Limitations of quantitative radionuclide bone scanning in the evaluation of total knee replacement.

To establish the value of quantitative radionuclide bone scanning after total knee replacement, 21 patients were scheduled for examination. Eight patients were scanned more than 1 year after surgery (group 1), and 13 within the first postsurgical year (group 2). Ratios were calculated for three regions of interest. The ratio was defined as the counts per pixel for each region of interest, normalized by dividing them by the counts per pixel of the ipsilateral femoral shaft. There was no significant difference in uptake between control subjects and patients in group 2, indicating that the test was not reliable within this time period. No statistical difference was found between the uptake scores in groups 1 and 2, demonstrating that an uninterpretable period of 1 year is perhaps too short. Using a ratio of more than three, seen more than 1 year after surgery as pathologic, a sensitivity of 100%, a specificity of 33%, and an accuracy of 75% was found. Quantitative bone scanning is a very sensitive test for detecting complications, but it is nonspecific in diagnosing loosening of total knee arthroplasties. The value of quantitative scanning presumably lies in the follow-up of patients as an objective method for the evaluation of sequential scanning. Nevertheless, radionuclide data need to be interpreted in correlation with clinical and radiologic findings.

Visualization and characterization of gastric contractions using a radionuclide technique.

With the use of the radionuclide gastric-emptying test and a new data processing method, the contraction characteristics of the stomach were analyzed. After ingestion of a radiolabeled test meal, dynamic images of the stomach were acquired and analyzed to determine the frequency, amplitude, and rate of gastric contractions in healthy subjects. The frequency of antral contractions was found to be inversely related with food retention in the stomach; in contrast, the amplitude of the contractions decreased progressively during the course of gastric emptying. The peaks of both antral contraction and filling rate and the time of their occurrence remained constant throughout gastric emptying. The observed patterns of phase distribution and sequential phase changes of the food in the stomach confirmed noninvasively what was already known from invasive technique, i.e., that the proximal stomach does not undergo phasic contractions and that, in the distal stomach, smooth muscle contraction originates in midcorpus and propagates aborally to the pylorus. The scintigraphic test can be used to noninvasively and quantitatively characterize gastric motor function and to delineate the spatial sequence of gastric contractions. This technique can be applied to study the pathophysiology of gastric emptying in various motor disorders.

Background correction in factor analysis of dynamic scintigraphic studies: necessity and implementation.

In factor analysis, structures are separated on the basis of their temporal behaviour, even if there is a partial overlap. Usually, the temporal behaviour of the system under study cannot be sampled in its true form due to a total overlap by the background. In the ROI (region of interest) method, background subtraction is used as a means to correct the problem. In factor analysis, this problem has been ignored for a long time. We prove that the factor analysis method gives incorrect results when there is a total overlap of a structure. By assuming a local homogeneity of the overlapping structure, we can greatly improve the solution found. Compared with the classical ROI method, our method is operator independent and organ specific.

Thrombus imaging with an I-123-labeled F(ab')2 fragment of an anti-human fibrin monoclonal antibody in a rabbit model.

The murine monoclonal antibody MA-15C5 binds to cross-linked fibrin but not to fibrinogen. Fab or F(ab')2 fragments of MA-15C5, labeled with iodine-123, were injected intravenously into nine rabbits with a nonocclusive 0.2-mL human plasma clot in the jugular vein and into eight control rabbits. Scintigrams obtained at hourly intervals after injection of the F(ab')2 fragment revealed a significantly higher accumulation of tracer in the clot region than in the contralateral region. The relative excess of tracer in the jugular vein region was significantly greater in the study animals than in the control animals throughout the study period. Blind reading of serial scans revealed no visible tracer accumulation in seven of eight control rabbits, whereas the scans of seven of nine study rabbits showed clearly visible accumulation (sensitivity = 77%, specificity = 87%). The Fab fragment of MA-15C5 had a lower affinity and bound less avidly to the blood clot in vivo. These results suggest that the F(ab')2 fragment has better imaging properties than the Fab fragment and that it may be useful for imaging blood clots in man.

Comparison of quantification methods of 111In-labelled platelet deposition in peripheral bypass grafts.

The action of antithrombotic drugs can be evaluated by measuring the deposition of 111In-labelled platelets on peripheral bypass grafts several days after injection. This evaluation can be performed qualitatively (visual interpretation on the daily images) or quantitatively. Four different methods which calculate the ratio of platelet uptake with a reference region are compared: two methods use a gamma camera and two a detector. A blood sample or the region under the sternal angle are used as reference. The daily ratio of the counts, recorded by a gamma camera in a region of interest covering the graft, and the blood radioactivity interpolated from a platelet survival curve appears to be the most reliable method. The information of all the ratios can be combined in a single thrombogenicity index which reflects the daily rise of a linear or exponential regression versus time.

Comparison of 133Xe washout curves after bolus inhalation, perfusion, and equilibration.

In 6 healthy subjects and 13 patients with chronic obstructive lung disease, 133Xe washout curves after bolus inhalation, perfusion and equilibration were compared, using a gamma camera and computerized data handling. In healthy subjects the washout after equilibration was significantly slower than after the two other procedures. As this phenomenon occurred at the basal zones, it was attributed to the presence of airway closure in some units. In patients, the three washouts were significantly different from each other. This indicated the existence of intraregional inhomogeneity in ventilation, perfusion and ventilation-perfusion ratio. Our conclusion is that comparison of these different washout methods yields valuable information not only on absolute values of pulmonary function but also on the intraregional distribution, which cannot be obtained by other examinations.

Horizontal gradient in ventilation distribution due to a localized chest wall abnormality.

Horizontal gradients in the distribution of ventilation and of regional vital capacities, as well as a reversed vertical, esophageal pressure gradient, were observed in a patient with a unilateral painful chest wall lesion. The distribution abnormalities disappeared after surgical treatment. These findings suggest that the interdependency between chest wall and lungs, and within the latter, between lobes, is an important factor determining the regional distribution of ventilation and the pleural pressure gradient in man.