Search

To evaluate the dose from the computed tomographic (CT) portion of positron emission tomography (PET)/CT to determine minimum CT acquisition parameters that provide adequate attenuation correction.Measurements were made with a PET/CT scanner or a PET scanner, five anthropomorphic phantoms (newborn to medium adult), and an ionization chamber. The CT dose was evaluated for acquisition parameters (10, 20, 40, 80, 160 mA; 80, 100, 120, 140 kVp; 0.5 and 0.8 second per rotation; 1.5:1 pitch). Thermoluminescent dosimetry was used to evaluate the germanium 68/gallium 68 rod sources. A phantom study was performed to evaluate CT image noise and the adequacy of PET attenuation correction as a function of CT acquisition parameters and patient size.The volumetric anthropomorphic CT dose index varied by two orders of magnitude for each phantom over the range of acquisition parameters (0.30 and 21.0 mGy for a 10-year-old with 80 kVp, 10 mAs, and 0.8 second and with 140 kVp, 160 mAs, and 0.8 second, respectively). The volumetric anthropomorphic CT dose index for newborn phantoms was twice that for adult phantoms acquired similarly. The rod source dose was 0.03 mGy (3-minute scan). Although CT noise varied substantially among acquisition parameters, its contribution to PET noise was minimal and yielded only a 2% variation in PET noise. In a pediatric phantom, PET images generated by using CT performed with 80 kVp and 5 mAs for attenuation correction were visually indistinguishable from those generated by using CT performed with 140 kVp and 128 mAs. With very-low-dose CT (80 kVp, 5 mAs) for the adult phantom, undercorrection of the PET data resulted.For pediatric patients, adequate attenuation correction can be obtained with very-low-dose CT (80 kVp, 5 mAs, 1.5:1 pitch), and such correction leads to a 100-fold dose reduction relative to diagnostic CT. For adults undergoing CT with 5 mAs and 1.5:1 pitch, the tube voltage needs to be increased to 120 kVp to prevent undercorrection.

With an Anger camera for scintigraphic recording of bremsstrahlung radiation from phosphorus-32, the distribution of intraperitoneal colloidal chromic phosphate was followed in patients with gynecologic tumors. Sequential pelvic, abdominal, and thoracic scintiphotos over a three-week period revealed rapid and persistent focal aggregation of the radiocolloid with no change in pelvic or peritoneal radionuclide distribution patterns. Visualization of intrathoracic lymph node uptake did not correlate with the presence of diaphragmatic tumor. This study demonstrates the utility of scintigraphy for monitoring the distribution of intraperitoneal beta emitters and the need for developing alternative methods of administering these therapeutic agents to achieve more uniform patterns of distribution.

The photon absorption method for measuring bone mineral mass has been used in a study of some 3,000 patients, including those with spinal cord injury, renal failure, endocrine disease, and osteoporosis. The fundamental equipment consists of a monochromatic photon source, scintillation detector, and scanning mechanism. The accuracy and reproducibility of this instrument were determined by comparing absorption measurement to chemical ashing studies on human bone. In clinical use, the method showed itself superior to other techniques for measuring small changes in bone mineral.

Transaxial emission computed tomography (ECT) was performed in dogs with experimentally induced abscesses, using 67Ga and several 99mTc-labeled organ-specific radiopharmaceuticals. Superimposition of 99mTc ECT images onto the 67Ga images gave the precise anatomic location of the abnormal foci of 67Ga uptake, correctly localizing a perinephric abscess, a splenic abscess, and a focus of osteomyelitis. This technique also permits further characterization of regions of decreased activity.

Radiographic and bone mineral (BM) data were collected over a three-year period on 195 patients with chronic renal failure. Most women maintained BM on dyalysis, whereas 44% of the men lost BM (p less than 0.05). Following transplantation, 86% of the patients either maintained or restored BM. After parathyroidectomy, only half of the women and 34% of the men gained BM. Normal radiographs may be associated with low BM values, but there is a correlation between decreasing BM and increasing renal osteodystrophy in women (p less than 0.05).

By using a 125I collimated point source to measure bone mineral, 700 measurements were obtained from the cortical bone of the lower arm in 303 patients with renal failure representing every stage of the disease. Of these patients, 123 had received transplants. The following conclusions can be drawn: (a) Prolonged azotemia leads to severe loss of bone mineral, which, in early stages, is only detectable using photon absorptiometry. (b) Gradual loss of bone mineral occurs during dialysis, (c) Parathyroidectomy slows this loss but fails to reverse it. (d) After transplantation, the rate of bone loss will either decrease or cease, but few patients show any increase in bone mineral. (e) Preliminary biochemical data on these patients show a relationship between bone mineral and creatinine, serum phosphate and serum calcium values.