A Novel Method to Suppress the Effect of Subdiaphragmatic Activity in 99mTc Myocardial Perfusion SPECT and Evaluation of Its Usefulness Using a Myocardial Phantom.

Background: Smoothing in 99mTc myocardial perfusion single-photon emission computed tomography (SPECT) often increases myocardial artifacts due to subdiaphragmatic activity near the heart. To reduce these artifacts, we developed a new process flow, masking on unsmoothed images (MUS), that includes the extraction of the myocardium by masking before smoothing. Methods: This study evaluated the relationships between matrix sizes and distances to the subdiaphragmatic activity using the MUS method compared to conventional methods using a combination of image reconstruction methods (filtered back-projection [FBP] and ordered subset expectation maximization [OSEM]) with or without corrections (attenuation [AC], scatter [SC], and resolution recovery [RR]) using a myocardial phantom. The results were compared for two matrix sizes (pixel sizes) (128×128 [3.3 mm] and 64×64 [6.6 mm]); four subdiaphragmatic activity distances (5, 10, 15, and 20 mm); and three reconstruction methods (FBP without correction; OSEM with RR; and OSEM with AC, SC, and RR). Results: In the conventional method, increasing distance resulted in interference with myocardial perfusion SPECT evaluation however, the artifacts were less apparent when the MUS method was applied. The images converted to 64×64 did not show the same effect as the 128×128 images, even when RR was used. The MUS method was useful for acquisition at 128×128, along with the use of RR in the reconstruction process. Conclusion: MUS mitigated the effects of subdiaphragmatic activity on myocardial perfusion SPECT, particularly combined with 128×128 acquisitions and iterative reconstruction with RR.

(90)Y bremsstrahlung emission computed tomography using gamma cameras.

OBJECTIVE: This study demonstrates images obtained by (90)Y bremsstrahlung emission computed tomography (BECT), and characterizes the system performance of gamma cameras. METHODS: (90)Y BECT images of phantoms were acquired using a gamma camera equipped with a medium energy general purpose parallel-hole collimator. Three energy window widths of 50% (57-94 keV) centered at 75 keV, 30% (102-138 keV) at 120 keV, and 50% (139-232 keV) at 185 keV were set on a (90)Y bremsstrahlung spectrum. The images obtained with three energy windows were reconstructed using filtered back projection (FBP) and ordered subsets expectation maximization (OSEM) methods. The images of the sum window were obtained by fusing the images of the 75, 120, and 185 keV windows. RESULTS: The OSEM method improved the full width at half maximum by 20% and the standard deviation by 9% compared with the FBP method. BECT displayed (90)Y biodistribution and quantified (90)Y activity. BECT images obtained with OSEM method using the 120 keV window showed the highest resolution and lowest uncertainty. The sum window showed the highest sensitivity, while its resolution was 10% inferior to that of the 120 keV window. One whole-body image can be taken over 100 min using the sum window. An absorber to cover the body surface reduced background by 30%. CONCLUSIONS: (90)Y BECT imaging can be used for patient assessment without modifying current treatment procedures.

Behaviors of cost functions in image registration between 201Tl brain tumor single-photon emission computed tomography and magnetic resonance images.

OBJECTIVE: We studied the behaviors of cost functions in the registration of thallium-201 (201Tl) brain tumor single-photon emission computed tomography (SPECT) and magnetic resonance (MR) images, as the similarity index of image positioning. METHODS: A marker for image registration [technetium-99m (99mTc) point source] was attached at three sites on the heads of 13 patients with brain tumor, from whom 42 sets of 99mTc-201Tl SPECT (the dual-isotope acquisition) and MR images were obtained. The 201Tl SPECT and MR images were manually registered according to the markers. From the positions where the two images were registered, the position of the 201Tl SPECT was moved to examine the behaviors of the three cost functions, i.e., ratio image uniformity (RIU), mutual information (MI), and normalized MI (NMI). RESULTS: The cost functions MI and NMI reached the maximum at positions adjacent to those where the SPECT and MR images were manually registered. As for the accuracy of image registration in terms of the cost functions MI and NMI, on average, the images were accurately registered within 3 degrees of rotation around the X-, Y-, and Z-axes, and within 1.5 mm (within 2 pixels), 3 mm (within 3 pixels), and 4 mm (within 1 slice) of translation to the X-, Y-, and Z-axes, respectively. In terms of rotation around the Z-axis, the cost function RIU reached the minimum at positions where the manual registration of the two images was substantially inadequate. CONCLUSIONS: The MI and NMI were suitable cost functions in the registration of 201Tl SPECT and MR images. The behavior of the RIU, in contrast, was unstable, being unsuitable as an index of image registration.

[Evaluation of the OS-EM parameter with automatic quantitative analysis for cerebral blood flow of the ECD tool].

The parameters of reconstruction iteration and subset of the ordered subset expectation maximization (OS-EM) method have a great impact on image quality. In a cerebral blood flow (CBF) examination, it is critical to produce consistent results when analyzing clinical data. We evaluated the number of iterations and subset of the OS-EM method to stabilize image quality using a normal case and an infarction case. In the maximum likelihood expectation maximization (ML-EM) method, it was confirmed that the convergence of an infarction case was somewhat delayed compared with a normal case. With the OS-EM method, we have obtained the same results. Based on the rCBF values, we postulate that the iteration value is more than 8 and the subset value is less than 10. Furthermore, multiplying the iteration by a subset value ranging from 50 to 60 helps in stabilizing the quality of CBF imaging.

[A paper sheet phantom for scintigraphic planar imaging: usefulness of pouch-laminated paper source].

In order to perform experimental measurements for evaluation of imaging device's performance, data acquisition technique, and clinical images on scintigraphic imaging, many kinds of phantoms are employed. However, since these materials are acrylic and plastic, the thickness and quality of those materials cause attenuation and scatter in itself. We developed a paper sheet phantom sealed with a pouch laminator, which can be a true radioactive source in air. In this study, the paper sheet phantom was compared to the acrylic liver phantom, with the thickness of 2 cm, which is commercially available. The results showed that although some scatter counts were contained within the image of the acrylic liver phantom, there were few scattered photons in the paper sheet phantom image. Furthermore, this laminated paper sheet phantom made handling of the source and its waste easier. If the paper sheet phantom will be designed more sophisticatedly, it becomes a useful tool for planar imaging experiments.

[Development and assessment of an automatic quantitative cerebral vascular reserve estimation tool for use with triple-injection 99mTc-ECD SPECT].

In nuclear medicine, cerebral vascular reserve(CVR) is evaluated using technetium-99m ethyl cysteinate dimer [99mTc-ECD] and acetazolamide(ACZ). We developed a protocol involving the intravenous injection of 99mTc-ECD in three divided doses(TIE method), and have found that the cerebrovascular response to ACZ depended on time after ACZ administration. However, it was difficult to obtain high-precision quantitative SPECT images by the conventional method because of complicated image processing and image degradation accompanying image subtraction. We recently developed software known as the Automatic Quantitative CVR Estimation Tool(hereinafter referred to as Triple AQCEL), which, after the input of simple parameters, enables us to carry out automatic reconstruction of quantitative SPECT images without image degradation due to subtraction. Triple AQCEL was determined to reduce image degradation caused by subtraction and to provide valid quantitative data. Because Triple AQCEL does not require manual determination of ROI or image selection for the reconstruction of quantitative SPECT images, reproducibility of regional cerebral blood flow by 3DSRT is ensured. Since all analyses in evaluation by the TIE method are automated and the operator plays no part in them, with the resulting increase of throughput, this software will contribute to improved reproducibility of regional cerebral blood flow data, and will be useful in clinical pathophysiological assessment both preoperatively and during postoperative follow-up.

[Development of an automatic analytical tool for quantitative cerebral blood flow measurement using 99mTc-ECD, and verification of clinical examples].

The following process conventionally has been followed to develop quantitative images of cerebral blood flow: (1) mean cerebral blood flow (mCBF) is calculated by the Patlak plot method; (2) a SPECT slice that includes the basal ganglia is selected; and (3) based on the value of mCBF calculated by the Patlak plot method, the SPECT slice is corrected by the Lassen method and developed into a SPECT image of quantitative regional cerebral blood flow. However, this process is complicated, and the values of rCBF have been reported to fluctuate because selection of the SPECT slice and the ROI setting are in the hands of the operator. We have developed new software that automates this analysis. This software enables automatic processing simply by inputting the value of mCBF in the normal hemisphere. Since there is no need for manual operations such as setting the ROI, reproducibility is improved as well. Regional cerebral blood flow as determined by this software is quite similar to that calculated by the conventional method, so the existing clinical evaluation does not need to be changed. This software is considered to be useful.

[Improvement in accuracy of quantitative assessment of the regional cerebral blood flow with 99mTc-ECD].

Mean cerebral blood flow (mCBF) in the slice including the basal ganglia (reference slice) is necessary for the quantification of regional CBF using Patlak plot and BUR methods on 99mTc-ECD cerebral perfusion SPECT. The mCBF was calculated from the mean counts of this slice. A region of interest (ROI) has been manually set on the reference slice to obtain the mean counts (manual ROI method). However, there was large variability observed in the value of rCBF in this method. We developed a 3DSRT method for improving the accuracy of the mean counts in the reference slice and evaluated the difference between the value of rCBF on manual ROI method and that on 3DSRT method in consecutive 11 patients with cerebral vascular disease. Difference in the value of mean counts of the reference slice was distributed within the 2 standard deviations (SD) with Blant-Altman analysis in 9 of 11 patients. Significant difference in the value of mean counts between two methods was observed in 2 of 11 patients. 3DSRT method is superior accuracy to the manual ROI method in the evaluation of the counts in the ROI. Lower accuracy in manual ROI method, therefore, results in the difference of the value of mean counts. 3DSRT method provides high accuracy with the various quantitative methods for the evaluation of rCBF using 99mTc-ECD.

[Three Dimensional Display in Nuclear Medicine].

Imaging techniques to obtain a tomographic image in nuclear medicine such as PET and SPECT are widely used. It is necessary to interpreting all of the tomographic images obtained in order to accurately evaluate the individual lesion, whereas three dimensional display is often useful in order to overview and evaluate the feature of the entire lesion or disease such as the position, size and abnormal pattern. In Japan, the use of three dimensional image analysis workstation with an application of the co-registration and image fusion between the functional images such as PET or SPECT and anatomical images such as CT or MRI has been generalized. In addition, multimodality imaging system such as a PET/CT and SPECT/CT has been widespread. Therefore, it is expected to improve the diagnostic accuracy using three dimensionally image fusion to functional images with poor anatomical information. In this commentary, as an example of a three dimensional display that are commonly used in nuclear medicine examination in Japan, brain regions, cardiac region and bone and tumor region will be introduced separately.

Improvement of the (99m)Tc-ECD brain uptake ratio (BUR) method for measurement of cerebral blood flow.

OBJECTIVE: The brain uptake ratio (BUR) method for the (99m)Tc-ECD SPECT, a non-invasive measurement method of rCBF, has been used in clinical practice in Japan, because it is simple to use. However, the accuracy of this method is limited, as it has problems in the determination of input function and the regression equation. The purpose of this study is to improve the BUR method by reconstructing the determination process of the input function and regression equation based on measurement of the rCBF by H (2) (15) O PET. METHOD: The input function was obtained by setting the region of interest on the ascending aorta instead of the aortic arch. The 3DSRT algorithm was used to obtain the anatomically standardized rCBF, and developed a semi-automatic analyzing software using C++ in order to stabilize the repeatability of the improved BUR (IBUR) method. The regression equation for the IBUR method was obtained by the H (2) (15) O PET rCBFs in 15 patients with the arterial blood sampling method. All the measurements in this study were performed with the patient in the resting state. RESULT: A good correlation was observed between the rCBF values measured by H (2) (15) O PET and the regional BURs measured by the IBUR method (r = 0.86, p < 0.0001). The rCBF values were calculated for only 5 min using a semi-automatic analyzing software. CONCLUSION: The BUR method was improved by changing the location of the input function from the aortic arch to the ascending aorta based on arterial blood flow dynamics, and reconstructing regression equation based on the rCBF values obtained using H (2) (15) O PET. This finding indicates the potential clinical usefulness of this method.