Cardiovascular risk factors and development of nomograms in an Italian cohort of patients with suspected coronary artery disease undergoing SPECT or PET stress myocardial perfusion imaging.

Introduction: Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) are non-invasive nuclear medicine techniques that can identify areas of abnormal myocardial perfusion. We assessed the prevalence of cardiovascular risk factors in patients with suspected coronary artery disease (CAD) undergoing SPECT or PET stress myocardial perfusion imaging (MPI). Based on significant risk factors associated with an abnormal MPI, we developed a nomogram for each cohort as a pretest that would be helpful in decision-making for clinicians. Methods: A total of 6,854 patients with suspected CAD who underwent stress myocardial perfusion imaging by SPECT or PET/CT was studied. As part of the baseline examination, clinical teams collected information on traditional cardiovascular risk factors: age, gender, body mass index, angina, dyspnea, diabetes, hypertension, hyperlipidemia, family history of CAD, and smoking. Results: The prevalence of cardiovascular risk factors was different in the two cohorts of patients undergoing SPECT (n = 4,397) or PET (n = 2,457) myocardial perfusion imaging. A statistical significance was observed in both cohorts for age, gender, and diabetes. At multivariable analysis, only age and male gender were significant covariates in both cohorts. The risk of abnormal myocardial perfusion imaging related to age was greater in patients undergoing PET (odds ratio 4% vs. 1% per year). In contrast, male gender odds ratio was slightly higher for SPECT compared to PET (2.52 vs. 2.06). In the SPECT cohort, smoking increased the risk of abnormal perfusion of 24%. Among patients undergoing PET, diabetes and hypertension increased the risk of abnormal perfusion by 63% and 37%, respectively. For each cohort, we obtained a nomogram by significant risk factors at multivariable logistic regression. The area under the receiver operating characteristic curve associated with the nomogram was 0.67 for SPECT and 0.73 for the PET model. Conclusions: Patients with suspected CAD belonging to two different cohorts undergoing SPECT or PET stress myocardial perfusion imaging can have different cardiovascular risk factors associated with a higher risk of an abnormal MPI study. As crude variables, age, gender, and diabetes were significant for both cohorts. Net of the effect of other covariates, age and gender were the only risk factors in common between the two cohorts. Furthermore, smoking and type of stress test were significant for the SPECT cohort, where as diabetes and hypertension were significant for the PET cohort. Nomograms obtained by significant risk factors for the two cohorts can be used by clinicians to evaluate the risk of an abnormal study.

Physiological provocation compared to acetazolamide in the assessment of cerebral hemodynamics: a case report.

BACKGROUND: Severe large vessel disease may lead to cerebral hemodynamic failure that critically impairs cerebral blood flow (CBF) regulation elevating the risk of ischemic events. Assessment of the condition is often based on changes in CBF during vasodilatation; however, pharmacologically induced vasodilation does not reflect the physiological condition during an ischemic event caused by hemodynamic failure. We compared a [15O]H2O PET brain scan during vasodilation to a [99mTc]HMPAO SPECT brain scan during an ongoing transient ischemic attack (TIA). CASE PRESENTATION: A single patient presenting with limb-shaking TIA underwent CT, Digital Subtraction Angiography, and two different modalities of cerebral perfusion scans: [15O]H2O PET and [99mTc]HMPAO SPECT. Acetazolamide was used in the PET scan to induce vasodilatation, and during the SPECT scan physiological stress, standing up rapidly, was used to induce limb-shaking TIA. CT-angiography and Digital Subtraction Angiography revealed an occlusion in the distal part of the right A2 segment of the anterior cerebral artery, with a corresponding infarction in the watershed area. Collaterals supplied the main vascular territory of the anterior cerebral artery. During rest, neither perfusion modalities demonstrated reduced perfusion outside of the ischemic core. However, we found a pronounced difference between the PET utilizing acetazolamide and the SPECT during the TIA. The PET scan demonstrated relative hypoperfusion in vascular territory supplied by collaterals, while the area around the ischemic core was not affected. Contrary, the SPECT had only minor relative hypoperfusion in the collateral-supplied area, whereas the watershed area proximal to the infarct core had pronounced relative hypoperfusion. CONCLUSIONS: The observed discrepancy in compromised areas during physiological provocation compared to pharmacological induced vasodilation questions the use of an unphysiological stressor for assessment of cerebrovascular hemodynamics. A physiological provocation test may achieve more clinically relevant evaluation.

Perfusion imaging predicts short-term clinical outcome in isolated posterior cerebral artery occlusion stroke.

BACKGROUND AND PURPOSE: Ischemic strokes due to isolated posterior cerebral artery (PCA) occlusions represent 5% of all strokes but have significant impacts on patients' quality of life, primarily due to visual deficits and thalamic involvement. Current guidelines for acute PCA occlusion management are sparse, and the prognostic value of perfusion imaging parameters remains underexplored. METHODS: We conducted a retrospective analysis of 32 patients with isolated PCA occlusions treated at Johns Hopkins Medical Institutions between January 2017 and March 2023. Patients underwent pretreatment perfusion imaging, with perfusion parameters analyzed using RAPID software. The primary outcome was short-term clinical outcome as measured by the National Institutes of Health Stroke Scale (NIHSS) at discharge. RESULTS: The median age of the cohort was 70 years, with 34% female and 66% male. Significant correlations were found between NIHSS at discharge and various perfusion parameters, including time-to-maximum (Tmax) >6 seconds (ρ = .55, p = .004), Tmax >8 seconds (ρ = .59, p = .002), Tmax >10 seconds (ρ = .6, p = .001), mismatch volume (ρ = .51, p = .008), and cerebral blood volume (CBV) < 34% (ρ = .59, p = .002). CONCLUSIONS: Tmax and CBV volumes significantly correlated with discharge NIHSS with marginal superiority of Tmax >10 seconds and CBV <42% volumes. These findings suggest that CT and MR perfusion imaging can play a crucial role in the acute management of PCA strokes, though larger, standardized studies are needed to validate these results and refine imaging thresholds specific to posterior circulation infarcts.

Prognostic value of transient ischemic dilatation by 13N-ammonia PET MPI for short-term outcomes in patients with non-obstructive CAD.

OBJECTIVE: Transient ischaemic dilatation (TID) had incremental diagnostic and prognostic value in obstructive coronary artery disease (CAD), but its clinical significance in patients with non-obstructive CAD remains unknown. We aimed to explore the prognostic value of TID in patients with non-obstructive CAD by 13N-ammonia PET imaging. METHODS: We retrospectively studied 131 consecutive patients with non-obstructive CAD undergoing one-day rest-stress 13N-ammonia PET myocardial perfusion imaging (MPI). TID was automatically generated using CardIQ Physio software. The receiver operative characteristic (ROC) curve was used to determine the optimal threshold of TID. The follow-up outcome was major adverse cardiac events (MACE), a composite of re-hospitalization for heart failure or unstable angina, late revascularization, non-fatal myocardial infarction, and cardiac death. Cardiac event-free survivals for normal and abnormal TID were compared using Kaplan-Meier plots and log-rank tests. RESULTS: During a median follow-up of 42.08 ± 17.67 months, 22 (16.7%) patients occurred MACE. The optimal cut-off value of TID was 1.03 based on MACE. Our preliminary outcome analysis suggests that TID-abnormal subjects had a lower overall survival probability. Furthermore, our multivariate analysis reveals abnormal TID was the only independent predictor for MACE in non-obstructive CAD. In the subgroup analysis, an abnormal TID was an independent predictor for MACE in patients with abnormal perfusion patterns. CONCLUSION: Among patients with non-obstructive CAD, PET-derived TID ≥ 1.03 may identify those with a high risk of subsequent MACE independently. It was also an independent risk factor for poor prognosis in patients with abnormal perfusion.

Left Ventricular Wall Motion as an Additional Valuable Parameter in Diabetic Patients with Normal Myocardial Perfusion Imaging.

BACKGROUND: Gated SPECT is an established technique for assessment of left ventricular function in cardiovascular disease patients. However, there is little information about the influence of diabetes mellitus on gated SPECT parameters. This study was established to assess gated SPECT parameters in Diabetes Mellitus (DM) and non-diabetes mellitus (non-DM) patients with normal Myocardial Perfusion Imaging (MPI). METHODS: In this analytical cross-sectional study, 314 patients (157 DM, 157 non-DM) with normal MPI were enrolled. Prevalence of risk factors for CAD like hypertension (HTN), and dyslipidemia were found to be significantly higher (p <0.01) in DM patients compared to non-DM. RESULTS: No statistically significant difference was observed among the TID, ESV, EDV, PFR, TTPF, and Wall Thickness (WT) parameters between DM and non-DM patients. Wall motion (Wm) in DM patients was significantly higher compared to non-DM patients. (3.9 ± 0.51 vs. 2.69 ± 0.48 for DM and non-DM patients, respectively, p-value:0.01). Also, there was no significant difference in Wm in the two groups with and without HTN. This shows the independent effect of DM on the Wm. CONCLUSION: This study believes that the Wm parameter should be noted for the early diagnosis or prevention of heart disease in DM patients. These findings can indicate the gradual changes in the movements of the left ventricle and the beginning of the progression of diabetic cardiomyopathy.

Prognostic value of single photon emission computed tomography myocardial perfusion imaging for the prediction of MACE in pre- kidney transplant recipients: A systematic review and meta-analysis.

BACKGROUND: Kidney transplantation provides substantial benefits in extending survival and improving quality of life for patients with end-stage renal disease. The incidence of major adverse cardiac events (MACE) increases with a decline of kidney function in patients with chronic kidney disease. After kidney transplantation, the incidence of MACE remains high. The objective of this study was to assess the prognostic significance of pre-transplant single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) in kidney transplant recipients. METHODS: A systematic literature search was performed between January 1st 2015 and March 26th 2024 in PubMed, EMBASE, Web of Science and The Cochrane Library to identify the prognostic value of SPECT MPI for developing MACE (primary outcome) and mortality (secondary outcome) in kidney transplant recipients (PROSPERO CRD42020188610). Risk of bias was assessed. Meta-analyses and subgroup analyses were performed using random-effects models. RESULTS: Six studies comprising 2090 SPECT MPI scans were included. Abnormal SPECT MPI scans were associated with an increased risk of MACE post-transplantation (HR 1.62, 95% CI 1.27-2.06, p < 0.001). Subgroup analyses showed consistent findings across various patient populations and methodological differences. Sensitivity analyses supported the robustness of our findings. CONCLUSIONS: Current evidence showed that pre-transplant SPECT MPI has significant prognostic value in identifying kidney transplant candidates at risk for MACE post-transplantation. Integrating SPECT MPI into preoperative assessments might enhance risk stratification and guide clinical decision-making. Prospective studies are needed to refine risk prediction models.

Effect of MR-guided perfusion imaging mismatch profiles within 6 h on endovascular thrombectomy outcomes.

BACKGROUND: The treatment of acute ischemic stroke (AIS) aims to achieve early vascular recanalization and reperfusion of the penumbra. However, the effect of early penumbral imaging within 6 h on clinical outcomes remains unclear. The objective of this study was to determine the effect of magnetic resonance-guided (MR-guided) perfusion imaging within 6 h after symptom onset on endovascular thrombectomy outcomes in AIS patients. METHODS: We prospectively collected the clinical information of consecutive AIS patients undergoing endovascular thrombectomy based on MR-guided perfusion imaging within 6 h after symptom onset from AISRNA and EVTRNA studies. The primary outcome was defined as the poor outcome (mRS > 2 within 90 days). The perfusion-weighted imaging/diffusion-weighted imaging (PWI/DWI) mismatch was assessed by an automated software. RESULTS: We enrolled 84 patients (25 in the mismatch ≤ 1.8 group and 59 in the mismatch > 1.8 group). Significant difference was found between the mismatch > 1.8 group and the mismatch ≤ 1.8 group for the incidence of disabling stroke (mRS > 2) within 90 days (40.7% vs. 68.0%, OR: 3.099, 95% CI: 1.154-8.323, P = 0.025). Intracranial hemorrhage occurred in 8 patients (13.6%) in the mismatch > 1.8 group and 10 patients in the mismatch ≤ 1.8 group (40.0%) (P = 0.010). The risk of severe cerebral edema was 2/59 (3.4%) vs. 7/25 (28.0%) (P = 0.004). These findings remained stable after adjustment. CONCLUSIONS: MR-guided perfusion imaging mismatch profiles within 6 h after symptom onset may be feasible to predictclinical outcomes and reduce clinically ineffective reperfusion after endovascular thrombectomy.

Advances in CT-based lung function imaging for thoracic radiotherapy.

The objective of this review is to examine the potential benefits and challenges of CT-based lung function imaging in radiotherapy over recent decades. This includes reviewing background information, defining related concepts, classifying and reviewing existing studies, and proposing directions for further investigation. The lung function imaging techniques reviewed herein encompass CT-based methods, specifically utilizing phase-resolved four-dimensional CT (4D-CT) or end-inspiratory and end-expiratory CT scans, to delineate distinct functional regions within the lungs. These methods extract crucial functional parameters, including lung volume and ventilation distribution, pivotal for assessing and characterizing the functional capacity of the lungs. CT-based lung ventilation imaging offers numerous advantages, notably in the realm of thoracic radiotherapy. By utilizing routine CT scans, additional radiation exposure and financial burdens on patients can be avoided. This imaging technique also enables the identification of different functional areas of the lung, which is crucial for minimizing radiation exposure to healthy lung tissue and predicting and detecting lung injury during treatment. In conclusion, CT-based lung function imaging holds significant promise for improving the effectiveness and safety of thoracic radiotherapy. Nevertheless, challenges persist, necessitating further research to address limitations and optimize clinical utilization. Overall, this review highlights the importance of CT-based lung function imaging as a valuable tool in radiotherapy planning and lung injury monitoring.

The Effect of Monitored Walking on Extracardiac Intestinal Activity in Myocardial Perfusion Imaging.

Various techniques have been used in attempts to reduce interfering gastrointestinal activity in myocardial perfusion imaging (MPI); however, these approaches have yielded inconsistent results. The goal of this study was to investigate the efficacy of monitored walking, a previously unexplored technique, in reducing subdiaphragmatic activity-related artifacts during pharmacologic stress 99mTc-tetrofosmin MPI with SPECT to improve the overall image quality. Methods: The study included patients who underwent MPI with pharmacologic stress. They were given a step counter immediately after the radiotracer injection and were randomized into a group A, with a request to walk at least 1,000 steps before imaging, and a group B, with no specific instructions about walking. The reconstructed SPECT images were assessed visually. Moderate and severe levels of subdiaphragmatic tracer activity were considered relevant for the interpretation of the scans. Additionally, myocardial and abdominal activity was semiquantitatively assessed on raw planar images, and the mean myocardium-to-abdomen count ratios were calculated. Results: We enrolled 199 patients (95 patients in group A and 104 patients in group B). Clinical characteristics did not differ significantly between the 2 groups. Patients in group A walked more steps than patients in group B (P < 0.001), but there were no differences in the proportion of accepted scans between the 2 groups (P = 0.41). Additionally, there were no differences in the proportion of relevant subdiaphragmatic activity between the groups (P = 0.91). The number of steps did not impact the acceptance rate (P = 0.29). Conclusion: A higher number of steps walked during the waiting period between pharmacologic stress and acquisition does not affect subdiaphragmatic activity-related artifacts or the proportion of accepted scans after pharmacologic stress. However, pedometer use and clear instructions motivate patients to walk while awaiting imaging. Larger studies are required to compare a higher-step-count group with a sedentary control group to assess the influence of walking on gastrointestinal artifacts in MPI.

3D quantitative myocardial perfusion imaging with hyperpolarized HP001(bis-1,1-(hydroxymethyl)-[1-13C]cyclopropane-d8): Application of gradient echo and balanced SSFP sequences.

PURPOSE: This study aims to show the viability of conducting three-dimensional (3D) myocardial perfusion quantification covering the entire heart using both GRE and bSSFP sequences with hyperpolarized HP001. METHODS: A GRE sequence and a bSSFP sequence, both with a stack-of-spirals readout, were designed and applied to three pigs. The images were reconstructed using 13 $$ {}^{13} $$ C coil sensitivity maps measured in a phantom experiment. Perfusion was quantified using a constrained decomposition method, and the estimated rest/stress perfusion values from 13 $$ {}^{13} $$ C GRE/bSSFP and Dynamic contrast-enhanced MRI (DCE-MRI) were individually analyzed through histograms and the mean perfusion values were compared with reference values obtained from PET( 15 $$ {}^{15} $$ O-water). The Myocardial Perfusion Reserve Index (MPRI) was estimated for 13 $$ {}^{13} $$ C GRE/bSSFP and DCE-MRI and compared with the reference values. RESULTS: Perfusion values, estimated by both DCE and 13 $$ {}^{13} $$ C MRI, were found to be lower than reference values. However, DCE-MRI's estimated perfusion values were closer to the reference values than those obtained from 13 $$ {}^{13} $$ C MRI. In the case of MPRI estimation, the 13 $$ {}^{13} $$ C estimated MPRI values (GRE/bSSFP: 2.3/2.0) more closely align with the literature value (around 3) than the DCE estimated MPRI value (1.6). CONCLUSION: This study demonstrated the feasibility of 3D whole-heart myocardial perfusion quantification using hyperpolarized HP001 with both GRE and bSSFP sequences. The 13 $$ {}^{13} $$ C perfusion measurements underestimated perfusion values compared to the 15 $$ {}^{15} $$ O PET literature value, while the 13 $$ {}^{13} $$ C estimated MPRI value aligned better with the literature. This preliminary result indicates 13 $$ {}^{13} $$ C imaging may more accurately estimate MPRI values compared to DCE-MRI.

Clinical Benefits of Arterial Spin-Labeling Magnetic Resonance Imaging for Primary Diffuse Large B-cell Lymphoma of the Central Nervous System Presenting With Lymphomatosis Cerebri: A Case Report.

Of the primary central nervous system (CNS) lymphomas, diffuse large B-cell lymphoma of the CNS (CNS-DLBCL) is an aggressive extranodal lymphoma that originates in the CNS. Lymphomatosis cerebri (LC) is an exceptionally rare subtype, posing diagnostic challenges due to the absence of abnormal enhancement and making the identification of suitable biopsy sites difficult. Arterial spin-labeling magnetic resonance imaging (ASL-MRI) is a non-invasive MRI technique that quantifies tumor blood flow. This report presents a case of CNS-DLBCL with LC, which was evaluated and biopsied using ASL-MRI of the brain. Herein, we present a case of a 32-year-old female who presented with abnormal involuntary movements and cognitive impairments. She underwent an MRI which showed a diffuse and infiltrative lesion in the bilateral basal ganglia, showing a high signal intensity area on fluid-attenuated inversion recovery (FLAIR) images with no contrast enhancement. Computed Tomography scans and Gallium-67 scintigraphy showed no abnormal uptake throughout the whole body. Although she received corticosteroid treatments, subsequent MRI showed an enlarged lesion, and she underwent a brain biopsy. The biopsy site was determined based on high perfusion demonstrated by ASL-MRI and the histological findings positive for B-cell markers led to diagnoses of CNS-DLBCL, specifically LC. Her symptoms improved following high-dose methotrexate and whole-brain irradiation. Subsequent MRI scans showed a dramatic improvement, and the high perfusion observed in the ASL-MRI disappeared. This report has emphasized the critical role of histopathology in diagnosing CNS-DLBCL presenting with LC, a highly aggressive lymphoma requiring prompt treatment. In this case, high ASL-MRI signal intensity indicated an increased area of tumor cell density suitable for biopsy. This is the first report to establish a relationship between cell density and ASL-MRI signal intensity in LC. The challenge in locating the optimal biopsy site due to the lack of contrast enhancement and the difference in tumor cell densities within high signal intensity areas on FLAIR imaging is presented. ASL-MRI provides information on tumor blood flow (TBF), which may be associated with higher tumor cell density, making it a valuable tool for identifying suitable biopsy sites. Thus, ASL-MRI is clinically beneficial for the biopsy of LC cases that show high signal intensity on FLAIR images without contrast enhancement.

A physics-informed deep learning framework for dynamic susceptibility contrast perfusion MRI.

BACKGROUND: Perfusion magnetic resonance imaging (MRI)s plays a central role in the diagnosis and monitoring of neurovascular or neurooncological disease. However, conventional processing techniques are limited in their ability to capture relevant characteristics of the perfusion dynamics and suffer from a lack of standardization. PURPOSE: We propose a physics-informed deep learning framework which is capable of analyzing dynamic susceptibility contrast perfusion MRI data and recovering the dynamic tissue response with high accuracy. METHODS: The framework uses physics-informed neural networks (PINNs) to learn the voxel-wise TRF, which represents the dynamic response of the local vascular network to the contrast agent bolus. The network output is stabilized by total variation and elastic net regularization. Parameter maps of normalized cerebral blood flow (nCBF) and volume (nCBV) are then calculated from the predicted residue functions. The results are validated using extensive comparisons to values derived by conventional Tikhonov-regularized singular value decomposition (TiSVD), in silico simulations and an in vivo dataset of perfusion MRI exams of patients with high-grade gliomas. RESULTS: The simulation results demonstrate that PINN-derived residue functions show a high concordance with the true functions and that the calculated values of nCBF and nCBV converge towards the true values for higher contrast-to-noise ratios. In the in vivo dataset, we find high correlations between conventionally derived and PINN-predicted perfusion parameters (Pearson's rho for nCBF: 0.84 ± 0.03 $0.84 \pm 0.03$ and nCBV: 0.92 ± 0.03 $0.92 \pm 0.03$ ) and very high indices of image similarity (structural similarity index for nCBF: 0.91 ± 0.03 $0.91 \pm 0.03$ and for nCBV: 0.98 ± 0.00 $0.98 \pm 0.00$ ). CONCLUSIONS: PINNs can be used to analyze perfusion MRI data and stably recover the response functions of the local vasculature with high accuracy.

Test-retest reproducibility of absolute myocardial blood flow obtained using stress dynamic CT myocardial perfusion imaging.

Background: Coronary artery disease (CAD) and coronary microvascular disease (CMD) are significant contributors to angina pectoris, necessitating reliable diagnostic techniques for effective management. While positron emission tomography has been the non-invasive gold standard for myocardial blood flow (MBF) quantification, stress dynamic CT myocardial perfusion imaging (CTMPI) has emerged as a promising alternative. This study aimed to evaluate the test-retest reproducibility of MBF measurements obtained using dynamic CTMPI. Methods: The study retrospectively analyzed MBF values from two dynamic CTMPI examinations conducted in the same patient cohort (n = 30) to examine the consistency of MBF quantification and the ability to visually detect and grade abnormal perfusion suggesting ischemia between the tests. Global and remote MBF were defined as the mean MBF and the maximum MBF of all segments, respectively. Results: MBF quantification revealed strong linear correlations between the tests (r = 0.89 for global MBF, r = 0.88 for remote MBF, and r = 0.82 for all segments), and intraclass correlation coefficients reflected high agreement between the tests (0.94 for global MBF, 0.93 for remote MBF, and 0.90 for all segments). Bland-Altman plots indicated a negligible mean difference with acceptable limits of agreements between the tests for global MBF, remote MBF, and all segments. Visual assessment of the CTMPI maps for abnormal perfusion suggesting ischemia yielded a good inter-test agreement with a weighted kappa value of 0.80. Conclusion: Dynamic CTMPI can consistently reproduce absolute MBF values and reliably detect myocardial perfusion abnormalities, potentially making it a robust diagnostic tool for evaluating the presence and severity of CAD and CMD.

Optogenetic Functional Activation Is Detrimental During Acute Ischemic Stroke in Mice.

BACKGROUND: Functional activation of the focal ischemic brain has been reported to improve outcomes by augmenting collateral blood flow. However, functional activation also increases metabolic demand and might thereby worsen outcomes. Indeed, preclinical and clinical reports have been conflicting. Here, we tested the effect of functional activation during acute ischemic stroke using distal middle cerebral artery occlusion in anesthetized mice. METHODS: Using transgenic mice expressing channelrhodopsin-2 in neurons, we delivered functional activation using physiological levels of transcranial optogenetic stimulation of the moderately ischemic cortex (ie, penumbra), identified using real-time full-field laser speckle perfusion imaging during a 1-hour distal microvascular clip of the middle cerebral artery. Neuronal activation was confirmed using evoked field potentials, and infarct volumes were measured in tissue slices 48 hours later. RESULTS: Optogenetic stimulation of the penumbra was associated with more than 2-fold larger infarcts than stimulation of the contralateral homotopic region and the sham stimulation group (n=10, 7, and 9; 11.0±5.6 versus 5.1±4.3 versus 4.1±3.7 mm3; P=0.008, 1-way ANOVA). Identical stimulation in wild-type mice that do not express channelrhodopsin-2 did not have an effect. Optogenetic stimulation was associated with a small increase in penumbral perfusion that did not explain enlarged infarcts. CONCLUSIONS: Our data suggest that increased neuronal activity during acute focal arterial occlusions can be detrimental, presumably due to increased metabolic demand, and may have implications for the clinical management of hyperacute stroke patients.

Subdiaphragmatic activity-related artifacts in myocardial perfusion scintigraphy.

BACKGROUND: Myocardial perfusion imaging (MPI) with single photon emission computed tomography is an established non-invasive technique for assessing myocardial ischemia. This method involves the intravenous administration of a radiopharmaceutical that accumulates in the heart muscle proportional to regional blood flow. However, image quality and diagnostic accuracy can be compromised by various technical and patient-related factors, including high non-specific radiopharmaceutical uptake in abdominal organs such as the stomach, intestines, liver, and gall-bladder, leading to subdiaphragmatic artifacts. These artifacts are particularly problematic for evaluating inferior wall perfusion and often necessitate repeated imaging, which decreases gamma camera availability and prolongs imaging times. CONCLUSIONS: Despite numerous investigated techniques to reduce interfering gastrointestinal activity, results have been inconsistent, and current MPI guidelines provide scant information on effective procedures to mitigate this issue. Based on our experience, some possible approaches to reducing artifacts include choosing stress testing with an exercise stress test, when possible, late imaging, fluid intake, and consuming carbonated water immediately before imaging.

Clinical and perfusion imaging characteristics of acute large vessel occlusion in intracranial atherosclerosis.

OBJECTIVES: This study aimed to compare clinical and perfusion imaging profiles in acute ischemic stroke with large vessel occlusion (AIS-LVO) between patients with intracranial atherosclerotic disease (ICAD) and non-ICAD who underwent endovascular treatment (EVT). METHODS: Data from AIS-LVO patients over the anterior circulation undergoing EVT across two stroke centers were retrospectively analyzed. Clinical profiles and perfusion parameters from automated processing of perfusion imaging were compared between ICAD and non-ICAD groups. Ischemic core was defined as relative cerebral blood flow < 30 % on CT perfusion or apparent diffusion coefficient ≤ 620 × 10-6 mm2/s on MR diffusion weighted imaging. RESULTS: A total of 111 patients were included (46 ICAD, 65 non-ICAD). The ICAD group exhibited a higher male proportion (60.9 % vs. 35.4 %), more M1 segment occlusions (78.3 % vs. 56.9 %), lower atrial fibrillation rates (17.4 % vs. 63.1 %), and lower baseline NIH Stroke Scale (NIHSS) scores (median [IQR]: 13 [8.75-18] vs. 15 [10-21]) at presentation compared to non-ICAD (all p < 0.05). However, there was no difference in NIHSS scores at discharge or in good functional outcomes (modified Rankin Scale 0-2) at 3 months between the two groups. ICAD patients also had smaller median ischemic core volumes (0 [IQR 0-9.7] vs. 4.4 [0-21.6] ml, p = 0.038), smaller median Tmax >6s tissue volulmes (89.3 [IQR 51.1-147.1] vs. 124.4 [80.5-178.6] ml, p = 0.017) and lower median HIR (hypoperfusion intensity ratio defined as Tmax >10s divided by Tmax >6s; 0.28 [IQR 0.09-0.42] vs. 0.44 [0.24-0.60], p = 0.003). Higher baseline NIHSS scores correlated with larger Tmax >6s lesion volumes as well as higher HIR value in non-ICAD patients, but not in ICAD patients. CONCLUSIONS: In anterior circulation of AIS-LVO, ICAD patients exhibited distinct clinical presentations and perfusion imaging characteristics when compared to non-ICAD patients. Perfusion imaging profiles may serve as indicators for identifying ICAD patients before EVT.

Quantitative Total-Body Imaging of Blood Flow with High Temporal Resolution Early Dynamic 18F-Fluorodeoxyglucose PET Kinetic Modeling.

Quantitative total-body PET imaging of blood flow can be performed with freely diffusible flow radiotracers such as 15O-water and 11C-butanol, but their short half-lives necessitate close access to a cyclotron. Past efforts to measure blood flow with the widely available radiotracer 18F-fluorodeoxyglucose (FDG) were limited to tissues with high 18F-FDG extraction fraction. In this study, we developed an early-dynamic 18F-FDG PET method with high temporal resolution kinetic modeling to assess total-body blood flow based on deriving the vascular transit time of 18F-FDG and conducted a pilot comparison study against a 11C-butanol reference. Methods: The first two minutes of dynamic PET scans were reconstructed at high temporal resolution (60×1 s, 30×2 s) to resolve the rapid passage of the radiotracer through blood vessels. In contrast to existing methods that use blood-to-tissue transport rate ( K 1 ) as a surrogate of blood flow, our method directly estimates blood flow using a distributed kinetic model (adiabatic approximation to the tissue homogeneity model; AATH). To validate our 18F-FDG measurements of blood flow against a flow radiotracer, we analyzed total-body dynamic PET images of six human participants scanned with both 18F-FDG and 11C-butanol. An additional thirty-four total-body dynamic 18F-FDG PET scans of healthy participants were analyzed for comparison against literature blood flow ranges. Regional blood flow was estimated across the body and total-body parametric imaging of blood flow was conducted for visual assessment. AATH and standard compartment model fitting was compared by the Akaike Information Criterion at different temporal resolutions. Results: 18F-FDG blood flow was in quantitative agreement with flow measured from 11C-butanol across same-subject regional measurements (Pearson R=0.955, p<0.001; linear regression y=0.973x-0.012), which was visually corroborated by total-body blood flow parametric imaging. Our method resolved a wide range of blood flow values across the body in broad agreement with literature ranges (e.g., healthy cohort average: 0.51±0.12 ml/min/cm3 in the cerebral cortex and 2.03±0.64 ml/min/cm3 in the lungs, respectively). High temporal resolution (1 to 2 s) was critical to enabling AATH modeling over standard compartment modeling. Conclusions: Total-body blood flow imaging was feasible using early-dynamic 18F-FDG PET with high-temporal resolution kinetic modeling. Combined with standard 18F-FDG PET methods, this method may enable efficient single-tracer flow-metabolism imaging, with numerous research and clinical applications in oncology, cardiovascular disease, pain medicine, and neuroscience.