Changes of cerebral structure and perfusion in subtypes of systemic sclerosis: a brain magnetic resonance imaging study.

OBJECTIVES: The characteristics of brain impairment in different subtypes of systemic sclerosis (SSc) (dcSSc, diffuse cutaneous SSc; lcSSc, limited cutaneous SSc) remain unclear. This study aimed to characterize cerebral structure and perfusion changes in different subtype of SSc patients using magnetic resonance (MR) imaging. METHODS: Seventy SSc patients (46.0 ± 11.7 years, 62 females) and 30 healthy volunteers (44.8 ± 13.7 years, 24 females) were recruited and underwent brain MR imaging and Montreal Cognitive Assessment (MoCA) test. Gray matter (GM) volumes were measured using voxel-based morphometry analysis on T1-weighted images. Voxel-based and regional cerebral blood flow (CBF) was calculated on arterial spin labelling images. The cerebral structural and perfusion measurements by MR imaging were compared among dcSSc, lcSSc and healthy subjects using one-way ANOVA. The correlations between clinical characteristics and MR imaging measurements were also analyzed. RESULTS: The dcSSc patients exhibited a significant reduction in GM volume in the para-hippocampal region (cluster p < 0.01, FWE corrected) compared with healthy volunteers. Whereas, SSc patients, particularly lcSSc patients, showed elevated CBF in cerebellum, insula, cerebral cortex, and subcortical structures (regional analyses: all p < 0.05; voxel-based analyses: cluster p < 0.01, FWE corrected). Furthermore, clinical characteristics of modified Rodnan skin score (mRSS) (r value ranged from -0.29 to -0.45), MoCA scores (r = 0.40) and antinuclear antibody (ANA) positivity (r=-0.33) were significantly associated with CBF in some regions (all p < 0.05). CONCLUSION: The manifestations of brain involvement vary among different subtypes of SSc. In addition, severe skin sclerosis may indicate higher risk of brain involvement in SSc patients.

Preserved myocardial viability in patients with chronic total occlusion of a single coronary artery.

OBJECTIVE: To assess the benefits of coronary collateral circulation on myocardial perfusion, viability and function in patients with total occlusion of a single coronary artery using the 99mTc-sestamibi SPECT and 18F-fluorodeoxyglucose PET. METHODS: 164 Consecutive patients were included who underwent coronary angiography results exhibited total occlusion of a single coronary artery and received 99mTc-MIBI SPECT and 18F-FDG PET within 90 days of angiography. Myocardial perfusion and viability in patients with collateral circulation and those without it were compared. Long-term follow-up was performed through a review of patient clinical records. RESULTS: Collateral circulation was present in 56 patients (34%) and absent in 108 patients (66%). The total perfusion defect size in patients with collateral circulation decreased when compared to those without (30% ± 13% to 35% ± 14%, P < .05). The myocardial viability was 22% ± 12% in patients with collateral circulation, and 12% ± 9% in those without (P < .001). The left ventricular ejection fraction was higher, and the end-diastolic and end-systolic left ventricular volumes were lower in patients with collateral circulation (39% ± 11%, 138 ± 66, 89 ± 57) compared to patients without collateral circulation (31% ± 9%, 177 ± 55, 125 ± 48, all P < .001, respectively). Multi-factor logistic regression identified that concerning the variables of sex, age, viable myocardium, collateral circulation, treatment type and others, only treatment type was significantly associated with therapeutic effects (OR 3.872, 95% CI 1.915-7.830, P < .001). CONCLUSION: Collateral circulation can preserve resting myocardial blood perfusion and myocardial viability, and help maintain the function of the left ventricular myocardium. The appropriate treatment strategy will have a substantial impact on the therapeutic outcome.

Evaluation of left ventricular volumes and ejection fraction by 99mTc-MIBI gated SPECT and 18F-FDG gated PET in patients with prior myocardial infarction.

BACKGROUND: This study aimed to compare the accuracy of gated-SPECT (GSPECT) and gated-PET (GPET) in the assessment of left ventricular (LV) end-diastolic volumes (EDVs), end-systolic volumes (ESVs) and LV ejection fractions (LVEFs) among patients with prior myocardial infarction (MI). METHODS: One hundred and sixty-eight consecutive patients with MI who underwent GSPECT and GPET were included. Of them, 76 patients underwent CMR in addition to the two imaging modalities. The measurements of LV volumes and LVEF were performed using Quantitative Gated SPECT (QGS), Emory Cardiac Toolbox (ECTB), and 4D-MSPECT (4DM). RESULTS: The correlation between GPET, GSPECT, and CMR were excellent for LV EDV (r = 0.855 to 0.914), ESV (r = 0.852 to 0.949), and LVEF (r = 0.618 to 0.820), as calculated from QGS, ECTB, and 4DM. In addition, subgroup analysis revealed that EDV, ESV, and LVEF measured by GPET were accurate in patients with different extents of total perfusion defect (TPD), viable myocardium, and perfusion/metabolic mismatch. Furthermore, multivariate regression analysis identified that mismatch score was associated with the difference in EDV (P < 0.05) measurements between GPET and CMR. CONCLUSIONS: In patients with MI, LV volumes and LVEF scores measured by both GSPECT and GPET imaging were comparable to those determined by CMR, but should not be interchangeable in individual patients.

Relationship of myocardial hibernation, scar, and angiographic collateral flow in ischemic cardiomyopathy with coronary chronic total occlusion.

BACKGROUND: The relationship between myocardial viability and angiographic collateral flow is not fully elucidated in ischemic cardiomyopathy (ICM) with coronary artery chronic total occlusion (CTO). We aimed to clarify the relationship between myocardial hibernation, myocardial scar, and angiographic collateral flow in these patients. METHODS AND RESULTS: Seventy-one consecutive ICM patients with 122 CTOs and 652 dysfunctional segments within CTO territories were retrospectively analyzed. Myocardial hibernation (perfusion-metabolism mismatch) and the extent of 18F-fluorodeoxyglucose (FDG) abnormalities were assessed using 99mTc-sestamibi and 18F-FDG imaging. Myocardial scar was evaluated by late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) imaging. Collateral flow observed on coronary angiography was assessed using Rentrop classification. In these patients, neither the extent nor frequency of myocardial hibernation or scar was related to the status of collateral flow. Moreover, the matching rate in determining myocardial viability was poor between any 2 imaging indices. The extent of 18F-FDG abnormalities was linearly related to the extent of LGE rather than myocardial hibernation. Of note, nearly one-third (30.4%) of segments with transmural scar still had hibernating tissue. Hibernation and non-transmural scar had higher sensitivity (63.0% and 66.7%) than collateral flow (37.0%) in predicting global functional improvement. CONCLUSIONS: Angiographic collateral cannot accurately predict myocardial viability, and has lower sensitivity in prediction of functional improvement in CTO territories in ICM patients. Hence, assessment of myocardial viability with non-invasive imaging modalities is of importance. Moreover, due to the lack of correlation between myocardial hibernation and scar, these two indices are complementary but not interchangeable.

Dual-time-point myocardial 18F-FDG imaging in the detection of coronary artery disease.

BACKGROUND: Myocardial 18F-deoxyglucose (18F-FDG) uptake has been observed to be enhanced in patients with coronary artery disease (CAD) under fasting conditions. However, whether the increased 18F-FDG is induced by myocardial ischemia and how to discriminate ischemic from physiological 18F-FDG uptake have rarely been investigated. METHODS: Under fasting conditions, 18F-FDG PET imaging was performed in 52 patients with suspected CAD. Two 18F-FDG imaging sessions were conducted within two hours after a single administration of 18F-FDG (dual-time-point imaging), and with an intervention of an exercise test after the first imaging. Abnormal 18F-FDG uptake was determined by the classification of the 18F-FDG distribution pattern, and the changes of the 18F-FDG distribution between the two PET imaging sessions were analyzed. 99mTc-sestamibi was injected at peak exercise and myocardial perfusion imaging (MPI) was conducted after 18F-FDG imaging. Coronary angiography was considered the reference for diagnosing CAD. RESULTS: Overall, 54.8% (17/31) of CAD patients and 36.2% (21/58) of stenotic coronaries showed exercise-induced abnormal uptake of 18F-FDG. Based on the classification of the 18F-FDG distribution pattern, the sensitivity and specificity of exercise 18F-FDG imaging to diagnose CAD was 80.6% and 95.2% by patient analysis, 56.9% and 98.0% by vascular analysis, respectively. Compared with MPI, 18F-FDG imaging had a tendency to have higher sensitivity (80.6% vs 64.5%, P = 0.06) on the patient level. CONCLUSION: Myocardial ischemia can induce 18F-FDG uptake. With the classification of the 18F-FDG distribution pattern, dual-time-point 18F-FDG imaging under fasting conditions is efficient in diagnosing CAD.

Abnormalities of myocardial perfusion and glucose metabolism in patients with isolated left ventricular non-compaction.

BACKGROUND: The prevalence of myocardial perfusion and glucose metabolic abnormalities and their significance in patients with isolated left ventricular non-compaction (ILVNC) have not been well investigated. METHODS: Seventeen ILVNC patients who underwent cardiac magnetic resonance (CMR) and (99m)Tc-sestamibi SPECT/fluorine-18 deoxyglucose ((18)F-FDG) PET imaging were included. Left ventricular non-compaction, regional wall motion abnormalities, left ventricular ejection fraction (LVEF), and delayed enhancement (DE) were estimated using CMR. Myocardial perfusion and metabolism were evaluated with SPECT/PET. RESULTS: Ninety-five (32.9%) segments were considered non-compacted. DE was present in 52 (18.0%) segments and 10 (58.8%) patients. The rate of occurrence of DE was significantly higher in compacted segments than in non-compacted segments (22.7% vs 8.4%, P = .003). Myocardial perfusion abnormalities were present in 92 (31.8%) segments, of which 66 were perfusion/metabolism match and 26 were perfusion/metabolism mismatch. The rate of occurrence of perfusion abnormality was similar between compacted and non-compacted segments (32.0% vs 31.6%, P = .948), but it was significantly higher in segments with DE than in those without DE (51.9% vs 27.4%, P = .001). None of the imaging features alone (non-compaction, DE, perfusion abnormalities, match or mismatch) showed significant correlations with LVEF (all P > .05). CONCLUSION: In the current study, myocardial perfusion/metabolism mismatch and match were observed in both non-compacted and compacted myocardium in ILVNC patients. Further research is warranted to determine their pathologic and clinical significance.

Characterization of kidneys in patients with systemic sclerosis by multi-parametric magnetic resonance quantitative imaging.

PURPOSE: To determine the usefulness of multiparametric magnetic resonance (MR) quantitative imaging in characterizing the kidneys in systemic sclerosis (SSc) patients. MATERIAL AND METHODS: Forty-six SSc patients (47.9 ± 12.8 years, 40 females) and 22 age- and sex- matched healthy volunteers (46.1 ± 13.8 years, 20 females) were recruited and underwent renal MR imaging by acquiring blood oxygen level dependent and saturated multi-delay renal arterial spin labeling (SAMURAI) sequences. The T2* value, T1 value, renal blood flow (RBF), arterial bolus arrival time (aBAT), and tissue bolus arrival time (tBAT) of renal cortex were measured and compared among diffuse cutaneous SSc (dcSSc) and limited cutaneous SSc (lcSSc) groups and healthy controls using One-way ANOVA and analyzed by logistic regression. RESULTS: Compared to healthy volunteers, SSc patients with normal estimated glomerular filtration rate (n = 40) had significantly lower T2* value (P = 0.026) in the left renal cortex, longer T1 value (right: P = 0.015; left: P = 0.023), lower RBF (right: P < 0.001; left: P < 0.001), and shorter tBAT (right: P < 0.001; left: P = 0.005) in both right and left renal cortex after adjusting for demographics. The dcSSc patients (n = 23) had significantly lower RBF in both right (226.7 ± 65.2 mL/100 g/min vs. 278.2 ± 73.5 mL/100 g/min, P = 0.022) and left (194.5 ± 71.5 mL/100 g/min vs. 252.7 ± 84.4 mL/100 g/min, P = 0.020) renal cortex compared to the lcSSc patients (n = 23) after adjusting for demographics, but the significance of the difference was attenuated after further adjusting for modified Rodnan skin score and digital ulcers. CONCLUSION: Multi-parametric MR quantitative imaging, particularly multi-delay ASL perfusion imaging, is a useful technique for characterizing the kidneys and classification of SSc patients.

Left ventricular functional changes after adenosine vasodilator stress evaluated by gated single-photon emission computed tomography.

OBJECTIVES: Gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging is useful in assessing left ventricular (LV) myocardial perfusion and function. This study evaluated the LV functional changes after adenosine vasodilator stress, using gated SPECT. METHODS: The study population consisted of 70 patients who underwent adenosine-mediated stress and rest SPECT. All patients underwent coronary angiography. Semi-quantitative assessment of perfusion was analyzed and produced the summed rest score (SRS), the summed stress score (SSS) and the summed difference score (SDS). The global LV function parameters [ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV)] and regional LV function [the summed motion score (SMS) and the summed thickening score (STS)] were quantified by gated SPECT. RESULTS: Patients were divided into 2 groups: group 1 comprised 16 patients with worsening of LVEF (LVEFrest-LVEFado ≥5%), and group 2 comprised the other 54 patients. Compared with group 2, patients in group 1 had a significantly higher SSS and SDS (9.1 ± 6.8 vs. 5.6 ± 4.5 and 6.6 ± 3.8 vs. 3.6 ± 4.0, respectively; p < 0.05) and the severity of coronary artery stenosis was more serious (p < 0.05). CONCLUSION: Worsening of LVEF after adenosine-induced vasodilator stress, as shown by (99m)Tc-MIBI gated SPECT, is a valuable nonperfusion marker of significant CAD.

Characterization and Assessment of Projection Probability Density Function and Enhanced Sampling in Self-Collimation SPECT.

We have recently reported a self-collimation SPECT (SC-SPECT) design concept that constructs sensitive detectors in a multi-ring interspaced mosaic architecture to simultaneously improve system spatial resolution and sensitivity. In this work, through numerical and Monte-Carlo simulation studies, we investigate this new design concept by analyzing its projection probability density functions (PPDF) and the effects of enhanced sampling, i.e. having rotational and translational object movements during imaging. We first quantitatively characterize PPDFs by their widths and edge slopes. Then we compare the PPDFs of an SC-SPECT and a series of multiple-pinhole SPECT (MPH-SPECT) systems and assess the impact of PPDFs - combined with enhanced sampling - on image contrast recovery coefficient and variance through phantom studies. We show the PPDFs of SC- SPECT have steeper edges and a wider range of width, and these attributes enable SC-SPECT to achieve better performance.

Diffusing capacity of lungs for carbon monoxide associated with subclinical myocardial impairment in systemic sclerosis: A cardiac MR study.

BACKGROUND: Systemic sclerosis (SSc) is characterised by microvascular and fibrotic lesions, which are located not only in skin but also in lungs and heart. OBJECTIVE: This study aimed to investigate the association between lung function and myocardial T1 values using cardiac MR (CMR) imaging in patients with SSc without cardiovascular symptoms. METHODS: The SSc patients and age- and sex-matched healthy subjects underwent CMR. The cardiac function and native T1 values of myocardium and lung function were measured. Spearman's rank correlations and linear regression analyses were performed to determine the association between lung function and myocardial T1. RESULTS: Forty-five SSc patients (aged 47.7±13.2 years, 40 females) and 23 (aged 46.0±14.4 years, 20 females) healthy subjects were enrolled. SSc patients exhibited considerably higher native T1 values compared with healthy subjects (1305.9±49.8 ms vs 1272.6±37.6 ms, p=0.006). Linear regression analysis revealed that decrease of diffusing capacity of lungs for carbon monoxide (DLCO) in SSc patients was notably associated with myocardial native T1 value before (ß -1.017; 95% CI -1.883 to -0.151; p=0.022) and after adjusting for confounding factors (ß -1.108; 95% CI -2.053 to -0.164; p=0.023). Moderate-to-severe decrease of DLCO was found to be significantly associated with myocardial native T1 value (ß 48.006; 95% CI 17.822 to 78.190; p=0.003) after adjusting for confounding factors. CONCLUSION: DLCO inversely correlates with myocardial native T1 values in SSc patients, particularly moderate-to-severely decreased DLCO, suggesting that DLCO might be a potential indicator for subclinical myocardial impairment in SSc patients.

Study of 99mTc absorption on micro-sized ion exchange resins to achieve high activity for SPECT.

In single-photon emission computed tomography (SPECT), a micro-sized 99mTc source is routinely used for performance measurement, geometry calibration, and system matrix generation. Therefore, a micro-sized source is critical in nuclear instrument production and quality control. Standard methods can only produce a point source with a large size and low total activity, as they are limited by the concentration of the 99mTc solution. The absorption of 99mTc on ion exchange resins has been used; however, few studies have quantitatively evaluated the absorption process and optimized the source activity. This paper proposes a procedure for producing a micro-sized 99mTc resin source with a super-high concentration, as well as a method for the fast measurement of the point source time-activity curve (TAC). Experiments on two resin point sources with diameters of 0.681 mm and 0.326 mm were carried out. Two semi-empirical models, including the first kinetic model and the pseudo-second-order rate equation model, were used to fit TACs. The results show the first kinetic model fit better, which suggests an acquisition time of 2-4 h is needed for optimization. The verification experiment demonstrates a resin point source with a diameter of 0.35 mm and total activity of 10.6 mCi (i.e., 59.1 Ci/mL concentration) was produced.

[Myocardial perfusion evaluation post percutaneous transluminal septal myocardial ablation in patients with hypertrophic obstructive cardiomyopathy by 99Tc(m) MIBI SPECT MPI].

OBJECTIVE: To evaluate the myocardial perfusion and function in patients with hypertrophic obstructive cardiomyopathy (HOCM) before and after percutaneous transluminal septal myocardial ablation (PTSMA). METHODS: Sixty-eight patients with hypertrophic obstructive cardiomyopathy were included and (99)Tc(m)-MIBI SPECT MPI was applied before and at 1 week after PTSMA, six-month follow-up was finished in 11 patients. Semi quantity and QGS quantity perfusion and function assessment was performed in 17 LV segments. RESULTS: Myocardial perfusion post-PTSMA was significantly reduced in 98% patients, especially in basal anterosepta, basal interseptal, mid-anteroseptal, mid-interseptal and apical septal segments compared with pre-PTSMA (all P < 0.05). Perfusion was significantly increased at 6 months follow-up than at 1 week post-PTSMA but still lower than pre-PTSMA (all P < 0.05). LVEF (evaluated by gated SPECT) was similar before and after the procedure (P > 0.05). Regional wall motion after PTSMA was lower than pre-PTSMA in basal anterior, basal anteroseptal, basal interseptal and basal inferior (P < 0.05). Regional wall thinkening was lower than pre-PTSMA in basal interseptal, mid-anteroseptal, mid-interseptal (P < 0.05). CONCLUSIONS: (99)Tc(m) MIBI SPECT can be used to monitor myocardial perfusion post PTSMA in patients with HOCM.

The Availability of the α7-Nicotinic Acetylcholine Receptor in Early Identification of Vulnerable Atherosclerotic Plaques: A Study Using a Novel 18F-Label Radioligand PET.

Background: It has been confirmed that the α7-nicotinic acetylcholine receptor (α7nAChR) is an important target for identifying vulnerable atherosclerotic plaques. Previously, we successfully designed and synthesized a series of 18F-labeled PET molecular probes targeting α7nAChR, which are mainly used in the diagnosis of Alzheimer's disease. Based on the characteristics of α7nAChR in blood vessels, we have firstly screened for a suitable novel 18F-labeled PET molecular probe ([18F]YLF-DW), with high selectivity for α7nAChR over α4ß2nAChR and a good effect for the imaging of atherosclerotic animal models, to effectively identify vulnerable atherosclerotic plaques at an early stage. Meanwhile, we compared it with the "gold standard" pathological examination of atherosclerosis, to verify the reliability of [18F]YLF-DW in early diagnosis of atherosclerosis. Methods: The vulnerable atherosclerotic plaques model of ApoE-/-mice were successfully established. Then based on the methods of 3D-QSAR and molecular docking, we designed oxazolo[4,5-b] pyridines and fluorenone compounds, which are targeted at α7nAChR. Through further screening, a novel alpha7 nicotinic acetylcholine receptor radioligand ([18F]YLF-DW) was synthesized and automatically 18F-labeled using a Stynthra RNplus module. Subsequently, we employed [18F]YLF-DW for the targeting of α7nAChR in atherosclerotic plaques and control group, using a micro-PET/CT respectively. After imaging, the mice were sacrificed by air embolism and the carotid arteries taken out for making circular sections. The paraffin embedded specimens were sectioned with 5 µm thickness and stained with oil red. After staining, immunohistochemistry experiment was carried out to verify the effect of micro-PET/CT imaging. Results: The micro-PET/CT imaging successfully identified the vulnerable atherosclerotic plaques in the carotid arteries of ApoE-/-mice; whereas, no signal was observed in normal control mice. In addition, compared with the traditional imaging agent [18F]FDG, [18F]YLF-DW had a significant effect on the early plaques imaging of carotid atherosclerosis. The results of oil red staining and immunohistochemistry also showed early formations of carotid plaques in ApoE-/-mice and provided pathological bases for the evaluation of imaging effect. Conclusion: We innovated to apply the novel molecular probe ([18F]YLF-DW) to the identification of vulnerable atherosclerotic plaques in carotid arteries, to detect atherosclerosis early inflammatory response and provide powerful input for the early diagnosis of atherosclerotic lesions, which may play an early warning role in cardiovascular acute events.

Likely Common Role of Hypoxia in Driving 18F-FDG Uptake in Cancer, Myocardial Ischemia, Inflammation and Infection.

First introduced in 1976, 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) has become an indispensable tool for diagnosis and prognostic evaluation of tumors, heart disease, as well as other conditions, including inflammation and infection. Because 18F-FDG can accurately reflect the glucose metabolism level of organs and tissues, it is known as a "century molecule" and is currently the main agent for PET imaging. The degree of 18F-FDG uptake by cells is related to both the rate of glucose metabolism and glucose transporter expression. These, in turn, are strongly influenced by hypoxia, in which cells meet their energy needs through glycolysis, and 18F-FDG uptake increased due to hypoxia. 18F-FDG uptake is a complex process, and hypoxia may be one of the fundamental driving forces. The correct interpretation of 18F-FDG uptake in PET imaging can help clinics make treatment decisions more accurately and effectively. In this article, we review the application of 18F-FDG PET in tumors, myocardium, and inflammation. We discuss the relationship between 18F-FDG uptake and hypoxia, the possible mechanism of 18F-FDG uptake caused by hypoxia, and the associated clinical implications.

Rescue Protocol to Improve the Image Quality of 18F-FDG PET/CT Myocardial Metabolic Imaging.

PURPOSE: 18F-FDG PET myocardial metabolic imaging is used to estimate myocardial viability. However, poor image quality can affect the accurate quantification of viable myocardium. We assessed the feasibility of a rescue protocol that reinjected low-dose 18F-FDG with simultaneous 1 to 2 U of insulin injection and oral administration of 10 g of glucose to improve the image quality of 18F-FDG PET myocardial metabolic imaging. PATIENTS AND METHODS: Fifty-one consecutive patients with poor quality to uninterpretable 18F-FDG PET/CT myocardial metabolic images received the rescue protocol immediately after the initial image acquisition. The postrescue image acquisition was performed 1 hour later. The rescue image quality was compared with the initial image. The qualitative visual estimation of the images was graded as follows: grade 0, homogeneous, minimal uptake; grade 1, predominantly minimal or mild uptake; grade 2, moderate uptake; and grade 3, good uptake. The myocardium-to-blood pool activity ratio (M/B) was measured to assess the image quality quantitatively. RESULTS: The grades of 0 to 3 were observed in 24 (47%), 27 (53%), 0 (0%), and 0 (0%) patients, respectively, for the initial imaging, and in 0 (0%), 3 (5.9%), 4 (7.8%), and 44 (86.3%) patients for the rescue imaging (P < 0.001). The rescue M/B was significantly higher than the initial M/B (3.4 ± 1.4 vs 1.6 ± 0.6, respectively; P < 0.001). CONCLUSIONS: The rescue protocol successfully and rapidly improved the quality of myocardial 18F-FDG metabolic imaging.

Self-Collimating SPECT With Multi-Layer Interspaced Mosaic Detectors.

Conventional single photon emission computed tomography (SPECT) relies on mechanical collimation whose resolution and sensitivity are interdependent, the best performance a SPECT system can attain is only a compromise of these two equally desired properties. To simultaneously achieve high resolution and sensitivity, we propose to use sensitive detectors constructed in a multi-layer in ter spaced mosaicdetectors (MATRICES) architecture to accomplish part of the collimation needed. We name this new approach self-collimation. We evaluate three self-collimating SPECT systems and report their imaging performance: 1) A simulated human brain SPECT achieves 3.88% sensitivity, it clearly resolves 0.5-mm and 1.0-mm hot-rod patterns at noise-free and realistic count-levels, respectively; 2) a simulated mouse SPECT achieves 1.25% sensitivity, it clearly resolves 50- [Formula: see text] and 100- [Formula: see text] hot-rod patterns at noise-free and realistic count-levels, respectively; 3) a SPECT prototype achieves 0.14% sensitivity and clearly separates 0.3-mm-diameter point sources of which the center-to-center neighbor distance is also 0.3 mm. Simulated contrast phantom studies show excellent resolution and signal-to-noise performance. The unprecedented system performance demonstrated by these 3 SPECT scanners is a clear manifestation of the superiority of the self-collimating approach over conventional mechanical collimation. It represents a potential paradigm shift in SPECT technology development.

Exercise (18)FDG imaging for the detection of CAD: What are the clinical hurdles?

Myocardial perfusion imaging (MPI) has been in clinical use for over 30 years, providing an effective, reliable, and relatively simple tool for diagnosis, risk stratification, and follow-up of patients with suspected or know coronary artery disease (CAD). The unique strength of nuclear imaging is its ability to provide tools for imaging biochemical and metabolic processes, and receptor and transporter functions at molecular and cellular levels in intact organisms under various physiologic conditions. Metabolic imaging using radiolabeled glucose analogues ((18)F-fluorodeoxyglucose [(18)FDG]) provides a unique ability to image myocardial ischemia directly ("hot spot" imaging) in patients with known or suspected CAD. Exercise (18)FDG imaging can potentially overcome some of the limitations of currently used stress-rest MPI. In this article, we describe recent studies using exercise (18)FDG for imaging myocardial ischemia and its potential use in routine clinical practice.

Correction to: IGF-1C domain-modified hydrogel enhanced the efficacy of stem cells in the treatment of AMI.

An amendment to this paper has been published and can be accessed via the original article.