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Biomedical subjects

G K Bahr

Publications and source records attributed to G K Bahr.

8 recordsLinked to original sources
PubMed1979

The relationship of information density to pre-set counts obtained in brain, lung and liver scintigraphy.

The total number of counts required per view for brain and lung scintigraphy to achieve information or count density (CD) of 1 000 counts/cm2 and 2 000 counts/cm2 for liver scans was examined. To achieve these CDs, 600 000 counts per view are required for brain scans. For the lung, 500 000 counts in anterior and posterior views are required; 400 000 counts in the lateral view are sufficient. For 2 000 CD in the liver scan, 600 000 counts should be obtained in the anterior view and 500 000 in the right lateral. This number of counts assures the desired CD in 97% of cases.

Brain↗
PubMed1978

Generation of iso-TDF maps: considerations for radiation therapy planning.

The NSD (nominal standard dose) concept has been useful in therapy for comparing various radiation treatment schedules. More recently, TDF (time, dose, and fractionation) factors were introduced. By incorporating treatment schedules (time and fractionation) with isodose summations, TDFs can be determined throughout the patient contour, including tissue in and outside the tumor volume. For this purpose an isodose summation program was modified to generate iso-TDF maps based on the treatment schedule. For schedules in which all fields are not treated every day, recovery is not inhibited throughout the total treatment volume. It was necessary to reevaluate the concept of "recovery time" for tissues outside the tumor volume and to introduce a "threshold to inhibit recovery" model. Clinical examples assuming this recovery model are presented.

Cobalt Radioisotopes↗
PubMed1978

Clinical comparison of technetium-99m diphosphonate and pyrophosphate in bone scintigraphy: concise communication.

Thirty patients had bone scintigraphy with both Tc-99m pyrophosphate (Tc-PPi) and Tc-99m diphosphonate (Tc-HEDP). The images were given a composite rating for quality and the basis of three sets of criteria, and were also compared for the number of lesions detected by each agent. The two agents provided no difference in scan quality. Nevertheless, in ten of the 30 patients, at least two of the three readers detected with Tc-HEDP lesions that were not seen with Tc-PPi, and in two such cases all three readers considered the Tc-PPi scan normal. In another of these ten, two of three readers felt the Tc-PPi image was norm, whereas all three detected the lesion with Tc-HEDP. The reverse never occurred (P less than 0.01).

Bone Neoplasms↗
PubMed1977

The use of photogrammetry in tissue compensator design. Part I: photogrammetric determination of patient topography.

The surface topography of a patient can be determined by photogrammetry before beginning radiotherapy. The source light of the therapy unit or simulator is used to project a grid pattern onto the patient, and this is then photographed together with control points consisting of miniature light bulbs mounted on a frame suspended from the wedge slot of the therapy machine. When the photograph is projected onto a graphics terminal for data entry into a computer, the three-dimensional topography of the patient's surface can be reconstructed as a two-dimensional matrix of discrete points. A computer algorithm can then design a tissue compensator to fit the individual patient.

Humans↗
PubMed1977

The use of photogrammetry in tissue compensator design. Part II: experimental verification of compensator design.

A computer algorithm for designing sheet lead tissue compensators is described. Corrections are made for scatter within the radiation field as well as the shape of the patient for the mantle fields used in treating Hodgkin's disease. The method was tested experimentally with a phantom and found to be clinically acceptable. The advantages of employing this technique with parallel opposed fields are emphasized.

Hodgkin Disease↗
PubMed1975

Thermographically measured normal skin temperature asymmetry in the human male.

The detection of thermal asymmetry may lead to the diagnosis of significant disease states, especially those of a neoplastic or vascular nature. Estimates of acceptable thermal asymmetry have been made; thermal asymmetry has not previously been quantified in normal subjects. In 10 normal male volunteers, ages 17-38, thermal difference between symmetric areas of the chest, abdomen, and back never exceeded 1 degrees C. Statistical treatment of these data suggests that thermal differences in excess of this in the male are abnormal.

Abdomen↗
PubMed1975

A non-linear programming method for optimizing parallel-hole collimator design.

A new method for optimizing the design of multi-aperture parallel-hole collimators for the gamma scintillation camera is presented. The method takes into account the frequency spectrum of a plane source object distribution as well as the energy of the radiation. A frequency dependent statistical figure of merit is calculated and combined with a weighted object distribution frequency spectrum to obtain an objective function which, when maximized, yields the optimum collimator design according to the chosen criteria. The optimization is performed by means of a sequential pattern search technique. The results show a positive correlation between te objective function and an experimental performance index evaluated for existing collimators. The optimal designs obtained by maximizing the objective function, under the assumption of no scatter within the source, exhibit somewhat higher sensitivity and lower resolution than the commercial low energy collimators tested. It is concluded that much of the resolution capability of very high resolution collimators is unused because of the limitation imposed by the intrinsic resolution of the detector assembly.

Computers↗