Clinical applications of pinhole single photon emission tomography

For some planar scintigraphic explorations, like thyroid or hip, the pinhole collimator is usually preferred to the usual parallel hole collimators because it allows a superior resolution. Progress in 3D tomography reconstruction methods allows single photon emission tomography (SPET) to be today performed using the-pinhole collimator with again the advantage of a higher resolution. Pinhole collimator imposes a short distance (a few centimetres) to the target area and a restricted field of view. Over the last ten years, the potential of pinhole SPET has been essentially investigated for the ankle and the hind foot, the detection of thyroid nodules or abnormal parathyroid glands, the exploration of axillary lymph nodes. The technique was usually compared to planar scintigraphy performed with parallel hole or pinhole collimator. Sometimes a comparison to standard (with parallel hole collimator) SPET or to a morphologic imaging technique was also available. All studies highlight the improvement in resolution afforded by the use of the pinhole collimator. In bone scintigraphy, the delineation of the structures was largely superior allowing the visualisation of significant details usually never seen on scintigraphic images. In thyroid scintigraphy, the better resolution allowed to detect more nodules (essentially infra-centimetre nodules), and to reduce the number of equivocal cases. For abnormal parathyroid gland detection, the number of false negative cases decreased, with a concomitant increase of true positive cases; the glands were more sharply delineated on the images. Pinhole SPET with Tc-99m-tetrofosmin was the only scintigraphic method able to successfully reveal the number of involved lymph nodes in patients with breast cancer. In conclusion pinhole single photon appears as a promising new scintigraphic method allowing to explore small areas with a high resolution.