I. Subcutaneous fat thickness has been measured by three different techniques in forty-one subjects. 2. Ultrasound provided the most accurate measurement in experienced hands. 3. A method based on electrical conductivity was also accurate but was unpleasant for the subject. 4.Harpenden calipers were the least satisfactory of the three techniques tested.Indirect estimation of total body fat has been employed increasingly in recent years in an attempt to assess various aspects of body composition. In the most widely used method skinfold thickness is estimated by means of Harpenden calipers (Edwards, Hammond, Healey, Tanner & Whitehouse, 1955; Fletcher, 1962); these require a certain amount of practice in use. Since the instrument measures a skinfold it is likely to be inaccurate, particularly in obese subjects where a greater bulk of tissue must be deformed to obtain a reading. Errors may also arise from the varying elastic properties of both fat and skin, and the measurement itself applies a number of stresses to the fat layer. For these reasons, alternative methods would be valuable, and we have compared the results of measurements obtained by the Harpenden calipers with those given by an ultrasonic technique. We have also used a modification of a method based on the variation of electrical conductivity of different body tissues (Bauereisen & Paerisch, 1953) in order to provide if possible an independent assessment of accuracy. E X P E R I M E N T A L SubjectsMeasurements of fat thickness were made on a total of forty-one subjects-twentysix men and fifteen women ranging in age from 16 to 87 years. They were selected at random from the wards of the hospital, and only those with oedematous states were excluded. In some subjects, measurements were made over the abdomen approximately 5 cm from the umbilicus and in others about 2.5 cm below the inferior angle of the left scapula. All three methods were used in measurements over the abdomen, but only ultrasound and Harpenden calipers were used at the infrascapular site. Abdominal fat thickness was measured by both ultrasonic and conductivity methods in twenty subjects, and by all three methods in fourteen subjects. Infrascapular fat thickness was estimated by Harpenden calipers and ultrasonic methods in twenty-one subjects.All observers were familiar with each of the three techniques, but in general each observer used one only, except when comparing the replilts obtained by two observers
A scintillation camera with digital data store has been used to assess renal function. Analysis of the renogram by deconvolution, using an on-line digital computer, shows promise as a means of expressing renal function in terms of tubular transit times for 123I-Hippuran.
The renogram in its standard form does not express the renal handling of Hippuran in its simplest and most explicit form. The curve obtained, R(t), is a convolution of the input function from the blood to the kidney, I(t), and the impulse response function of the kidney, H(t). H(t) is the response to a bolus injection and represents the renal handling in its simplest form. It can be calculated by deconvolution since I(t) and R(t) can both be obtained in the investigation. A method involving Laplace transforms is used.
A serial study on 32 patients with bone metastases following cancer of the breast or prostate was performed over three years. Up to ten sets of images (average of four) per patient were obtained during this period using 99Tcm methylene diphosphonate as the radiopharmaceutical. Ninety-three paired serial images of individual lesions were qualitatively assessed for change by three physicians in nuclear medicine and the results were compared with the quantitative results from computer analysis. The reproducibility of the quantitative approach was determined by the analysis of 20 paired lesions by three physicists. It was found that quantitative changes in uptake of less than 20% between images were generally not detected by the medical observers; a change of 41% had only a 95% probability of being identified as change by the physicians. Although much more reproducible in determining changes in individual lesions, the quantitative approach was found to be inferior to the qualitative assessment of overall change in the majority of cases which involve multiple lesions. The basic assumption that uptake varies proportionally with progression of the bone lesion is discussed an is considered in some instances to be untenable. The conclusion is drawn that the determination of progression from changes of uptake in longstanding lesions is uncertain and is subsidiary in importance to the detection of new lesions.
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