Attenuation-corrected Images Research Articles

Myocardial creep-induced misalignment artifacts in PET/MR myocardial perfusion imaging

PurposeMisalignment between positron emission tomography (PET) datasets and attenuation correction (AC) maps is a potential source of artifacts in myocardial perfusion imaging (MPI). We assessed the impact of adenosine on the alignment of AC maps derived from magnetic resonance (MR) and PET datasets during MPI on a hybrid PET/MR scanner.MethodsTwenty-eight volunteers underwent adenosine stress and rest 13N-ammonia MPI on a PET/MR. We acquired Dixon sequences for the creation of MRAC maps. After reconstruction of the original non-shifted PET images, we examined MRAC and PET datasets for cardiac spatial misalignment and, if necessary, reconstructed a second set of shifted PET images after manually adjusting co-registration. Summed rest, stress, and difference scores (SRS, SSS, and SDS) were compared between shifted and non-shifted PET images. Additionally, we measured the amount of cranial movement of the heart (i.e., myocardial creep) after termination of adenosine infusion.ResultsRealignment was necessary for 25 (89.3%) stress and 12 (42.9%) rest PET datasets. Median SRS, SSS, and SDS of the non-shifted images were 6 (IQR = 4–7), 12 (IQR = 7–18), and 8 (IQR = 2–11), respectively, and of the shifted images 2 (IQR = 1–6), 4 (IQR = 7–18), and 1 (IQR = 0–2), respectively. All three scores were significantly higher in non-shifted versus shifted images (all p < 0.05). The difference in SDS correlated moderately but significantly with the amount of myocardial creep (r = 0.541, p = 0.005).ConclusionMisalignment of MRAC and PET datasets commonly occurs during adenosine stress MPI on a hybrid PET/MR device, potentially leading to an increase in false-positive findings. Our results suggest that myocardial creep may substantially account for this and prompt for a careful review and correction of PET/MRAC data.

Interpretation of myocardial perfusion SPECT with attenuation correction. Part 2

Objective: to investigate the possibilities of a combined single photon emission computed tomography/computed tomography (SPECT/CT) system during myocardial perfusion studies and to examine the features of their interpretation. Subjects and methods. In April 2013 to April 2019, the Department of Radionuclide Diagnosis, National Medical Research Center of Cardiology, performed myocardial perfusion SPECT with attenuation correction (AC) in 3144 patients with various cardiovascular diseases. Based on the experience gained, the authors expanded and adjusted the principles of processing and interpreting the results of this study, which they had first set forth in 2014. Special emphasis is placed on the interpretation of apical and septal perfusion defects and diffuse perfusion irregularity, on the demonstration of the role of current reconstruction algorithms in obtaining highest-quality myocardial images, and on the assessment of self-potentialities of lowdose CT findings at myocardial SPECT/CT, as well as on proposals to standardize quantitative parameters for perfusion assessment at myocardial SPECT/CT. Results. AC affected in large measure the interpretation of myocardial perfusion SPECT in most cases. Apical perfusion defect appeared on AC images was observed in 50% of patients without established coronary heart disease and could be interpreted as a normal variant (apical thinning). The diffuse irregularity of perfusion radiopharmaceutical tracer accumulation in the application of the current reconstruction algorithms stood out in a separate pattern as a sign of microcirculatory disturbances. Low-dose CT data allow visualization of a severe thoracic abnormality at imaging and should be reflected in the conclusion. The perfusion study descriptions based on an analysis of AC and nAC images had a greater interoperator consistency than those based on an analysis of only nAC images (w = 0.915 and 0.809, respectively; p = 0.027). At the same time, the use of arithmetic means of the extent of transient ischemia (Reversibility Extent) is better consistent with visual analysis (= 0.08Ѓ}1.46%, p = 0.49). Conclusion. The use of AC and current iterative algorithms at myocardial perfusion SPECT should be part of a mandatory study protocol, since this affects to a large extent the diagnostic value of the technique. The borderline values of disturbed perfusion parameters at AC should be reconsidered.

Visually assessed coronary and cardiac calcium outperforms perfusion data during scintigraphy in the prediction of adverse outcomes

ObjectivesTo determine whether calcifications of the coronary arteries (coronary artery calcium 0 to 4 score), or extending the assessment also to cardiac valves and thoracic aorta (overall calcium 0 to 8 score), as seen on computed tomography for attenuation correction during stress-scintigraphy (SPECT-CT), are associated with total mortality and non-fatal myocardial infarction. We aimed to assess whether these calcifications added to the prognostic value of SPECT imaging. BackgroundThe presence/amount of calcium in the coronary arteries, but also in the heart valves and aorta, has been associated with cardiovascular (CV) and all-cause mortality. This information can be obtained during SPECT-CT examinations, where low resolution CT images are co-registered for attenuation correction of myocardial perfusion, but then discarded. MethodsClinical data were collected on 353 consecutive patients submitted to stress SPECT-CT between Sept 2010 and Oct 2012, for suspected coronary artery disease (CAD). Follow-up data on outcomes were collected retrospectively. ResultsMean age was 72 and 58% were male. Mean follow-up was 6.4 years, during which 48 subjects died (15 from CV causes) and 10 had non-fatal myocardial infarction (MI). Reversible perfusion defects were detected in 55 patients (15.6%), 39 of whom (11%) had >mild defects. The presence of a calcium score > 1 in the attenuation correction images was the strongest univariate predictor of all-cause death or MI (hazard ratio 7.21, p < .001). On multivariate analysis, controlling for age, gender and myocardial perfusion defects an overall calcium score > 2 remained a predictor of all-cause death or non-fatal MI (hazard ratio 4.12, p < .001). ConclusionsVisual assessment of coronary or overall coronary, cardiac and aortic calcium in the CT images used for attenuation correction during SPECT-CT is feasible and reproducible. It was strongly associated with all-cause death and MI, even after controlling for clinical variables and myocardial perfusion data. This simple visual calcium assessment does not add additional costs or radiation, and may significantly improve risk-assessment of patients with suspected CAD undergoing SPECT-CT. Condensed abstractCalcium in the coronary arteries, heart valves and aorta has been associated with worse prognosis. We sought to determine whether assessment of such calcifications on computed tomography images (co-registered for myocardial perfusion attenuation correction and then discarded) are independently associated with long-term outcome on top of available data.We enrolled 353 consecutive patients, referred for suspected coronary artery disease. An overall calcium score > 1 in the attenuation correction images was the strongest univariate (hazard ratio 7.21, p < .001) and multivariate predictor of all-cause death or non-fatal MI (hazard ratio 4.12, p < .001), even after controlling for clinical variables and myocardial perfusion data.

The role of 18FDG PET/CT imaging of aortic atherosclerosis: prospective study and technique optimization

BackgroundAtherosclerosis is an inflammatory disease of the inner wall of large and medium-sized arteries. The progress of atherosclerosis based on a lot of factors, including systemic involvement of disease, the precise vascular arterial affection, and the degree of flow obstruction. We aim in this study to estimate the FDG uptake of the aortic wall in the early and delayed imaging and to correlate this with the morphologic changes detected by CT.ResultsThis is a prospective study that was performed through 1 year. The study included 50 patients [30 males (60%) and 20 females (40%)] with male to female mean ratio 1.5:1 and their mean age 58.3 ± 15.7 years. Each patient underwent dual time-point 18F-FDG PET CT imaging at ~ 60 min (Early images) and 180 min (delayed images) after the administration of 18F-FDG. For each patient, the global 18F-FDG uptake in the aorta was determined by manually drawing regions of interest (ROIs) around the outer part of the arterial wall on every slice of the attenuation-corrected transverse PET CT images. Per-patient, per-time-point, per-vessel, and per-ROI radiotracer decay-corrected and body weight-corrected SUVs were calculated, resulting in a single mean value of maximum SUV for the aorta. The aortic wall FDG uptake was measured in both early and delayed images and expressed in terms of SUVmax. Then Retention index percentage of the aorta was measured. The retention index percentage was calculated by subtracting the SUVmax in early images from the SUVmax in delayed images and dividing by SUVmax in early images.ConclusionAortic wall FDG uptake can be used as an additional parameter as well as a biomarker on evaluation of the arterial atherosclerotic activity. Delayed post 3 h FDG imaging is more accurate than the routine early post 1 h imaging in evaluating the atherosclerotic activity.

Imaging technology for myocardial perfusion single-photon emission computed tomography 2018 in Japan.

Recently, nuclear cardiology has dramatically advanced by a new technology development such as the device, short-term acquisition system, image reconstruction algorithm andimage analysis. Although these innovations have been gradually employed in routine examinations, we did not investigate the current use of image acquisition, image reconstruction, and image analysis with myocardial perfusion single-photon emission computed tomography (MPS). We investigated the current status of MPS imaging technology in Japan. We carried out a survey using a Web-based questionnaire system, the opening of which was announced via e-mail, and it was available on a website for 3 months. We collected data on the current use of MPS with 201Tl and/or 99mTc agents with respect to routine protocols, image acquisition, image reconstruction, and image analysis. We received responses to the Web-based questionnaire from 178 and 174 people for 99mTc and 201Tl MPS, respectively. The routine protocols of MPS of stress-rest and rest-stress MPS on 1-day protocols with 99mTc were 41.2% and 14.5%, respectively, and the rest-only scan response rate was 23.7%, whereas that of 201Tl MPS was 65.9% with stress-rest MPS, 19.0% with rest-only MPS, and 10.9% with stress-rest MPS adding a rest scan 24h after injection. The filtered back projection (FBP) method is most commonly used image reconstruction method, yielding 70.5% for 99mTc MPS and 76.8% for 201Tl MPS, including combined FBP and ordered subset expectation maximization method. The results for no-correction (NC) images were 49.2% with 99mTc MPS and 55.2% with 201Tl MPS including the response of NC and combined attenuation correction (AC) and scatter correction (SC) (i.e., ACSC) images. The AC or ACSC images of 99mTc and 201Tl were provided by 30-40% of the institutions surveyed. We investigated the current status of MPS imaging technology in Japan, and found that although the use of various technical developments has been reported, some of these technologies have not been utilized effectively. Hence, we expect that nuclear medicine technology will be used more effectively to improve diagnosis.

Predictors of Myocardial Ischemia in Preoperative Oncology Patients Who Underwent Fluorodeoxyglucose-Positron Emission Tomography Study.

Background:Coronary artery calcification (CAC) can be visually estimated on computed tomography (CT) attenuation correction (CTAC) of positron emission tomography (PET). The visual estimation of CAC from CTAC scans performed for PET/CT is comparable to the standard CAC score scan. Myocardial perfusion imaging (MPI) with single-photon emission CT (SPECT) is commonly performed for risk stratification before oncologic surgery.Objective:We investigated the value of visual estimation of CAC from CTAC of PET/CT as well as other factors such as coronary artery disease (CAD) risk factors and type of cancer as predictors of MPI ischemia.Methods:Retrospectively, we identified 268 patients who underwent PET/CT and MPI for preoperative cardiac evaluation. Visual estimation of CAC was performed and classified into four categories.Results:The results of visual CAC were as follows: 47.8% – zero CAC, 32.8% – mild CAC, 14.2% – moderate CAC, and 5.2% – severe CAC. The majority of patients (85.8%) had normal MPI, whereas 14.2% were abnormal. There was a strong association between ischemia on MPI and CAC seen on CTAC (P < 0.01), dyslipidemia (P < 0.01), family history of CAD (P < 0.05), smoking (P < 0.01), and type of malignancy (P < 0.01).Conclusion:A strong association exists between visual estimation of CAC on CTAC and MPI. Zero is highly associated with normal MPI, but moderate-to-severe CAC is associated with abnormal MPI, in addition smoking, dyslipidemia, and certain cancer are associated with ischemic MPI; subsequently, preoperative cardiac testing is warranted in these subsets of patients.

Quantitative SPECT/CT-Technique and Clinical Applications.

The continuous development of SPECT over the past 50years has led to improved image quality and increased diagnostic confidence. The most influential developments include the realization of hybrid SPECT/CT devices, as well as the implementation of attenuation correction and iterative image reconstruction techniques. These developments have led to a preference for SPECT/CT devices over SPECT-only systems and to the widespread adoption of the former, strengthening the role of SPECT/CT as the workhorse of Nuclear Medicine imaging. New trends in the ongoing development of SPECT/CT are diverse. For example, whole-body SPECT/CT images, consisting of acquisitions from multiple consecutive bed positions in the manner of PET/CT, are increasingly performed. Additionally, in recent years, some interesting approaches in detector technology have found their way into commercial products. For example, some SPECT cameras dedicated to specific organs employ semiconductor detectors made of cadmium telluride or cadmium zinc telluride, which have been shown to increase the obtainable image quality by offering a higher sensitivity and energy resolution. However, the advent of quantitative SPECT/CT which, like PET, can quantify the amount of tracer in terms of Bq/mL or as a standardized uptake value could be regarded as most important development. It is a major innovation that will lead to increased diagnostic accuracy and confidence, especially in longitudinal studies and in the monitoring of treatment response. The current work comprises two main aspects. At first, physical and technical fundamentals of SPECT image formation are described and necessary prerequisites of quantitative SPECT/CT are reviewed. Additionally, the typically achievable quantitative accuracy based on reports from the literature is given. Second, an extensive list of studies reporting on clinical applications of quantitative SPECT/CT is provided and reviewed.

Prostate cancer evaluation using PET quantification in 68Ga-PSMA-11 PET/MR with attenuation correction of bones as a fifth compartment.

Tissues with low magnetic resonance (MR) signals, such as bones and lungs differ considerably in their attenuation properties, requiring special considerations for attenuation correction. We evaluated the impact of using the five-compartment segmentation model, which incorporates bones, in 68Ga-PSMA-11 PET/MR studies in patients undergoing evaluation for prostate cancer. Prostate cancer patients underwent dedicated prostate 68Ga-PSMA-11 PET/MR followed by whole-body 68Ga-PSMA-11 PET/CT. Coronal µmap images of the pelvis derived from four- and five-compartment segmentation models of magnetic resonance attenuation correction (MRAC) were produced. Standardized uptake values (SUV) calculated by the four and five-compartment MRAC models and by computed tomography attenuation correction (CTAC) were compared and correlated in normal prostate tissue, gluteus muscle, sacrum, intra-prostatic lesions and metastases (i.e., bone lesions and involved lymph nodes), and prostatic lesions to gluteus (L/G) ratio. Twenty-six patients (mean age 69.4±9.3 years) were included in the study. Twenty-five patients presented for prostate cancer staging and one patient was evaluated for recurrent disease. There was a statistically significant difference between SUVs of the gluteus, sacrum, prostatic lesions and normal prostate tissue measured by the four-compartment vs. the five-compartment MRAC models, with a medium effect size. Very good to good correlation between SUV measured using the four-compartment MRAC model and SUV measured using the five-compartment model were noted in all lesional and non-lesional areas. Very good to good correlation was noted between four-compartment MRAC and CTAC SUVs of prostatic lesions and L/G ratio and between five-compartment MRAC and CTAC SUVs of prostatic lesions, L/G ratio and metastatic lesions. 68Ga-PSMA-11 PET/MR using the five-compartment segmentation model affects SUV measurements in prostate lesions and in the normal prostate and therefore patient follow-up studies must be conducted using the same segmentation model.

P6148Visually assessed coronary and cardiac calcium outperforms perfusion data during scintigraphy in the prediction of adverse outcomes

Abstract Background The presence and amount of calcium in the coronary arteries, but also in the heart valves and aorta, has been clearly associated with cardiovascular and all-cause mortality and this information might be prognostically useful during SPECT-CT examinations, where CT images are co-registered for attenuation correction of myocardial perfusion, but then discarded. Objectives This study sought to determine whether the assessment of calcifications of the coronary arteries, cardiac valves and thoracic aorta in the computed tomography images co-registered for attenuation correction during stress-scintigraphy (SPECT-CT) is associated with long-term mortality and cardiac events on top of other available data. Methods Baseline data were collected prospectively on 353 consecutive patients, referred for suspected coronary artery disease (CAD) with no previously known CAD who underwent stress SPECT-CT between Sept 2010 and Oct 2012. Retrospective analysis was performed on follow-up data for outcomes. Results Patients (mean age 72 years. 58% males) had a mean follow-up of 6.4 years, during which 48 died (15 from cardiovascular causes) and 10 had a non-fatal myocardial infarction (MI). Reversible myocardial perfusion defects were detected in 55 patients (15.6%), 39 of whom (11%) had more than mild defects. The presence of an overall visual calcium score &gt;1 in the attenuation correction images was the most strong univariable (hazard ratio 8.99, p&lt;0.0001) and multivariable (hazard ratio 4.76, p&lt;0.0001) predictor of all-cause death or non-fatal MI on top of age, gender, irreversible myocardial perfusion defects and revascularization after the test. Multivariable models Clinical + SPECT + Overall Calcium Ischemic Cardiac Events HR CI (95%) p-value χ2 Age 1.058 1.0234 to 1.093 0.0008 Male gender 1.63 0.88 to 3.024 0.1183 Fixed perfusion defect 3.924 1.63 to 9.426 0.0022 Overall Calcium &gt;1 4.765 2.2 to 10.32 &lt;0.0001 71.69 Kaplan-Meier Conclusions Visual assessment of coronary or overall coronary, cardiac and aortic calcium in the CT images used for attenuation correction during SPECT-CT is feasible, reproducible and strongly associated with hard cardiac events and all-cause death, beyond clinical variables and myocardial perfusion data. This incredibly easy visual calcium assessment does not require additional costs or radiation and may heavily impact on better risk-assessment of patients with suspected CAD undergoing SPECT-CT.

Usefulness of the frontal lobe bottom and cerebellum tuber vermis line as an alternative clue to set the axial angle parallel to the AC-PC line in I-123 IMP SPECT imaging: a retrospective study.

We aimed to investigate whether the frontal lobe bottom and cerebellum tuber vermis (FLB-CTV) line on brain perfusion scintigraphy, using iodine-123 isopropyl iodoamphetamine single photon emission computed tomography (I-123 IMP SPECT) images, is useful to determine an axial angle parallel to the anterior commissure-posterior commissure (AC-PC) line. We measured the angular differences between the AC-PC line and the FLB-CTV line on midsagittal brain magnetic resonance imaging (MRI) scans of 100 patients. We also evaluated the angular differences of the FLB-CTV line between the IMP SPECT images and the computed tomography for attenuation correction (CTAC) images in the same 100 patients, using a reference line on the CTAC images. Furthermore, the inter-reader reproducibility of the FLB-CTV line measurements on IMP SPECT images of 50 patients between two readers was evaluated using the intra-class correlation coefficient (ICC) and 95% confidence interval (CI). The mean and standard deviation of the angular differences between the AC-PC and FLB-CTV lines on midsagittal brain MRI scans were - 1.24° and 1.14°, respectively. The mean and the standard deviation of the angular differences of the FLB-CTV line in the IMP SPECT and CTAC images were 0.87° and 0.48°, respectively. The ICC of the FLB-CTV line measurements on IMP SPECT images was 0.99 (95% CI 0.98-0.99). We demonstrated that the FLB-CTV line was almost parallel to the AC-PC line and could be reconstructed using IMP SPECT images. The FLB-CTV line can be used as additional evidence to set the axial angle parallel to the AC-PC line.

Comparison of Different Attenuation Correction Methods for Dual Gating Myocardial Perfusion SPECT/CT

Dual respiratory-cardiac gating realizes motion-freeze myocardial perfusion single photon emission computed tomography (SPECT). The aim of this paper is to evaluate the performance of various attenuation maps for dual gating cardiac SPECT. We used extended cardiac-torso phantom with Tc-99m-sestamibi distribution to generate a dataset with both respiratory and cardiac motion and then grouped them based on six respiratory and eight cardiac phases. The corresponding attenuation correction (AC) maps were used to simulate different CT protocols: dual gating CT (DCT), respiratory gated CT (RCT), cine average CT (ACT), interpolated CT (ICT), helical CTs at end-inspiration (HCT-in), end-expiration (HCT-ex), and mid-respiration (HCT-mid), respectively. One hundred and twenty noise-free and realistic noisy projections were generated over 180° from RAO to LPO and reconstructed by OS-EM method using different AC maps. The reconstructed images in different respiratory phases were registered to one reference end-expiration phase and summed up as a cardiac image for each cardiac phase. The corresponding polar maps were generated and further analyzed using 17-segment plots. Relative difference (RD) of the average intensity was computed in each segment using the polar maps with DCT-AC as reference. Substantial artifacts could be found in HCT-in AC images in every cardiac phase. For all eight noise-free cardiac phases, the average RDmax for AC with ACT, HCT-ex, HCT-in, HCT-mid, RCT, and ICT comparing to DCT were 4.76%, 4.95%, 10.54%, 4.23%, 2.39%, and 2.76%, respectively. For all eight noisy cardiac phases, the average RDmax for AC with ACT, HCT-ex, HCT-in, HCT-mid, RCT, and ICT comparing to DCT were 4.09%, 5.04%, 9.24%, 4.02%, 3.22%, and 2.85%, respectively. The ICT and RCT have the best AC performance for dual gating SPECT, while HCT-ex, HCT-in, HCT-mid, and ACT show inferior results. Since RCT and DCT are not commonly used in clinics due to complex implementation and radiation concern, ICT is recommended, followed by HCT-mid or HCT-ex for AC in dual gating cardiac SPECT with good accuracy and relative low radiation dose.

Design, Implementation, and Evaluation of a Head and Neck MRI RF Array Integrated with a 511 keV Transmission Source for Attenuation Correction in PET/MR.

The goal of this work is to further improve positron emission tomography (PET) attenuation correction and magnetic resonance (MR) sensitivity for head and neck applications of PET/MR. A dedicated 24-channel receive-only array, fully-integrated with a hydraulic system to move a transmission source helically around the patient and radiofrequency (RF) coil array, is designed, implemented, and evaluated. The device enables the calculation of attenuation coefficients from PET measurements at 511 keV including the RF coil and the particular patient. The RF coil design is PET-optimized by minimizing photon attenuation from coil components and housing. The functionality of the presented device is successfully demonstrated by calculating the attenuation map of a water bottle based on PET transmission measurements; results are in excellent agreement with reference values. It is shown that the device itself has marginal influence on the static magnetic field B0 and the radiofrequency transmit field B1 of the 3T PET/MR system. Furthermore, the developed RF array is shown to outperform a standard commercial 16-channel head and neck coil in terms of signal-to-noise ratio (SNR) and parallel imaging performance. In conclusion, the presented hardware enables accurate calculation of attenuation maps for PET/MR systems while improving the SNR of corresponding MR images in a single device without degrading the B0 and B1 homogeneity of the scanner.

Gated single-photon emission computed tomography myocardial perfusion imaging is superior to computed tomography attenuation correction in discriminating myocardial infarction from attenuation artifacts in men and right coronary artery disease.

In single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) studies, attenuation artifacts frequently cause false positives, which can be partially overcome by computed tomography attenuation correction (CT-AC) or gated acquisition [gated myocardial perfusion imaging (GMPI)]. The purpose of this study is to evaluate their relative diagnostic performances for coronary artery disease (CAD). We enrolled 181 patients who underwent gated SPECT with CT-AC in this study. Two observers who were blinded to the clinical data interpreted the GMPI and CT-AC images. Coronary angiography was considered as the reference standard. The diagnostic efficacy was evaluated based on sex, BMI, and individual coronary arteries. The diagnostic accuracy of GMPI was higher than that of nonattenuation correction overall, as well as for men, overweight individuals, and right CAD (P<0.05). Compared with CT-AC, GMPI overall had a higher specificity (96.3 vs. 86.9%, P=0.014) but the same sensitivity, achieving an increased accuracy and area under the curve (AUC, P>0.05). For diagnosing right CAD, GMPI had a higher diagnostic efficacy (AUC: 0.733 vs. 0.596, P<0.001) because of its higher sensitivity (52.0 vs. 26.0%, P=0.008); for men, the diagnostic efficacy of GMPI was significantly higher than that of CT-AC (AUC: 0.754 vs. 0.681, P=0.038). Both CT-AC and GMPI led to an increased diagnostic efficacy compared with nonattenuation correction in differentiating attenuation artifacts from fixed perfusion defects. These improvements were, however, more obvious for GMPI than for CT-AC, especially in men and right CAD.

Impact of Tissue Classification in MRI-Guided Attenuation Correction on Whole-Body Patlak PET/MRI.

The aim of this work is to investigate the impact of tissue classification in magnetic resonance imaging (MRI)-guided positron emission tomography (PET) attenuation correction (AC) for whole-body (WB) Patlak net uptake rate constant (Ki) imaging in PET/MRI studies. WB dynamic PET/CT data were acquired for 14 patients. The CT images were utilized to generate attenuation maps (μ-mapCTAC) of continuous attenuation coefficient values (Acoeff). The μ-mapCTAC were then segmented into four tissue classes (μ-map4-classes), namely background (air), lung, fat, and soft tissue, where a predefined Acoeff was assigned to each class. To assess the impact of bone for AC, the bones in the μ-mapCTAC were then assigned a predefined soft tissue Acoeff (0.1cm-1) to produce an AC μ-map without bones (μ-mapno-bones). Thereafter, both WB static SUV and dynamic PET images were reconstructed using μ-mapCTAC, μ-map4-classes, and μ-mapno-bones (PETCTAC, PET4-classes, and PETno-bones), respectively. WB indirect and direct parametric Ki images were generated using Patlak graphical analysis. Malignant lesions were delineated on PET images with an automatic segmentation method that uses an active contour model (MASAC). Then, the quantitative metrics of the metabolically active tumor volume (MATV), target-to-background (TBR), contrast-to-noise ratio (CNR), peak region-of-interest (ROIpeak), maximum region-of-interest (ROImax), mean region-of-interest (ROImean), and metabolic volume product (MVP) were analyzed. The Wilcoxon test was conducted to assess the difference between PET4-classes and PETno-bones against PETCTAC for all images. The same test was also adopted to compare the differences between SUV, indirect Ki, and direct Ki images for each evaluated AC method. No significant differences in MATV, TBR, and CNR were observed between PET4-classes and PETCTAC for either SUV or Ki images. PET4-classes significantly overestimated ROIpeak, ROImax, ROImean, as well as MVP scores compared with PETCTAC in both SUV and Ki images. SUV images exhibited the highest median relative errors for PET4-classes with respect to PETCTAC (RE4-classes): 6.91%, 6.55%, 5.90%, and 6.56% for ROIpeak, ROImax, ROImean, and MVP, respectively. On the contrary, Ki images showed slightly reduced RE4-classes (indirect 5.52%, 5.95%, 4.43%, and 5.70%, direct 6.61%, 6.33%, 5.53%, and 4.96%) for ROIpeak, ROImax, ROImean, and MVP, respectively. A higher TBR was observed on indirect and direct Ki images relative to SUV, while direct Ki images demonstrated the highest CNR. Four-tissue class AC may impact SUV and Ki parameter estimation but only to a limited extent, thereby suggesting that WB Patlak Ki imaging for dynamic WB PET/MRI studies is feasible. Patlak Ki imaging can enhance TBR, thereby facilitating lesion segmentation and quantification. However, patient-specific Acoeff for each tissue class should be used when possible to address the high inter-patient variability of Acoeff distributions.

Quantitative assessment of 18F-FDG PET in patients with Hodgkin lymphoma: is it significantly affected by contrast-enhanced computed tomography attenuation correction?

The reliability of visual and quantitative response assessment may be impaired owing to inconsistent scanning protocols and image reconstruction methods of 2-deoxy-2-[F]fluoro-D-glucose (F-FDG) PET. Hence, this study investigates the effect of contrast-enhanced computed tomography (CT) attenuation correction in patients with Hodgkin lymphoma. In 10 consecutive patients undergoing either staging or response assessment, F-FDG PET images were attenuation-corrected once on the basis of unenhanced CT and additionally using contrast-enhanced CT. Reconstruction was performed in both cases with ordered subset expectation maximization (OSEM) and ultra-high definition (UHD) algorithm. While maximum and peak standardized uptake value (SUV) were obtained from tumour tissue (lesionSUVmax and lesionSUVpeak), maximum and mean SUVs were determined within the background regions liver (liverSUVmax and liverSUVmean) and mediastinal blood pool (mbpSUVmax and mbpSUVmean). After switching to contrast-enhanced CT attenuation correction, lesionSUVmax and lesionSUVpeak increased on average by 2.55±3.24 (P=0.018) and 3.64±3.22% (P=0.008), respectively, with OSEM and by 4.59±5.49 (P=0.005) and 3.84±5.65% (P=0.005), respectively, with UHD reconstruction. LiverSUVmax and liverSUVmean showed a mean rise of 7.15±4.27 (P=0.005) and 6.97±2.18% (P=0.005), respectively, in the OSEM data sets and of 7.24±6.59 (P=0.017) and 6.29±2.83% (P=0.005), respectively, in the UHD images. The average increases of mbpSUVmax and mbpSUVmean were 10.82±4.89 (P=0.005) and 12.40±3.73% (P=0.005), respectively, after OSEM, compared with 13.11±14.93 (P=0.005) and 11.50±12.19% (P=0.005), respectively, after UHD reconstruction. As the use of CT contrast fluids results in a stronger SUV increase within the liver and mediastinal blood pool than within lymphoma tissue, this may have clinical consequences regarding visual and quantitative response assessment. Ideally, CT scans for PET attenuation correction should therefore be performed in the absence of a contrast agent.

The importance of appropriate reporting and investigation of incidental findings on computed tomography attenuation correction images during myocardial perfusion scintigraphy

We present a case of lung cancer incidentally detected as a pulmonary nodule on computed tomography attenuation correction (CTAC) images during myocardial perfusion scintigraphy (MPS). Unfortunately, the incidental lesion was not fully investigated following MPS report and had developed into metastatic lung carcinoma when diagnosed over 1 year later, with failure of subsequent emergent chemotherapy. The disease appeared to be localized when initially detected during MPS. This case highlights the importance and potential clinical value of routine review of CTAC images in MPS with appropriate reporting and further investigation of suspicious incidental findings. In addition, the importance of effective communication between nuclear medicine department and treating team is clear to ensure suspicious incidental findings are given sufficient credence and thoroughly investigated promptly to avoid adverse clinical outcomes.

Impact of Misregistration between the Myocardial Perfusion Images and CT Attenuation Correction Map on the %up Take with 17 Segments Polar Map

Computed tomography (CT) attenuation correction of myocardial perfusion in single-photon emission computed tomography (SPECT) /CT systems is possibility of misregistration between emission and transmission scans. This study aimed to evaluate the influence of misregistration using a polar map of 17 segments model. Using the fusion software, we assessed the magnitude and direction of misregistration in 200 consecutive myocardial perfusion SPECT images with 99mTechnetium (99mTc) tetrofosmin. After registration, CT data was shifted by ±1, ±2, and ±3 pixels along the cephalad/caudal, dorsal/ventral, and left/right axes, respectively. The registered image was compared with the shifted image. Misregistration between the SPECT and CT images occurred by 1-2 pixels in 127 cases (63.5%) and by 2 or more pixels in four cases (2%); the maximum misregistration was 1.2±0.4 pixels on average. The polar map scoring was most significantly affected by 3 pixel ventral shift. A ventral shift of 1 pixel affected the scores for the anterolateral and inferolateral segments, whereas a caudal shift of 1 pixel affected the scores for the anterior segment. Since the 17 segments model can evaluate the position more precisely than the five segments model, it is possible to evaluate up to 1 pixel misregistration.

Respiratory motion correction in prostate cancer positron emission tomography: A study on patients and phantom simulation

Introduction: To investigate the effects of breathing cycle and tree diaphragm motions on prostate cancer tumors standard uptake value (SUV) during positron emission tomography (PET) and to correct it. Materials and methods: Respiratory motion traces were simulated on the common patient breathing cycle and tree diaphragm motions using the 4D NCAT phantom. Lesions with different activities and diameters were simulated in prostate. This study was conducted in two phases. In the first phase; the generated PET sinograms taken from GATE (Geant4 Application Tomography Emission) Monte Carlo simulations corrected using computed tomography attenuation correction involving the cycle. In the next phase; on the obtained images, the motion-correction was carried out using software for Tomographic Image Reconstruction (STIR). By considering respiration- averaged computed as a true value, the SUVs were measured and analyzed for different motions. Results: In uncorrected measurements, the mean, minimum and maximum SUVs were 0.4%, 0.09% and 2% respectively, whilst in corrected measurements, these value were reported as 3.5%, 0.7% and 14% respectively. Conclusion: The respiratory motion-induced errors in tumor quantification and delineation. The SUVs depending on the phase of the raspatory. Motion correction could enhance the SUVs in prostate cancer PET.

A deep learning approach for 18F-FDG PET attenuation correction

BackgroundTo develop and evaluate the feasibility of a data-driven deep learning approach (deepAC) for positron-emission tomography (PET) image attenuation correction without anatomical imaging. A PET attenuation correction pipeline was developed utilizing deep learning to generate continuously valued pseudo-computed tomography (CT) images from uncorrected 18F-fluorodeoxyglucose (18F-FDG) PET images. A deep convolutional encoder-decoder network was trained to identify tissue contrast in volumetric uncorrected PET images co-registered to CT data. A set of 100 retrospective 3D FDG PET head images was used to train the model. The model was evaluated in another 28 patients by comparing the generated pseudo-CT to the acquired CT using Dice coefficient and mean absolute error (MAE) and finally by comparing reconstructed PET images using the pseudo-CT and acquired CT for attenuation correction. Paired-sample t tests were used for statistical analysis to compare PET reconstruction error using deepAC with CT-based attenuation correction.ResultsdeepAC produced pseudo-CTs with Dice coefficients of 0.80 ± 0.02 for air, 0.94 ± 0.01 for soft tissue, and 0.75 ± 0.03 for bone and MAE of 111 ± 16 HU relative to the PET/CT dataset. deepAC provides quantitatively accurate 18F-FDG PET results with average errors of less than 1% in most brain regions.ConclusionsWe have developed an automated approach (deepAC) that allows generation of a continuously valued pseudo-CT from a single 18F-FDG non-attenuation-corrected (NAC) PET image and evaluated it in PET/CT brain imaging.

A study of false apical defects in myocardial perfusion imaging with SPECT/CT

An important problem of myocardial SPECT/CT imaging with attenuation correction (AC) is a reduction of radiotracer activity at the apex in reconstructed images. This problem is known as the false apical defect. False apical defects mask real defects and lead to interpretation uncertainties. The aim of the present work is to study this phenomenon to understand the cause of apical defects on AC images. Mathematical modeling and clinical studies are carried out. Special mathematical models were designed to study the effect of the myocardial left ventricle (LV) form and the effect of patient constitution on false apical defects severity. Computer simulations of the SPECT/CT myocardial perfusion imaging procedure with and without attenuation correction were performed. The dependence of apical false defects on the LV form and on the data acquisition scheme was studied. The results of mathematical modeling have shown that the cause of false apical defects is not associated with attenuation correction. Rather, it is related to the LV form, especially to the presence of anatomical apical thinning. The LV form with apical thinning in diastole phase can not be exactly reconstructed by using the standard data acquisition schemes with limited 32 and 60 views. The reconstruction error appears in the rounded apical region in reconstructions with and without attenuation correction. But, in non-AC images, this error is masked by the second error related to the lack of attenuation correction. Interpretation based on the results of two compensating errors cannot be reliable. Taking into account the results obtained, we suggest the following hypothesis: gated systolic AC images can be useful in the interpretations of findings at the apex. This hypothesis was confirmed in preliminary clinical study.