Quantification of pulmonary fixation of thallium: right lung or left lung ?

The intensity of pulmonary fixation of thallium in effort constitutes a tracer prognostication recognized in coronaries. Subsequently to the first studies conducted in planar mode, it is usually appreciated on the left pulmonary apex, while the acquisitions in tomographic mode validate its study on the entire right lung. In this work we make the comparison of the results obtained in 59 patients, indign of coronary-pathy (probability < 5%), the pulmonary activity being measured on the left lung apex or on the entire right lung. The pulmonary interest region is traced either on left apex (IRll) or on the entire right pulmonary field (IRrl). The myocardial IR (IRc) is limited to a LV wall, visually appearing as 'normally' fixating. The fixation ratios ll/c and rl/c are normalized to the surface of IR. The following values were observed: - ll/c = 0.33 ± 0.05 (0.22 to 0.44), normal value ≤ 0.43; - rl/c = 0.35 ± 0.05 (0.24 to 0.48), normal value ≤ 0.45. The two modes of measurement give values quite comparable in the same patients (l = 0.87, p < 0.001, n = 59). The intra- (D0 and D60) and inter-observer reproducibilities are good and comparable for the two methods. In conclusion, in case of acquisitions in tomographic mode it appears logically to study the right pulmonary fixation rather than the left because: 1- IR is more extended, and non-amputated by the cardiac print; 2- the pulmonary activity is less affected by the spurious effect of Compton scattering of myocardial origin; 3- the possibility of observing the functional behavior of an entire lung and of studying possible regional inequalities