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The purpose of this study was to assess the value of technetium-99m methoxyisobutylisonitrile (MIBI) single-photon emission tomography (SPET) and an iterative reconstruction algorithm for the preoperative localisation of parathyroid adenomas (PTAs). Seventy-two patients (26 male, 46 female, mean age 58+/-16 years) with known primary hyperparathyroidism were examined preoperatively. First, a thyroid examination was performed to detect possible MIBI-accumulating thyroid lesions. Planar scans were then acquired 15 and 120 min and tomographic images 120 min after intravenous injection of 740 MBq 99mTc-MIBI, using a triple-head gamma camera (Picker Prism 3000). Additionally, 99mTc-MIBI/ 99mTc-pertechnetate subtraction scintigraphy of the early planar images was performed. The SPET data were evaluated using an iterative reconstruction (multiplicative iterative SPET reconstruction: MISR) as well as a standard algorithm (FBP: filtered back-projection with application of a 3-D low-pass postfilter). The weight of the resected PTAs ranged from 110 mg to 5 g. Using planar MIBI scans, correct localisation of the side of the PTA was possible in 81% of cases (58% for PTAs weighing less than 500 mg). Sensitivity increased to 94% using SPET and FBP, while with MISR it rose further, to 97%. Patients with PTAs weighing less than 500 mg showed a sensitivity of 88% with MISR and 81% with FBP. Furthermore, there was a clear improvement in image quality using MISR. None of the normal parathyroid glands were visualised. This study indicates that, in comparison with planar scintigraphy, 99mTc-MIBI SPET is a more sensitive and specific tool for topographical localisation of PTAs, especially those that are small. There is a further improvement in sensitivity and image quality when iterative reconstruction is used instead of FBP.

Aim: From a model of iodine metabolism exhalation coefficients shall become derived to calculate 131I exhalation by patients after a radioiodine treatment. The validity of these exhalation coefficients shall be reviewed by whole body activity measurements of relatives of patients, who inhaled the radioiodine exhaled by the patients in their homes. The exposure of relatives to patients of a nuclear medical ward after release by exhalation of iodine-131 is investigated., Methods: Iodine 131I-activity of 17 relatives to patients who had to undergo a radioiodine therapy became measured in a whole body counter only a few days after release of the patient from the nuclear medical ward. The results of the measurements have been compared with the results of calculations according to the model of iodine metabolism., Results: The calculated values of incorporated radioiodine in the relatives of the patient at time of measurement (Amodel) correlate with the measured whole body activity (AGK) according to the regression: Amodel = AGK -47.3 (r2 = 0.959). This relation holds if 2.1 micrograms of iodine become exhaled per day of the 60 micrograms of iodine which are the daily intake of iodine by food. The exposure of all relatives did never exceed 100 microSveff. Using the same model parameters the effective dose equivalent of the relatives to our patients rises up to 6.5 mSv under ambulant radio therapy condition., Conclusion: The daily exhalation of 131I is able to be calculated by a mathematical model of iodine metabolism. After staying of patients at least 3 days in a nuclearmedical ward the exposure of relatives of patients in their home does not exceed the value of 100 microSveff by inhalation of iodine-131. This are 10% of the limit of 1 mSveff according to the Recommendations of the Commission on Radiological Protection (ICRP 60). Radioiodine therapy outside of a hospital and "iodine therapy tourisme" of German patients to other countries cannot be accepted.

Aim: Of the study was to assess the influence of the patient age and the survival of patients undergoing bone scintigraphy on the calculations of the theoretical lifetime loss., Patients and Methods: The evaluated data set included 216 patients undergoing a bone scan for the first time in 1980. From 182 patients a study end point (either the date of death, or existing registration in the German resident office on the 31.12.1995) was obtained. The theoretical life time loss was based on the formalism previously presented by Schicha und Wellner (13)., Results: In 74% of the examined patients a malignant disease was present. 28% of the patients had died within one year of the examination. At the end of the follow-up period, of at least 15 years, 58% of the patients were deceased. The theoretical lifetime loss due to radiation exposure within this specified patient group was estimated to be 0.152 d/mSv. Assuming an age distribution of the general population and statistically derived life expectancy, this value should be 0.437 d/mSv., Conclusion: The estimates regarding the risk of diagnostic procedures using ionizing radiation should take into account the limited life expectancy of patients in hospitals.

First SPECT results using a multiplicative iterative reconstruction algorithm are presented. The superiority of the iterative technique over filtered backprojection is demonstrated in two thyroid SPECT studies. Obvious benefits of the new reconstruction technique are better defined outlines of the imaged organ and patient body as well as negligible artificial image amplitudes outside the patient.

A new iterative strategy for determination of the source distribution in single-photon emission tomography (SPECT) simulates mathematically the scintigraphic imaging process during direction sum computation. Limited spatial resolution and gamma-ray attenuation are taken into account using simplifying approximations. Highly resolved low-noise tomograms without obvious artifacts are obtained. Results of phantom measurements as well as cases of thyroid and brain perfusion imaging are presented to demonstrate the capabilities of the method.

We have tested an iterative reconstruction procedure against the usual filtered back-projection in 14 patients with SPECT-examinations of various liver diseases. The aim of the examinations was to assess the presence of liver tumors in most cases. Further indications were Budd-Chiari syndromes and a liver malconfiguration in one case. Three of six haemangiomas and both liver metastases were better delineated with the iterative method, in one patient the haemangioma was visible only with this method. An irregular pattern after filtered back-projection led to misinterpretation as multiple metastases in another patient in whom there was no irregularity after iteration. Diagnostic improvement was not reached in the Budd-Chiari syndromes or in an atypical liver configuration, with a more homogeneous pattern after iteration however. The iterative reconstruction procedure was superior to the filtered back-projection method in the detection of small focal liver diseases.