Quantitative SPECT Imaging Research Articles

Current status of radioimmunotherapy

Radioimmunotherapy with radiolabeled monoclonal antibodies is increasingly effective for hematopoietic tumors, with a number of investigators reporting persistent major responses. Radioimmunotherapy for solid tumors has been more difficult and only an occasional major response has been reported and these have so far not been persistent. Toxicity is predominantly hematopoietic, with platelets being most sensitive to the effects of radiation. Even at ultra-high doses (up to 28 mCi/kg of 131I), second organ toxicity has not been reached. Rational approaches to dose planning are becoming possible with improvements in dosimetry, based on quantitative SPECT and PET imaging. Current therapeutic indices for tumor/marrow, the most radiosensitive organ, are in the range of 5–10 to I. This is probably still too low for curative treatment of solid tumors, and further refinements, perhaps based on novel antibody formulations, are needed.

Evaluation of reconstruction algorithms in SPECT neuroimaging. I. Comparison of statistical noise in SPECT neuroimages with 'naive' and 'realistic' predictions

In the presence of statistical noise, an iterative reconstruction algorithm (IRA) for the quantitative reconstruction of SPECT brain images overcomes major limitations of applying the standard filtered back projection (FBP) reconstruction algorithm to projection data which have been degraded by convolution of the true radioactivity distribution with a finite-resolution distance-dependent detector response: (a) the non-uniformity within the grey (or white) matter voxels which results even though the true model is uniform within these voxels; (b) a significantly lower ratio of grey/white matter voxel values that in the true model; and (c) an inability to detect an altered radioactivity value within the grey (or white) matter voxels. It is normally expected that an algorithm which improves spatial resolution and quantitative accuracy might also increase the magnitude of the statistical noise in the reconstructed image. However, the noise properties in the IRA images are very similar to those in the FBP images. Thus, the IRA should provide the potential for quantitative SPECT imaging of normal physiological responses or diseases involving both the brain grey and white matter.

Quantitative IPM spect imaging analysis in major depression : Jay D. Amsterdam, M.D., P. David Mozley, M.D. (by invitation) Depression Research Unit, University of Pennsylvania School of Medicine, Philadelphia, PA 19104

Quantitative IPM spect imaging analysis in major depression : Jay D. Amsterdam, M.D., P. David Mozley, M.D. (by invitation) Depression Research Unit, University of Pennsylvania School of Medicine, Philadelphia, PA 19104

Comparison of in-111 Granulocytes and Tc-99m Albumin Colloid for Bone Marrow Scintigraphy by the Use of Quantitative SPECT Imaging

A comparison of In-111 oxinate labeled autologous granulocytes and Tc-99m albumin colloid for bone marrow scintigraphy is reported. The aim of this report was to determine if the intense uptake in the liver and spleen with nano-sized colloids, which hampers the evaluation of the skeletal parts surrounding the liver, is reduced by the use of radiolabeled granulocytes. This study is based on a retrospective analysis of 19 abdominal tomographic examinations with In-111 granulocytes performed to detect septic foci. After correction for attenuation and scattering of photons was performed, the uptake in the bone marrow of the lumbar spine was seen to be related to the liver, spleen, and tissue background activity. The results in this study were compared with corresponding data from 20 normal liver/spleen tomographic examinations performed with Tc-99m nanocolloid, which is routinely used for bone marrow scintigraphy. The bone marrow/liver activity ratio for granulocytes varied, but it exceeded the corresponding mean ratio for colloid in all examinations. The mean values for granulocyte uptake 3 and 20 hours after injection was, respectively, about 6 and almost 10 times higher than were those for colloid. The activity ratios between bone marrow and spleen as well as between bone marrow and tissue background was not improved and or may even have been reduced by the use of granulocytes. It is suggested that granulocytes labeled in vitro by Tc-99m hexamethylpropylene amineoxime (HMPAO) or in vivo by monoclonal antigranulocyte antibodies may provide techniques for improved bone marrow imaging.

Quantitative spect isonitrile imaging accurately defines the “area at risk” during coronary occlusion

Quantitative spect isonitrile imaging accurately defines the “area at risk” during coronary occlusion

Use of indium-111-labeled OC-125 monoclonal antibody in the detection of ovarian cancer

This is a preliminary study to evaluate the utility of using the monoclonal antibody (CO-125) labeled with indium-111 to image recurrences of ovarian cancer. This technique has been investigated in 23 patients with ovarian cancer and the results have been compared with blood OC-125 levels, CT scans, and findings at second-look surgery. Following infusion of 1 mg of F(ab′) 2 fragments (1–2 mCi 111In), quantitative SPECT and planar imaging was obtained daily for 72 hr along with analysis of serum. The nuclear medicine scans of the tumor site recurrences were technically excellent. When compared to second-look laparotomy, there were 2 true negatives, 2 false positives, 14 true positives, and 2 false negatives by nuclear imaging. CT scans correlated less well with surgery, but serum OC-125 levels correlate more closely with nuclear scans and second-look surgery. Those with multiple small metastatic implants showed a pattern of diffuse uptake which increased with time, whereas those with nodal or larger recurrences showed a more focal uptake. The combination of favorable biodistribution and positive images, especially in patients with normal antigen levels and negative CT scans, suggests a role for OC-125 monoclonal antibody imaging in their clinical management. However, further investigation is needed to determine whether nuclear scans can replace second-look surgery. If it can show that enough 111In-labeled antibody accumulates in the tumor site to justify radioimmunotherapy, then 90Y (a pure beta emitter) could be exchanged for 111In. This is potentially a method of radioimmunotherapy for recurrent ovarian carcinoma.

Quantitative SPECT imaging for diagnosis and dosimetry in radionuclide therapy

Effective therapeutic treatment with in vivo administered radioactivity depends on the localization of appropriate concentrations in tissues to be treated. Accurate assessment of both diagnostic and therapeutic concentrations of radiopharmaceuticals is the goal of quantitative SPECT imaging. The technology of SPECT imaging has significantly improved over the past 5 years, and routine quantitation for SPECT users may not be far away. The four operational steps by quantitative SPECT imaging are described, along with technical factors that require further development before it can be used routinely.

Quantitative SPECT imaging: influence of object size.

In positron emission tomography (PET) the measured radionuclide concentration or recovery coefficient (RC) in the transverse plane has been shown to be dependent on source size. The RC dependence on object size was therefore experimentally measured for gamma camera SPECT system to determine the influence of additional factors such as: (a) geometrical spatial resolution of each collimator type, (b) scattering effects at each photon energy due to surrounding background, (c) influence of choice of reconstruction filter and (d) photon penetration through the collimator septa. Data were acquired for different collimator types using 99Tcm (140 keV) and 131I (364 keV) to partly differentiate between photon scattering and collimator penetration effects. Results obtained demonstrated that thick septa collimators with low penetration fraction (theoretical leakage less than 3%) are required to minimize the measured response dependence on source size and to obtain a relatively unique relationship independent of photon energy and background activity. Measurements of this type are important for quantitative SPECT imaging in radioimmunoimaging or radioimmunotherapy.