage converter, a microcontroller and a digital display. The heart of this device, and what makes it unique is the pyro-electric detector, which measures radiation by converting heat from absorbed incident X-rays into an electric current. This current is then converted to a voltage and digitised. The detector consists of a ferro-electric crystal; two types were tested: lithium tantalate and lithium niobate. X-ray measurement in mammography is challenging because of its relatively low photon energy range, from 11 keV to 15 keV equivalent mean energy, corresponding to a peak tube potential from 22 to 36 kV. Consequently, energy fluence rate or intensity is low compared with that of common diagnostic X-ray. The instrument is capable of measuring intensities as low as 0.25 mW m(-2) with precision greater than 99%. Not only was the instrument capable of performing in the clinical environment, with high background electromagnetic interference and vibration, but its performance was not degraded after being subjected to 140 roentgen (3.6 x 10(-2) C kg(-2) air) as measured by piezo-electric (d33) or pyro-electric coefficients.

Equipment Design↗
PubMed1986

Acute lobular nephronia.

Acute lobular nephronia is an unusual form of localized renal infection, which has a characteristic computerized tomographic and ultrasonographic appearance, and should be distinguished from abscess or other renal masses. Treatment is nonoperative, consisting of intensive antibiotic therapy.

Acute Disease↗
PubMed1982

Diagnosis of vertebral fractures. A comparison of conventional radiography, conventional tomography, and computed axial tomography.

Thirty patients with acute thoracic, lumbar, or thoracolumbar fractures, dislocations, or fracture-dislocations were evaluated with standard radiographs, conventional polytomography, and computerized axial tomography. The resulting ninety studies were coded, randomized, and independently interpreted by three radiologists. The diagnostic accuracy of the interpretations based on the computerized tomography scans combined with standard radiographs equaled that of the interpretations based on just the tomograms in the evaluation of fractures of posterior elements. In addition, computerized tomography was superior to the other methods in demonstrating impingement on the neural canal as well as injuries to other organ systems. Also, when compared with conventional polytomography, computerized tomography could be completed with less risk to the patient (no changes in position and ten times less radiation). We concluded that computerized tomography should replace conventional polytomography as the initial study to augment standard radiographs in the assessment of thoracic and lumbar fractures. Conventional polytomography should be reserved for patients in whom precise evaluation of the pars interarticularis is deemed necessary.

Adolescent↗
PubMed1981

Hemorrhagic angiomyolipoma: demonstration by computed tomography.

Preoperative tissue specific diagnosis of renal angiomyolipomas is now frequently made by computed tomography (CT). Although hemorrhage of these hypervascular tumors is a common cause for presentation, it is rarely recognized preoperatively. We present two cases of large, solitary angiomyolipoma complicated by perinephric and intratumoral hemorrhage demonstrated by CT.

Adult↗
PubMed1980

Computerized tomographic assessment of retroperitoneal hemorrhage after percutaneous renal biopsy.

Computerized tomography demonstrated evidence of retroperitoneal hemorrhage in more than one half (12) of 21 patients who had had renal biopsies. This frequency is much greater than that generally reported and reflects a lack of sensitivity of the routinely followed clinical practices in detecting retroperitoneal hemorrhage. Computerized tomography offers a sensitive, noninvasive method of detecting and evaluating size and site of retroperitoneal hemorrhage.

Biopsy, Needle↗
PubMed1979

Computed tomography of the retroperitoneum following nephrectomy.

Twenty-five patients were examined by computed tomography (CT) after nephrectomy. CT was useful in the detection of postoperative complications and local recurrence of tumor. Ultrasound was difficult because of rib artifacts or bowel gas, and a fluid-filled bowel often simulated tumor: oral contrast material was useful during CT. Local recurrence was demonstrated by CT in 8 patients in whom it was clinically suspected. Recurrent tumor was simulated by scarring in 3 cases and by an accessory or residual spleen in 2. Operative complications included one hematoma and one retroperitoneal abscess. CT could be useful in following up selected patients after nephrectomy.

Adult↗
PubMedDate not supplied

The influence of ambient and viewbox light upon visual detection of low-contrast targets in a radiograph.

Thirty-one observers (five radiologists, five radiology residents, and 21 nonradiologists) examined low-contrast images of 13 polyvinylchloride cylinders. Image density ranged from 1.91 to 2.05 OD units with a background density of 2.09 OD units. The experiment tested visual performance under various clinically relevant lighting conditions by asking the observers to locate a groove in each cylinder. Use of low ambient light and restricting light from surrounding veiwboxes significantly improved performance (P less than 0.0001). In general, the less the amount of extraneous light, the higher was the detection rate. Some observers did significantly better than others. Reduced scattering of light within the eye is suggested as an explanation for their increased performance.

Humans↗