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Biomedical subjects

P Schmidlin

Publications and source records attributed to P Schmidlin.

At least 19 recordsLinked to original sources
PubMed1992

Assessment of an attenuation correction for SPET by means of PET images.

The attenuation correction for single photon emission computed tomography (SPET) data developed by Luig et al. was tested with positron emission tomography (PET) data. Since the PET attenuation correction is very precise, it may be used as a reliable measure of the functionality of the SPET correction. It was found that, in the case of homogeneous attenuation and activity distribution, the results of Luig's correction are equivalent to those obtained with the PET correction. Inhomogeneous distributions of activity are corrected satisfactorily as long as the absorption of the medium is sufficiently homogeneous. Inhomogeneous absorption, however, leads to inadequate correction. In the case of sections through the lung, Luig's method might 'correct' the data in the wrong direction.

Humans↗
PubMed1989

Recurrence of colorectal tumors: PET evaluation.

Positron emission tomography (PET) was used in the follow-up of patients with colorectal malignancies to differentiate between recurrent colorectal tumor and scar. Patients were examined with oxygen-15-labeled water and with fluorine-18-labeled deoxyglucose (FDG). FDG was injected intravenously to assess tumor metabolism. The tracer concentration was quantitatively evaluated by means of a region-of-interest technique and standardized for both injected dose and body volume. Of 29 patients, 21 had recurrent colorectal malignancy, and eight had a nonmalignant mass. All malignancies were seen on the PET cross sections. Nonmalignant lesions had a low FDG accumulation on images obtained 60 minutes after injection. While the tumor-soft tissue ratio was highest shortly after the intravenous injection of FDG, the tumor-scar ratio was highest 60 minutes after injection. It was possible to differentiate tumor from non-malignant tissue with FDG with the use of standardized concentration values and tumor-soft tissue ratios. Imaging with O-15-labeled water gave no additional information.

Adult↗
PubMed1987

Predictive value of exercise renography for presurgical evaluation of nephrogenic hypertension.

Functional omicron-iodohippurate scintigrams were obtained in 18 hypertensive patients. Each patient was examined in the prone position and during exercise. An exercise-induced transient, bilateral, hippurate transport disturbance was sought as an expression of an exercise-mediated cortical perfusion abnormality. The study sought to test the hypothesis that patients who present evidence for an exercise-induced renal perfusion disturbance would have stabilized hypertension that was no longer surgically curable because of morphological changes of the peripheral vasculature. All 18 patients continued on to therapy: 13 proceeded to renovascular reconstructive surgery, 2 had a unilateral nephrectomy, and 3 were treated with percutaneous transluminal renal angioplasty. During preoperative exercise renography, evidence of bilateral renal dysfunction developed in 10 of 18 hypertensive patients during ergometric stress (abnormal exercise response). Following surgical therapy nine of these patients with abnormal exercise scintigrams continued to have hypertensive disease, while one patient was cured. The exercise renograms of eight hypertensive patients were not influenced by the exercise protocol, and operation cured seven of these eight patients. The results suggest that an accentuated vascular response to exercise occurs in the maintenance phase of renovascular hypertension, a disturbance not observed while the hypertension is curable by surgical therapy.

Antihypertensive Agents↗
PubMed1987

Clinical evaluation of patients with hypertension and exercise-induced renal dysfunction.

An exercise-mediated renal omicron-iodohippurate transport abnormality was recently identified in patients with hypertension. The disturbance was not observed in normotensive controls. To learn more about this transient functional disturbance of the kidney, we obtained gamma camera hippurate renograms in 45 patients with hypertension. The final diagnoses indicated that 27 patients had essential hypertension, 15 had renal parenchymal or renovascular hypertension, 2 had malignant hypertension, and 1 had hypertension of pregnancy. We documented age, height, weight, global and unilateral renal function, blood pressure status, and antihypertensive medication used at time of scintigraphy. We also noted the serum catecholamine, sodium, and potassium levels. All patients were scintigraphed at rest and during exercise. The scintigraphic examination documented exercise-induced renal dysfunction in 28 (62%) patients (abnormal exercise renogram), while 17 (38%) had renograms not noticeably influenced by the exercise protocol (normal exercise renogram). When the results of scintigraphy were compared with the clinical data, a weak correlation was found between patient overweight and an abnormal response to exercise. There was no significant difference between groups with normal and abnormal exercise renograms with respect to the other parameters assessed. Exercise renography was not useful for differentiating renal and essential hypertension. Renography appears to demonstrate an exercise-mediated, transient, renal perfusion disturbance in certain patients with hypertension. The examination appears to assess a new parameter in hypertensive disease. Thus, the gamma camera renogram should be reevaluated in the patient with hypertension.

Adolescent↗
PubMed1986

Evaluation of scintigraphic data of renal transplants.

Scintigraphic data obtained during 594 examinations of renal transplants were evaluated by an experienced physician. Each examination included both the measurement of a radioiodine hippurate uptake curve, and a technetium 99m diethylenetriamine pentaacetic acid (DTPA) time-activity curve describing renal perfusion. Features were extracted from both curves. Discriminant analysis of the features resulted in a computer classification of the grafts. This classification was compared with the physician's diagnosis. Congruence between the computer classification and the diagnosis supported the diagnosis, and revealed those features which were able to lead to the correct diagnosis. The analysis was used to assess graft function, and to identify acute tubular necrosis and acute, as well as chronic, rejection. The computer classification was in agreement with the diagnosis in about 80% of the acute rejections, in 86% of all instances of acute tubular necrosis, and in 80% of chronic rejections. The procedure can be used to mutually improve the diagnosis of both physician and computer.

Acute Disease↗
PubMed1985

Renal perfusion and mean vascular transit time.

A method was developed to determine the mean vascular (arterio-venous) transit time (MVTT) of renal transplants. The renal transit times were calculated from perfusion curves obtained when grafts were examined with 99mTc-DTPA. About 400 examinations were performed during a 6-month period. As a result, influences of clinical complications on transit times were demonstrated. It was found that the individual MVTT is not a suitable parameter for assessment of renal grafts since individual transit times vary widely.

Graft Rejection↗
PubMed1985

Estimating the effective renal plasma flow from the hippurate renogram.

A method for estimating the effective renal plasma flow (ERPF) from renograms is presented. Renograms obtained in 91 patients were used to test the method. The clearance values derived from renography were compared with those obtained with infusion clearance. It was shown that the ERPF was able to be estimated from the renogram with a standard error of +/- 94 ml min-1.

Glomerular Filtration Rate↗
PubMed1975

Development and comparison of computer methods for organ motion correction in scintigraphy.

The process of organ motion correction in scintigraphy is analysed in the frequency domain. The sequence of the chi- and gamma- coordinates registered during scintigraphic recording is converted to a frequency spectrum by a discrete Fourier transform. In the frequency domain motion correction is performed by linear filtering. Every convolution filter in the time domain corresponds to a linear filter in the frequency domain, and the filter form in the frequency domain is a good measure of the quality of the correction. With the aid of frequency analysis simple convolution filters in the time domain are developed. The usual centre of gravity method is not a convolution filter and has an unfavourable frequency behaviour. By means of phantom measurements the following correction methods are tested: the usual (non-convolutional) centre of gravity method, the convolutional centre of gravity method, a weighted convolutional centre of gravity method and the Fourier filtering method.

Computers↗