Three-dimensional registration of myocardial perfusion SPECT and CT coronary angiography

OBJECTIVE: In this study, we describe a new technique for three-dimensional registration of CT coronary angiography (CTCA) and gated myocardial perfusion SPECT. METHODS: Twelve patients with known or suspected CAD who underwent CTCA and gated SPECT were enrolled retrospectively. Coronary arteries and their branches were traced using CTCA data manually and reconstructed in three-dimensions. Gated SPECT data were registered and mapped to a left ventricle binary model extracted from CTCA data using manual, rigid and nonrigid registration methods. RESULTS: Three-dimensional reconstruction and volume visualization of both modalities were successfully achieved for all patients. All 3 registration methods gave better quality based on visual inspection, and nonrigid registration gave significantly better results than the other registration methods (p < 0.05). The cost function for three-dimensional registration using nonrigid registration (235.3 +/- 13.9) was significantly better than those of manual and rigid registration (218.5 +/- 15.3 and 223.7 +/- 17.0, respectively). Inter-observer reproducibility error was within acceptable limits for all methods, and there were no significant difference among the methods. CONCLUSION: This technique of image registration may assist the integration of information from gated SPECT and CTCA, and may have clinical application for the diagnosis of ischemic heart disease.     

Dual Energy CT lung perfusion imaging--correlation with SPECT/CT

Objective

Aims were (1) to determine the diagnostic accuracy of Dual Energy CT (DECT) in the detection of perfusion defects and (2) to evaluate the potential of DECT to improve the sensitivity for PE.

Methods

15 patients underwent Dual Energy pulmonary CT angiography (DE CTPA) and a combination of lung perfusion SPECT/CT and ventilation scintigraphy. CTPA and DE iodine distribution maps as well as perfusion SPECT/CT and inhalation scintigrams were reviewed for pulmonary embolism (PE) diagnosis. DECT and SPECT perfusion images were assessed regarding localization and extent of perfusion defects. Diagnostic accuracy of DE iodine (perfusion) maps was determined with reference to SPECT/CT. Diagnostic accuracies for PE detection of DECT and of SPECT/CT with ventilation scintigraphy were calculated with reference to the consensus reading of all modalities.

Results

DE CTPA had a sensitivity/specificity of 100%/100% for acute PE, while the combination of SPECT/CT and ventilation scintigraphy had a sensitivity/specificity of 85.7%/87.5%. For perfusion defects, DECT iodine maps had a sensitivity/specificity of 76.7% and 98.2%.

Conclusion

DECT is able to identify pulmonary perfusion defects with good accuracy. This technique may potentially enhance the diagnostic accuracy in the assessment of PE.     

Dual-energy perfusion CT of non-diseased lung segments using dual-source CT: correlation with perfusion SPECT

Purpose

To determine the utility of dual-energy perfusion CT (DEpCT) of non-diseased lung segments, using dual-source CT, in comparison with perfusion single-photon emission computed tomography (SPECT).

Materials and methods

28 patients (18 male and 10 female; mean age 63 years; age range 18–86 years) underwent DEpCT and SPECT within a 3-day interval. The presence and location of perfusion defects in each segment of the lungs were evaluated.

Results

Perfusion defects were noted in 7 of 361 segments (1.9 %) by DEpCT and in 19 of 361 segments (5.3 %) by perfusion SPECT. DEpCT was in good agreement with perfusion SPECT for 338 of 361 segments (93.6 %). Intraobserver agreement was also good, ranging from 93.4 to 93.6 % (κ = 0.64–0.75, p < 0.01).

Conclusion

For non-diseased lung segments, DEpCT correlated well with SPECT.     

Prevalence of misregistration between SPECT and CT for attenuation-corrected myocardial perfusion SPECT

Background  Nonuniform attenuation artifacts may reduce the diagnostic accuracy of cardiac single photon emission computed tomography (SPECT) studies. Compensation strategies using an attenuation map (eg, from x-ray tomography) have been reported to improve accuracy. Because the computed tomography (CT) and SPECT images are obtained sequentially, misregistration of the emission and transmission scans can occur. Our objective was to qualitatively assess these misregistration errors. Methods and Results  This study included 60 patients who consecutively underwent CT attenuation-corrected myocardial perfusion studies acquired on a SPECT/CT system equipped with a nondiagnostic CT scanner. The cardiac SPECT/CT and fused images were reviewed and qualitatively assessed for misregistration of the heart between the CT and emission image data sets. The degree of misregistration was qualitatively rated on a 5-point scale. Misregistration was judged to be none in 4 of 55 patients, minimal in 9, mild in 19, moderate in 21, and severe in 2 patients. Five studies could not be assessed because of severe artifacts on CT. Conclusions  Forty-two percent of the CT attenuation-corrected myocardial perfusion studies had moderate to severe cardiac misregistration qualitatively. Our data suggest that careful review of attenuation correction maps and registration is needed to avoid reconstruction artifacts due to misregistration. Preliminary results of this study were presented at the 2005 Society of Nuclear Medicine Annual Meeting, Seattle, Wash, September 29–October 2, 2005.     

Myocardial perfusion SPECT with 99mTc-tetrofosmin and thoracic SPECT with Gallium-67 SPECT in a patient with chest pain and a history of sarcoidosis

We present the case of a 54-year-old male patient, with history of diagnosed sarcoidosis some years ago and myocardial involvement, who being asymptomatic, shows chest pain because of which he goes to the emergency room of the hospital. During the first hours of his admission the pain relieves with nonsteroidal antiinflammatory medication, an electrocardiogram demonstrates changes of early repolarisation with pericardial involvement, the enzymes don't rise and the echocardiogram reveals a slight pericardial effusion. The differential diagnosis is between a chest pain due to ischemia, and the secondary to myopericarditis in the clinical context of a sarcoidosis. Myocardial perfusion rest SPECT is required which is compatible with lateral acute myocardial infarction (AMI) with extension to inferior wall. A coronary angiography was carried out and showed two vessels disease (RCA and Cx), PTCA and stent were carried out successfully. During the admission a thoracic scintigraphy and SPECT with gallium -67 showed an uptake in lateral wall of left ventricle (LV). Nothing about active sarcoidosis was found.     

Attenuation correction of myocardial SPECT images with X-ray CT: effects of registration errors between X-ray CT and SPECT

PURPOSE: Attenuation correction with an X-ray CT image is a new method to correct attenuation on SPECT imaging, but the effect of the registration errors between CT and SPECT images is unclear. In this study, we investigated the effects of the registration errors on myocardial SPECT, analyzing data from a phantom and a human volunteer. METHODS: Registerion (fusion) of the X-ray CT and SPECT images was done with standard packaged software in three dimensional fashion, by using linked transaxial, coronal and sagittal images. In the phantom study, an X-ray CT image was shifted 1 to 3 pixels on the x, y and z axes, and rotated 6 degrees clockwise. Attenuation correction maps generated from each misaligned X-ray CT image were used to reconstruct misaligned SPECT images of the phantom filled with 201Tl. In a human volunteer, X-ray CT was acquired in different conditions (during inspiration vs. expiration). CT values were transferred to an attenuation constant by using straight lines; an attenuation constant of 0/cm in the air (CT value = -1,000 HU) and that of 0.150/cm in water (CT value = 0 HU). For comparison, attenuation correction with transmission CT (TCT) data and an external gamma-ray source (99mTc) was also applied to reconstruct SPECT images. RESULTS: Simulated breast attenuation with a breast attachment, and inferior wall attenuation were properly corrected by means of the attenuation correction map generated from X-ray CT. As pixel shift increased, deviation of the SPECT images increased in misaligned images in the phantom study. In the human study, SPECT images were affected by the scan conditions of the X-ray CT. CONCLUSION: Attenuation correction of myocardial SPECT with an X-ray CT image is a simple and potentially beneficial method for clinical use, but accurate registration of the X-ray CT to SPECT image is essential for satisfactory attenuation correction.     

SPECT肺灌注与CT异机融合图像评价非小细胞肺癌肺功能的价值

objective The aim of this study was to assess the value of fusion SPECT perfusion and CT images acquired separately at 2 time-points in evaluating regional lung function of patients with stage Ⅲ non-small cell lung cancer(NSCLC).Methods Thirty-two patients with untreated stage Ⅲ NSCLC underwent pulmonary function test(PFT),CT and SPECT imaging.Two series of images were registered by software fusion based on external markers by Philips Pinnacle3 planning treatment system.The SPECT/CT fu sion images were graded by comparing lung perfusion defect with the area of radiological abnormality.Grade O:no lung perfusion defect in the area of radiological abnormality.Grade 1:the area of lung perfusion defect was similar to the size of radiological abnormality.Grade 2:the area of lung perfusion defect was bigger than that of radiological abnormality.and extended to 1 pulmonary lobe.Grade 3:the area of lung perfusion defect exceeded 1 pulmonary lobe.Statistically significant difference was evaluated by Pearson X2-test using SPSS 13.0 software.Results In 32 patients with stage Ⅲ NSCLC,31 patients had lung perfusion defects.There were 13 patients with grade 1,8 with grade 2,10 with grade 3.There was statistically significant difference between central lung cancer and peripheral lung cancer(X2=10.495,P＜0.05);8 patients had PFT abnormality.There was also statistically significant difference between the positive rate of SPECT/CT fusion images and PFT[96.9%(31/32)vs 25.0%(8/32),X2=34.724,P＜0.05].Conclusion The fusion of SPECT lung perfusion and CT images acquired separately at 2 different time-points is a feasible technique for assessing the regional lung function of patients with stageⅢNSCLC,thereby offering more information for surgical planning,prediction of postoperative lung function and optimization of radiation treatment plans.     

SPECT肺灌注与CT异机融合图像评价非小细胞肺癌肺功能的价值

目的 探讨SPECT肺灌注与CT异机融合图像评价Ⅲ期非小细胞肺癌(NSCLC)患者区域肺功能的意义.方法 选择Ⅲ期NSCLC患者32例,治疗前行肺功能测试和胸部CT扫描,并在相同体位下行SPECT肺灌注显像,两套图像均传至Philips Pinnacle3放射治疗计划系统,依据外标记点进行手动异机图像融合.参考CT与SPECT肺灌注融合图像,按灌注缺损区与肿瘤病灶的大小关系分为4级:0级为无灌注受损;1级为肿瘤及其周围局部肺灌注受损;2级为1叶肺灌注受损;3级为超过1叶肺灌注受损.采用SPSS 13.0软件,行PearsonX2检验.结果 32例Ⅲ期NSCLC患者中,31例有程度不等的肺灌注缺损,其中1级13例,2级8例,3级10例.中央型NSCLC患者肺灌注缺损较周围型NSCLC患者严重,差异有统计学意义(X2=10.495,P＜0.05).8例患者肺功能测试有不同程度的异常.CT与SPECT肺灌注融合图像阳性率96.9%(31/32),较肺功能测试阳性率25.0%(8/32)高,差异有统计学意义(X2=34.724,P＜0.05).结论 SPECT肺灌注与CT异机融合图像能更好显示Ⅲ期NSCLC患者区域肺组织的功能状况,为此类患者制订手术方案、预测术后肺功能、优化放疗计划等提供更多的信息.     

Respiratory average CT for attenuation correction in myocardial perfusion SPECT/CT

Objective

Cine average CT (CACT) and interpolated average CT (IACT) have been proposed to improve attenuation correction (AC) for PET/CT in oncologic and cardiac studies. This study aims to evaluate their effectiveness on myocardial perfusion SPECT/CT using computer simulation and physical phantom experiments.

Methods

We first simulated normal male with ^99mTc-sestamibi distribution using digital XCAT phantom with respiratory motion amplitudes of 2, 3, and 4 cm. Average activity and attenuation maps represented static SPECT and CACT, while the attenuation maps of end-inspiration and end-expiration represented two helical CTs (HCTs), respectively. Sixty noise-free and noisy projections were simulated over 180° using an analytical parallel-hole projector. We then filled 673 MBq ^99mTc into an anthropomorphic torso phantom with normal heart or heart with a defect which placed on a programmable respiratory platform to model various respiratory amplitudes. Sixty projections were acquired over 180° using a clinical SPECT/CT scanner. The CACT, standard HCT, and 2 HCTs at extreme phases were acquired. Interpolated CT phases were generated between them using affine plus b-spline registration, and IACT was obtained by averaging the interpolated phases and the 2 original extreme phases for both simulation and phantom experiments. Projections were reconstructed with AC using CACT, IACT, and HCTs, respectively. Polar and 17-segment plots were analyzed by relative difference (RD) of the uptake. Two regions-of-interest (ROI) were drawn on the defect and background area to obtain the intensity ratio (IR).

Results

No substantial difference was observed on the polar plots generated from different AC methods, while the quantitative RD measurements showed that SPECT_CACT were most similar to the original phantom, followed by SPECT_IACT, with RD_max <8 and <10% in the simulation study. The RD of SPECT_HCTs deviated from the original phantom and SPECT_CACT in various segments, with RD_max of 19.76 and 16.68% in the simulation and phantom experiment, respectively. The IR of SPECT_HCTs fluctuated more from the truth for higher motion amplitude.

Conclusions

Both CACT-AC and IACT-AC reduced respiratory artifacts and improved quantitation in myocardial perfusion SPECT as compared to HCT-AC. The use of IACT further reduced the radiation dose.

     

Impact of CT attenuation correction by SPECT/CT in brain perfusion images

Purpose  

The aim of this study was to elucidate the regional differences between brain perfusion single photon emission computed tomography (SPECT) images reconstructed with a uniform attenuation correction using Chang’s method (AC-Chang) and a non-uniform attenuation correction with CT using SPECT/CT (AC-CT).     

Attenuation correction of myocardial SPECT perfusion images with low-dose CT: evaluation of the method by comparison with perfusion PET.

In cardiac SPECT, specificity is significantly affected by artifacts due to photon absorption. As the success of attenuation correction depends mainly on high-quality attenuation maps, SPECT low-dose CT devices are promising. We wanted to evaluate the usefulness of a SPECT low-dose CT device in myocardial perfusion scintigraphy. For the evaluation of attenuation correction systems, primarily comparisons with coronary angiography are used. Because the comparison of a method showing myocardial perfusion with an investigation displaying the morphology of vessels yields some difficulties, we chose perfusion PET with (13)N-ammonia as the reference method. METHODS: We prospectively analyzed 23 patients (6 women, 17 men) with known or suspected coronary artery disease. Rest studies and studies under pharmacologic stress with adenosine were performed. After simultaneous injection of (13)N-ammonia and (99m)Tc-sestamibi, a dynamic PET acquisition was started. The SPECT study was performed about 2 h later. Based on 20-segment polar maps, SPECT with and without attenuation correction was compared with PET-derived perfusion values and ammonia uptake values. The PET uptake images were also smoothed to adjust their resolution to the resolution of the SPECT images. RESULTS: The concordance of SPECT and PET studies was improved after attenuation correction. The main effect was seen in the inferior wall. Especially in the apex and anterolateral wall, there were differences between SPECT and PET studies not attributable to attenuation artifacts. Because these differences diminished after smoothing of the PET studies, they might be due to partial-volume effects caused by the inferior resolution of the SPECT images. CONCLUSION: The x-ray-derived attenuation correction leads to SPECT images that represent myocardial perfusion more accurately than nonattenuation-corrected SPECT images. The benefit of the method is seen primarily in the inferior wall. The low resolution of the SPECT system may lead to artifacts due to partial-volume effects. This phenomenon must be considered when perfusion PET is used as a reference method to investigate the effect of attenuation correction.     

Generation of planar images from lung ventilation/perfusion SPECT

OBJECTIVE: To develop a method of producing lung ventilation and perfusion (V/Q) planar images using forward projection of reconstructed single-photon emission computed tomography (SPECT) images through approximate attenuation (micro) maps generated from the lung emission scans alone, as transmission-based micro maps may not be routinely available. METHODS: Synthetic micro maps are derived from (99m)Tc photopeak and "scatter" windows for the attenuation correction of the SPECT images. The attenuation-corrected SPECT images are forward projected at appropriate angles to give the equivalent of planar images. This method allows high-count planar images, as well as the SPECT images, to be produced from a single SPECT acquisition. In addition, isolated "single lung" views of lateral and medial projections without "shine-through" from the contra-lateral lung, which have not been available previously, can be formed. RESULTS: Comparison of reprojected images produced from CT-derived or synthetic micro maps displayed similar detail and radiopharmaceutical distribution. In a blinded comparison of "true" planar images with those from reprojecting the SPECT data using the synthetic micro maps, no difference in mismatched defect detection was found, and hence it was confirmed that the reprojected planar images could replace true planar images with no loss in planar diagnostic sensitivity. CONCLUSIONS: The reprojected planar images provide high-count, high-quality images, which are comparable with conventional 2D images.     

Evaluation of brain perfusion SPECT imaging using 99mTc-ECD

Fundamental and clinical evaluation was performed on 99mTc-ECD, a new agent for brain perfusion SPECT. Radiochemical purity reaches a plateau of approximately 98% at 30 min after reconstitution and remains stable up to 24 hours later. A biodistribution study showed approximately 5% injected dose in the brain, very slow brain washout of 5.6% per hour on the average, and rapid washout from the other organ mainly through the urinary system. Brain ECD distribution was determined within 2 min postinjection and remained stable for up to 1 hour. Three hours later, slight but significant changes in brain distribution were observed, that were relative reduction of cerebral cortical activity and gray to white matter activity ratio, and relative elevation of white matter and thalamic activities. Comparative studies of ECD images with IMP and HMPAO images revealed that radioactivity contrast between affected and unaffected areas was less prominent in ECD than in IMP in cerebral and cerebellar cortical lesions, more prominent in ECD than in IMP in striatal and thalamic lesions, and somewhat more prominent in ECD than in HMPAO in both lesions. Imaging around 1 hour postinjection seems to be more appropriate than immediate postinjection imaging because of the clearance of the extracranial radioactivity and somewhat better radioactivity contrast between affected and unaffected areas.     

Respiratory lung motion analysis using a nonlinear motion correction technique for respiratory-gated lung perfusion SPECT images

Objective This study evaluated the respiratory motion of lungs using a nonlinear motion correction technique for respiratory-gated single photon emission computed tomography (SPECT) images. Methods The motion correction technique corrects the respiratory motion of the lungs nonlinearly between two-phase images obtained by respiratory-gated SPECT. The displacement vectors resulting from respiration can be computed at every location of the lungs. Respiratory lung motion analysis is carried out by calculating the mean value of the body axis component of the displacement vector in each of the 12 small regions into which the lungs were divided. In order to enable inter-patient comparison, the 12 mean values were normalized by the length of the lung region along the direction of the body axis. Results This method was applied to 25 Technetium (Tc)-99m-macroaggregated albumin (MAA) perfusion SPECT images, and motion analysis results were compared with the diagnostic results. It was confirmed that the respiratory lung motion reflects the ventilation function. A statistically significant difference in the amount of the respiratory lung motion was observed between the obstructive pulmonary diseases and other conditions, based on an unpaired Student's t test (P < 0.0001). Conclusions A difference in the motion between normal lungs and lungs with a ventilation obstruction was detected by the proposed method. This method is effective for evaluating obstructive pulmonary diseases such as pulmonary emphysema and diffuse panbronchiolitis.     

Evaluation of a decision support system for interpretation of myocardial perfusion gated SPECT

PURPOSE: We have recently presented a decision support system for interpreting myocardial perfusion scintigraphy (MPS). In this study, we wanted to evaluate the system in a separate hospital from where it was trained and to compare it with a quantification software package. METHODS: A completely automated method based on neural networks was trained for the interpretation of MPS regarding myocardial ischaemia and infarction using 418 MPS from one hospital. Features from each examination describing rest and stress perfusion, regional and global function were used as inputs to different neural networks. After the training session, the system was evaluated using 532 MPS from another hospital. The test images were also processed with the quantification software package Emory Cardiac Toolbox (ECTb). The images were interpreted by experienced clinicians at both the training and the test hospital, regarding the presence or absence of myocardial ischaemia and/or infarction and these interpretations were used as gold standard. RESULTS: The neural network showed a sensitivity of 90% and a specificity of 85% for myocardial ischaemia. The specificity for the ECTb was 46% (p < 0.001), measured at the same sensitivity. The neural network sensitivity for myocardial infarction was 89% and the specificity 96%. The corresponding specificity for the ECTb was 54% (p < 0.001). CONCLUSION: A decision support system based on neural networks presents interpretations more similar to experienced clinicians compared to a conventional automated quantification software package. This study shows the feasibility of disseminating the expertise of experienced clinicians to less experienced physicians by the use of neural networks.