Absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) provide incremental diagnostic and prognostic information over relative perfusion alone. Recent development of dedicated cardiac SPECT cameras with better sensitivity and temporal resolution make dynamic SPECT imaging more practical. In this study, we evaluate the measurement of MBF using a multipinhole dedicated cardiac SPECT camera in a pig model of rest and transient occlusion at stress using 3 common tracers: 201 Tl, 99m Tc-tetrofosmin, and 99m Tc-sestamibi. Methods: Animals (n 5 19) were injected at rest/stress with 99m Tc radiotracers (370/1,100 MBq) or 201 Tl (37/110 MBq) with a 1-h delay between rest and dipyridamole stress. With each tracer, microspheres were injected simultaneously as the gold standard measurement for MBF. Dynamic images were obtained for 11 min starting with each injection. Residual resting activity was subtracted from stress data and images reconstructed with CT-based attenuation correction and energy window-based scatter correction. Dynamic images were processed with kinetic analysis software using a 1-tissue-compartment model to obtain the uptake rate constant K 1 as a function of microsphere MBF. Results: Measured extraction fractions agree with those obtained previously using ex vivo techniques. Converting K 1 back to MBF using the measured extraction fractions produced accurate values and good correlations with microsphere MBF: r 5 0.75-0.90 (P , 0.01 for all). The correlation in the MFR was between r 5 0.57 and 0.94 (P , 0.01). Conclusion: Noninvasive measurement of absolute MBF with stationary dedicated cardiac SPECT is feasible using common perfusion tracers. St udies using PET have demonstrated that absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR 5 stress/ rest MBF) provide incremental diagnostic and prognostic information over relative perfusion alone (1-4). Imaging of myocardial perfusion is much more commonly performed with SPECT than with PET, but MBF measurements are not typically acquired.Measuring MBF is difficult with standard SPECT cameras because of the need for attenuation and scatter correction and the need to rotate around the patient for 3-dimensional imaging. Recent studies have shown that it is possible to obtain an index of the MFR without a direct measure of MBF using a combination of dynamic planar followed by static SPECT acquisitions (5) and that this can provide some prognostic information (6). Other studies have demonstrated that rapid camera rotation can provide dynamic tomographic data and hence a measure of MFR (7) and the arterial input function (8), suggesting that accurate measures of MBF could be possible (9). The practicality of measuring MBF has increased greatly, however, with the advent of dedicated cardiac cameras.Dedicated cardiac cameras such as the DSPECT system (Spectrum Dynamics Medical Inc.) or the Discovery NM 530c/ 570c cameras (GE Healthcare) have greatly improved sensitivity and do not rotate around the patient (10). These features allow d...
Translation of a source relative to a multipinhole camera caused only small changes in homogeneous phantoms with SPS changing <1.5. Inhomogeneous attenuating media cause much larger changes to occur when the source is translated. Changes in SPS of up to six were seen in an anthropomorphic phantom for axial translations. Attenuation correction removes the position-dependent changes in attenuation.
Dynamic SPECT measurement of MBF and MFR in pigs can be performed with 1/4 (Tc99m-tracers) or 1/2 (Tl-201) of the standard injected activity without significantly reducing accuracy and precision.
Rotenone derivatives have shown promise in myocardial perfusion imaging (MPI). CMICE-013 is a novel 123 I-labeled rotenone derivative developed for SPECT MPI. The objective of this study was to assess the image quality of CMICE-013 and compare its uptake with tetrofosmin, sestamibi, and 201 Tl in vivo in a porcine model of stress-induced myocardial ischemia. Methods: Microspheres were injected simultaneously with the radiotracer injections at rest and stress to measure blood flow. Mimicking a 1-d tetrofosmin protocol, stress imaging used 3 times as much activity and occurred 1 h after the rest injection. SPECT images were obtained at both rest and stress. After imaging, the heart was sectioned into 44-50 pieces. In each heart sample, the tracer uptake was measured in a γ counter. The images were aligned, and the decay-corrected ratio of the signals at rest and stress was used to separate the well-counter signal into rest and stress components. The uptake at rest and stress was compared with microsphere flow measurements. Results: The CMICE-013 images showed good contrast between the heart and surrounding organs, with heart-to-liver and heart-to-lung uptake ratios similar to those of the standard tracers. Uptake of CMICE-013 was 1.5% of the injected dose at rest and increased more rapidly with increased blood flow than did the standard SPECT tracers. The percentage injected dose of CMICE-013 taken up by the heart was greater (P , 0.05) than 201 Tl, tetrofosmin, or sestamibi at flows greater than 1.5 mL/min/g. Conclusion: CMICE-013 is a promising new SPECT MPI agent. Repeat ed unexpected shutdowns of several of the major nuclear reactors producing 99 Mo has led to ongoing concern over the stability of the supply of 99m Tc and, consequently, interest in developing alternative tracers. Myocardial perfusion imaging (MPI) remains one of the more common tests performed with 99m Tclabeled agents. For MPI, PET is a potential option using either 82 Rb or 13 N ammonia, because the parent isotope for 82 Rb generators ( 82 Sr) and ammonia are both cyclotron-produced. Interest in PET MPI is growing; however, the number of MPI SPECT scans obtained annually in North America is still orders of magnitude larger and likely to remain so for many years. Thus, a SPECT alternative to 99m Tc MPI tracers remains an important goal.Clinical trials of the 18 F-labeled PET tracer flurpiridaz (1,2) have shown excellent contrast between the heart and surrounding organs and performance superior to standard 99m Tc-based tracers for the identification of disease. This tracer inhibits mitochondrial complex I and derives its specificity for cardiac imaging from the high concentration of mitochondria in the heart. Other compounds that target mitochondrial complex I have been studied previously in SPECT. An iodinated rotenone compound (I-ZIROT) was shown to have excellent uptake in the heart and excellent extraction at higher blood flows (3,4), which is in contrast to the standard SPECT 99m Tc tracers that have a roll-off in their extraction, prod...
Cross talk and self-scatter were shown to produce quantification errors in phantoms as well as in vivo. The standard TEW provided inaccurate results due to the inclusion of unscattered photons in the scatter windows. The modified TEW improved the scatter estimate and reduced the quantification errors in phantoms and in vivo.
AC significantly improves the accuracy of low-count myocardial perfusion SPECT half-time imaging for the detection of disease compared to NC. Compared to PET, there was no significant difference among AC, AC-DEW, and AC-ESSE.
The author has granted a non exclusive license allowing Library and Archives Canada to reproduce, publish, archive, preserve, conserve, communicate to the public by telecommunication or on the Internet, loan, distrbute and sell theses worldwide, for commercial or non commercial purposes, in microform, paper, electronic and/or any other formats. AVIS: L'auteur a accorde une licence non exclusive permettant a la Bibliotheque et Archives Canada de reproduire, publier, archiver, sauvegarder, conserver, transmettre au public par telecommunication ou par I'lnternet, preter, distribuer et vendre des theses partout dans le monde, a des fins commerciales ou autres, sur support microforme, papier, electronique et/ou autres formats. Bien que ces formulaires aient inclus dans la pagination, il n'y aura aucun contenu manquant. Canada A b stract Dual-isotope imaging via energy discrimination is a major strength of SPECT but image quality is degraded by cross-talk interference. Direct application of clinically developed cross-talk correction techniques in small-animals is not ideal. Reduced sub ject size may allow adequate quantification with simpler cross-talk correction meth ods. This study evaluated four simple cross-talk correction methods for In-lll/T c-99m small-animal imaging: triple energy window (TEW), applied pre-and post correction, convolution subtraction, and a vendor-supplied correction. Each method was evaluated using a three-syringe phantom filled with either Tc-99m, In-111, or a mixture of the two at five different ratios. The optimal method was tested on in-vivo rat images. A modified TEW applied in projection space visually provided the best removal of In-111 cross-talk and reduced it quantitatively by 96%. The mixed sy ringe ratios were recovered to within 5%. In-vivo testing provided inconclusive results indicating that a true dual-isotope study is still necessary.
Dual isotope SPECT allows simultaneous measurement of two different tracers in vivo. With In111 (emission energies of 171keV and 245keV) and Tc99m (140keV), quantification of Tc99m is degraded by cross talk from the In111 photons that scatter and are detected at an energy corresponding to Tc99m. TEW uses counts recorded in two narrow windows surrounding the Tc99m primary window to estimate scatter. Iterative TEW corrects for the bias introduced into the TEW estimate resulting from un‐scattered counts detected in the scatter windows. The contamination in the scatter windows is iteratively estimated and subtracted as a fraction of the scatter‐corrected primary window counts. The iterative TEW approach was validated with a small‐animal SPECT/CT camera using a 2.5mL plastic container holding thoroughly mixed Tc99m/In111 activity fractions of 0.15, 0.28, 0.52, 0.99, 2.47 and 6.90. Dose calibrator measurements were the gold standard. Uncorrected for scatter, the Tc99m activity was over‐estimated by as much as 80%. Unmodified TEW underestimated the Tc99m activity by 13%. With iterative TEW corrections applied in projection space, the Tc99m activity was estimated within 5% of truth across all activity fractions above 0.15. This is an improvement over the non‐iterative TEW, which could not sufficiently correct for scatter in the 0.15 and 0.28 phantoms.
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