Role of F-18 FDG positron emission tomography (PET) in the assessment of myocardial viability

The Curious Case of the Missing Limb on FDG PET Imaging

ABSTRACT

A 58-year-old woman with poorly controlled diabetes, peripheral vascular disease, and end-stage renal disease requiring hemodialysis was referred for 18 F-FDG PET/CT to evaluate for source of sepsis. She had history of prior left forefoot and right second toe amputation, as well as left lower-limb dry gangrene for which she declined surgical management. We present a case of a nonamputated lower limb demonstrating regions of absolute photopenia, consistent with dry gangrene.

Positron Emission Tomography (PET) with 18F-FGA for Diagnosis of Myocardial Infarction in a Coronary Artery Ligation Model

Location and extent of necrosis are valuable information in the management of myocardial infarction (MI). Methods. We investigated 2-deoxy-2-18F-fluoro glucaric acid (FGA), a novel infarct-avid agent, for positron emission tomography (PET) of MI. We synthesized FGA from commercially available 18F-fluoro-2-deoxy-2-D-glucose (FDG). MI was induced in mice by permanently occluding the left anterior descending coronary artery. Biodistribution of FGA was assessed 1 h after FGA injection (11 MBq). PET/CT was conducted 1 h, 6 h, 1 d, 3 d, and 4 d after MI. Subcellular compartment of FGA accumulation in necrosis was studied by tracing the uptake of biotin-labeled glucaric acid with streptavidin-HRP in H2O2-treated H9c2 cardiomyoblasts. Streptavidin-reactive protein bands were identified by LC-MS/MS. Results. We obtained a quantitative yield of FGA from FDG within 7 min ( $\text{radiochemical}\text{purity}>99\%$ ). Cardiac uptake of FGA was significantly higher in MI mice than that in control mice. Imaging after 1 h of FGA injection delineated MI for 3 days after MI induction, with negligible background signal from surrounding tissues. Myocardial injury was verified by tetrazolium staining and plasma troponin (47.63 pg/mL control versus 311.77 pg/mL MI). In necrotic H9c2 myoblasts, biotinylated glucaric acid accumulated in nuclear fraction. LC-MS/MS primarily identified fibronectin in necrotic cells as a putative high fidelity target of glucaric acid. Conclusion. FGA/PET detects infarct early after onset of MI and FGA accumulation in infarct persists for 3 days. Its retention in necrotic cells appears to be a result of interaction with fibronectin that is known to accumulate in injured cardiac tissue.

Incremental value of myocardial wall motion and thickening to perfusion alone by gated SPECT myocardial perfusion imaging for viability assessment in patients with ischemic heart failure

PURPOSE

The objective of this study was to assess the incremental value of myocardial wall motion and thickening compared with perfusion alone obtained from gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) in diagnosing myocardial viability in patients with ischemic heart failure.

METHODS

Eighty-three consecutive patients with ischemic heart failure who underwent both 99mTc-MIBI gated SPECT MPI and 18F-FDG positron emission tomography (PET) myocardial metabolic imaging were retrospectively enrolled. SPECT/PET myocardial viability was defined as the reference standard. Segmental myocardial perfusion, wall motion, and thickening were measured by an automated algorithm from gated SPECT MPI. Univariate and stepwise multivariate analysis were conducted to establish an optimal multivariate model for predicting hibernating myocardium and scar.

RESULTS

Among the 1411 segments evaluated, 774 segments had normal perfusion and 637 segments had decreased perfusion. The latter were classified by 18F-FDG PET into 338 hibernating segments and 299 scarred segments. The multivariate regression analysis showed that the model that combined myocardial perfusion uptake with wall motion and thickening scores had the optimal predictive efficiency to distinguish hibernating myocardium from scar in the segments with decreased perfusion. The model had the largest C-statistic (0.753 vs 0.666, P < 0.0001), and the global chi-square was increased from 53.281 to 111.234 when compared with perfusion alone (P < 0.001).

CONCLUSIONS

Assessment of myocardial wall motion and thickening in addition to conventional perfusion uptake in the segments with decreased perfusion enables better differentiation of hibernating myocardium from scar in patients with ischemic heart failure. Considering wide availability and high cost-effectiveness, regional myocardial function integrated with perfusion on gated SPECT MPI has great promise to become a clinical tool in the assessment of myocardial viability.

Molecular imaging of myogenic stem/progenitor cells with [18F]-FHBG PET/CT system in SCID mice model of post-infarction heart

Preclinical and clinical studies have shown that stem cells can promote the regeneration of damaged tissues, but therapeutic protocols need better quality control to confirm the location and number of transplanted cells. This study describes in vivo imaging while assessing reporter gene expression by its binding to a radiolabelled molecule to the respective receptor expressed in target cells. Five mice underwent human skeletal muscle-derived stem/progenitor cell (huSkMDS/PC EF1-HSV-TK) intracardial transplantation after induction of myocardial infarction (MI). The metabolic parameters of control and post-infarction stem progenitor cell-implanted mice were monitored using 2-deoxy-18F-fluorodeoxyglucose ([18F]-FDG) before and after double promotor/reporter probe imaging with 9-(4-18F-fluoro-3-[hydroxymethyl]butyl)guanine ([18F]-FHBG) using positron emission tomography (PET) combined with computed tomography (CT). Standardized uptake values (SUVs) were then calculated based on set regions of interest (ROIs). Experimental animals were euthanized after magnetic resonance imaging (MRI). Molecular [18F]-FHBG imaging of myogenic stem/progenitor cells in control and post-infarction mice confirmed the survival and proliferation of transplanted cells, as shown by an increased or stable signal from the PET apparatus throughout the 5 weeks of monitoring. huSkMDS/PC EF1-HSV-TK transplantation improved cardiac metabolic ([18F]-FDG with PET) and haemodynamic (MRI) parameters. In vivo PET/CT and MRI revealed that the precise use of a promotor/reporter probe incorporated into stem/progenitor cells may improve non-invasive monitoring of targeted cellular therapy in the cardiovascular system.

Extracellular vesicles from human embryonic stem cell-derived cardiovascular progenitor cells promote cardiac infarct healing through reducing cardiomyocyte death and promoting angiogenesis

Human pluripotent stem cells (hPSCs)-derived cardiovascular progenitor cells (CVPCs) are a promising source for myocardial repair, while the mechanisms remain largely unknown. Extracellular vesicles (EVs) are known to mediate cell–cell communication, however, the efficacy and mechanisms of hPSC-CVPC-secreted EVs (hCVPC-EVs) in the infarct healing when given at the acute phase of myocardial infarction (MI) are unknown. Here, we report the cardioprotective effects of the EVs secreted from hESC-CVPCs under normoxic (EV-N) and hypoxic (EV-H) conditions in the infarcted heart and the long noncoding RNA (lncRNA)-related mechanisms. The hCVPC-EVs were confirmed by electron microscopy, nanoparticle tracking, and immunoblotting analysis. Injection of hCVPC-EVs into acutely infracted murine myocardium significantly improved cardiac function and reduced fibrosis at day 28 post MI, accompanied with the improved vascularization and cardiomyocyte survival at border zones. Consistently, hCVPC-EVs enhanced the tube formation and migration of human umbilical vein endothelial cells (HUVECs), improved the cell viability, and attenuated the lactate dehydrogenase release of neonatal rat cardiomyocytes (NRCMs) with oxygen glucose deprivation (OGD) injury. Moreover, the improvement of the EV-H in cardiomyocyte survival and tube formation of HUVECs was significantly better than these in the EV-N. RNA-seq analysis revealed a high abundance of the lncRNA MALAT1 in the EV-H. Its abundance was upregulated in the infarcted myocardium and cardiomyocytes treated with hCVPC-EVs. Overexpression of human MALAT1 improved the cell viability of NRCM with OGD injury, while knockdown of MALAT1 inhibited the hCVPC-EV-promoted tube formation of HUVECs. Furthermore, luciferase activity assay, RNA pull-down, and manipulation of miR-497 levels showed that MALAT1 improved NRCMs survival and HUVEC tube formation through targeting miR-497. These results reveal that hCVPC-EVs promote the infarct healing through improvement of cardiomyocyte survival and angiogenesis. The cardioprotective effects of hCVPC-EVs can be enhanced by hypoxia-conditioning of hCVPCs and are partially contributed by MALAT1 via targeting the miRNA.

Human Radiation Dosimetry for Orally and Intravenously Administered 18F-FDG

Intravenous access is difficult in some patients referred for ¹⁸F-FDG PET imaging. Extravasation at the injection site and accumulation in central catheters can lead to limited tumor ¹⁸F-FDG uptake, erroneous quantitation, and significant image artifacts. In this study, we compared the human biodistribution and dosimetry for ¹⁸F-FDG after oral and intravenous administrations sequentially in the same subjects to ascertain the dosimetry and potential suitability of orally administered ¹⁸F-FDG as an alternative to intravenous administration. We also compared our detailed intravenous ¹⁸F-FDG dosimetry with older dosimetry data. Methods: Nine healthy volunteers (6 male and 3 female; aged 19-32 y) underwent PET/CT imaging after oral and intravenous administration of ¹⁸F-FDG. Identical preparation and imaging protocols (except administration route) were used for oral and intravenous studies. During each imaging session, 9 whole-body PET scans were obtained at 5, 10, 20, 30, 40, 50, 60, 120, and 240 min after ¹⁸F-FDG administration (370 ± 16 MBq). Source organ contours drawn using CT were overlaid onto registered PET images to extract time-activity curves. Time-integrated activity coefficients derived from time-activity curves were given as input to OLINDA/EXM for dose calculations. Results: Blood uptake after orally administered ¹⁸F-FDG peaked at 45-50 min after ingestion. The oral-to-intravenous ratios of ¹⁸F-FDG uptake for major organs at 45 min were 1.07 ± 0.24 for blood, 0.94 ± 0.39 for heart wall, 0.47 ± 0.12 for brain, 1.25 ± 0.18 for liver, and 0.84 ± 0.24 for kidneys. The highest organ-absorbed doses (μGy/MBq) after oral ¹⁸F-FDG administration were observed for urinary bladder (75.9 ± 17.2), stomach (48.4 ± 14.3), and brain (29.4 ± 5.1), and the effective dose was significantly higher (20%) than after intravenous administration (P = 0.002). Conclusion: ¹⁸F-FDG has excellent bioavailability after oral administration, but peak organ activities occur later than after intravenous injection. These data suggest PET at 2 h after oral ¹⁸F-FDG administration should yield images that are comparable in biodistribution to conventional clinical images acquired 1 h after injection. Oral ¹⁸F-FDG is a palatable alternative to intravenous ¹⁸F-FDG when venous access is problematic.

Multimodal and Multiscale Analysis Reveals Distinct Vascular, Metabolic and Inflammatory Components of the Tissue Response to Limb Ischemia

Ischemia triggers a complex tissue response involving vascular, metabolic and inflammatory changes.

Methods: We combined hybrid SPECT/CT or PET/CT nuclear imaging studies of perfusion, metabolism and inflammation with multicolor flow cytometry-based cell population analysis to comprehensively analyze the ischemic tissue response and to elucidate the cellular substrate of noninvasive molecular imaging techniques in a mouse model of hind limb ischemia.

Results: Comparative analysis of tissue perfusion with [^99mTc]-Sestamibi and arterial influx with [^99mTc]-labeled albumin microspheres by SPECT/CT revealed a distinct pattern of response to vascular occlusion: an early ischemic period of matched suppression of tissue perfusion and arterial influx, a subacute ischemic period of normalized arterial influx but impaired tissue perfusion, and a protracted post-ischemic period of hyperdynamic arterial and normalized tissue perfusion, indicating coordination of macrovascular and microvascular responses. In addition, the subacute period showed increased glucose uptake by [¹⁸F]-FDG PET/CT scanning as the metabolic response of viable tissue to hypoperfusion. This was associated with robust macrophage infiltration by flow cytometry, and glucose uptake studies identified macrophages as major contributors to glucose utilization in ischemic tissue. Furthermore, imaging with the TSPO ligand [¹⁸F]-GE180 showed a peaked response during the subacute phase due to preferential labeling of monocytes and macrophages, while imaging with [⁶⁸Ga]-RGD, an integrin ligand, showed prolonged post-ischemic upregulation, which was attributed to labeling of macrophages and endothelial cells by flow cytometry.

Conclusion: Combined nuclear imaging and cell population analysis reveals distinct components of the ischemic tissue response and associated cell subsets, which could be targeted for therapeutic interventions.

Imaging the myocardial ischemic cascade

Non-invasive imaging plays a growing role in the diagnosis and management of ischemic heart disease from its earliest manifestations of endothelial dysfunction to myocardial infarction along the myocardial ischemic cascade. Experts representing the North American Society for Cardiovascular Imaging and the European Society of Cardiac Radiology have worked together to organize the role of non-invasive imaging along the framework of the ischemic cascade. The current status of non-invasive imaging for ischemic heart disease is reviewed along with the role of imaging for guiding surgical planning. The issue of cost effectiveness is also considered. Preclinical disease is primarily assessed through the coronary artery calcium score and used for risk assessment. Once the patient becomes symptomatic, other imaging tests including echocardiography, CCTA, SPECT, PET and CMR may be useful. CCTA appears to be a cost-effective gatekeeper. Post infarction CMR and PET are the preferred modalities. Imaging is increasingly used for surgical planning of patients who may require coronary artery bypass.

Imaging of isoproterenol-induced myocardial injury with 18F labeled fluoroglucaric acid in a rat model

Positron emission tomography (PET) of myocardial infarction (MI) by infarct avid imaging has the potential to reduce the time to diagnosis and improve diagnostic accuracy. The objective of this work was to synthesize ¹⁸F-labeled glucaric acid (FGA) for PET imaging of isoproterenol-induced cardiomyopathy in a rat model.

METHODS

We synthesized ¹⁸F-FGA by controlled oxidation of ¹⁸F-fluorodeoxy glucose (FDG), mediated by 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) in presence of NaBr and NaOCl in highly-buffered reaction conditions. After ascertaining preferential uptake of ¹⁸F-FGA in necrotic as compared to normal H9c2 myoblasts, the biodistribution and circulation kinetics of ¹⁸F-FGA was assessed in mice. Moreover, the potential of ¹⁸F-FGA to image myocardial damage was investigated in a rat model of isoproterenol-induced cardiomyopathy. Isoproterenol-induced myocardial injury was verified at necropsy by tissue staining and plasma cardiac troponin levels.

RESULTS

Synthesis of radiochemically pure ¹⁸F-FGA was accomplished by a 5 min, one step oxidation of ¹⁸F-FDG. Reaction yield was quantitative and no side-products were detected. Biodistribution studies showed rapid elimination from the body (k_e = 0.83 h^-1); the major organ of ¹⁸F-FGA accumulation was kidney. In the rat model, isoproterenol-treatment resulted in significant increase in cardiac troponin. PET images showed that the hearts of isoproterenol-treated rats accumulated significant amounts of ¹⁸F-FGA, whereas healthy hearts showed negligible uptake of ¹⁸F-FGA. Target-to-nontarget contrast for ¹⁸F-FGA accumulation became significantly more pronounced in 4 h images as compared to images acquired 1 h post-injection.

CONCLUSION

¹⁸F-FGA can be easily and quantitatively synthesized from ubiquitously available ¹⁸F-FDG as a precursor. The resultant ¹⁸F-FGA has a potential to serve as an infarct-avid agent for PET imaging of MI. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: ¹⁸F-FGA/PET will complement existing perfusion imaging protocols in therapeutic decision making, determination of revascularization candidacy and success, differentiation of ischemia from necrosis in MI, discrimination of myocarditis from infarction, and surveillance of heart transplant rejection.

Preclinical PET imaging of HIP/PAP using 1'-18F-fluoroethyl-β-D-lactose

Purpose

This study aims at preclinical evaluation of a recently reported lactose analogue, 1'-¹⁸F-fluoroethyl-β-D-lactose (¹⁸F-FEL), in binding to hepatocarcinoma-intestine-pancreas and pancreatitis-associated protein (HIP/PAP) in vitro and in vivo.

Methods

In this study, a multifunctional module was employed for the automated synthesis of ¹⁸F-FEL. Additional radiochemical purity, biodistribution, in vitro and in vivo competition, metabolic stability and micro-PET studies were performed using T3M4 and SK-BR-3 xenografts. Expression of HIP/PAP in T3M4 and SK-BR-3 tumor sections and cell lines were tested with immunohistochemistry (IHC) and western blot analysis.

Results

The synthesis of ¹⁸F-FEL was completed in 30 min, with a radiochemical yield of 20 ± 5% and specific activity of 14.2 ± 7.1 GBq/μmol. ¹⁸F-FEL exhibited high HIP/PAP-binding affinity with a half maximal inhibitory concentration (IC50) of 22.0 ± 4.0 nM. ¹⁸F-FEL demonstrated high stability and specific tumor accumulation, which was reduced by approximately 80% in a PET competition assay by co-injection of β-D-lactose. High expression of HIP/PAP was detected in T3M4 tumors and cell line, but negative result was found for SK-BR-3 cell line.

Conclusion

¹⁸F-FEL has a high binding property to HIP/PAP, high stability and excellent pharmacokinetics in vivo and therefore warrants further evaluation in a proof-of-concept study in humans.

Fabrication of Synthetic Mesenchymal Stem Cells for the Treatment of Acute Myocardial Infarction in Mice

RATIONALE

Stem cell therapy faces several challenges. It is difficult to grow, preserve, and transport stem cells before they are administered to the patient. Synthetic analogs for stem cells represent a new approach to overcome these hurdles and hold the potential to revolutionize regenerative medicine.

OBJECTIVE

We aim to fabricate synthetic analogs of stem cells and test their therapeutic potential for treatment of acute myocardial infarction in mice.

METHODS AND RESULTS

We packaged secreted factors from human bone marrow-derived mesenchymal stem cells (MSC) into poly(lactic-co-glycolic acid) microparticles and then coated them with MSC membranes. We named these therapeutic particles synthetic MSC (or synMSC). synMSC exhibited a factor release profile and surface antigens similar to those of genuine MSC. synMSC promoted cardiomyocyte functions and displayed cryopreservation and lyophilization stability in vitro and in vivo. In a mouse model of acute myocardial infarction, direct injection of synMSC promoted angiogenesis and mitigated left ventricle remodeling.

CONCLUSIONS

We successfully fabricated a synMSC therapeutic particle and demonstrated its regenerative potential in mice with acute myocardial infarction. The synMSC strategy may provide novel insight into tissue engineering for treating multiple diseases.

PET scan before CABG in diabetes

Background and objectives

Since the role of positron emission tomography (PET) scanning in diabetes is not clear, this study sought to assess the usefulness of PET scanning for viability in this patient group.

Methods

Forty-four per cent insulin-treated, and 56% non-insulin-treated diabetic patients with severely impaired left ventricular function (LVEF 29± 9%) underwent first coronary artery bypass grafting (CABG). Pre-operative viability was assessed by PET scan.

Results

Eighty-two per cent of patients received ≥3 grafts. Twenty-seven patients were discharged home and followed for a mean 3.5±1.6 years. Postoperative LVEF improved to 40±9 (p<0.0001). Multiple regression analysis indicated that the only variable that predicted improvement in global LV function was presence of hibernating segments at PET scan. The single variable that predicted deterioration of LVEF was the number of segments with reduced perfusion and metabolism at PET scan.

Conclusion

PET scan is an accurate tool for prediction of global left ventricular function recovery following CABG in people with diabetes.

Infection Imaging With (18)F-FDS and First-in-Human Evaluation

PURPOSE

The noninvasive imaging of bacterial infections is critical in order to reduce mortality and morbidity caused by these diseases. The recently reported (18)F-FDS ((18)F-2-fluorodeoxy sorbitol) as a PET (positron emission tomography) tracer can be used to image Enterobacteriaceae-specific infections and provides a potential alternative to this problem compared with other probes for imaging infections. In this study, automatic synthesis, validation of (18)F-FDS and a first-in-human study were performed and discussed.

METHODS

A multifunctional synthesis module was employed for the radiosynthesis of (18)F-FDG ((18)F-2-fluorodeoxy glucose) and (18)F-FDS starting from (18)F ion using two-pot three-step fully automated reactions. The behavior of (18)F-FDS as an in vivo imaging probe for infections was evaluated in an Escherichia coli mouse infection model. The first detailed pharmacokinetic and biodistribution parameters were obtained from healthy human volunteers.

RESULTS

The uptake of (18)F-FDS in an E. coli mouse-myositis infection model was easily differentiated from other organs and normal muscle. Intensive lesion uptake declined after antibiotic treatment. In the pilot human study, no adverse effects due to (18)F-FDS were observed up to 24 h post-injection. The radiotracer was rapidly cleared from the circulation and excreted mainly through the urinary system.

CONCLUSION

We conclude that (18)F-FDS PET holds great potential for appropriate and effective for the imaging of bacterial infections in vivo. These preliminary results indicate that further clinical studies are warranted.

Simplified protocol of cardiac 18F-fluorodeoxyglucose positron emission tomography viability study in normoglycemic patients with known coronary artery disease

PURPOSE

The purpose was to evaluate quality of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) myocardial scans and its correlation with background glucose (BG) after simplified 5% intravenous glucose load protocol.

METHODS

An intravenous glucose load protocol was applied in 69 normoglycemic patients with confirmed coronary artery disease. The blood glucose level was measured every 15 min.

RESULTS

Eighty-four percent of images were optimal, 8.7% suboptimal, and 7.3% uninterpretable. The quality of 18F-FDG-PET was BG independent and body mass index dependent (P=.0007).

CONCLUSIONS

Simplified glucose load protocol is a safe and efficient method of preparation for FDG cardiac viability study in patients with normoglycemia.

Modeling 18F-FDG kinetics during acute lung injury: experimental data and estimation errors

Background

There is increasing interest in Positron Emission Tomography (PET) of 2-deoxy-2-[18F]flouro-D-glucose (¹⁸F-FDG) to evaluate pulmonary inflammation during acute lung injury (ALI). We assessed the effect of extra-vascular lung water on estimates of ¹⁸F-FDG-kinetics parameters in experimental and simulated data using the Patlak and Sokoloff methods, and our recently proposed four-compartment model.

Methodology/Principal Findings

Eleven sheep underwent unilateral lung lavage and 4 h mechanical ventilation. Five sheep received intravenous endotoxin (10 ng/kg/min). Dynamic ¹⁸F-FDG PET was performed at the end of the 4 h period. ¹⁸F-FDG net uptake rate (Ki), phosphorylation rate (k₃), and volume of distribution (F_e) were estimated in three isogravitational regions for each method. Simulations of normal and ALI ¹⁸F-FDG-kinetics were conducted to study the dependence of estimated parameters on the transport rate constants to (k₅) and from (k₆) the extra-vascular extra-cellular compartment. The four-compartment model described 85.7% of the studied ¹⁸F-FDG-kinetics better than the Sokoloff model. Relative to the four-compartment model the Sokoloff model exhibited a consistent positive bias in Ki (3.32 [1.30–5.65] 10⁻⁴/min, p<0.001) and showed inaccurate estimates of the parameters composing Ki (k₃ and F_e), even when Ki was similar for those methods. In simulations, errors in estimates of Ki due to the extra-vascular extra-cellular compartment depended on both k₅ and k₅/k₆, with errors for the Patlak and Sokoloff methods of 0.02 [−0.01–0.18] and 0.40 [0.18–0.60] 10⁻³/min for normal lungs and of −0.47 [−0.89–0.72] and 2.35 [0.85–3.68] 10⁻³/min in ALI.

Conclusions/Significance

¹⁸F-FDG accumulation in lung extra-vascular fluid, which is commonly increased during lung injury, can result in substantial estimation errors using the traditional Patlak and Sokoloff methods. These errors depend on the extra-vascular extra-cellular compartment volume and its transport rates with other compartments. The four-compartment model provides more accurate quantification of ¹⁸F-FDG-kinetics than those methods in the presence of increased extra-vascular fluid.

Predictive value of left ventricular remodeling by area strain based on three-dimensional wall-motion tracking after PCI in patients with recent NSTEMI

We aimed to explore whether a novel left ventricular performance index, area strain (AS), based on three-dimensional wall-motion tracking (3-D-WMT) done before and after percutaneous coronary intervention (PCI) could predict left ventricular (LV) remodeling in patients with recent non-ST elevation myocardial infarction (NSTEMI). Sixty-one patients (53.6 ± 8.8 years) with recent NSTEMI were enrolled. Coronary angiography and PCI were undertaken for reperfusion. Parameters of myocardial deformation (including LV end-diastolic volume, LV end-systolic volume, LV ejection fraction, LV global and regional peak area strain) were measured by 3-D-WMT before and 1 week after reperfusion therapy. Six months after reperfusion, LV negative remodeling was defined as lack of improvement in LV function, with increase in LV end-diastolic volume ≥15%. Patients were subdivided into remodeled group (n = 25) and non-remodeled group (n = 36) at follow-up. Patients with negative LV remodeling had significantly higher cardiac troponin I (cTnI) levels at baseline (21.21 ± 12.22 vs. 15.56 ± 8.91 ng/mL; p = 0.0357), higher B-type natriuretic peptide (BNP) level (247.56 ± 177.39 vs. 170.53 ± 97.89 pg/mL; p = 0.0336) and reduced global AS (-27.9 ± 4.6% vs. -31.9 ± 4.3%; p = 0.001) than those without remodeling. Global AS at baseline had a significantly close correlation with cTnI level 36 h after MI (r = 0.71, p < 0.001). Moreover, a weak relationship was found between LV global AS at baseline and BNP level 24 h after myocardial infarction (r = 0.423, p < 0.001). By multivariate logistic regression analysis, lack of improvement of global AS 1 week after PCI was found to be a powerful independent predictor of negative LV remodeling at follow-up (OR = 1.41, 95% CI 1.28-3.27, p = 0.003). In particular, a global AS ≤32% (absolute value) showed a sensitivity and a specificity of 86.1% and 68.0% in predicting negative LV remodeling. These data suggest that AS could be used to assess myocardial global and regional LV function with good feasibility and repeatability. Global AS 1 week after PCI is a good independent predictor of negative LV remodeling after 6-month follow-up.

PET/CT imaging in mouse models of myocardial ischemia

Different species have been used to reproduce myocardial infarction models but in the last years mice became the animals of choice for the analysis of several diseases, due to their short life cycle and the possibility of genetic manipulation. Many techniques are currently used for cardiovascular imaging in mice, including X-ray computed tomography (CT), high-resolution ultrasound, magnetic resonance imaging, and nuclear medicine procedures. Cardiac positron emission tomography (PET) allows to examine noninvasively, on a molecular level and with high sensitivity, regional changes in myocardial perfusion, metabolism, apoptosis, inflammation, and gene expression or to measure changes in anatomical and functional parameters in heart diseases. Currently hybrid PET/CT scanners for small laboratory animals are available, where CT adds high-resolution anatomical information. This paper reviews mouse models of myocardial infarction and discusses the applications of dedicated PET/CT systems technology, including animal preparation, anesthesia, radiotracers, and images postprocessing.

Technetium-99m-labelled HL91 and technetium-99m-labelled MIBI SPECT imaging for the detection of ischaemic viable myocardium: a preliminary study

PURPOSE

The assessment of myocardial viability has become an important aspect of the diagnostic and prognostic work-up of patients with coronary artery disease. Technetium-99m labelled sestamibi ((99m)Tc-MIBI) myocardial perfusion imaging may underestimate the viability of ischaemic myocardium. Technetium-99m labelled 4,9-diaza-3,3,10,10-tetramethyldodecan-2,11-dione dioxime ((99m)Tc-HL91) is a hypoxia-avid agent which can identify acutely ischaemic viable myocardium in a canine model using a standard gamma camera. The aim of this study was to evaluate uptake character of ischaemic viable myocardium and diagnostic performance of single-photon emission computed tomography (SPECT) imaging by (99m)Tc-HL91 and (99m)Tc-MIBI in detecting ischaemic viable myocardium in coronary heart disease.

METHODS

A total of 41 patients with coronary artery disease were recruited from March 2008 to May 2009. For detecting ischaemic viable myocardium, SPECT imaging by (99m)Tc-HL91 and (99m)Tc-MIBI were performed in all patients before coronary revascularization. Six patients with single ischaemic myocardial segment received a 2-day SEPCT/CT imaging protocol and the uptake of (99m)Tc-HL91 in ischaemic myocardium was quantitatively analysed. The remaining 35 patients received a 1-day (99m)Tc-HL91 and (99m)Tc-MIBI SPECT imaging protocol. Resting (99m)Tc-MIBI myocardial perfusion imaging in 3-18 months after revascularization was used as the standard methodology to evaluate the myocardial viability.

RESULTS

In 41 patients, 66 ischaemic myocardial segments were proven to be viable and 12 to be necrotic by resting (99m)Tc-MIBI myocardial perfusion imaging after coronary revascularization. Furthermore, 60 viable segments with negative uptake of (99m)Tc-MIBI showed positive uptake of (99m)Tc-HL91. The remaining six viable segments and 12 necrotic segments showed both negative uptake of (99m)Tc-HL91 and (99m)Tc-MIBI. The sensitivity, specificity, accuracy, Younden Index, positive predictive value and negative predictive value for evaluating ischaemic viable myocardium were 90·9%, 100%, 92·3%, 90·9%, 100% and 66·7%, respectively. Ischaemic viable myocardium had the negative (99m)Tc-MIBI uptake and positive (99m)Tc-HL91 uptake, which demonstrated a mismatched uptake character. Quantitative analysis indicated the uptake of (99m)Tc-HL91 in viable myocardium was increasing in the first 1-3 h and remained stable at the 3-4 h after injection.

CONCLUSION

Functional SPECT imaging with (99m)Tc-HL91 and (99m)Tc-MIBI can be used to detect the seriously ischaemic but viable myocardium with a mismatched uptake character. The uptake of (99m)Tc-HL91 in the viable myocardium reached a stable level at 3-4 h after injection.

Assessment of lung inflammation with 18F-FDG PET during acute lung injury

OBJECTIVE

The purpose of this review is to describe the current experimental and clinical data regarding the fundamentals and applications of (18)F-FDG PET during acute lung injury (ALI) and acute respiratory distress syndrome (ARDS).

CONCLUSION

Lung inflammation is a key feature of ALI. During ALI, FDG PET can be used to monitor lung neutrophils, which are essential cells in the pathophysiologic mechanisms of ALI. Pulmonary FDG kinetics are altered during experimental and human ALI and are associated with regional lung dysfunction, histologic abnormalities, and prognosis. FDG PET may be a valuable noninvasive method for gaining comprehensive understanding of the mechanisms of ALI/ARDS and for evaluating therapeutic interventions.

Nuclear scan studies in critical care

The field of nuclear cardiology has grown significantly over the past decade. This is a reflection of the value seen by providers in these safe and effective procedures. Nuclear scan studies are noninvasive and versatile in their usefulness. These studies assist in determining the likelihood of future cardiac events, guide approaches to revascularization, and assist in evaluation of the adequacy of revascularization procedures. Critical thinking and decision-making abilities are two key requirements for nurses in the critical care environment. Knowledge and understanding of the nuclear scan studies indicated for patients help nurses advocate for those in their care.

Design of targeted cardiovascular molecular imaging probes

Molecular imaging relies on the development of sensitive and specific probes coupled with imaging hardware and software to provide information about the molecular status of a disease and its response to therapy, which are important aspects of disease management. As genomic and proteomic information from a variety of cardiovascular diseases becomes available, new cellular and molecular targets will provide an imaging readout of fundamental disease processes. A review of the development and application of several cardiovascular probes is presented here. Strategies for labeling cells with superparamagnetic iron oxide nanoparticles enable monitoring of the delivery of stem cell therapies. Small molecules and biologics (e.g., proteins and antibodies) with high affinity and specificity for cell surface receptors or cellular proteins as well as enzyme substrates or inhibitors may be labeled with single-photon-emitting or positron-emitting isotopes for nuclear molecular imaging applications. Labeling of bispecific antibodies with single-photon-emitting isotopes coupled with a pretargeting strategy may be used to enhance signal accumulation in small lesions. Emerging nanomaterials will provide platforms that have various sizes and structures and that may be used to develop multimeric, multimodal molecular imaging agents to probe one or more targets simultaneously. These platforms may be chemically manipulated to afford molecules with specific targeting and clearance properties. These examples of molecular imaging probes are characteristic of the multidisciplinary nature of the extraction of advanced biochemical information that will enhance diagnostic evaluation and drug development and predict clinical outcomes, fulfilling the promise of personalized medicine and improved patient care.

Challenges in the diagnosis of blunt cardiac injuries

INTRODUCTION

Blunt thoracic injuries (BTIs) are directly responsible for 20-25% of all deaths, worldwide. Involvement of heart in BTIs is largely underestimated and ignored, but reasonable estimate would be around 15%. This study was planned to emphasize on clinical-presentation and diagnosis of blunt cardiac injuries (BCIs).

RESULTS

Clinical presentation of BCIs, varied from mild chest discomfort to haemodynamic shock secondary to rapid exsanguinations. Non-specific presentation with associated injuries diverts physician's attention and delayed appearance of clinical features makes diagnosis further difficult. Cardiac markers and ECG are not specific, but high sensitivity of 100% could be reached using combination of elevated cardiactroponin levels and alterations in ECG. Transoesophageal or transthoracic echocardiography, angiography, intravascular ultrasound and nuclear scan have proven to detect cardiac injuries in BTIs, but lack specificity.

CONCLUSION

Patients with suspicious-ECG finding need cardiac-monitoring for at least 24 hours. Haemodynamically stable young (<55 years) subjects, without underlying cardiac diseases and with normal-ECG and cardiac marker, could be discharged safely.

Current status of 3-T cardiovascular magnetic resonance imaging

Continued advances in radiofrequency hardware and tailored software have, in recent times, greatly increased the power and performance of magnetic resonance imaging for noninvasive evaluation of cardiovascular diseases. Magnetic resonance imaging can uniquely be manipulated to trade temporal resolution and spatial resolution against each other, depending on whether detailed structural or functional information is required. However, to date, a number of cardiovascular magnetic resonance applications have been somewhat limited due to signal-to-noise ratio constraints, reflecting the narrow imaging window imposed by physiological cardiac motion. By increasing the operating field strength from 1.5 to 3 T, it is possible (in principle) to double the signal-to-noise ratio, which in turn may be "traded" for improvements in spatial resolution, coverage, or imaging speed. In this context, the development of parallel imaging has set the stage for impressive performance improvements in contrast-enhanced magnetic resonance angiography at 3 T. Indeed, one could argue that without parallel acquisition, the bang for the buck in going from 1.5 to 3 T would be limited. In this paper, we discuss the current status of 3-T magnetic resonance imaging for cardiovascular imaging, considering the relative gains and limitations relative to 1.5 T.

Imaging of VEGF receptor in a rat myocardial infarction model using PET

Myocardial infarction (MI) leads to left ventricular (LV) remodeling, which leads to the activation of growth factors such as vascular endothelial growth factor (VEGF). However, the kinetics of a growth factor's receptor expression, such as VEGF, in the living subject has not yet been described. We have developed a PET tracer (64Cu-DOTA-VEGF121 [DOTA is 1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid]) to image VEGF receptor (VEGFR) expression after MI in the living subject.

METHODS

In Sprague-Dawley rats, MI was induced by ligation of the left coronary artery and confirmed by ultrasound (n = 8). To image and study the kinetics of VEGFRs, 64Cu-DOTA-VEGF121 PET scans were performed before MI induction (baseline) and on days 3, 10, 17, and 24 after MI. Sham-operated animals served as controls (n = 3).

RESULTS

Myocardial origin of the 64Cu-DOTA-VEGF121 signal was confirmed by CT coregistration and autoradiography. VEGFR specificity of the 64Cu-DOTA-VEGF121 probe was confirmed by in vivo use of a 64Cu-DOTA-VEGFmutant. Baseline myocardial uptake of 64Cu-DOTA-VEGF121 was minimal (0.30 +/- 0.07 %ID/g [percentage injected dose per gram of tissue]); it increased significantly after MI (day 3, 0.97 +/- 0.05 %ID/g; P < 0.05 vs. baseline) and remained elevated for 2 wk (up to day 17 after MI), after which time it returned to baseline levels.

CONCLUSION

We demonstrate the feasibility of imaging VEGFRs in the myocardium. In summary, we imaged and described the kinetics of 64Cu-DOTA-VEGF121 uptake in a rat model of MI. Studies such as the one presented here will likely play a major role when studying pathophysiology and assessing therapies in different animal models of disease and, potentially, in patients.

The synthesis of 18F-FDS and its potential application in molecular imaging

PURPOSE

2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) is the most commonly used positron emission tomography (PET) tracer for oncological and neurological imaging, but it has limitations on detecting tumor or inflammation in brain gray matter. In this study, we describe the development of 2-deoxy-2-[(18)F]fluorosorbitol ((18)F-FDS) and its possible application in lesion detection around brain area.

PROCEDURES

(18)F-FDS was obtained by reduction of FDG using NaBH(4) (81 +/- 4% yield in 30 min). Cell uptake/efflux experiments in cell culture and small animal PET imaging on tumor and inflammation models were performed.

RESULTS

Despite the low accumulation in cell culture, (18)F-FDS had good tumor uptake and contrast in the subcutaneous U87MG tumor model (4.54%ID/g at 30 min post-injection). Minimal uptake in the normal mouse brain facilitated good tumor contrast in both U87MG and GL-26 orthotopic tumor models. (18)F-FDS also had increased uptake in the inflamed foci of the TPA-induced acute inflammation model.

CONCLUSIONS

Because of the ease of synthesis and favorable in vivo kinetics, (18)F-FDS may have potential applications in certain cases where FDG is inadequate (e.g., brain tumor).

Expectations of surgeons from an imager

In the last decade, we have witnessed an extraordinary development of new cardiac imaging techniques. Some are already in routine use while other promising techniques, such as 3D and intracardiac echocardiography, are still taking their first steps in clinical applications and have not yet revealed all their potential. Heart failure surgery is also evolving rapidly toward less-invasive procedures with the introduction of video-assisted robotic valve repair/replacement surgery, percutaneous delivery of epicardial restraint devices, mitral edge-to-edge clips, coronary sinus mitral annuloplasty rings, and stem cell therapy. These rapid developments are challenging for the imager and the surgeon and mandate a close collaboration between the two disciplines to minimize surgical risk and improve the outcome of patients who have heart failure.

Surgical aspects of congestive heart failure

Despite tremendous advances in the medical management of congestive heart failure the gold standard for the treatment of end stage congestive heart failure remains cardiac transplantation. The acknowledged critical limitation of sufficient suitable organ donors has resulted in the refinement and development of novel surgical alternatives for the treatment of congestive heart failure. These approaches include the extension of current conventional cardiac operations such as mitral valve repair to the failing ventricle, surgically reconstructing the size and shape of the failing left ventricle in order to optimize geometry and render it a more efficient pump, and partial or complete replacement of the ventricle with a mechanical device. The continued evolution of such therapies is likely to one day have a significant epidemiologic impact on patients suffering from end stage heart failure.

Diagnosis of myocardial contusion after blunt chest trauma using18F-FDG positron emission tomography

Cardiac contusion is an infrequent complication of blunt chest trauma. The definite diagnosis of myocardial contusion is complex and needs a number of examinations such as electrocardiography, echocardiography, cardiac enzyme and radionuclide perfusion scan. We present a patient who had a blunt chest trauma from a car accident resulting in an acute myocardial infarction without injury to coronary arteries. The non-viable myocardium was diagnosed with (18)F-fluorodeoxyglucose positron emission tomography (FDG PET) combined with (201)Tl perfusion single photon emission tomography (SPECT). This is the first report of FDG PET for the diagnosis of myocardial contusion in blunt myocardial trauma.