Simultaneous Dual-isotope Imaging Research Articles

Diagnostic value of simultaneous 99mTc-sestamibi/123I-BMIPP imaging parameters for predicting the improvement of left ventricular wall motion after acute myocardial infarction using CZT SPECT system

Abstract Background Although the presence of 99mTc-sestamibi/123I-BMIPP-mismatch, the reverse redistribution (RR) of 99mTc-sestamibi and RR of 123I-BMIPP in patients with acute myocardial infarction (AMI) are known to significant markers for predicting the improvement of LV wall motion in the infarcted territory in chronic phase, few studies were performed to analyze them by simultaneous dual-isotope imaging using cadmium-zinc-telluride (CZT) SPECT system. Purpose The purpose of this study was to evaluate whether the presence of 99mTc-sestamibi/123I-BMIPP-mismatch or RR of 99mTc-sestamibi, RR of 123I-BMIPP make better prediction of the improvement of LV wall motion in the infarcted territory. Methods We evaluated 42 consecutive patients with AMI who had undergone both dual-isotope SPECT in acute phase and stress myocardial SPECT using 99mTc-tracers in chronic phase by Discovery NM530c. The presence of 99mTc-sestamibi/123I-BMIPP-mismatch, RR of 99mTc-sestamibi and RR of 123I-BMIPP were determined using traditional definition. The improvement of LV wall motion in the infarcted territory from acute phase to chronic phase was assessed using QGS. Results Of 42 patients, the improvement of LV wall motion in the infarcted territory from acute phase to chronic phase was found in 29 patients. The presence of 99mTc-sestamibi/123I-BMIPP-mismatch and RR of 99mTc-sestamibi and RR of 123I-BMIPP were significantly linked to predict the improvement of LV wall motion (p=0.0001, p=0.0001 and p=0.002, respectively). To predict the improvement of LV wall motion in the infarcted territory in chronic phase, the presence of 99mTc-sestamibi/123I-BMIPP-mismatch showed sensitivity of 93%, specificity of 85% and accuracy of 91%, while RR of 99mTc-sestamibi and RR of 123I-BMIPP had sensitivities of 72%, 48%, specificities of 85%, 100% and accuracies of 76%, 64%, respectively. The multivariate discriminant analysis revealed that the combination of 99mTc-sestamibi/123I-BMIPP-mismatch, RR of 99mTc-sestamibi and RR of 123I-BMIPP best predicted the improvement of LV wall motion in the infarcted territory in chronic phase with sensitivity of 93%, specificity of 85% and accuracy of 91% (chi-square=40.6), compared with RR of 99mTc-sestamibi and RR of 123I-BMIPP only (sensitivity 79%, specificity 85% and accuracy of 81%, chi-square=16.9). Conclusions The addition of 99mTc-sestamibi/123I-BMIPP-mismatch on RR of 99mTc-sestamibi and RR of 123I-BMIPP in patients with AMI, help better predict the improvement of LV wall motion in the infarcted territory in chronic phase. Funding Acknowledgement Type of funding sources: None.

Prediction of the improvement of left ventricular wall motion after acute myocardial infarction by simultaneous dual-isotope imaging with 99mTc-sestamibi/123I-BMIPP using cadmium-zinc-telluride SPECT

Abstract Background/Introduction Although both the presence of 99mTc-sestamibi/123I-BMIPP mismatch and the reverse redistribution of 99mTc-sestamibi in patients with acute myocardial infarction (AMI) are known to significant markers for predicting the improvement of left ventricular (LV) wall motion in the infarcted territory in chronic phase, few studies evaluated them by simultaneous dual-isotope (99mTc-sestamibi/123I-BMIPP) imaging using cadmium-zinc-telluride (CZT) SPECT system. Purpose The purpose of this study was to evaluate whether the presence of 99mTc-sestamibi/123I-BMIPP mismatch or the reverse redistribution of 99mTc-sestamibi make better prediction of the improvement of LV wall motion in the infarcted territory. Methods We evaluated 30 consecutive patients with AMI who had undergone both dual-isotope (99mTc-sestamibi/123I-BMIPP) SPECT in acute phase and stress myocardial SPECT using 99mTc-tracers in chronic phase by Discovery NM530c. Both 99mTc-sestamibi/123I-BMIPP mismatch and reverse redistribution of 99mTc-sestamibi were determined using traditional definition. The improvement of LV wall motion in the infarcted territory from acute phase to chronic phase was assessed using QGS. Results Of 30 patients, the improvement of LV wall motion in the infarcted territory from acute phase to chronic phase was found in 20 patients. Both the presence of 99mTc-sestamibi/123I-BMIPP mismatch and reverse redistribution of 99mTc-sestamibi were significantly linked to predict the improvement of LV wall motion (p=0.0001, p=0.011, respectively). The respective sensitivities, specificities and accuracies in the prediction of the improvement of LV wall motion in the infarcted territory were 90%, 90% and 90% with 99mTc-sestamibi/123I-BMIPP mismatch, and 60%, 90%, 70% with reverse redistribution of 99mTc-sestamibi. Conclusions In the simultaneous 99mTc-sestamibi/123I-BMIPP dual-isotope imaging using CZT SPECT system, both the presence of 99mTc-sestamibi/123I-BMIPP mismatch and the reverse redistribution of 99mTc-sestamibi in acute phase are useful for predicting the improvement of LV wall motion in chronic phase, but the presence of 99mTc-sestamibi/123I-BMIPP mismatch is superior to the reverse redistribution of 99mTc-sestamibi for it. Funding Acknowledgement Type of funding source: None

Prediction of myocardial viability in chronic phase in patients with acute myocardial infarction by simultaneous dual-isotope imaging with 99mTc-sestamibi/123I-BMIPP SPECT using CZT camera system

Abstract Objectives The objective of this study was to determine the optimal cut-off value of % uptake of simultaneous dual-isotope (99mTc-sestamibi/123I-BMIPP) SPECT in patients with acute myocardial infarction (AMI) for prediction of myocardial viability in chronic phase. Methods We evaluated 30 consecutive patients with AMI who had undergone both dual-SPECT in acute phase and stress myocardial SPECT using 99mTc-tracers in chronic phase by Discovery NM530c. Regional % uptake with a 17-segment model was obtained using QPS software. The presence of myocardial viability was defined when regional % uptake ≥50% in 99mTc SPECT at rest in chronic phase was observed. Receiver operating characteristic (ROC) curves were analyzed to determine the optimal cutoff values of regional % uptake in both left anterior descending artery (LAD) territory and non-LAD coronary territory in acute phase to predict the myocardial viability in chronic phase. Results The cutoff values for prediction of viable myocardium were %uptake ≥47% for 99mTc-sestamibi, %uptake ≥31% for 123I-BMIPP in acute phase in LAD territory and %uptake ≥52% for 99mTc-sestamibi, %uptake ≥48% for 123I-BMIPP in non-LAD territory. The respective sensitivities, specificities and the area under the ROC curve (AUC) values in the prediction of myocardial viability were 92%, 92% and 0.94 with 99mTc-sestamibi, 90%, 85%, 0.92 with 123I-BMIPP in LAD territory, and 81%, 93% and 0.92 with 99mTc-sestamibi, 81%, 90%, 0.92 with 123I-BMIPP in non-LAD territory. There were no significant differences in AUC values between 99mTc-sestamibi and 123I-BMIPP in both LAD territory and non-LAD coronary territory. Conclusions In the simultaneous 99mTc-sestamibi/123I-BMIPP dual-isotope imaging in patients with AMI, these results suggest that not only 99mTc-sestamibi SPECT, but also 123I-BMIPP SPECT may be possible to predict the presence of myocardial viability in chronic phase. But it should be noted that the optimal cutoff values of regional % uptake in acute phase to predict the myocardial viability may differ for LAD territory and non-LAD coronary territory. Funding Acknowledgement Type of funding source: None

Shortened acquisition time in simultaneous 99mTc-tetrofosmin and 123I-β-methyl-p-iodophenyl pentadecanoic acid dual-tracer imaging with cadmium-zinc-telluride detectors in patients undergoing primary coronary intervention for acute myocardial infarction.

The use of cadmium-zinc-telluride-based scanners may increase the clinical feasibility of simultaneous dual-isotope imaging. In the current study, we sought to investigate a potential acquisition time in simultaneous Tc-tetrofosmin/I-β-methyl-p-iodophenyl pentadecanoic acid dual-isotope imaging using a Discovery NM/CT 670 cadmium-zinc-telluride. Simultaneous Tc-tetrofosmin/I-β-methyl-p-iodophenyl pentadecanoic acid dual-isotope imaging was performed in 29 patients who had undergone primary percutaneous coronary intervention for acute myocardial infarction. Referenced images with an acquisition time of 65 s/view (16.25 min) were reframed to produce images with acquisition times of 33, 16, and 8 s/view. The values for the quantitative-gated single-photon emission computed tomography (SPECT) and the quantitative perfusion SPECT were compared. The quantitative-gated SPECT values for images with 33, 16, and 8 s/views showed good consistency with those for 65 s/view (the lower 95% confidence intervals for the intraclass correlation were ≥0.80). The quantitative perfusion SPECT values for Tc-tetrofosmin images with 33, 16, and 8 s/views also showed good consistency with those for 65 s/view; however, the quantitative perfusion SPECT values for I-β-methyl-p-iodophenyl pentadecanoic acid images with an acquisition time of 8 s/view were not consistent with the reference acquisition time of 65 s/view. The quantitative-gated SPECT and quantitative perfusion SPECT values obtained from images with shorter acquisition times correlated with the values obtained from images with a reference acquisition time of 65 s/view; however, tracer-specific predisposition should be considered. These findings suggest that it is possible to reduce acquisition time when performing simultaneous Tc-tetrofosmin/I-β-methyl-p-iodophenyl pentadecanoic acid dual-tracer imaging with the novel cadmium-zinc-telluride scanner.

Comparative Cardiac Phantom Study Using Tc-99m/I-123 and Tl-201/I-123 Tracers with Cadmium-Zinc-Telluride Detector-Based Single-Photon Emission Computed Tomography.

A recently introduced single-photon emission computed tomography (SPECT), based on cadmium-zinc-telluride (CZT) detectors (D-SPECT), supports high energy resolution for cardiac imaging. Importantly, the high energy resolution may allow simultaneous dual-isotope (SDI) imaging (e.g., using Tc-99m and I-123). We quantitatively evaluated Tc-99m/I-123 SDI imaging by D-SPECT in comparison with conventional T1-201/I-123. Energy resolution was measured as a percentage of the full width at half maximum (FWHM) for Tc-99m, I-123, and Tl-201. The impact of cross-talk and reconstructed image contrast were quantified by measuring the contrast-to-noise ratio (CNR), and the transmural defect contrast in the left ventricle wall (C TD) induced by a difference in energy, for combinations of Tc-99m/I-123 or Tl-201/I-123, using an RH-2 cardiac phantom. Corresponding measurement was also carried out in Anger SPECT (A-SPECT). The energy resolution of the D-SPECT system was 5.4%/5.1% for Tc-99m/I-123 and 5.4%/5.3% for Tl-201/I-123, which was approximately two times higher than the A-SPECT. No notable difference was confirmed in the CNRs of the two systems, but T1-201/I-123 showed overall higher value than Tc-99m/I-123. Compared to A-SPECT, C TD of D-SPECT significantly increased with both Tc-99m/I-123 and T1-201/I-123 (p< 0.05). In DSPECT, the combination of Tc-99m/I-123 had a slightly better C TD than T1-201/I-123. In addition, C TD of Tc-99m/I-123 was improved with scatter correction at both nuclides (p< 0.05), but in Tl-201/I-123, no significant improvement was confirmed in I-123 (p> 0.05). D-SPECT was considered to be capable of performing high-quality SDI imaging using Tc-99m/I-123.

2459Diagnostic value of simultaneous dual-isotope imaging with 99mTc-sestamibi and 123I-BMIPP using cadmium-zinc-telluride SPECT system in patients with acute myocardial infarction

2459Diagnostic value of simultaneous dual-isotope imaging with 99mTc-sestamibi and 123I-BMIPP using cadmium-zinc-telluride SPECT system in patients with acute myocardial infarction

Dynamic dual-isotope molecular imaging elucidates principles for optimizing intrathecal drug delivery.

The intrathecal (IT) dosing route offers a seemingly obvious solution for delivering drugs directly to the central nervous system. However, gaps in understanding drug molecule behavior within the anatomically and kinetically unique environment of the mammalian IT space have impeded the establishment of pharmacokinetic principles for optimizing regional drug exposure along the neuraxis. Here, we have utilized high-resolution single-photon emission tomography with X-ray computed tomography to study the behavior of multiple molecular imaging tracers following an IT bolus injection, with supporting histology, autoradiography, block-face tomography, and MRI. Using simultaneous dual-isotope imaging, we demonstrate that the regional CNS tissue exposure of molecules with varying chemical properties is affected by IT space anatomy, cerebrospinal fluid (CSF) dynamics, CSF clearance routes, and the location and volume of the injected bolus. These imaging approaches can be used across species to optimize the safety and efficacy of IT drug therapy for neurological disorders.

Novel SPECT Technologies and Approaches in Cardiac Imaging

Recent novel approaches in myocardial perfusion single photon emission CT (SPECT) have been facilitated by new dedicated high-efficiency hardware with solid-state detectors and optimized collimators. New protocols include very low-dose (1 mSv) stress-only, two-position imaging to mitigate attenuation artifacts, and simultaneous dual-isotope imaging. Attenuation correction can be performed by specialized low-dose systems or by previously obtained CT coronary calcium scans. Hybrid protocols using CT angiography have been proposed. Image quality improvements have been demonstrated by novel reconstructions and motion correction. Fast SPECT acquisition facilitates dynamic flow and early function measurements. Image processing algorithms have become automated with virtually unsupervised extraction of quantitative imaging variables. This automation facilitates integration with clinical variables derived by machine learning to predict patient outcome or diagnosis. In this review, we describe new imaging protocols made possible by the new hardware developments. We also discuss several novel software approaches for the quantification and interpretation of myocardial perfusion SPECT scans.

A preliminary feasibility study of simultaneous dual-isotope imaging with a solid-state dedicated cardiac camera for evaluating myocardial perfusion and fatty acid metabolism.

Simultaneous dual-isotope SPECT imaging with 201Tl and (123)I-β-methyl-p-iodophenylpentadecanoic acid (BMIPP) is used to study the perfusion-metabolism mismatch. It predicts post-ischemic functional recovery by detecting stunned myocardium. On the other hand, (99m)Tc-MIBI is another radioisotope widely used in myocardial perfusion imaging because of its better image quality and lower radiation exposure than 201Tl. However, since the photopeak energies of (99m)Tc and (123)I are very similar, crosstalk hampers the simultaneous use of these two radioisotopes. To overcome this problem, we conducted simultaneous dual-isotope imaging study using the D-SPECT scanner (Spectrum-Dynamics, Israel) which has a novel detector design and excellent energy resolution. We first conducted a basic experiment using cardiac phantom to simulate the condition of normal perfusion and impaired fatty acid metabolism. Subsequently, we prospectively recruited 30 consecutive patients who underwent successful percutaneous coronary intervention for acute myocardial infarction, and performed (99m)Tc-MIBI/(123)I-BMIPP dual-isotope imaging within 5 days after reperfusion. Images were interpreted by two experienced cardiovascular radiologists to identify the infarcted and stunned areas based on the coronary artery territories. As a result, cardiac phantom experiment revealed no significant crosstalk between (99m)Tc and (123)I. In the subsequent clinical study, (99m)Tc-MIBI/(123)I-BMIPP dual-isotope imaging in all participant yielded excellent image quality and detected infarcted and stunned areas correctly when compared with coronary angiographic findings. Furthermore, we were able to reduce radiation exposure to significantly approximately one-eighth. In conclusion, we successfully demonstrated the practical application of simultaneous assessment of myocardial perfusion and fatty acid metabolism by (99m)Tc-MIBI and (123)I-BMIPP using a D-SPECT cardiac scanner. Compared with conventional (201)TlCl/(123)I-BMIPP dual-isotope imaging, the use of (99m)Tc-MIBI instead of (201)TlCl improves image quality as well as lowers radiation exposure.

Simultaneous dual-isotope imaging based on an artificial neural network for evaluating myocardial perfusion and fatty acid metabolism

BackgroundWe contrived a scatter correction method based on an artificial neural network (ANN) and applied it to the simultaneous evaluation of myocardial perfusion and fatty acid metabolism in single-photon emission computed tomography (SPECT). MethodsThe count data of three energy windows were used as inputs of the ANN. The count ratios of the estimated primary-to-total photons for 99mTc and 123I, which were used to reconstruct 99mTc and 123I images, were calculated using the ANN. In a phantom study, single- and dual-isotope imaging with 99mTc/123I and 201Tl/123I was performed by means of a cardiac phantom simulating patients with and without obesity. In a human study, five normal volunteers and ten patients with myocardial infarction underwent myocardial perfusion and fatty acid metabolism imaging with single and dual SPECT with combinations of 99mTc-methoxyisobutylisonitrile/123I-beta-methyl(p-iodophenyl)pentadecanoic acid (BMIPP) and 201Tl/123I-BMIPP as tracers. ResultsTechnetium-99m yielded more homogeneous images than 201Tl because of the lower degree of photon attenuation, especially in the condition of obese patients, resulting in clearer visualization of the perfusion-metabolism mismatch. Dual 99mTc/123I SPECT offered comparable images with single SPECT in assessing myocardial damage. ConclusionsThe method effectively separated 99mTc and 123I primary photons and proved applicable to 99mTc/123I dual-isotope myocardial SPECT.

Physical phantom evaluation of simultaneous 99mTc/123I SPECT imaging

Abstract Simultaneous dual-isotope imaging from two different energy gamma rays such as 99mTc and 123I is a promising technology in nuclear medicine. Its advantages are to abbreviate the acquisition procedure with an identical geometrical registration of the different isotope images, the same physiological condition without motion artifacts, and help patient throughput and comfort. However, the energy photopeaks of 99mTc and 123I radionuclides are very close. We had developed a new approach for accurate cross-talk and scatter corrections in simultaneous 99mTc/123I based on independent components analysis (ICA). Nevertheless, a large number of input energy windows are required as ICA input components, which is not useful in clinical application because commercial cameras have only 3–8 energy windows. The aim of this work was to design a new method through wavelet transformation followed by ICA with multiple energy windows (W_eICA) for cross-talk and scatter correction using a smaller number of energy windows in clinical use. There were three cylinders (A–C) with identical volume of 20 ml. Cylinder A was filled with 99mTc solution of 18.5 MBq, cylinder B with 123I solution of 18.5 MBq, and cylinder C with 99mTc solution of 55.5 MBq. The Image matrix size was 128×128 and pixel size was 3.9 mm. Three kinds of images were acquired by energy window setting. (1) For single-isotope imaging only, energy windows of 20% centered at 140 keV for 99mTc and at 159 keV for 123I were used. (2) In the asymmetric energy window method (AEW), energy window of 15% centered at 140 keV for 99mTc in conjunction with 10% asymmetric energy window in an upper bound at 159 keV for 123I was acquired. (3) Then we set six energy windows with 15 keV width ranging from 83 to 173 keV to form six images as input components of ICA. After the W_eICA method derived 99mTc/123I images alone, we compared the images from the W_eICA approach and the AEW method. In the results, the recovery rate of 99mTc was 1.03 and that of 123I was 1.07 from the W_eICA method. Besides, the recovery rate of 99mTc was 0.84 and that of 123I was 1.05 from the AEW approach. According to our results, the W_eICA method not only decreased the number of energy windows but also separated dual-isotope photopeaks successfully. The results have demonstrated that the W_eICA method improved the quantitative accuracy and might be an effective tool for simultaneous dual-isotope SPECT imaging.

Compensation of Cross-Contamination in Simultaneous 201Tl/99mTc Myocardial Perfusion SPECT Imaging

Introduction: It is a common protocol to use 201Tl for the rest and 99mTc for the stress cardiac SPECT imaging. Theoretically, both types of imaging may be performed simultaneously using different energy windows for each radionuclide. However, a potential limitation is the cross-contamination of scattered photons from 99mTc and collimator X-rays into the 201Tl energy window. We used a middle energy window method to correct this cross-contamination. Material and Methods: Using NCAT, a typical software torso phantom was generated. An extremely thin line source of 99mTc activity was placed inside the cardiac region of the phantom and no activity in the other parts. The SimSET Monte Carlo simulator was used to image the phantom in different energy windows. To find the relationship between projections in different energy windows, deconvolution theory was used. We investigated the ability of the suggested functions in three steps: Monte Carlo simulation, phantom experiment and clinical study. In the last step, SPECT images of eleven patients who had angiographic data were acquired in different energy windows. All of these images were compared by determining the contrast between a defect or left ventricle cavity and the myocardium. Results: We found a new 2D kernel which had an exponential pattern with a much higher center. This function was used for modeling 99mTc down scatter distribution from the middle window image. X-ray distribution in the 201Tl window was also modeled as the 99mTc photopeak image convolved by a Gaussian function. Significant improvements in the contrasts of the simultaneous dual 201Tl images were found in each step before and after reconstruction. In comparison with other similar methods, better results were acquired using our suggested functions. Conclusion: Our results showed contrast improvement in thallium images after correction, however, many other parameters should be evaluated for clinical approaches. There are many advantages in simultaneous dual isotope imaging. It halves imaging time and reduces patient waiting time and discomfort. Identical rest/stress registration of images also facilitates physicists’ motion or attenuation corrections and physicians’ image interpretation.

Application of Three-Class ROC Analysis to Task-Based Image Quality Assessment of Simultaneous Dual-Isotope Myocardial Perfusion SPECT (MPS)

The diagnosis of cardiac disease using dual-isotope myocardial perfusion SPECT (MPS) is based on the defect status in both stress and rest images, and can be modeled as a three-class task of classifying patients as having no, reversible, or fixed perfusion defects. Simultaneous acquisition protocols for dual-isotope MPS imaging have gained much interest due to their advantages including perfect registration of the (201)Tl and (99m)Tc images in space and time, increased patient comfort, and higher clinical throughput. As a result of simultaneous acquisition, however, crosstalk contamination, where photons emitted by one isotope contribute to the image of the other isotope, degrades image quality. Minimizing the crosstalk is important in obtaining the best possible image quality. One way to minimize the crosstalk is to optimize the injected activity of the two isotopes by considering the three-class nature of the diagnostic problem. To effectively do so, we have previously developed a three-class receiver operating characteristic (ROC) analysis methodology that extends and unifies the decision theoretic, linear discriminant analysis, and psychophysical foundations of binary ROC analysis in a three-class paradigm. In this work, we applied the proposed three-class ROC methodology to the assessment of the image quality of simultaneous dual-isotope MPS imaging techniques and the determination of the optimal injected activity combination. In addition to this application, the rapid development of diagnostic imaging techniques has produced an increasing number of clinical diagnostic tasks that involve not only disease detection, but also disease characterization and are thus multiclass tasks. This paper provides a practical example of the application of the proposed three-class ROC analysis methodology to medical problems.

SEPARATION OF TWO RADIONUCLIDES IN SIMULTANEOUS DUAL-ISOTOPE IMAGING WITH INDEPENDENT COMPONENT ANALYSIS

Simultaneous dual-isotope imaging has contributions from two different energy gamma rays, such as Tc-99m (140KeV) and I-123 (159KeV). Dual-isotope Tc-99m/I-123 imaging has capability in nuclear medicine applications for brain perfusion or presynaptic and postsynaptic dopamine system and for myocardial perfusion system. It reduces acquisition time and makes registration much easier. But the disadvantages of dual-isotope technique are the scatter and cross-talk between the two emitted gamma-ray photons. We proposed a new method to correct for cross-talk from primary and scattered photons using independent component analysis (ICA), which was compared to conventional energy-window method (CONW). In this paper we investigated the performance of ICA to separate Tc-99m and I-123 energy spectra from dual-isotope simulated data to obtain images of each isotope. In Tc-99m images, the estimated image was extracted from mixed dual-isotope imaging using ICA with the percentage bias (P) about -11% and the mean square error (MSE) of 80.48. The counts of Tc-99m were overestimated by CONW method with P &lt; 66% and MSE of 1860.28. ICA could reduce the contamination significantly from I-123 to Tc-99m window. In I-123 images, the cross-talk was disappeared in both methods, but the percentage bias for ICA (&lt; -18%) was less than that of CONW (&lt; -57%). The MSE was 104.63 for the ICA case and 960.15 for the CONW case. The results demonstrated that ICA method improved the quantitative accuracy and can be a promising and effective tool for dual-isotope imaging.

Gamma camera PET with low energy collimators: characterization and correction of scatter

Imaging of myocardial viability with fluorodeoxyglucose (FDG) is possible with positron emission tomography (PET) and with SPECT. The image resolution from SPECT is poor but the data is reported to provide clinical information comparable to PET. Studies have just begun to appear using gamma camera PET and either axial slat collimators or open frame graded absorbers to image myocardial viability. Alternatively, it may be possible to use standard low energy collimators en detecting coincidences. Although image quality may suffer, it may be possible to devise methods such that no clinical information is lost. Such an approach also paves the way for dual isotope sequential or simultaneous imaging of coincidence and single photons. Here, we characterize the scatter fraction and scatter distribution of gamma camera PET with low energy collimators, and investigate the improvements possible with a convolution-subtraction scatter correction scheme. Monte Carlo simulations, line sources, a realistic phantom, and a human study were used. The scatter fraction was found to be almost identical to that obtained with axial slat collimators on a triple head gamma camera hybrid PET scanner. Images acquired with low energy collimators were degraded but still of good quality compared to acquisitions using axial collimation. The scatter correction scheme showed a degree of improvement over reconstructions without scatter correction. This approach is useful not only toward making sequential or simultaneous dual isotope imaging possible, but may also be useful to save time in a busy clinic that does both SPECT scans and cardiac FDG studies, since collimators would not need to be changed.

Quantitative simultaneous /sup 99m/Tc//sup 123/I SPECT: design study and validation with Monte Carlo simulations and physical acquisitions

Simultaneous dual isotope imaging (/sup 99m/Tc//sup 123/I) has potential clinical applications but has not been implemented in the clinic. The aim of this work was to design an artificial neural network (ANN) for crosstalk and scatter correction using a smaller number of energy windows (8) than we had previously proposed (26) to allow implementation on some clinical cameras, and to validate our approach using realistic Monte Carlo simulations and anthropomorphic brain phantom acquisitions. Monte Carlo simulations of dual isotope SPECT studies of a digital brain phantom and physical acquisitions of the striatal brain phantom were used to validate our approach. Corrected projections were reconstructed using an iterative ordered subsets expectation maximization (OSEM) algorithm that modeled nonuniform attenuation and variable collimator response in the projector/backprojector. Results: In Monte Carlo simulations, ANN26 and ANN8 yielded similarly accurate quantitation of /sup 123/I activity (bias <7%) in all brain structures. An asymmetric windowing method (AW) yielded accurate estimation in the striata (bias <7%) but not in other brain structures. The estimation bias of /sup 99m/Tc primary activity was <10% in all brain structures with ANN26 and ANN8.

Parameterization of Pb X-ray contamination in simultaneous Tl-201 and Tc-99m dual-isotope imaging

In simultaneous Tl-201 and Tc-99m dual isotope imaging, Pb X-rays are a significant source of contamination in the Tl image. In order to characterize this contamination, we simulated images of line sources in the Tc and Tl photopeak windows using an experimentally verified Monte Carlo program. The line sources were placed at various distances from the collimator face and emitted photons with energies from 88 to 140.5 keV. The Ph X-ray contamination line source response function in the Tl window was fitted well by a Gaussian plus an exponential function. The width of these two functions changed linearly with distance. Parameterization of the Ph X-ray response was done by simultaneously fitting the Ph X-ray response functions at various distances with fitting functions that were determined empirically to model the distance dependence of the Gaussian and exponential components of the Ph X-ray response. The parameterized model of Ph X-ray contamination is useful in developing methods to model Ph X-ray contamination in Tl-201 data by Tc-99m. This Ph X-ray contamination model can be used in iterative reconstruction-based cross-talk compensation for simultaneous Tc/Tl dual isotope imaging.

Enhanced cross-talk correction technique for simultaneous dual-isotope imaging: a TL-201/Tc-99m myocardial perfusion SPECT dog study.

A newly developed cross-talk correction method for simultaneous dual-isotope SPECT imaging was tested in a canine model. The method is based on the assumption that the transformations, which modify the primary energy window images into the scatter images as viewed in the other energy windows, are known. These transformations were found by measuring the point spread functions (PSFs) in two different energy windows for both isotopes in water. The dual-isotope correction method is described by two convolution equations which were applied in frequency space. The equations take into account the different spatial distributions of the primary and scatter cross-talk photons. The new enhancement of the method was in applying restoration filters to the resulting corrected images. Three separate studies were acquired in our dog study: two single-isotope and one dual-isotope study. The single isotope images were used as references. The contrast between the left ventricle cavity (LVC) and the myocardium was used in transaxial and short-axis slices as a parameter to evaluate results of dual-isotope correction method with restoration. The change in contrast in the dual-isotope corrected images in both energy windows, i.e., Tc-99m primary window (140 keV) and Tl-201 primary window (70 keV), was significant. The only exception was for the short-axis Tc-99m window images. The corrected 140 keV dual-isotope short-axis slice had the contrast of 0.60 vs 0.58, which was the value in the noncorrected dual-isotope short-axis slice. For dual-isotope 140 keV transaxial slice, the contrast changed from 0.72 to 0.82 after correction. In comparison, for single-isotope Tc-99m 140 keV transaxial slice, contrast changed from 0.62 to 0.84 after restoration correction. There was less change in contrast in the short-axis Tc-99m 140 keV slice, i.e., from 0.56 to 0.61. In the Tl-201 primary window for the transaxial slices the improvement of contrast was from 0.38 to 0.64, and for short-axis slices from 0.22 to 0.32 after correction. In the same 70 keV energy window for single-isotope Tl-201 images, contrast improved from 0.61 to 0.69 and from 0.35 to 0.38 for transaxial and short-axis slice, respectively, after applying restoration correction. In conclusion, the presented dual-isotope correction method with restoration improves the quality of the simultaneous rest Tl-201/stress Tc-99m sestamibi SPECT imaging.

A new dual-isotope convolution cross-talk correction method: a Tl-201/Tc-99m SPECT cardiac phantom study.

Simultaneous dual-isotope SPECT imaging provides a clear advantage in situations where two concurrent metabolic, anatomic, or background measurements are desired. It obviates the need for two separate imaging sessions, reduces patient motion problems, and provides exact image registration between images. However, a potential limitation of dual-isotope SPECT imaging is contribution of scattered and primary photons from one radionuclide into the second radionuclide's photopeak energy window, referred to here as cross-talk. Cross-talk in both photopeak energy windows can significantly degrade image quality, resolution, and quantitation to an unacceptable level. Simple cross-talk correction method used in dual-radionuclide in vitro counting, even applied on a pixel-by-pixel basis, does not account for the differences in spatial distribution of the photopeak and cross-talk photons. Here a new convolution cross-talk correction method is presented. The convolution filters are derived from point response functions (PRFs) for Tc-99m and Tl-201 point sources. Three separate acquisitions were performed, each with two 20% wide energy windows, one centered at 140 keV and another at 70 keV. The first acquisition was done with Tc-99m solution only, the second with Tl-201 solution only, and the third with a mixture of Tc-99m and Tl-201. The nonuniform RH-2 thorax-heart phantom was used to test a new correction technique. The main difficulty and limitation of the convolution correction approach is caused by the variation in PRF as a function of depth. Thus, average PRF should be used in the creation of an approximative filter.(ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous maximal exercise radionuclide angiography and thallium stress perfusion imaging

Gold-195m is a new ultra-short-lived radionuclide that can be used for cardiac studies. Accurate, reproducible ejection fraction and ventricular wall motion studies can be obtained from first-transit angiography using commercially available imaging and image-processing equipment. The short half-life of gold-195m (30.5 seconds) makes simultaneous dual isotope imaging possible and substantially reduces the radiation exposure from the isotope angiography. The feasibility and possible benefits of performing dual radionuclide studies were evaluated during a single exercise stress test in 24 subjects with known coronary artery disease (CAD) and in 20 normal volunteers. High-quality first-transit angiograms were obtained in all subjects. An 83% sensitivity and 95% specificity for detecting CAD with thallium-201 imaging was noted in this investigation, suggesting that its diagnostic accuracy was not altered by simultaneous dual isotone imaging. When segmental left ventricular (LV) wall motion was compared with thallium-201 perfusion imaging, divergent results were noted in 15 of 44 subjects. An analysis of the ejection fraction (EF) results at rest and stress provided additional information that could be useful in assessing the clinical significance of such differences in segmental wall motion and perfusion. Simultaneous dual isotope imaging appears to be appropriate for situations in which both LV perfusion and function require evaluation. The use of gold-195m allows such information to be obtained from a single exercise test and can thereby reduce the cost and time required for noninvasive evaluations of patients for CAD.