A. Vandecruys

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.

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.

A new vertex-finding algorithm for the oblique rotation step in factor analysis

The use of an oblique transformation to obtain physiological factors from a factor analysis of dynamic scintigraphic studies was suggested ten years ago. The technique uses a vertex-seeking routine to enable these factors and their contribution images to be formed. This paper investigates a new vertex-finding algorithm, based on an optimization of a function of the vertices. The algorithm also converges in the cases where the previous algorithm of Barber and Cavailloles diverges.

[Functional pulmonary exploration using a scintillation camera and 133Xe test procedure and data handling (author's transl)]

Our test procedure for measuring regional ventilation, perfusion and V/Q-ratio by means of a gamma camera and 133Xe is explained and discussed, as well as our programmes to correct the defo

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. (auth)