High Pressure Nebulization (PIPAC) Versus Injection for the Intraperitoneal Administration of mRNA Complexes.

PURPOSE: Pressurized intraperitoneal aerosol chemotherapy (PIPAC) is a novel technique delivering drugs into the abdominal cavity as an aerosol under high pressure. It is hypothesized to have advantages such as enhancing tissue uptake, distributing drugs homogeneously within the closed and expanded abdominal cavity and higher local concentration of drugs in the peritoneal cavity. However, the clinical trials of PIPAC so far are limited to liquid chemotherapeutic solution, and the applicability of biomolecules (such as mRNA, siRNA and oligonucleotide) is not known. We aimed to investigate the feasibility of administrating mRNA lipoplexes to the peritoneal cavity via high pressure nebulization. METHODS: We firstly investigated the influences of nebulization on physicochemical properties and in vitro transfection efficiency of mRNA lipoplexes. Then, mRNA lipoplexes were delivered to healthy rats through intravenous injection, intraperitoneal injection and PIPAC, respectively. RESULTS: mRNA lipoplexes can withstand the high pressure applied during the PIPAC procedure in vitro. Bioluminescence localized to the peritoneal cavity of rats after administration by IP injection and nebulization, while intravenous injection mainly induced protein expression in the spleen. CONCLUSION: This study demonstrated that local nebulization is feasible to apply mRNA complexes in the peritoneal cavity during a PIPAC procedure.

Tauroursodeoxycholic acid dampens oncogenic apoptosis induced by endoplasmic reticulum stress during hepatocarcinogen exposure.

Hepatocellular carcinoma (HCC) is characterized by the accumulation of unfolded proteins in the endoplasmic reticulum (ER), which activates the unfolded protein response (UPR). However, the role of ER stress in tumor initiation and progression is controversial. To determine the impact of ER stress, we applied tauroursodeoxycholic acid (TUDCA), a bile acid with chaperone properties. The effects of TUDCA were assessed using a diethylnitrosamine-induced mouse HCC model in preventive and therapeutic settings. Cell metabolic activity, proliferation and invasion were investigated in vitro. Tumor progression was assessed in the HepG2 xenograft model. Administration of TUDCA in the preventive setting reduced carcinogen-induced elevation of alanine and aspartate aminotransferase levels, apoptosis of hepatocytes and tumor burden. TUDCA also reduced eukaryotic initiation factor 2α (eIf2α) phosphorylation, C/EBP homologous protein expression and caspase-12 processing. Thus, TUDCA suppresses carcinogen-induced pro-apoptotic UPR. TUDCA alleviated hepatic inflammation by increasing NF-κB inhibitor IκBα. Furthermore, TUDCA altered the invasive phenotype and enhanced metabolic activity but not proliferation in HCC cells. TUDCA administration after tumor development did not alter orthotopic tumor or xenograft growth. Taken together, TUDCA attenuates hepatocarcinogenesis by suppressing carcinogen-induced ER stress-mediated cell death and inflammation without stimulating tumor progression. Therefore, this chemical chaperone could represent a novel chemopreventive agent.

Modulation of the unfolded protein response impedes tumor cell adaptation to proteotoxic stress: a PERK for hepatocellular carcinoma therapy.

BACKGROUND: Functional disturbances of the endoplasmic reticulum (ER) lead to activation of the unfolded protein response (UPR), which is involved in the consecutive steps of carcinogenesis. In human hepatocellular carcinoma (HCC), the UPR is shown to be activated; however, little is known about the UPR kinetics and effects of UPR modulation in HCC. METHODS: We sequentially monitored the UPR over time in an orthotopic mouse model for HCC and explored the effects of UPR modulation on cell viability and proliferation in vitro and in the mouse model. RESULTS: The expression of ER-resident chaperones peaked during tumor initiation and increased further during tumor progression, predominantly within the nodules. A peak in Ire1 signaling was observed during tumor initiation. The Perk pathway was activated during tumor progression, and the proapoptotic target Chop was upregulated from week 5 and continued to rise, especially in the tumors. The Atf6 pathway was modestly activated only after tumor initiation. Consistent with the UPR activation, electron microscopy demonstrated ER expansion and reorganization in HCC cells in vivo. Strikingly, under ER stress or hypoxia, the Perk inhibitor and not the Ire1 inhibitor reduced cell viability and proliferation via escalating proteotoxic stress in vitro. Notably, the Perk inhibitor significantly decreased tumor burden in the mouse model. CONCLUSION: We provide the first evaluation of the UPR dynamics in a long-term cancer model and identified a small molecule inhibitor of Perk as a promising strategy for HCC therapy.

Therapeutic effects of artesunate in hepatocellular carcinoma: repurposing an ancient antimalarial agent.

OBJECTIVES: Artemisinins are antimalarial drugs that exert potent anticancer activity. We evaluated the effects of artesunate, a semisynthetic derivative of artemisinin, on tumor growth, angiogenesis, the unfolded protein response, and chemoresistance in hepatocellular carcinoma. MATERIALS AND METHODS: The effect of artesunate was examined in HepG2 and BWTG3 cells under normoxic and hypoxic conditions and in a diethylnitrosamine-induced mouse model. Histology was performed with hematoxylin/eosin and reticulin staining. The expression of chemoresistance-related transporters and angiogenic and unfolded protein response factors was determined. Cytotoxicity was assessed by alanine and aspartate transaminase, lactate dehydrogenase, water-soluble tetrazolium salt, and caspase-3 activity assays. Small animal imaging was performed using dynamic contrast-enhanced MRI and choline PET to assess tumor progression. RESULTS: Artesunate dose dependently reduced cell viability (from 50 µmol/l; P<0.05) and increased caspase-3 activity (P<0.05) in HepG2 and BWTG3 cells. These effects were enhanced by hypoxia (from 12.5 µmol/l; P<0.01). Moreover, artesunate downregulated vascular endothelial growth factor and placental growth factor expression in vitro (both P<0.05) and in vivo (both P<0.01). In mice, artesunate decreased vessel density and tumor burden (both P<0.05). These in-vivo effects were enhanced by combination with sorafenib (P<0.05 and P=0.07, respectively), without apparent hepatotoxicity. Furthermore, artesunate modulated the unfolded protein response in vitro and in vivo, increasing proapoptotic signaling, and did not induce doxorubicin chemoresistance. CONCLUSION: These findings indicate that artesunate could offer a new approach to the therapy of hepatocellular carcinoma. Clinical trials with artesunate as monotherapy or in combination with current hypoxia-inducing approaches are necessary.

Low-dose micro-CT imaging for vascular segmentation and analysis using sparse-view acquisitions.

The aim of this study is to investigate whether reliable and accurate 3D geometrical models of the murine aortic arch can be constructed from sparse-view data in vivo micro-CT acquisitions. This would considerably reduce acquisition time and X-ray dose. In vivo contrast-enhanced micro-CT datasets were reconstructed using a conventional filtered back projection algorithm (FDK), the image space reconstruction algorithm (ISRA) and total variation regularized ISRA (ISRA-TV). The reconstructed images were then semi-automatically segmented. Segmentations of high- and low-dose protocols were compared and evaluated based on voxel classification, 3D model diameters and centerline differences. FDK reconstruction does not lead to accurate segmentation in the case of low-view acquisitions. ISRA manages accurate segmentation with 1024 or more projection views. ISRA-TV needs a minimum of 256 views. These results indicate that accurate vascular models can be obtained from micro-CT scans with 8 times less X-ray dose and acquisition time, as long as regularized iterative reconstruction is used.

Improved quantification in pinhole gated myocardial perfusion SPECT using micro-CT and ultrasound information.

Absolute quantification using single photon emission computed tomography (SPECT) was demonstrated in vitro and in large immobile organs in vivo. To determine the feasibility of in vivo quantification of myocardial perfusion in pinhole gated SPECT, we added an ultrasound derived partial volume correction factor to attenuation and scatter corrections, in combination with gated acquisitions. In nine male Wistar rats, cardiac ultrasound was performed prior to SPECT/CT scans to determine the myocardial wall thickness. SPECT/CT scans were then performed 30 min after injection of (99m) Tc Tetrofosmin. Animals were killed and six midventricular segments of the left ventricle were excised and counted in a γ-well counter. Using AMIDE, regional myocardial activity was measured after combined scatter correction (SC) and attenuation correction (AC). These image derived activities were compared with the ex vivo counted activity. To correct for the partial volume effect, a recovery coefficient was determined from a phantom study, to determine the thickness specific partial volume effect. Combined AC and SC led to a significant underestimation of activity compared with ex vivo data (root mean squared error = 0.145 mCi g(-1)). The recovery coefficient calculated from the phantom study showed a linear relationship with object size from 1 to 6 mm, positioned in the vicinity of the center of the field of view (R(2) = 0.98). Correction of nongated SPECT images with a recovery coefficient derived from the diastolic phase results in a global overestimation with root mean squared error = 0.04 mCi g(-1). Nongated SPECT images corrected with a recovery coefficient with a weighted average ratio diastolic and systolic phase led to an improved root mean squared error of 0.03 mCi g(-1). Combining attenuation correction with scatter correction and a gated partial volume correction yields the best correlation with ex vivo counting (root mean squared error = 0.021 mCi g(-1) (systolic) and 0.025 mCi g(-1) (diastolic). This study demonstrates a method for improved segmental myocardial perfusion quantification in pinhole gated SPECT, using combined attenuation-, scatter- and ultrasound-derived partial volume effect corrections.

Regional quantitative analysis of small animal myocardial sympathetic innervation and initial application in streptozotocin induced diabetes.

BACKGROUND: In several disease models it is known that heterogeneous dysinnervation occurs in the sympathetic nervous system. We therefore adapted the (123)I-MIBG imaging procedure in small animals to allow quantification of both global and regional uptake and wash-out rate using high specific activity (123)I-MIBG in the myocardium of rats. After evaluation of the image procedure in normal animals, we then applied our imaging protocol to visualize the regional dysinnervation in cardiac autonomic neuropathy occurring in streptozotocin-induced diabetes. METHODS: Seven normal Lewis rats underwent (123)I-MIBG pinhole SPECT with low specific activity (123)I-MIBG (lsa MIBG) and high specific activity (123)I-MIBG (hsa MIBG) with a 2 week interval. Twelve normal rats and 12 rats 8 weeks after streptozotocin injection underwent the same hsa MIBG imaging protocol. The imaging protocol consisted of two SPECT acquisitions for every animal. The imaging sequence started at 20 min after tracer injection. The percentage of injected activity (%IA) and the wash-out rate in the global myocardium were measured. Left ventricular regional MIBG kinetics were analyzed in the six midventricular segments of the 17 segment model. RESULTS: Compared with lsa MIBG, the wash-out rate of hsa MIBG was significantly slower, in association with a higher cardiac uptake. Regional analysis showed a maximal uptake in the anterolateral segment, without significant differences between segments. We noted a significantly higher global wash-out rate in the streptozotocin group compared to controls (p < 0.05). Regional analysis confirmed the increased wash-out rate, reaching statistical significance in the inferior and the inferoseptal walls. CONCLUSION: High-quality (123)I-MIBG images and accurate measurements can be obtained using hsa (123)I-MIBG with image acquisitions performed at relatively early time points. Small animal MIBG SPECT imaging allows for regional analysis of the myocardium. In the streptozotocin group, wash-out of MIBG is globally increased, compatible with a higher sympathetic tonus or decreased reuptake of MIBG. The highest increase is located in the inferior, inferoseptal and anteroseptal walls. These findings further suggest the occurrence of diabetic cardiomyopthy after streptozotocin injection.

Longitudinal assessment of parotid function in patients receiving tomotherapy for head-and-neck cancer.

BACKGROUND AND PURPOSE: Conventional radiotherapy is associated with high doses to the salivary glands which causes xerostomia and adverse effects on quality of life. The study aims to investigate the potential of helical tomotherapy (Hi-Art Tomotherapy) to preserve parotid function in head-and-neck cancer patients. PATIENTS AND METHODS: Seven consecutive patients treated with helical tomotherapy at the UZ Brussel, Belgium, were included. During planning, priority was attributed to planning target volume (PTV) coverage: > or =95% of the dose must be delivered to > or =95% of the PTV. Elective nodal regions received 54 Gy (1.8 Gy/fraction). A dose of 70.5 Gy (2.35 Gy/fraction) was prescribed to the primary tumor and pathologic lymph nodes = simultaneous integrated boost scheme. If possible, the mean parotid dose was kept below 26 Gy. Salivary gland function was assessed by technetium scintigraphy. RESULTS: There was a significant dose-response relationship between mean parotid dose and functional recuperation. If the mean dose was kept <31 Gy, a recuperation of 75% can be expected at 12 months. The authors equally observed a significant correlation between salivary excretion (SE) and the percentage of parotid gland receiving a dose <26 Gy (V26%). In order to preserve 75% of SE, 46% of the parotid volume should receive a dose <26 Gy. CONCLUSION: With the use of heLical tomography the parotid gland function can largely be preserved since the mean dose to the entire gland as well as glandular volume receiving >26 Gy can be reduced.

SPECT imaging with 99mTc-labeled EGFR-specific nanobody for in vivo monitoring of EGFR expression.

PURPOSE: Overexpression of the epidermal growth factor receptor (EGFR) occurs with high incidence in various carcinomas. The oncogenic expression of the receptor has been exploited for immunoglobulin-based diagnostics and therapeutics. We describe the use of a llama single-domain antibody fragment, termed Nanobody, for the in vivo radioimmunodetection of EGFR overexpressing tumors using single photon emission computed tomography (SPECT) in mice. METHODS: Fluorescence-activated cell sorting (FACS) analysis was performed to evaluate the specificity and selectivity of 8B6 Nanobody to bind EGFR on EGFR overexpressing cells. The Nanobody was then labeled with (99m)Tc via its C-terminal histidine tail. Uptake in normal organs and tissues was assessed by ex vivo analysis. In vivo tumor targeting of (99m)Tc-8B6 Nanobody was evaluated via pinhole SPECT in mice bearing xenografts of tumor cells with either high (A431) or moderate (DU145) overexpression of EGFR. RESULTS: FACS analysis indicated that the 8B6 Nanobody only recognizes cells overexpressing EGFR. In vivo blood clearance of (99m)Tc-8B6 Nanobody is relatively fast (half-life, 1.5 h) and mainly via the kidneys. At 3 h postinjection, total kidney accumulation is high (46.6+/-0.9%IA) compared to total liver uptake (18.9+/-0.6%IA). Pinhole SPECT imaging of mice bearing A431 xenografts showed higher average tumor uptake (5.2+/-0.5%IA/cm(3)) of (99m)Tc-8B6 Nanobody compared to DU145 xenografts (1.8+/-0.3%IA/cm(3), p<0.001). CONCLUSION: The EGFR-binding Nanobody investigated in this study shows high specificity and selectivity towards EGFR overexpressing cells. Pinhole SPECT analysis with (99m)Tc-8B6 Nanobody enabled in vivo discrimination between tumors with high and moderate EGFR overexpression. The favorable biodistribution further corroborates the suitability of Nanobodies for in vivo tumor imaging.

Dynamic bioluminescence imaging for quantitative tumour burden assessment using IV or IP administration of D: -luciferin: effect on intensity, time kinetics and repeatability of photon emission.

INTRODUCTION: In vivo bioluminescence imaging (BLI) is a promising technique for non-invasive tumour imaging. D: -luciferin can be administrated intraperitonealy or intravenously. This will influence its availability and, therefore, the bioluminescent signal. The aim of this study is to compare the repeatability of BLI measurement after IV versus IP administration of D: -luciferin and assess the correlation between photon emission and histological cell count both in vitro and in vivo. MATERIALS AND METHODS: Fluc-positive R1M cells were subcutaneously inoculated in nu/nu mice. Dynamic BLI was performed after IV or IP administration of D: -luciferin. Maximal photon emission (PE(max)) was calculated. For repeatability assessment, every acquisition was repeated after 4 h and analysed using Bland-Altman method. A second group of animals was serially imaged, alternating IV and IP administration up to 21 days. When mice were killed, PE(max) after IV administration was correlated with histological cell number. RESULTS: The coefficients of repeatability were 80.2% (IV) versus 95.0% (IP). Time-to-peak is shorter, and its variance lower for IV (p < 0.0001). PE(max) was 5.6 times higher for IV. A trend was observed towards lower photon emission per cell in larger tumours. CONCLUSION: IV administration offers better repeatability and better sensitivity when compared to IP. In larger tumours, multiple factors may contribute to underestimation of tumour burden. It might, therefore, be beneficial to test novel therapeutics on small tumours to enable an accurate evaluation of tumour burden.

Intramyocardial Implantation of bone marrow-derived stem cells enhances perfusion in chronic myocardial infarction: dependency on initial perfusion depth and follow-up assessed by gated pinhole SPECT.

UNLABELLED: Cell therapy-induced changes in the perfusion of areas of myocardial infarction (MI) remain unclear. This study investigated whether an original pinhole SPECT technique could be applied to a rat MI model to analyze local improvement in myocardial perfusion relating to engraftment sites of bone marrow-derived stem cells (BMSCs). METHODS: Four-month-old MI rats were either untreated (n = 8) or treated (n = 10) by intramyocardial injection of (111)In-labeled BMSCs. Early distribution of (111)In-BMSCs within the MI target was evidenced by dual (111)In/(99m)Tc pinhole SPECT 48 h later. Myocardial perfusion was serially monitored by (99m)Tc-sestamibi pinhole gated SPECT up to 3 mo after transplantation. RESULTS: Forty-eight hours after transplantation, (111)In-BMSCs were observed in all treated rats and in 18 of their 32 underperfused MI segments (<70% sestamibi uptake before transplantation). During the subsequent 3-mo follow-up, the perfusion of MI segments worsened in untreated rats (absolute change in sestamibi uptake, -3% +/- 3%; P < 0.05) but improved in treated rats (+4% +/- 7%; P < 0.05). This perfusion improvement was unrelated to the initial detection of (111)In-BMSCs (+2% +/- 6% in segments with (111)In-BMSCs vs. +5% +/- 7% in those without; not statistically significant) but was strongly associated with less severe perfusion defects before transplantation (+6% +/- 6% in segments with 60%-70% sestamibi uptake [n = 19] vs. -1% +/- 6% in those with <60% uptake [n = 13]; P = 0.003). CONCLUSION: When BMSCs are injected within chronic MI, perfusion enhancement predominates in the MI areas showing a high enough residual perfusion before treatment but not in those of the initial cell engraftment, giving evidence of dependency on the perfusion and metabolic environment at implantation sites.

123I-2-iodo-tyrosine, a new tumour imaging agent: human biodistribution, dosimetry and initial clinical evaluation in glioma patients.

PURPOSE: 123I-2-iodo-tyrosine (123I-2IT) has been identified as a promising new amino acid tracer in animals. Uptake is mediated by LAT1 transport, which is increased in tumour cells. In this study we present the human biodistribution and first clinical results in glioma patients. METHODS: For the biodistribution study, six male volunteers received 60-95 MBq 123I-2IT. Whole-body scans and blood and urine samples were obtained up to 24 h after injection; dosimetry was calculated using OLINDA 1.0 software. Initial clinical evaluation of 123I-2IT SPECT was performed in 35 patients with suspected or known glioma, either as primary diagnosis or for detection of recurrence. Tumour-to-background (T/B) ratios were calculated for semi-quantitative analysis. The results were correlated with clinical and MRI follow-up data or histology. RESULTS: 123I-2IT showed both renal and intestinal clearance. Bladder (0.12 mGy/MBq) and small intestine (0.03 mGy/MBq) received the highest absorbed doses. The effective dose equivalent and effective dose were estimated at 0.020 and 0.016 mSv/MBq, respectively. In patients, 123I-2IT SPECT did not differentiate between neoplastic and non-neoplastic lesions after an indeterminate MRI. In follow-up of known glioma, 13/15 patients with disease recurrence had increased T/B values (range 1.39-3.91). Out of seven recurrence-negative patients, two showed an important increase in T/B, in one case due to radionecrosis (T/B 1.59) and in the other probably due to residual but stable disease (T/B 2.07). CONCLUSION: 123I-2IT has a favourable biodistribution for a tumour imaging agent. It shows increased uptake in central nervous system glioma and is potentially useful in the follow-up of glioma patients.

Feasibility of in vivo dual-energy myocardial SPECT for monitoring the distribution of transplanted cells in relation to the infarction site.

PURPOSE: Cell therapy using bone marrow mesenchymal stem cells (BMSCs) shows promise in the treatment of myocardial infarction (MI) but accurate cell delivery within MI areas remains critical. In the present study, we tested the feasibility of in vivo pinhole SPECT imaging for monitoring the sites of intramyocardial implanted BMSCs in relation to targeted MI areas in rats. METHODS: BMSCs were labelled with (111)In-oxine and injected within the fibrotic areas of 3-month-old MI in ten rats. Two days later, dual (111)In/(99m)Tc-sestamibi pinhole SPECT was recorded for localisation of (111)In-BMSCs on a 15-segment left ventricular (LV) division. Additional (99m)Tc-sestamibi pinhole SPECT had been performed 1 month earlier and on the day before transplantation. In vitro counting on histological sections was used to validate the pinhole SPECT determination of (111)In-BMSC activity within LV segments. RESULTS: The underperfused MI area (segments with <70% uptake) was stable between the (99m)Tc-sestamibi SPECT study recorded at 1 month (4.6+/-1.9 segments) and at 1 day (4.7+/-2.3 segments) before transplantation. (111)In-BMSCs were detected by dual-energy SPECT in 56 segments: 33 (59%) were underperfused MI segments but 23 (41%) were not (14 adjacent and nine remote segments). Finally, (111)In-labelled BMSCs were not detected in 14 out of the 47 (30%) underperfused MI segments. CONCLUSION: When BMSCs are injected within MI areas in rats, sites of early cell retention do not always match the targeted MI areas. The dual-energy pinhole SPECT technique may be used for monitoring the sites of early retention of implanted BMSCs and the data obtained may have critical importance when analysing the effects of cardiac cell therapy.

Initial infarct size predicts subsequent cardiac remodeling in the rat infarct model: an in vivo serial pinhole gated SPECT study.

UNLABELLED: The rat infarct model is widely used to study left ventricular (LV) remodeling, a main cause of heart failure characterized by progressive LV dilatation. Using pinhole collimators and advances in data processing, gated SPECT was recently adapted to image the rat heart. The aim of this study was to assess this new imaging technique for predicting and quantifying variable LV remodeling from the rat infarct model. METHODS: Pinhole 99mTc-sestamibi gated SPECT was validated for determining LV volume and identifying the necrotic and nonviable LV segments (<50% of 99mTc-sestamibi uptake) in rats, and it was applied to monitor rat LV function from 48 h to 12 wk after occlusion of the left anterior descending coronary artery (LAD) (n = 20) or sham operation (n = 9). RESULTS: In LAD-occluded rats, 48-h SPECT necrosis was large (> or =30% LV) in 6, limited (<30% LV) in 6, and undetectable in 8. End-diastolic volume of LAD-occluded rats was equivalent to that of sham-operated rats at 48 h (320 +/- 84 microL vs. 293 +/- 48 microL; not significant) but became higher at 12 wk (501 +/- 191 microL vs. 343 +/- 46 microL; P = 0.01). The follow-up increase in end-diastolic volume, which reflects the remodeling process, was closely related to the initial extent of necrosis revealed by the SPECT images (P < 0.001; R2= 0.85). This increase was limited in sham-operated rats (50 +/- 15 microL) and in the LAD-occluded rats with undetectable necrosis (55 +/- 35 microL) but it was around 3- and 7-fold higher in the LAD-occluded rats with limited (165 +/- 57 microL) and large (366 +/- 113 microL) necrosis, respectively. CONCLUSION: The variable LV remodeling documented after coronary occlusion in rats closely relates to the variable extent of necrosis provided by this model. Pinhole gated SPECT allows this remodeling to be predicted and quantified and, hence, constitutes an original tool for the experiments scheduled on the rat infarct model.

OSEM reconstruction, associated with temporal fourier and depth-dependant resolution recovery filtering, enhances results from sestamibi and 201Tl 16-interval gated SPECT.

UNLABELLED: Gated SPECT recorded with 16 intervals determines left ventricular (LV) ejection fraction more accurately than does gated SPECT recorded with 8 intervals but produces higher image noise. This study aimed to assess the results from sestamibi and (201)Tl 16-interval gated SPECT when both signal-to-noise ratio and spatial resolution were enhanced with an original method of reconstruction. METHODS: Forty patients with coronary artery disease underwent (201)Tl and sestamibi 16-interval gated SPECT and, to be used as a reference, cardiac MRI. Assessments of global and regional LV function provided by ordered-subsets expectation maximization (OSEM) with depth-dependant resolution recovery and temporal Fourier filtering were compared with those from conventional filtered backprojection (FBP) previously optimized by screening various filter frequencies and various temporal smoothing levels. RESULTS: For both tracers, LV ejection fraction was determined best when the association of OSEM with depth-dependant resolution recovery was used alone, with temporal Fourier filtering, or with a slight 2-frame temporal smoothing: Mean absolute values of relative errors ranged from 3.2% to 3.6% (4.0%-7.9% for FBP), and coefficient correlation ranged from 0.91 to 0.93 (0.70-0.91 for FBP). Among these 3 reconstruction methods, the association of OSEM with depth-dependant resolution recovery with temporal Fourier filtering provided the highest signal-to-noise ratio, with mean increases of 54% for sestamibi and 80% for (201)Tl when compared with FBP, and the best analysis of segmental contractility, with exact agreement rates with MRI being 73% for (201)Tl and 79% for sestamibi. CONCLUSION: OSEM associated with temporal Fourier filtering and depth-dependant resolution recovery filtering enhances the LV function assessment provided by sestamibi and (201)Tl 16-interval gated SPECT and dramatically reduces image noise, a property that enhances and facilitates image interpretation.