A dynamic cardiac phantom was used as a reference to compare the volumes reconstructed with 4-D echocardiography and gated single-photon emission computed tomography (SPECT). 4-D echocardiography used a new prototype of rotating scan head to acquire ultrasound (US) images during a cardiac cycle, associated with a new protocol (left ventricular 4-D or LV 4-D) to reconstruct the volume deformations of the heart as a function of time. Gated SPECT data were acquired with a standard single-head gamma camera, and the reconstructions were carried out using the Mirage software released by Segami. The influences of different LV 4-D parameters were tested and analyzed. End-diastolic volume, end-systolic volume, and ejection fraction were measured using both LV 4-D and gated SPECT. Results obtained showed a straight correlation between the two examinations. The agreement confirmed the relevance of the comparisons. This study is an initial step before conducting clinical trials to exhaustively compare the two modalities.

UNLABELLED:Ex vivo measurements in animals are used frequently in the field of nuclear medicine for the characterization of newly developed radioligands and for drug development. In vivo SPECT would replace these ex vivo measurements in a relatively large number of cases if one were able to adequately image small organs. The pinhole collimator has been used extensively to obtain greater detail in planar imaging. However, using a pinhole collimator for SPECT is difficult because it requires a heavy collimated detector to rotate around a small object with a constant radius of rotation.METHODS:We have developed a mechanism in which the gantry and collimator are fixed and the animal rotates. Hollow cylinders of different sizes were made to enable imaging of small animals of different sizes: mice, hamsters, and rats. The cylinder is mounted on a stepping motor-driven system and positioned exactly above the pinhole collimator of an ARC3000 camera with a 1-mm pinhole insert. The stepping motor is controlled by the Hermes acquisition/processing system. After imaging each projection, a signal is given to rotate the stepping motor with the desired number of angular degrees. Filtered backprojection, adapted to pinhole SPECT, was used for reconstruction. The system allows adjustments of the radius of rotation and along the axis of the cylinder to select the field of view. Calibration experiments were performed to ensure that the axis of rotation was exactly in the middle of the cylinder. Phantom experiments were performed to assess sensitivity, spatial resolution, and uniformity of the system and to test the system for distortion artifacts. In addition, a brain dopamine transporter rat study and a hamster myocardial study were performed to test the clinical feasibility of the entire system.RESULTS:In the line source experiment, the spatial resolution obtained in air was 1.3 mm full width at half maximum, with a radius of rotation of 33 mm. Furthermore, the system has good uniformity and is capable of detecting cold spots of 2-mm diameter. The animal studies showed that it was feasible to image receptors or transporters and organs with sufficient detail in a practical setup.CONCLUSION:A rotating cylinder mechanism for pinhole SPECT is feasible and shows the same characteristics as conventional pinhole SPECT with a rotating camera head, without distortion artifacts. This mechanism permits pinhole SPECT to replace many ex vivo animal experiments.

Long-lived Co-57 flood sources, used for routine quantitative monitoring of scintillation camera hood-held uniformity, have recently become available with nominal activities of 370 MBq and higher. Non-uniformity problems have been observed. These are presumably related to high overall count rates from Co-57 and other radioactive cobalt isotopes present as impurities. This was investigated in five different cameras from four manufacturers using three cobalt sources of different ages and strengths. Count rates were measured within the energy range 30 keV to 1200 keV, and compared to the count rates in the 122 keV photopeak window. For a new flood source placed on the collimator, the overall count rate was about 400% of the photopeak window count rate. About 200% was due to high energy photons with energies above 134 keV. The count rate diminished when the source was moved away to a distance of 50 cm. The high energy contribution was less with the older sources, due to the faster decay of the cobalt impurities. Uniformity images were visually and quantitatively evaluated. Non-uniformity patterns were observed. These were dependent on the actual source area viewed by the camera, the age of the source, the distance of the source from the collimator, and the type of camera. Problems can be circumvented by purchasing lower activity sources (180 MBq), and increasing the source-collimator distance. Uniformity must first be carefully assessed before the source is put into use.

Measurements were made on the tomographic imaging abilities of a rotating slant hole collimator and a rotating scintillation camera system using a standard heart phantom and thallium-201. This allowed a comparison to be made between these and published results for conventional imaging and the seven pinhole technique under standardised conditions. Although better intraplanar resolutions were obtained with the rotating slant hole, the rotating camera was found to give superior definition of a defect and less propagation between reconstructed sections of the phantom.

The potential value of thallium-201 scintigraphy as a means of selecting patients for appro- priate coronary care unit admission was evaluated.Studies were made prospectively on 203 patients with possible acute myocardial infarction but atypical history and non-diagnostic electrocardiogram at a time when the clinical diagnosis was still in doubt.Under conventional circumstances, this particular group of patients will be admitted to the coronary care unit for observation in order to rule out myocardial infarction by further clinical evaluation.Scintigraphy was performed upon arrival in the coronary care unit and within 10 hours after the last episode of chest pain.Of 203 patients, 49 had positive, 47 had questionable, and 107 had normal thallium-201 scintiscans.Serial serum enzyme determinations and further clinical follow-up disclosed acute myocardial infarction in 34 patients: all had abnormal scans.Of47 patients subsequently determined to present with unstable angina, 27 had abnormal scans, ofwhom 7 subsequently developed acute myocardial infarction.Of 24 patients with previous myocardial infarc- tion, 18 patients had abnormal scans.None of either the 25 patients with stable angina or the 73 patients with atypical complaints showed frank perfusion defects, though questionable abnormal scintiscans were obtained in 5 and 12 patients in these groups, respectively.It is concluded that thallium-201 scintigraphy, when performed within a time interval of 10 hours after the last episode ofchest pain, may be ofvalue as a means of selecting those patients requiring further stay in hospital and observation in the coronary care unit.

To assess the prevalence and clinical relevance of right ventricular involvement in acute inferior wall infarction, 78 consecutive patients with the latter condition were studied with thallium-201 and technetium-99m pyrophosphate myocardial imaging. Right ventricular involvement was determined from superimposition of the 45 ° left anterior oblique thallium-201 and technetium-99m pyrophosphate images. All 78 patients showed thallium-201 defects. Sixty-four patients had positive pyrophosphate scans, and 24 of these (37.5 percent) showed right ventricular involvement. None of the patients with right ventricular involvement in this consecutive series showed the classic signs of severe right ventricular failure, although subclinical right ventricular dysfunction may have been present. There was no significant difference in the incidence of cardiogenic shock between the groups with and without right ventricular involvement. It is concluded that right ventricular involvement in acute inferior wall infarction is relatively frequent but not necessarily associated with severe right-sided pump failure. In patients with acute inferior wall infarction and severe pump failure, dual imaging provides a simple noninvasive method of identifying the subgroup of patients with right ventricular involvement who may benefit from volume loading.

Thallium-201 scintigraphy was performed during the pain free period in 98 patients with unstable angina. Scintiscans were positive in 39 patients, questionable in 27 patients and normal in 32 patients. Eighty-one patients responded favorably to treatment (group I). Seventeen patients had complicated courses (group II) and despite maximal treatment with propranolol either developed infarction (six patients) or continued to have angina necessitating coronary surgery (11 patients). In group I during the pain free period 26 of 81 patients had positive thallium-201 scans, whereas 20 patients had an abnormal ECG at that time; during angina 18 patients had transient ECG changes. In group II during the pain free period 13 of 17 patients had positive scans, whereas two patients had abnormal ECG at that time; during angina 12 patients showed transient ECG changes. The sensitivity to recognize group II was 76% for thallium-201 scintigraphy, 11% for ECG during the pain free period; 70% for ECG during angina; 94% for the combination of either positive scans or abnormal ECG. Thus, 1) positive thallium-201 scans occur in patients with unstable angina, 2) positive scans can be obtained during the pain free period, 3) thallium-201 scans are more frequently positive in patients with complicated course.

A clinicopathological study was performed in 23 patients who died from acute transmural myocardial infarction and who had been studied with thallium-201 during the acute phase. Twenty patients died within five days and three later than five days after scintigraphy. The scintigraphic location and the estimated size of infarction in vivo were correlated with postmortem findings. There was good agreement in 91% between scintigraphic and postmortem location of infarction and in 70% between the ECG and postmortem findings. The size of infarction as determined from computer-processed schematic drawings of postmortem slices of the heart correlated well with the size determined from processed schematic drawings of the scintiscans (r = 0.91 for anterior infarction, r = 0.97 for inferior infarction, r = 0.86 for anterior-inferior infarction). It is concluded that thallium-201 scintigraphy provided more precise location of infarction than the ECG and that the size of the scintigraphically abnormal area reflected the extent of necrotic myocardium.

Conflicting views exist regarding the origin and location of the oral radioactivity seen in salivary gland scintigraphy with 99mTc-pertechnetate. The normal accumulation of oral activity was studied in a series of healthy subjects by sequential scintigraphy (anterior and lateral views) after intravenous injection of 2 mCi of 99mTc-pertechnetate. Ligation of the parotid ducts and/or cannulation of the submandibular ducts, which prevented their secretions from reaching the oral cavity, established that the oral activity was due entirely to radioactive saliva secreted by the parotid and submandibular glands. Pertechnetate mouthwash studies confirmed that radioactive saliva is absorbed to oral mucosa and that adsorption to the lingual mucosa in the major contributor to the oral activity. Pertechnetate uptake in sublingual and minor salivary glands of the oral cavity was not visualized, thereby invalidating scintigraphy in the study of these glands. In the diagnosis of salivary gland disorders, oral activity is a useful indicator of major salivary gland function.