Using iodine-123 labelled radiotracers, the presence of 2.5% high-energy photons causes image deterioration due to increased scatter. To investigate the influence of these photons on image quality, we measured the spectrum of 123I with a medium-energy (ME), a low-energy all-purpose (LEAP) and a low-energy high-resolution (LEHR) collimator. Even in air, using low-energy collimators a high baseline activity was observed over the total energy detection range of the gamma camera. The 159-keV photopeak to scatter activity ratio fell from 5.9 for ME to 3.6 and 2.9 for LE collimators. Acquisition of images with LEHR collimators with energy windows set at 159 keV and 500 keV demonstrated that the 159-keV LEHR image is a combination of the ME image of the object and of the LEHR 500-keV image. Because of their important septal penetration and greater geometric detection efficiency compared with the 159-keV photons of 123I, the contribution of high-energy photons is dependent on the source-detector distance. For a small source placed in air, the scatter to photopeak activities varied from 17.4% at 80 cm to 37.8% at 5 cm distance from an LEHR collimator. Considering only the scatter problem, ME collimators are the best choice for 123I studies. When using LE collimators for high-resolution tomography with 123I-labelled compounds, scatter contribution from high-energy photons has to be corrected for quantitative analysis or when dual-isotope studies are performed, whether or not these studies are acquired simultaneously.

In the particular setting of this preliminary study evaluating the reproducibility of FP-CIT single-photon emission computed tomography interpretation in a group of nuclear medicine physicians with various experiences, interobserver agreement was suboptimal. Collegial discussion and standardized interpretation criteria could contribute to an improved reproducibility.

Iodine-123 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) can be used to image myocardial fatty acid regional distribution and utilisation with single-photon emission tomography (SPET). By visual analysis, a mismatching with regional uptake of BMIPP less than that of a perfusion tracer has been shown to predict myocardial viability and functional improvement after restoration of flow in patients with myocardial infarction. The current study aimed to evaluate a newly developed quantitative method of analysis of sestamibi and BMIPP uptake for the prediction of functional recovery after revascularization in patients with acute infarction. BMIPP and gated sestamibi SPET studies at rest were obtained before and >3 months after revascularization in 18 patients with recent infarction. A colour-coded polar map was generated from the comparison of sestamibi and BMIPP uptake. Depending on the relative distribution of the two tracers, different patterns of uptake were identified and their extent expressed as percentages of the surface of the whole left ventricle and of the three main coronary artery territories. At follow-up, recovery was defined as a > or =5% increase in ejection fraction compared with baseline. Receiver-operating characteristic curve analysis was performed to analyse the data. At baseline, significant correlations were found between ejection fraction and the % surface with decreased sestamibi or BMIPP uptake (r=-0.68, P= 0.001, and r=-0.72, P<0.0001, respectively). When combining both tracers, ejection fraction was significantly associated with the extent of myocardium showing decreased sestamibi uptake with lower BMIPP uptake (mismatching; r=-0.68, P=0.001). At follow-up, significant functional recovery was found in 13/18 patients. By ROC curve analysis, the optimal pattern of distribution predicting recovery was a mismatching with uptake of sestamibi <70% and uptake of BMIPP at least 10% lower. For this parameter, optimal cut-off of extent was 10% of the whole left ventricle surface (sensitivity 69%, specificity 80%, accuracy 72%) and 25% of the infarct-related arterial territory (sensitivity 77%, specificity 80%, accuracy 78%). The areas under the curve were 79% for the left ventricle surface and 72% for the individual arterial territories. These results suggest that in patients with acute infarction, quantitative analysis of sestamibi and BMIPP could offer an objective and reproducible method for estimating the severity of cardiac dysfunction and predicting the evolution of ejection fraction after revascularization.

Despite lower blurring on end diastolic compared with summed images, non-scatter corrected end diastolic data were least accurate for the diagnosis of coronary artery disease in patients with a high prevalence of disease. Scatter correction, by improving the delineation of perfusion defects, increased the accuracy of quantitative MPI for the diagnosis of CAD in a large number of patients, more particularly in those with a small heart.

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