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Our previous study demonstrated that a cadmium telluride (CdTe)-based single-photon emission computed tomography (SPECT) system with good energy resolution could provide dual-radioisotope SPECT images of a patient who had been administered with two kinds of radioisotope simultaneously. To obtain two quantitative physiological parametric images from these radioisotope images by using compartment model analysis, the concentrations of the dual-radioisotope in the blood sample need to be measured. In this paper, a CdTe-based well counter was developed to measure the concentrations of a dual-radioisotope of 99mTc and 123I, and its performance was evaluated. The counter consists of four detector panels. Each detector panel consists of two detector modules, and each module has $16\,\, {\times } \,\, 16$ CdTe detector pixels with a pitch of 2.5 mm; the eight detector modules give our system a field of view ( $ {x} {\times } \,\, {y} {\times } {z}$ ) of $4\,\, {\times } \,\, 4\,\, {\times } \,\, 8$ cm3. The crosstalk correction coefficient $ {{{\alpha }}}$ , which is the ratio of the count rate in the 99mTc-energy window to that in the 123I-energy window, was obtained by measuring the single-radioisotope solution of 123I. When the dual-radioisotope of 99mTc and 123I was measured, the true count rate of 99mTc was obtained by subtracting the crosstalk count rate ( $ {{{\alpha }}} \,\, {\times }$ the count rate of 123I) from the uncorrected count rate of 99mTc. To evaluate the measurement accuracy, dual- and single-radioisotope solutions were measured, and the mean percentage error of the measured count rate of dual-radioisotope solutions to that of the single-radioisotope solution was obtained. The energy resolutions full width at half maximum of the CdTe-based well counter were 6.95% and 6.93% at 140.5 keV and 159 keV, respectively, and were higher than that of a conventional NaI (Tl) scintillation detector (10% at 140.5 keV). The count loss in the CdTe detector was 1.7% at 44 kcps. For the dual-radioisotope measurement, the percentage errors (mean percentage% ± standard deviation%, ${N} \,\, {=}$ 3) of the count rate of 99mTc and 123I at a high count rate (99mTc: 44 kcps, 123I: 28 kcps) were −1.9% ± 0.0% and −3.5% ± 1.1%, respectively. On the other hand, the percentage errors of the count rate of 99mTc and 123I at a low count rate (99mTc: 3 kcps, 123I: 4 kcps) were −0.4% ± 0.3% and 0.2% ± 0.6%, respectively. The CdTe-based well counter measured each concentration of 99mTc and 123I in mixed solutions with high accuracy.

The goal of this study is to evaluate the quantitative accuracy of measuring in vivo tracer concentrations using multiplexed multi-pinhole microSPECT with CT-based attenuation correction (AC) and simple methods for scatter compensation. Phantom and in vivo rat cardiac images were acquired and reconstructed with no photon AC, with AC only, with attenuation and dual-energy window scatter correction, and using a reduced attenuation coefficient to compensate for scatter. Absolute calibration was also acquired using small sources to minimize self-attenuation and scatter. The phantom tracer concentrations measured with SPECT were compared to dose calibrator measurements. The rats were sacrificed and the cardiac activity measured in vivo was compared to well counter measurements of cardiac activity. With no correction, the tracer concentrations measured in phantoms was as much as 30% below the true value for the largest phantom (52 mm diameter). AC improved the accuracy of quantification, but overestimated activity concentrations by up to 5% for the larger phantoms. With DEW scatter correction, activity concentration measured with SPECT agrees with the dose calibrator measurements to within $ -2 \pm 2\% $ and with a reduced attenuation coefficient, the agreement was better than $ -1 \pm 1\% $ . In rats injected with $^{99{\rm m}}{\rm Tc}$ -tetrofosmin, SPECT measurements of total cardiac activity were $24\pm 2\% $ below well counter measurements with no corrections, $5\pm 3\% $ above well counter measurements with only attenuation correction, $3\pm 3\% $ below with DEW scatter correction, and $1\pm 3\% $ below with reduced attenuation correction.

A novel device has been constructed that measures the positron-emitting radio-tracer concentration in arterial blood by extracting blood with a peristaltic pump and then measuring the activity concentration by detecting coincident pairs of 511-keV photons with a pair of heavy inorganic scintillators attached to photomultiplier tubes. The sensitivity of this device was experimentally determined to be 610 counts/s per mu Ci/ml, and it has a paralyzing dead time of 1.2 mu s, which makes it capable of measuring blood activity concentrations as high as 1 mCi/ml. Its performance is compared to that of two other blood monitoring methods: discrete blood samples counted with a well counter and a device that uses a plastic scintillator to detect positrons directly. The positron detection efficiency of this device for /sup 18/F is greater than that of the plastic scintillation counter, and it also eliminates the radioisotope-dependent correction factors necessary to convert count rate to absolute concentration. >

Cardiovascular research uses the microsphere technique as a tool to measure regional blood flow. Although the technique is extremely powerful, the instruments used to assay the microspheres limit the number of different tracers that can be used in one animal to 5 or 6. As is often the case, many more measurements per animal are needed, and the limitation necessitates using many more animals per experiment. This in turn increases costs and decreases the quality of the data, since no animal is its own control for the full set of experiments. A large germanium well counter designed for microsphere work has been evaluated. The detector is 9.8cm long, 5.7cm in diameter, with a 2.1cm well bore. The useable well has a 1.5cm diameter and reaches to within 2cm from the far end of the detector. Energy resolution ranges from 3 keV FWHM at 100 keV to 5 keV FWHM at 500 keV. Detector performance matches well that predicted from Monte Carlo calculations. The counter will increase the research utility of the microsphere technique in a cost-effective manner.

A well-type detector is described for the assay of gamma emitters over a Curie-to-nanoCurie activity range. A large plastic scintillator/photomultiplier is DC-coupled for current measurements at high activities, with pulse counting covering the low activities. The two techniques overlap for two decades in the uCi region, particularly troublesome for the alternative detectors: gas-filled ionization chambers or NaI(Tl) well counters. The plastic well is interfaced to a microcomputer for data acquisition and control of the phototube high voltage, the key to the nine-decade dynamic range.