P De Bondt

Validation of planar and tomographic radionuclide ventriculography by a dynamic ventricular phantom.

&NA; Although there is increasing interest in the automatic processing of tomographic radionuclide ventriculography (TRV) studies, validation is mainly limited to a comparison of TRV results with data from planar radionuclide ventriculography (PRV) or gated perfusion single photon emission computed tomography (SPECT). The aim of this study was to use a dynamic physical cardiac phantom to validate the ejection fraction (EF) and volumes from PRV and TRV studies. A new dynamic left ventricular phantom was constructed and used to obtain 21 acquisitions in the planar and tomographic mode. The directly measured volumes and EFs of the phantom during the acquisitions were considered as the gold standard for comparison with TRV and PRV. EFs were calculated from PRV by background‐corrected end‐diastolic and end‐systolic frames. Volumes and EFs were calculated from TRV by region growing with different lower thresholds to search for the optimal threshold. EF from PRV correlated significantly with the real EF (r = 0.94, P = 0.00). The optimal threshold value for volume calculation from TRV in 336 cases was 50% (r = 0.98, P = 0.00) yielding the best slope after linear regression. When considering these calculated end‐diastolic and end‐systolic volumes, EF correlated well (r = 0.99, P = 0.00) with the real EF, and this correlation was significantly (P = 0.04) higher than that of the EF from PRV. Our experiments prove that EF measured by TRV yields more accurate results compared with PRV in dynamic cardiac phantom studies.

Radiolabelled thymidines and deoxyuridines for measuring cellular proliferation in tumours--an update.

Given the unique incorporation of thymidine nucleotides into DNA, during S and early G2 phase, as opposed to other nucleotides, the proliferation of tumour cells in vitro and in vivo has been studied extensively using autoradiography to detect the uptake of tritiated thymidine into cellular DNA. The proportion of labelled cells seen shortly after administration of tritiated thymidine (the labelling index) is a measure of the proportion of cells that were in S phase and thus actively dividing. Unfortunately, an assessment of the labelling index requires invasive biopsy and is invariably subject to sampling errors. Accordingly, several authors have developed radiolabelled thymidines and deoxyuridines for non-invasive and repetitive positron emission tomography (PET) and conventional gamma camera imaging. These radiopharmaceuticals are of special interest for monitoring therapy since changes in the proliferative status of tumours induced by effective treatment are likely to precede volumetric changes, which are assessed by conventional radiology. Thus, rapid repetitive imaging of tumour uptake of these radiopharmaceuticals could allow for a more rapid assessment of therapeutic efficacy than is possible when using conventional radiology.

Tc-99m MDP uptake in herniated stomach tissue.

A 50-year-old woman with midthoracic pain was referred for bone scintigraphy to exclude vertebral disease. Although planar and tomographic images of the spine revealed no vertebral abnormalities, increased Tc-99m MDP uptake was found in a prevertebral thoracic mass corresponding to herniated stomach tissue as shown by computed tomography. In the abssnce of infrediaphragmatic stomach visualization, gastric trapping of unreduced pertechnetate cannot explain this finding. In addition, chemical binding to hydroxyapatite crystals and amorphous salt, as seen in long-standing metastatic caloification, may not explain this because computed tomography revealed no calcifications. Instead, local tissue anoxia with increased lactate production and pH reduction resulting in an increased tissue affinity for Tc-99m MDP should be considered.