Computers in nuclear medicine: introductory concepts

Computers play an important role in image and data processing in nuclear medicine. Applications extend from relatively simple mathematical processing of in vitro specimen assays to more sophisticated image reconstruction procedures for emission tomography. The basic concepts and terminology associated with computer applications in image and data processing in nuclear medicine are presented here.     

Radionuclide imaging of soft tissue neoplasms

Two classes of radiopharmaceuticals may be used for imaging tumors of the musculoskeletal system. The first is comprised of soft tissue or tumor specific agents such as gallium-67, bleomycin, and radionuclide-labeled antibodies, which may be useful for detecting and localizing these tumors. The other class of tracer is comprised of those with avidity for bone. The 99mTc-labeled-phosphate skeletal imaging compounds have been found to localize in a variety of soft tissue lesions, including benign and malignant tumors. In 1972, Enneking began to include bone scans in the preoperative evaluation of soft tissue masses. Later, he and his associates reported that these scans were useful in planning operative treatment of sarcomas by detecting involvement of bone by the tumors. Nearly all malignant soft tissue tumors take up bone-seeking radiopharmaceuticals, and bone involvement was indicated in two-thirds of the scans we reviewed. About half of benign soft tissue lesions had normal scans, but the other half showed uptake within the lesion and a few also showed bone involvement. Careful, thorough imaging technique is essential to proper evaluation. Multiple, high-resolution static gamma camera images in different projections are necessary to adequately demonstrate the presence or absence of soft tissue abnormality and to define the precise relationship of the tumor to the adjacent bone.     

The value, limitations, and applications of nuclear dacryocystography

Nuclear dacryocystography is simple, relatively harmless method of evaluating patients suspected of having abnormalities of the nasolacrimal drainage system. A group of normal saline containing approximately 100 muCi of 99mTc-pertechnetate is placed on the conjunctiva near the lateral canthus, and serial scintigrams are obtained as the pertechnetate flows along the tear strips, through the nasolacrimal drainage system, into the nasal fossa. By using a pinhole collimator with a very small aperture (1mm), the canaliculi, the nasolacrimal sac, and the nasolacrimal duct are readily visualized. When flow is impaired, the site of obstruction can often be identified. Contrast dacryocystography provides similar information but requires the injection of contrast material directly into a canaliculus. Nuclear dacryocystography provides good functional assessment of nasolacrimal drainage but has serious shortcomings in defining pathologic anatomy. Contrast dacryocystography outlines the anatomy well but often misses minor obstructions. The two studies are complementary and together provide an effective means of evaluating the nasolacrimal drainage system.     

Special characteristics and potential for dynamic function studies with PET

The possibility of utilizing the PET approach to the investigation of dynamic physiologic processes has not been limited so far by radiation exposure to the patient but rather considerations by the technical limitations of PET imaging devices. In the past few years, several PET designs have been optimized specifically for fast dynamic studies. The most recent of these designs incorporates cesium fluoride detectors to achieve high counting rate capabilities. At this time, the value of fast dynamic studies with PET can be only theorized but expectations for the modality rest on solid physiologic hypotheses. The incorporation of time-of-flight information into the PET reconstruction process promises to further enhance the capabilities of fast PET devices by the improvement of temporal resolution through signal-to-noise ratio increase. PET devices incorporating time-of-flight information are beyond the drawing board stage and are now under construction.