Partial Volume Effect Correction Research Articles

When structure affects function--the need for partial volume effect correction in functional and resting state magnetic resonance imaging studies.

Both functional and also more recently resting state magnetic resonance imaging have become established tools to investigate functional brain networks. Most studies use these tools to compare different populations without controlling for potential differences in underlying brain structure which might affect the functional measurements of interest. Here, we adapt a simulation approach combined with evaluation of real resting state magnetic resonance imaging data to investigate the potential impact of partial volume effects on established functional and resting state magnetic resonance imaging analyses. We demonstrate that differences in the underlying structure lead to a significant increase in detected functional differences in both types of analyses. Largest increases in functional differences are observed for highest signal-to-noise ratios and when signal with the lowest amount of partial volume effects is compared to any other partial volume effect constellation. In real data, structural information explains about 25% of within-subject variance observed in degree centrality – an established resting state connectivity measurement. Controlling this measurement for structural information can substantially alter correlational maps obtained in group analyses. Our results question current approaches of evaluating these measurements in diseased population with known structural changes without controlling for potential differences in these measurements.

Distinct regional age effects on [11C]AZ10419369 binding to 5-HT1B receptors in the human brain

PurposeAge-related changes in the serotonin system have been described, and proposed to be associated with behavioral changes observed particularly in the elderly population. The 5-HT1B receptor is thought to have a regulatory role in a number of physiological functions, and has been implicated in several age-related diseases. The purpose of the present study was to examine if the availability of 5-HT1B receptors is decreasing with age in healthy subjects. MethodsData from five previous studies were reanalyzed and pooled, generating data from fifty-one healthy subjects, age 20 to 70, that had been examined with positron emission tomography (PET) and the 5-HT1B specific radioligand [11C]AZ10419369 at baseline conditions. The binding potential (BPND) in cortical and subcortical areas was calculated using the simplified reference tissue model (SRTM). After correction for partial volume effects (PVEc), the correlation between age and regional BPND was examined. ResultsA statistically significant negative correlation between age and BPND was obtained for neocortical regions and the ventral striatum (VST). The average reduction in BPND per decade was 8% in cortex and 4% in VST. The BPND in the caudate nucleus and the putamen was mainly unaffected by age. ConclusionThe 5-HT1B receptor availability decreases by age in cortical regions, whereas it remains stable in the caudate nucleus and putamen. By consequence, age-matching of control subjects will be necessary in future clinical studies.

Surface-based partial-volume correction for high-resolution PET

Tissue radioactivity concentrations, measured with positron emission tomography (PET) are subject to partial volume effects (PVE) due to the limited spatial resolution of the scanner. Last generation high-resolution PET cameras with a full width at half maximum (FWHM) of 2–4mm are less prone to PVEs than previous generations. Corrections for PVEs are still necessary, especially when studying small brain stem nuclei or small variations in cortical neuroreceptor concentrations which may be related to cytoarchitectonic differences. Although several partial-volume correction (PVC) algorithms exist, these are frequently based on a priori assumptions about tracer distribution or only yield corrected values of regional activity concentrations without providing PVE corrected images. We developed a new iterative deconvolution algorithm (idSURF) for PVC of PET images that aims to overcome these limitations by using two innovative techniques: 1) the incorporation of anatomic information from a cortical gray matter surface representation, extracted from magnetic resonance imaging (MRI) and 2) the use of anatomically constrained filtering to attenuate noise. PVE corrected images were generated with idSURF implemented into a non-interactive processing pipeline. idSURF was validated using simulated and clinical PET data sets and compared to a frequently used standard PVC method (Geometric Transfer Matrix: GTM). The results on simulated data sets show that idSURF consistently recovers accurate radiotracer concentrations within 1–5% of true values. Both radiotracer concentrations and non-displaceable binding potential (BPnd) values derived from clinical PET data sets with idSURF were highly correlated with those obtained with the standard PVC method (R2=0.99, error=0%–3.2%). These results suggest that idSURF is a valid and potentially clinically useful PVC method for automatic processing of large numbers of PET data sets.

Application of partial volume effect correction and 4D PET in the quantification of FDG avid lung lesions.

The aim of this study is to assess a software-based method with semiautomated correction for partial volume effect (PVE) to quantify the metabolic activity of pulmonary malignancies in patients who underwent non-gated and respiratory-gated 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG)-positron emission tomography (PET)/x-ray computed tomography(CT). The study included 106 lesions of 55 lung cancer patients who underwent respiratory-gated FDG-PET/CT for radiation therapy treatment planning. Volumetric PET/CT parameters were determined by using 4D PET/CT and non-gated PET/CT images. We used a semiautomated program employing an adaptive contrast-oriented thresholding algorithm for lesion delineation as well as a lesion-based partial volume effect correction algorithm. We compared respiratory-gated parameters with non-gated parameters by using pairwise comparison and interclass correlation coefficient assessment. In a multivariable regression analysis, we also examined factors, which can affect quantification accuracy, including the size of lesion and the location of tumor. This study showed that quantification of volumetric parameters of 4D PET/CT images using an adaptive contrast-oriented thresholding algorithm and 3D lesion-based partial volume correction is feasible. We observed slight increase in FDG uptake by using PET/CT volumetric parameters in comparison of highest respiratory-gated values with non-gated values. After correction for partial volume effect, the mean standardized uptake value (SUVmean) and total lesion glycolysis (TLG) increased substantially (p value <0.001). However, we did not observe a clinically significant difference between partial volume corrected parameters of respiratory-gated and non-gated PET/CT scans. Regression analysis showed that tumor volume was the main predictor of quantification inaccuracy caused by partial volume effect. Based on this study, assessment of volumetric PET/CT parameters and partial volume effect correction for accurate quantification of lung malignant lesions by using respiratory non-gated PET images are feasible and it is comparable to gated measurements. Partial volume correction increased both the respiratory-gated and non-gated values significantly and appears to be the dominant source of quantification error of lung lesions.

Combined MR-assisted motion and partial volume effects corrections - impact on PET data quantification.

Our goal in this study was to characterize the combined effect of MR-assisted motion correction (MC) and partial volume effects correction (PVEC) on the estimation of [11C]NNC112 binding potential (BP) in healthy volunteers. 29 subjects were scanned on the Siemens 3T MR-BrainPET scanner prototype. Emission data were acquired in list mode format for 90-minutes following the i.v. administration of ~8 mCi of [11C]NNC112. The head attenuation map was obtained from the MPRAGE data using an atlas-based method. Head motion estimates were derived from the MR data and used to correct the PET data in LOR space before image reconstruction [1]. PVEC was applied to the motion corrected data using the region-based voxel-wise (RBV) method [2] and regions of interest (ROIs) defined from the MPRAGE images using FreeSurfer and the measured point-spread function [3]. BPnd for each of the ROIs was estimated in PMOD using the simplified reference tissue kinetic (SRTM) model and the cerebellum as a reference tissue. Maximum translations of up to 9 mm and rotations of up to 12 degrees have been observed in this group of subjects (Figure ​(Figure1).1). Less variability in the tissue time activity curves (TACs) was noted after MC (the curves before and after MC for a representative subject are shown in Figure ​Figure2).2). The percentage changes in BPnd after MC and PVEC revealed both under- and overestimation in the ROIs analyzed (Figure ​(Figure3).3). The cumulative effect exceeded 100% for some of the structures analyzed. Figure 1 Maximum translations (left) and rotations (right) measured in 29 healthy volunteers scanned for 90 minutes Figure 2 TACs in the left and right caudate and cerebellar cortices before (left) and after (right) MR-assisted motion correction Figure 3 Percent change in NNC112 BPnd after motion and partial volume effects corrections Significant motion and PVE were observed in all the subjects, biasing the PET estimates. The combined effect is difficult to predict, depending on the size and location of the structure of interest and patient compliance. Without addressing these issues, the value of the BPnd’s derived from these data is questionable.

Image derived input function applied in CBF Studies with [15O]water PET in an integrated MR-PET.

To quantify CBF studies using [15O]water PET an input function must be provided, e.g. by means of arterial blood sampling. An image derived input function (IDIF) gained from the dynamic PET images may be a non-invasive alternative. The time-activity curve (TAC) of the blood can be obtained from a volume of interest (VOI) capturing the internal carotid artery (ICA). Five healthy young volunteers were administered 555 MBq [15O]water four times each, by bolus intravenous injection. A 3 min PET listmode acquisition was started at the time of the injection (3TMR-BrainPET). Blood was automatically withdrawn from the radial artery to measure its TAC (TACblood, coincidence detector). A T1-weighted MPRAGE image (192x256x256 voxels, 1 mm3) was acquired. Applying corrections, the PET data were iteratively (OSEM3D) reconstructed (frame length 4s, 153x256x256 voxels, 1.25x1.25x1.25 mm3) and filtered (4mm 3D Gaussian). VOIs defining the ICAs in the MPRAGE image were transferred to the dynamic PET images to obtain an IDIF (TACcar). The dispersion and delay of TACblood were corrected (TACbloodcorr) using a one-compartment model and the whole-brain TAC. Cerebral blood flow (CBF) was quantified applying the autoradiographic 15O-water model using both TACbloodcorr and TACcar as input data. Compared to TACbloodcorr, TACcar is affected by the partial volume effect (PVE) and the spillover (SP) from the temporal lobe. The PVE factor and the SP factor were 0.21±0.05 and 0.24±0.10, respectively. Global CBF differed by 8.4% ± 9.4%, when the TACcar after correction for PVE and SP was used as input data instead of TACbloodcorr. The inherently coregistered, high-resolution 3TMR-BrainPET data are a suitable prerequisite for measuring the IDIF. After correction for PVE and SP, the IDIF may replace invasive measurement of 15O-activity.

Wavelet-based partial volume effect correction for simultaneous MR/PET of the carotid arteries.

Simultaneous MR/PET scanners allow for the exploration and development of novel PVE correction techniques without the challenges of coregistration of MR and PET. The development of a wavelet-based PVE correction method, to improve PET quantification, has proven successful in brain PET.2 We report here the first attempt to apply these methods to simultaneous MR/PET imaging of the carotid arteries. The American College of Radiology (ACR) phantom was injected with 18F-FDG for a lesion to background ratio of 2.5. As per ACR protocol, hot cylinders (“lesions”) were injected with 30.71MBq and the phantom background was injected with 12.95MBq. The ACR phantom was then scanned on the Siemens mCT and Siemens Biograph mMR. One patient was injected with 446.6MBq of 18F-FDG and scanned after a circulation time of 90 minutes on the Siemens Biograph mMR. The MR/PET acquisition consisted of the system standard Dixon attenuation correction sequence. Wavelet-based PVE correction was performed to incorporate high frequency wavelet information from MR images into PET images to improve resolution. Qualitative and quantitative uptake parameters where measured to assess the efficacy of the method used. Qualitative comparisons in the ACR phantom and a patient without and with wavelet-based PVE correction demonstrated slight improvement in image quality. Line profiles drawn through the 8mm cylinder and 25mm cylinder and demonstrated an improvement of quantification in the wavelet-based PVE corrected PET image compared to the non-corrected PET image. Standard deviation of SUV before and after PVE correction in the left and right carotid arteries was decreased demonstrating partial volume effect correction. The technique applied here demonstrated an improvement in both resolution and quantification in the phantom and the patient. These results demonstrate the feasibility of wavelet-based PVE correction to provide improved quantification for MR/PET in the carotid arteries.

Masamune: a tool for automatic dynamic PET data processing, image reconstruction and integrated PET/MRI data analysis.

We describe a novel semi-automated pipeline which integrates advanced data analysis tools for MR and PET with advanced PET reconstruction correction methods (partial volume effect correction [PVC], motion correction [MC], attenuation correction [AC]) in a user-friendly Matlab graphical user interface (GUI). The reconstruction and analysis GUI is written in Matlab. Computationally intensive tasks in the pipeline are automatically transferred to a high-performance computing cluster and retrieved. Descriptions of the commercial packages used can be found in their corresponding references. SPM8 [1] is used in MC and AC processing. Comkat [2] and PMOD [3] are used for kinetic modeling. FSL [4] and SPM8 are used for group analysis. Freesurfer [5] is used for regions-of-interest (ROI) definition and smoothing. Data preprocessing: Head-motion is derived from a number of sources: echo-planar MR images, MR-based motion navigators, and directly from the PET data when MR data is unavailable (e.g. during shimming). Subsequently, the ME-MPRAGE is reoriented to the reference position. Cortical and subcortical ROIs are labeled using FreeSurfer; similarly, the MPRAGE is registered to MNI-space for generating subject-specific atlases. Image reconstruction: An OP-OSEM algorithm is used for PET reconstruction [6]. MC [7] and PVC [8] can be performed using the results from data preprocessing. AC can be imported directly from CT, using MR-images [9], or through atlas-based methods. Automated Bolus Arrival Time (BAT) & Image-Derived Input Function: The singles count rate is recorded during PET acquisition. The BAT is determined by fitting a trilinear piecewise function and used as the reference time. Time-of-Flight MR can then be used to segment the arteries of the head and an image-derived input function can be determined using short frames. We presented a novel pipeline which interfaces with a number of different commercial software to provide improved PET data quantification.

CATHEPSIN B KNOCKOUT REDUCES PGLU-ABETA AND ABETA, AND IMPROVES MEMORY DEFICITS, IN THE APPLON MOUSE MODEL OF AD

acquired 30-60 min p.i. using 12 MBq of tracer while data analyses consisted of VOI-based cortical standard-uptake-value-ratio (SUVR) analyses, including partial volume effect correction. Results: A total of 128 microPET recordings were acquired. Baseline results revealed elevated SUVR of 1.04 6 0.08 in the APP-Swe treatment group compared to their vehicle controls (0.98 6 0.05; p1⁄40.07). At 16 months follow-up SUVR in GSMtreated APP-Swemice remained nearly constant while the APP-Swe vehicle group showed a slightly increasing signal compared to baseline (+2.1% vs. +4.7%; p1⁄40.39). At 18months GSM-treated APP-Swemice again remained constant whereas the vehicle group showed a marked increase (+1.2% vs. +12.7%; p<0.01). WT mice remained constant over time. Conclusions: This is the first amyloid-PET monitored long-lasting GSM treatment study in a transgenic AD model. GSM treatment could prevent amyloidogenesis compared to vehicle. The strength of PET lies in the non-invasive possibility of assessing individual plaque-load kinetics and therefore enabling coping with inter-animal variations.

A brief overview of novel approaches to FDG PET imaging and quantification

The widespread implementation of hybrid FDG PET/CT worldwide has brought about a paradigm shift in the use of diagnostic imaging—molecular imaging combining morphological and functional data is now at the forefront of patient management in many clinical settings, not only for initial diagnosis, staging, monitoring of response to treatment and detection of recurrence, but also for prognostication and disease characterization. Although developments have focused particularly on the qualitative visual analysis of images, FDG PET allows elaborate quantification, which should be explored much more in the future and ideally standardized worldwide. In this brief overview, we outline the state of the art of novel and quantitative approaches to FDG imaging, i.e. standard uptake value, partial volume effect and partial volume correction, multiple-time-point imaging, assessment of global disease burden and PET/MRI, all of which we expect to see evolving as powerful tools in the coming years and enhancing sensitivity and specificity in variety of clinical settings, in which FDG PET imaging has not yet shown its full potential.

Glucose hypometabolism is highly localized, but lower cortical thickness and brain atrophy are widespread in cognitively normal older adults.

Several studies have suggested that glucose hypometabolism may be present in specific brain regions in cognitively normal older adults and could contribute to the risk of subsequent cognitive decline. However, certain methodological shortcomings, including a lack of partial volume effect (PVE) correction or insufficient cognitive testing, confound the interpretation of most studies on this topic. We combined [(18)F]fluorodeoxyglucose ([(18)F]FDG) positron emission tomography (PET) and magnetic resonance (MR) imaging to quantify cerebral metabolic rate of glucose (CMRg) as well as cortical volume and thickness in 43 anatomically defined brain regions from a group of cognitively normal younger (25 ± 3 yr old; n = 25) and older adults (71 ± 9 yr old; n = 31). After correcting for PVE, we observed 11-17% lower CMRg in three specific brain regions of the older group: the superior frontal cortex, the caudal middle frontal cortex, and the caudate (P ≤ 0.01 false discovery rate-corrected). In the older group, cortical volumes and cortical thickness were 13-33 and 7-18% lower, respectively, in multiple brain regions (P ≤ 0.01 FDR correction). There were no differences in CMRg between individuals who were or were not prescribed antihypertensive medication. There were no significant correlations between CMRg and cognitive performance or metabolic parameters measured in fasting plasma. We conclude that highly localized glucose hypometabolism and widespread cortical thinning and atrophy can be present in older adults who are cognitively normal, as assessed using age-normed neuropsychological testing measures.

Pseudo-continuous arterial spin labeling MRI study of schizophrenic patients

Arterial spin labeling (ASL) magnetic resonance imaging (MRI) is a novel noninvasive technique that can measure regional cerebral blood flow (rCBF). To our knowledge, few studies have examined rCBF in patients with schizophrenia by ASL-MRI. Here we used pseudo-continuous ASL (pCASL) to examine the structural and functional imaging data in schizophrenic patients, taking the regional cerebral gray matter volume into account. The subjects were 36 patients with schizophrenia and 42 healthy volunteers who underwent 3-tesla MRI, diffusion tensor imaging (DTI), and pCASL. We evaluated the gray matter volume imaging, DTI, and pCASL imaging data in a voxel-by-voxel statistical analysis. The schizophrenia patients showed reduced rCBF in the left prefrontal and bilateral occipital cortices compared to the healthy volunteers. There was a significant reduction of gray matter volume in the left inferior frontal cortex in the schizophrenia patients. With respect to the fractional anisotropy (FA) values in the DTI, there were significant FA reductions in the left superior temporal, left external capsule, and left inferior prefrontal regions in the patients compared to the controls. ConclusionOur pCASL study with partial volume effect correction together with volumetry and DTI data demonstrated hypoactivity in the left prefrontal area beyond structural abnormalities in schizophrenia patients. There were also hypofunction areas in bilateral occipital cortices, although structural abnormalities were not apparent.

A study on comparative analysis of SUVs before and after correction with use of recovery coefficient (RC) in partial volume effect (PVE)

This study calculated the recovery coefficient (RC) to correct for the partial volume effect (PVE) of a positron emission tomography/computed tomography (PET/CT) scanner by conducting a phantom experiment and analysing the standardised uptake value (SUVs) before and after the correction by applying the calculated RC to the data of a real PET/CT scan. An American College of Radiology (ACR) phantom was used to dilute 20·72 MBq (0·56 mCi) fluorine-18 fluoro-deoxy-glucgose (18F-FDG) uniformly in 1000 ml distilled water, which was injected into a hot cylinder (2·5, 1·6, 1·2 and 0·8 cm in diameter). In addition, 18F-FDG in 33·30 MBq (0·90 mCi), 22·20 MBq (0·60 mCi) and 16·65 MBq (0·45 mCi) was diluted uniformly in 6440 ml distilled water, which was filled with background radioactivity. Subsequently, the experiment was conducted three times under a hot cylinder to background radioactivity ratio (H/B ratio) of 4∶1, 6∶1 and 8∶1. The equipment of Biograph Truepoint 40 was used to conduct a phantom experiment and scan patients based on the whole body protocol. This research purposed 30 patients who visited this hospital to undergo a PET/CT scan from July to August 2011 and were diagnosed with lung cancer. The RC calculated based on the study results was used to compare and analyse the SUVs before and after the PVE correction. When the H/B ratio was 4∶1, the RC was 0·75, 0·72, 0·40 and 0·27 at a hot cylinder diameter of 2·5, 1·6, 1·2 and 0·8 cm, respectively. When the H/B ratio was 6∶1, the respective RC was 0·74, 0·59, 0·55 and 0·43. The respective RC at an H/B ratio of 8∶1 was 0·77, 0·76, 0·58 and 0·42. Overall, the RC decreased with decreasing size of the hot spot region. Among the patients diagnosed with lung cancer, 30 patients were selected randomly for sampling to compare and analyse the maximum SUVs before and after the correction. The average SUVs before and after the correction were 7·83 and 10·31.

Recovery coefficients determination for partial volume effect correction in oncological PET/CT images considering the effect of activity outside the field of view

The partial volume effect (PVE) has a great impact in quantitative PET/CT imaging. Correction methods have been recently proposed by many authors to make the image quantification more accurate. This work presents a methodology for determining the recovery coefficients (RCs) for PVE correction in PET/CT images. It was taken into account the radioactivity outside the field of view (FOV), which is expected in a patient image acquisition. The NEMA image quality phantom and the NEMA scatter phantom were used. The phantoms were filled with (18)F-FDG for different sphere-to-background ratios. The RCs have been determined from image acquisitions in a Siemens Biograph 16 Hi-Rez PET/CT scanner with and without the scatter phantom. The RC values that ranged from 0.38 to 1.00 without the scatter phantom exhibited a wider variation when this latter was taken into account (from 0.27 to 1.02). This more realistic estimation must be considered if one takes into account that an incorrect SUV measure in tumors leads to errors in the evaluation of the response to therapy based on PET/CT images. The activity outside the FOV should be considered in RCs determination to improve the RC-based PVE correction method.

Partial volume effect estimation and correction in the aortic vascular wall in PET imaging

We evaluated the impact of partial volume effect (PVE) in the assessment of arterial diseases with 18FDG PET. An anthropomorphic digital phantom enabling the modeling of aorta related diseases like atherosclerosis and arteritis was used. Based on this phantom, we performed GATE Monte Carlo simulations to produce realistic PET images with a known organ segmentation and ground truth activity values. Images corresponding to 15 different activity-concentration ratios between the aortic wall and the blood and to 7 different wall thicknesses were generated. Using the PET images, we compared the theoretical wall-to-blood activity-concentration ratios (WBRs) with the measured WBRs obtained with five measurement methods: (1) measurement made by a physician (Expert), (2) automated measurement supposed to mimic the physician measurements (Max), (3) simple correction based on a recovery coefficient (Max-RC), (4) measurement based on an ideal VOI segmentation (Mean-VOI) and (5) measurement corrected for PVE using an ideal geometric transfer matrix (GTM) method. We found that Mean-VOI WBRs values were strongly affected by PVE. WBRs obtained by the physician measurement, by the Max method and by the Max-RC method were more accurate than WBRs obtained with the Mean-VOI approach. However Expert, Max and Max-RC WBRs strongly depended on the wall thickness. Only the GTM corrected WBRs did not depend on the wall thickness. Using the GTM method, we obtained more reproducible ratio values that could be compared across wall thickness. Yet, the feasibility of the implementation of a GTM-like method on real data remains to be studied.

Usefulness of partial volume effect-corrected F-18 FDG PET/CT for predicting I-131 accumulation in the metastatic lymph nodes of patients with thyroid carcinoma

The purpose of this study was to evaluate the clinical usefulness of partial volume effect (PVE)-corrected F-18 FDG PET/CT for predicting I-131 accumulation in metastatic lymph nodes (mLNs) during I-131 therapy for papillary thyroid carcinoma (PTC). Sixty-five mLNs in 31 PTC patients who underwent F-18 FDG PET/CT in an initial radioiodine therapy (RIT) were retrospectively evaluated. Of these, 25 mLNs were I-131-positive and 40 were I-131-negative. SUVmax and SUVmax with PVE correction (cSUVmax) were measured for each mLN, where PVE correction was performed utilizing a simple table lookup correction method. Then, SUVmax/cSUVmax was compared between I-131-positive and I-131-negative mLNs, including the analyses for the mLNs with small-sized (<1cm) and weak FDG accumulation (SUVmax <3.5). The predictability for I-131 accumulation with SUVmax/cSUVmax was also compared. For all 65 mLNs, SUVmax/cSUVmax was significantly higher in I-131-negative than I-131-positive mLNs (p<0.0001). Only in cSUVmax, I-131-negative mLNs were significantly higher than I-131-positive, in terms of the 30 small-sized mLNs (p=0.0001) and 14 mLNs with weak FDG uptake (p=0.007). The highest accuracy in predictability for I-131 accumulation was significantly better with cSUVmax (92%) than SUVmax (62%) (p<0.0001). PVE-corrected F-18 FDG PET/CT is a valuable predictor of I-131 accumulation in mLNs during RIT.

Predictive value of pre-therapy 18F-FDG PET/CT for the outcome of 18F-FDG PET-guided radiotherapy in patients with head and neck cancer

The aim of this study was to evaluate the predictive role of pre-therapy fluorodeoxyglucose (FDG) uptake parameters of primary tumour in head and neck cancer (HNC) patients undergoing intensity-modulated radiotherapy (IMRT) with simultaneous integrated boost (SIB) on FDG-positive volume-positron emission tomography (PET) gross tumour volume (PET-GTV). This retrospective study included 19 patients (15 men and 4 women, mean age 59.2 years, range 23-81 years) diagnosed with HNC between 2005 and 2011. Of 19 patients, 15 (79 %) had stage III-IV. All patients underwent FDG PET/CT before treatment. Metabolic indexes of primary tumour, including metabolic tumour volume (MTV), maximum and mean standardized uptake value (SUVmax, SUVmean) and total lesion glycolysis (TLG) were considered. Partial volume effect correction (PVC) was performed for SUVmean and TLG estimation. Correlations between PET/CT parameters and 2-year disease-free survival (DFS), local recurrence-free survival (LRFS) and distant metastasis-free survival (DMFS) were assessed. Median patient follow-up was 19.2 months (range 4-24 months). MTV, TLG and PVC-TLG predicting patients' outcome with respect to all the considered local and distant disease control endpoints (LRFS, DMFS and DFS) were 32.4 cc, 469.8 g and 547.3 g, respectively. SUVmean and PVC-SUVmean cut-off values predictive of LRFS and DFS were 10.8 and 13.3, respectively. PVC was able to compensate errors up to 25 % in the primary HNC tumour uptake. Moreover, PVC enhanced the statistical significance of the results. FDG PET/CT uptake parameters are predictors of patients' outcome and can potentially identify patients with higher risk of treatment failure that could benefit from more aggressive approaches. Application of PVC is recommended for accurate measurement of PET parameters.

SU-D-500-04: Impact of Delineation and Partial Volume Effects Correction On PET Uptake Heterogeneity Quantification Through Textural Features Analysis for Therapy Response in Oncology

Purpose: characterization of intra tumoral tracer uptake heterogeneity in PET imaging for response to therapy assessment applications in oncology has been investigated in several recent studies. The use of textural features to quantify this heterogeneity has shown promising results for response to therapy prediction. However, there is no study available yet regarding the potential impact of pre-processing steps on the resulting heterogeneity quantification. The goal of this work was therefore to assess the dependency of heterogeneity parameters obtained through textural features on delineation and partial volume effects (PVE) correction (PVC). Methods: fifty patients with esophageal cancer were retrospectively analyzed. PVC of each FDG PET image was performed using iterative deconvolution with wavelet-based denoising. The tumors were delineated using fixed (FT) and adaptive thresholding (AT), and the fuzzy locally adaptive Bayesian (FLAB) algorithm. From the resulting delineations, uptake heterogeneity was quantified using the following features, selected for their reproducibility and robustness: entropy (E), homogeneity (H), dissimilarity (D), intensity variability (IV), size-zone variability (SZV) and high intensity emphasis (HIE). The results obtained with FLAB (the most accurate) on the non-corrected image were chosen as reference. Variability with respect to this reference depending on delineation or PVC was assessed using Bland-Altman analysis. Impact on the associated predictive value regarding the identification on non-responders was assessed by comparing areas under the receiver operating characteristic curves. Results: heterogeneity parameters were more dependent on delineation than PVC. The most sensitive parameters were IV and SZV (90–100% variability). The most independent were E, H and HIE (10–50%). The impact on the corresponding predictive value was not significant, except for SZV and HIE after deconvolution (p<0.04). Conclusion: some heterogeneity parameters were highly sensitive on pre-processing steps, whereas others such as entropy and homogeneity could be derived with high reliability independently on delineation or PVC. French Ministry of Research

SU-D-500-03: A Correction of Partial Volume Effect for Using PET to Define Metabolically Active Tumor Volume for Pancreatic Cancer

Purpose: Accurate delineation of tumor volume based on PET is affected by partial volume effect (PVE) that has been shown to Result in underestimations of the standardized uptake value (SUV), leading to decreased metabolically‐active tumor volume (MATV). Here we assess the impact of a PVE correction on the SUV and the PET defined MATV in patients with pancreatic cancer. Methods: A voxel‐by‐voxel PVE correction method utilizing a recovery coefficient (RC) approach is implemented for correction in the region of interest (ROI). A profile‐analysis study was used to define the ideal‐cutoff‐values (IDCVs) to threshold PET. The RC and the IDCVs were calculated using NEMA phantom. The pancreas tumor volumes were delineated on the T1 with contrast and diffusion‐weighted MRI (DWI), and on the PET using four different cutoff values: 2.5‐SUV, tumor‐to‐background (T/B) ratio, 42% of SUVmax, and IDCVs. The PVE‐corrected PET and MATV were compared with the original PET, and the resulted tumor sizes were compared with those from contrast‐enhanced CT and MRI. Results: For all patients studied, the mean RC was 0.72 (ranging 0.58 – 0.81) based on tumor diameter on the CT (ranging 1.9 – 5.8) cm, and tumor‐to‐background ratio (ranging 2.4 – 8.7). The mean SUVmax values in the ROI were 8.2 (ranging 3.9 – 13.1) and 10.6 (ranging 5.57 – 16.37) g/ml, respectively, before and after PVE correction. Generally, all of the 2.5‐SUV, T/B ratio, and 42% SUVmax showed an increase of up to 34% in the MATV after PVE correction except for the IDCVs MATV was reduced by 21%. The differences between tumor sizes from CT, T1, and DWI and those from PET with PVE‐correction were reduced compared to those without correction. Conclusion: The partial volume effect correction considerably impacts PET SUV and improves the PET‐defined metabolic ‐ ally‐active tumor volume, particularly for small pancreatic tumors.

Quantification of opioid receptor availability following spontaneous epileptic seizures: Correction of [11C]diprenorphine PET data for the partial-volume effect

Previous positron emission tomography (PET) studies in refractory temporal lobe epilepsy (TLE) using the non-selective opioid receptor antagonist [(11)C]diprenorphine (DPN) did not detect any changes in mesial temporal structures, despite known involvement of the hippocampus in seizure generation. Normal binding in smaller hippocampi is suggestive of increased receptor concentration in the remaining grey matter. Correction for partial-volume effect (PVE) has not been used in previous DPN PET studies. Here, we present PVE-corrected DPN-PET data quantifying post-ictal and interictal opioid receptor availability in humans with mTLE. Eight paired datasets of post-ictal and interictal DPN PET scans and eleven test/retest control datasets were available from a previously published study on opioid receptor changes in TLE following seizures (Hammers et al., 2007a). Five of the eight participants with TLE had documented hippocampal sclerosis. Data were re-analyzed using regions of interest and a novel PVE correction method (structural functional synergistic-resolution recovery (SFS-RR); (Shidahara et al., 2012)). Data were denoised, followed by application of SFS-RR, with anatomical information derived via precise anatomical segmentation of the participants' MRI (MAPER; (Heckemann et al., 2010)). [(11)C]diprenorphine volume-of-distribution (VT) was quantified in six regions of interest. Post-ictal increases were observed in the ipsilateral fusiform gyri and lateral temporal pole. A novel finding was a post-ictal increase in [(11)C]DPN VT relative to the interictal state in the ipsilateral parahippocampal gyrus, not observed in uncorrected datasets. As for voxel-based (SPM) analyses, correction for global VT values was essential in order to demonstrate focal post-ictal increases in [(11)C]DPN VT. This study provides further direct human in vivo evidence for changes in opioid receptor availability in TLE following seizures, including changes that were not evident without PVE correction. Denoising, resolution recovery and precise anatomical segmentation can extract valuable information from PET studies that would be missed with conventional post-processing procedures.