Positron Emission Tomography Component Research Articles

Feasibility of biology-guided radiotherapy using PSMA-PET to boost to dominant intraprostatic tumour

BackgroundBiology-guided radiotherapy (BgRT) delivers dose to tumours triggered from positron emission tomography (PET) detection. Prostate specific membrane antigen (PSMA) PET uptake is abundant in the dominant intraprostatic lesion (DIL). This study investigates the feasibility of BgRT to PSMA-avid subvolume in the prostate region. MethodsPatients enrolled in the prospective randomized trial ProPSMA at our institution were included (ID: ANZCTR12617000005358). Gross tumour volumes (GTVs) were delineated on the PET component of a PET/CT scan from a standardized uptake value (SUV) threshold technique. Suitability for BgRT requires a strong signal-to-background ratio with a surrounding tissue free of significant PSMA uptake. The signal-to-background ratio was quantified from the calculation of the normalized SUV (nSUV), defined as the ratio between SUVmax within the GTV and SUVmean inside a 3D margin expansion of the GTV. The PSMA distribution surrounding the tumour was quantified as a function of the distance from the GTV. ResultsIn this cohort of 84 patients, 83 primary tumours were included. Prostate volume ranged from 19 cm3 to 148 cm3 (median = 52 cm3; IQR = 39 cm3 – 63 cm3). SUVmax inside the prostate was between 2 and 125 (median = 19; IQR = 11 – 30). More than 50% of GTVs generated with threshold between 25%SUVmax (median volume = 10.0 cm3; IQR = 4.5 cm3 – 20.0 cm3) and 50%SUVmax (median volume = 1.9 cm3; IQR = 1.1 cm3 – 3.8 cm3) were suitable for BgRT by using nSUV ≥ 3 and a margin expansion of 5 mm. ConclusionsIt is feasible to identify GTVs suitable for BgRT in the prostate. These GTVs are characterized by a strong signal-to-background ratio and a surrounding tissue free of PSMA uptake.

Performance characteristic evaluation of a bismuth germanate-based high-sensitivity 5-ring discovery image quality positron emission tomography/computed tomography system as per National Electrical Manufacturers Association NU 2-2012.

National Electrical Manufacturers Association (NEMA) provides guidelines to assess the performance of Positron Emission Tomography (PET). A PET/CT scanner, Discovery IQ, GE Medical systems, Milwaukee, USA was installed in our department which has high a sensitivity PET component. We have performed the NEMA NU-2 2012 quality control tests to evaluate this system on site before clinical use. Performance measurements of the PET scanner were made using the NEMA NU2-2012 procedures for spatial resolution, scatter fraction, sensitivity, count rate loss and random coincidence estimation, Noise Equivalent Count Rate (NECR) and image quality. As per NU2 2012, spatial resolution was measured at 1 cm, 10 cm and 20 cm vertically from the centre and at each of these points resolution was measured at tangential, radial and axial directions. Sensitivity was measured at centre and 10 cm off center vertically from the center. The system sensitivity is reported as an average of the two measured values. Scatter fraction and NECR measurements, Image quality test was also performed. The tangential, radial and axial FWHM were 4.99 mm, 4.20 mm and 4.79 mm at 1 cm off centre, 5.49 mm, 4.69 mm and 4.81 mm at 10 cm off centre and 7.99 mm, 5.07 mm and 4.95 mm at 20 cm off centre respectively. The absolute sensitivity of this scanner was found to be 20.1 cps/kBq. The scatter fraction calculated from the decay method was 37.94% and NECR was 125 kcps. The peak NECR was achieved at activity concentration of 8.7 KBq/ml and the count loss below the peak NECR was found to be 0.68%. Image quality test for, contrast recovery, background variability and lung error residual mean met all specifications. Overall PET performance of Discovery IQ whole-body scanner was satisfactory and the scanner met all the performance specifications required by NEMA 2012.

What is the Diagnostic Performance of 18F-FDG-PET/MRI in the Detection of Bone Metastasis in Patients with Breast Cancer?

To evaluate the diagnostic performance of 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/magnetic resonance imaging (MRI) in the detection of bone metastasis in patients with breast cancer. From August 2018 to January 2019, a total of 23 patients with pathologically confirmed invasive breast cancer underwent whole-body hybrid 18F-FDG -PET/MRI for initial staging and follow-up of their malignancies. The number of the bone metastasis was recorded for each patient. The total 18F-FDG-PET/MRI protocol was compared with PET only and the contrast enhanced fused (CE) component for the detection of bone metastasis. Eight (26%) of 23 patients had bone metastasis. Bone metastases were dominantly localized in the spine (63%) and pelvis (25%). In terms of the total number of detected bone metastasis, there was a statistically significant difference between 18F-FDG-PET/MRI (mean 3.57; median 0; range, 0-2) and PET only component (mean 2.87; median 0; range, 0-1) (p=0.026), but no statistically significant difference was detected between 18F-FDG-PET/MRI and whole-body CE MRI (mean 3.43; median 0; range 0-2) (p=0.083). Whole-body hybrid 18F-FDG-PET/MRI is superior to PET component only, but no statistically significant difference between hybrid 18F-FDG-PET/MRI and whole-body CE MRI is found for the detection of bone metastasis in patients with breast cancer.

Assessment of Striatal Dopamine Transporter Binding in Individuals With Major Depressive Disorder

Major depressive disorder (MDD) might involve dopamine (DA) reductions. The DA transporter (DAT) regulates DA clearance and neurotransmission and is sensitive to DA levels, with preclinical studies (including those involving inescapable stressors) showing that DAT density decreases when DA signaling is reduced. Despite preclinical data, evidence of reduced DAT in MDD is inconclusive. Using a highly selective DAT positron emission tomography (PET) tracer ([11C] altropane), DAT availability was probed in individuals with MDD who were not taking medication. Levels of DAT expression were also evaluated in postmortem tissues from donors with MDD who died by suicide. This cross-sectional PET study was conducted at McLean Hospital (Belmont, Massachusetts) and Massachusetts General Hospital (Boston) and enrolled consecutive individuals with MDD who were not taking medication and demographically matched healthy controls between January 2012 and March 2014. Brain tissues were obtained from the Douglas-Bell Canada Brain Bank. For the PET component, 25 individuals with current MDD who were not taking medication and 23 healthy controls recruited from McLean Hospital were included (all provided usable data). For the postmortem component, 15 individuals with depression and 14 healthy controls were considered. PET scan. Striatal and midbrain DAT binding potential was assessed. For the postmortem component, tyrosine hydroxylase and DAT levels were evaluated using Western blots. Compared with 23 healthy controls (13 women [56.5%]; mean [SD] age, 26.49 [7.26] years), 25 individuals with MDD (19 women [76.0%]; mean [SD] age, 26.52 [5.92] years) showed significantly lower in vivo DAT availability in the bilateral putamen and ventral tegmental area (Cohen d range, -0.62 to -0.71), and both reductions were exacerbated with increasing numbers of depressive episodes. Unlike healthy controls, the MDD group failed to show an age-associated reduction in striatal DAT availability, with young individuals with MDD being indistinguishable from older healthy controls. Moreover, DAT availability in the ventral tegmental area was lowest in individuals with MDD who reported feeling trapped in stressful circumstances. Lower DAT levels (and tyrosine hydroxylase) in the putamen of MDD compared with healthy controls were replicated in postmortem analyses (Cohen d range, -0.92 to -1.15). Major depressive disorder, particularly with recurring episodes, is characterized by decreased striatal DAT expression, which might reflect a compensatory downregulation due to low DA signaling within mesolimbic pathways.

Mini EXPLORER II: a prototype high-sensitivity PET/CT scanner for companion animal whole body and human brain scanning

As part of the EXPLORER total-body positron emission tomography (PET) project, we have designed and built a high-resolution, high-sensitivity PET/CT scanner, which is expected to have excellent performance for companion animal whole body and human brain imaging. The PET component has a ring diameter of 52 cm and an axial field of view of 48.3 cm. The detector modules are composed of arrays of lutetium (yttrium) oxyorthosilicate (LYSO) crystals of dimensions 2.76 × 2.76 × 18.1 mm3 coupled to silicon photomultipliers (SiPMs) for read-out. The CT component is a 24 detector row CT scanner with a 50 kW x-ray tube. PET system time-of-flight resolution was measured to be 409 ± 39 ps and average system energy resolution was 11.7% ± 1.5% at 511 keV. The NEMA NU2-2012 system sensitivity was found to be 52–54 kcps MBq−1. Spatial resolution was 2.6 mm at 10 mm from the center of the FOV and 2.0 mm rods were clearly resolved on a mini-Derenzo phantom. Peak noise-equivalent count (NEC) rate, using the NEMA NU 2-2012 phantom, was measured to be 314 kcps at 9.2 kBq cc−1. The CT scanner passed the technical components of the American College of Radiology (ACR) accreditation tests. We have also performed scans of a Hoffman brain phantom and we show images from the first canine patient imaged on this device.

Radiomics Analysis of PET and CT Components of PET/CT Imaging Integrated with Clinical Parameters: Application to Prognosis for Nasopharyngeal Carcinoma.

To investigate the prognostic performance of radiomics features, as extracted from positron emission tomography (PET) and X-ray computed tomography (CT) components of baseline 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) PET/CT images and integrated with clinical parameters, in patients with nasopharyngeal carcinoma (NPC). One hundred twenty-eight NPC patients (85 vs. 43 for training vs. validation), containing a subset of 86 patients with local-regional advanced stage, were enrolled. All patients underwent pretreatment PET/CT scans (mean follow-up time 24 ± 14months). Three thousand two hundred seventy-six radiomics features extracted from PET or CT components and 13 clinical parameters were used to predict progression-free survival (PFS). Univariate analysis with Benjamini-Hochberg false discovery rate (FDR) correction was first used to screen significant features, and redundant features with Spearman's correlation > 0.8 were further eliminated. Then, seven multivariate models involving PET features and/or CT features and/or clinical parameters (denoted as clinical, PET, CT, clinical + PET, clinical + CT, PET + CT and clinical + PET + CT) were constructed by forward stepwise multivariate Cox regression. Model performance was evaluated by concordance index (C-index). Sixty patients encountered events (28 recurrences, 17 metastases, and 15 deaths). Six clinical parameters, 3 PET features, and 14 CT features in training cohort and 4 clinical parameters, 10 PET features, and 4 CT features in subset of local-regional advanced stage were significantly associated with PFS. Combining PET and/or CT features with clinical parameters showed equal or higher prognostic performance than models with PET or CT or clinical parameters alone (C-index 0.71-0.76 vs. 0.67-0.73 and 0.62-0.75 vs. 0.54-0.75 for training and validation cohorts, respectively), while the prognostic performance was significantly improved in local-regional advanced cohort (C-index 0.67-0.84 vs. 0.64-0.77, p value 0.001-0.059). Radiomics features extracted from the PET and CT components of baseline PET/CT images provide complementary prognostic information and improved outcome prediction for NPC patients compared with use of clinical parameters alone.

Performance evaluation of the PET component of a hybrid PET/CT-ultrafast ultrasound imaging instrument

We recently introduced a hybrid imaging instrument, PETRUS, based on a combination of positron emission tomography (PET) for molecular imaging, x-ray computed tomography (CT) for anatomical imaging, co-registration and attenuation correction, and ultrafast ultrasound imaging (UUI) for motion-correction, hemodynamic and biomechanical imaging. In order to ensure a precise co-registration of simultaneous PET-UUI acquisitions, ultrasound probes attached to an ultrafast ultrasound scanner are operated in the field of view (FOV) of a small animal PET/CT scanner using a remote-controlled micro-positioner. Here we explore the effect of the presence of ultrasound probes on PET image quality. We compare the performance of PET and image quality with and without the presence of probes in the PET field of view, both in vitro following the NEMA-NU-4-2008 standard protocol, and in vivo in small animals. Overall, deviations in the quality of images acquired with and without the ultrasound probes were under 10% and under 7% for the NEMA protocol and in vivo tests, respectively. Our results demonstrate the capability of the PETRUS device to acquire multimodal images in vivo without significant degradation of image quality.

Small animal, positron emission tomography-magnetic resonance imaging system based on a clinical magnetic resonance imaging scanner: evaluation of basic imaging performance.

Development of advanced preclinical imaging techniques has had an important impact on the field of biomedical research, with positron emission tomography (PET) imaging the most mature of these efforts. Developers of preclinical PET scanners have joined the recent multimodality imaging trend by combining PET imaging with other modalities, such as magnetic resonance imaging (MRI). Our group has developed a combined PET-MRI insert for the imaging of animals up to the size of rats in a clinical 3T MRI scanner. The system utilizes a sequential scanner configuration instead of the more common coplanar geometry. The PET component of the system consists of a ring of 12 liquid-cooled, SiPM-based detector modules ( ). System performance was evaluated with the NEMA NU 4-2008 protocol. Spatial resolution is 5cm from the center of the field-of-view measured from single-slice rebinned filtered backprojection-reconstructed images. Peak noise equivalent count rate is 17.7kcps at 8.5MBq; peak sensitivity is 2.9%. The MRI component of the system is composed of a 12-cm-diameter birdcage transmit/receive coil with a dual-preamplifier interface possessing very low noise preamplifiers. System performance was evaluated using American College of Radiology-based methods. Image homogeneity is 99%; the ghosting ratio is 0.0054. The signal-to-noise ratio is 95 and spatial resolution is . There was no discernable cross-modality interference.

Comparison of Visceral Fat Measures with Cardiometabolic Risk Factors in Healthy Adults.

We aimed to evaluate the associations of visceral adiposity with cardiometabolic risk factors in normal subjects with integrated 18F-Fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT). A total of 58 normal subjects who underwent 18F-FDG PET/CT scan for cancer screening were included in this study. Volume and average Hounsfield unit (HU) of visceral adipose tissue (VAT) was measured from CT components of integrated PET/CT. Standardized uptake values (SUVmax) of liver, spleen, lumbar spine and ascending aorta (AA) were measured from PET components of integrated PET/CT. Body mass index (coefficient 78.25, p = 0.0259), glucose (37.62, p<0.0001), insulin (348.90, p = 0.0011), logarithmic transformation of homeostatic model assessment index-insulin resistance (-2118.37, p = 0.0007), and VAT HU (-134.99, p<0.0001) were independently associated with VAT volume. Glucose (0.1187, p = 0.0098) and VAT volume (-0.004, p<0.0001) were found to be associated with VAT HU. Both VAT volume and VAT HU of whole abdominal cavity is significantly associated with cardiometabolic risk factors.

Positron Emission Tomography

The aim of this study to evaluate the positron emission tomography (PET) scan technology and its role as a diagnostic tool in health care. New PET technology provide the integrated PET and CT or MRI scan have been applicated globally. &#x0D; In performing PET scan, a small amount of a radioactive substance (18F-FDG is widely used) is injected into a vein, and this substance is absorbed mainly by organs and tissues that use the most energy.The patients recieve internal radiation exposure from injected radiotracer and external radiation from CT component technology. PET and integrated PET seem to be used in oncology for diagnosis, tumor staging, evaluation after therapy and fnding recurrent cancer. &#x0D; An integrated PET/CT scan combines images from PET scan reveals any abnormal activity that might be going on tissues and organs inside the body, while a CT scan provides detailed pictures ofthere. In general, PET/CT can be considered similarly accurate to PET/MRI as whole-body staging approach. But PET/MRI will be indicated and performed superiorly to PET/CT that require high soft tissue contrast. The average specifc activity of 18F-FDG was equal to 3.5 to 4.3 MBq/kg. In PET/CT examination,the injected18F-FDG activity was on an average 300 MBq for adult patient, and by using TOF technology the average activity decreased to 250 MBq.The average e?ective dose related to whole body PET/CT was about 14.3 mSv (8.6 mSv due to CT scan, 5.7 mSv due to PET-FDG component). Another center reported the average e?ective dose was 4.4 mSv for PET component alone and totally 13.5 mSv for PET/CT examination. A PET technology and integrated PET with CT or MRI as new machine for diagnostic imaging can be used mainly for oncologic patients. The PET/MRI technology is superior to PET/CT in detecting soft tissue contrast of organs and tissues.

Patient doses from PET-CT procedures.

Positron emission tomography (PET) was installed for the first time in Bulgaria in 2009, and nowadays two hybrid PET-computed tomography (CT) systems are in operation. The aim of this work is to estimate patient doses from PET-CT procedures and to explore potential for optimisation. Data were retrospectively collected for 50 patients examined with the system Philips Gemini TF and for 58 patients examined with the system GE Discovery 600. Whole-body examinations with radiopharmaceutical (18)F-2-fluoro-2-deoxy-D-glucose (FDG) were performed on all patients. Patient effective doses from the CT component of the examination were calculated with CT Expo software and compared with doses estimated applying the National Radiological Protection Board (NRPB) conversion coefficients. Effective doses from the PET component were calculated applying the ICRP 80 conversion coefficients. For the first system, average effective doses from CT component were 8.0 and 8.9 mSv, applying CT Expo and NRPB coefficients, respectively, and 4.9 mSv from PET component. For the second system, the corresponding values were 7.8, 8.7 and 5.9 mSv. These results for patient effective doses are relatively lower or comparable to other similar surveys. Reasons for the observed differences are analysed and presented.

Recovery and normalization of triple coincidences in PET.

Triple coincidences in positron emission tomography (PET) are events in which three γ-rays are detected simultaneously. These events, though potentially useful for enhancing the sensitivity of PET scanners, are discarded or processed without special consideration in current systems, because there is not a clear criterion for assigning them to a unique line-of-response (LOR). Methods proposed for recovering such events usually rely on the use of highly specialized detection systems, hampering general adoption, and/or are based on Compton-scatter kinematics and, consequently, are limited in accuracy by the energy resolution of standard PET detectors. In this work, the authors propose a simple and general solution for recovering triple coincidences, which does not require specialized detectors or additional energy resolution requirements. To recover triple coincidences, the authors' method distributes such events among their possible LORs using the relative proportions of double coincidences in these LORs. The authors show analytically that this assignment scheme represents the maximum-likelihood solution for the triple-coincidence distribution problem. The PET component of a preclinical PET/CT scanner was adapted to enable the acquisition and processing of triple coincidences. Since the efficiencies for detecting double and triple events were found to be different throughout the scanner field-of-view, a normalization procedure specific for triple coincidences was also developed. The effect of including triple coincidences using their method was compared against the cases of equally weighting the triples among their possible LORs and discarding all the triple events. The authors used as figures of merit for this comparison sensitivity, noise-equivalent count (NEC) rates and image quality calculated as described in the NEMA NU-4 protocol for the assessment of preclinical PET scanners. The addition of triple-coincidence events with the authors' method increased peak NEC rates of the scanner by 26.6% and 32% for mouse- and rat-sized objects, respectively. This increase in NEC-rate performance was also reflected in the image-quality metrics. Images reconstructed using double and triple coincidences recovered using their method had better signal-to-noise ratio than those obtained using only double coincidences, while preserving spatial resolution and contrast. Distribution of triple coincidences using an equal-weighting scheme increased apparent system sensitivity but degraded image quality. The performance boost provided by the inclusion of triple coincidences using their method allowed to reduce the acquisition time of standard imaging procedures by up to ∼25%. Recovering triple coincidences with the proposed method can effectively increase the sensitivity of current clinical and preclinical PET systems without compromising other parameters like spatial resolution or contrast.

Performance evaluation of the Ingenuity TF PET/CT scanner with a focus on high count-rate conditions

This study evaluated the positron emission tomography (PET) imaging performance of the Ingenuity TF 128 PET/computed tomography (CT) scanner which has a PET component that was designed to support a wider radioactivity range than is possible with those of Gemini TF PET/CT and Ingenuity TF PET/MR. Spatial resolution, sensitivity, count rate characteristics and image quality were evaluated according to the NEMA NU 2–2007 standard and ACR phantom accreditation procedures; these were supplemented by additional measurements intended to characterize the system under conditions that would be encountered during quantitative cardiac imaging with 82Rb. Image quality was evaluated using a hot spheres phantom, and various contrast recovery and noise measurements were made from replicated images. Timing and energy resolution, dead time, and the linearity of the image activity concentration, were all measured over a wide range of count rates. Spatial resolution (4.8–5.1 mm FWHM), sensitivity (7.3 cps kBq–1), peak noise-equivalent count rate (124 kcps), and peak trues rate (365 kcps) were similar to those of the Gemini TF PET/CT. Contrast recovery was higher with a 2 mm, body-detail reconstruction than with a 4 mm, body reconstruction, although the precision was reduced. The noise equivalent count rate peak was broad (within 10% of peak from 241–609 MBq). The activity measured in phantom images was within 10% of the true activity for count rates up to those observed in 82Rb cardiac PET studies.

Parallel ICA of FDG-PET and PiB-PET in three conditions with underlying Alzheimer's pathology.

The relationships between clinical phenotype, β-amyloid (Aβ) deposition and neurodegeneration in Alzheimer's disease (AD) are incompletely understood yet have important ramifications for future therapy. The goal of this study was to utilize multimodality positron emission tomography (PET) data from a clinically heterogeneous population of patients with probable AD in order to: (1) identify spatial patterns of Aβ deposition measured by (11C)-labeled Pittsburgh Compound B (PiB-PET) and glucose metabolism measured by FDG-PET that correlate with specific clinical presentation and (2) explore associations between spatial patterns of Aβ deposition and glucose metabolism across the AD population. We included all patients meeting the criteria for probable AD (NIA–AA) who had undergone MRI, PiB and FDG-PET at our center (N = 46, mean age 63.0 ± 7.7, Mini-Mental State Examination 22.0 ± 4.8). Patients were subclassified based on their cognitive profiles into an amnestic/dysexecutive group (AD-memory; n = 27), a language-predominant group (AD-language; n = 10) and a visuospatial-predominant group (AD-visuospatial; n = 9). All patients were required to have evidence of amyloid deposition on PiB-PET. To capture the spatial distribution of Aβ deposition and glucose metabolism, we employed parallel independent component analysis (pICA), a method that enables joint analyses of multimodal imaging data. The relationships between PET components and clinical group were examined using a Receiver Operator Characteristic approach, including age, gender, education and apolipoprotein E ε4 allele carrier status as covariates. Results of the first set of analyses independently examining the relationship between components from each modality and clinical group showed three significant components for FDG: a left inferior frontal and temporoparietal component associated with AD-language (area under the curve [AUC] 0.82, p = 0.011), and two components associated with AD-visuospatial (bilateral occipito-parieto-temporal [AUC 0.85, p = 0.009] and right posterior cingulate cortex [PCC]/precuneus and right lateral parietal [AUC 0.69, p = 0.045]). The AD-memory associated component included predominantly bilateral inferior frontal, cuneus and inferior temporal, and right inferior parietal hypometabolism but did not reach significance (AUC 0.65, p = 0.062). None of the PiB components correlated with clinical group. Joint analysis of PiB and FDG with pICA revealed a correlated component pair, in which increased frontal and decreased PCC/precuneus PiB correlated with decreased FDG in the frontal, occipital and temporal regions (partial r = 0.75, p < 0.0001). Using multivariate data analysis, this study reinforced the notion that clinical phenotype in AD is tightly linked to patterns of glucose hypometabolism but not amyloid deposition. These findings are strikingly similar to those of univariate paradigms and provide additional support in favor of specific involvement of the language network, higher-order visual network, and default mode network in clinical variants of AD. The inverse relationship between Aβ deposition and glucose metabolism in partially overlapping brain regions suggests that Aβ may exert both local and remote effects on brain metabolism. Applying multivariate approaches such as pICA to multimodal imaging data is a promising approach for unraveling the complex relationships between different elements of AD pathophysiology.

Evaluation of the PET component of simultaneous [18F]choline PET/MRI in prostate cancer: comparison with [18F]choline PET/CT

The aim of this study was to evaluate the positron emission tomography (PET) component of [(18)F]choline PET/MRI and compare it with the PET component of [(18)F]choline PET/CT in patients with histologically proven prostate cancer and suspected recurrent prostate cancer. Thirty-six patients were examined with simultaneous [(18)F]choline PET/MRI following combined [(18)F]choline PET/CT. Fifty-eight PET-positive lesions in PET/CT and PET/MRI were evaluated by measuring the maximum and mean standardized uptake values (SUVmax and SUVmean) using volume of interest (VOI) analysis. A scoring system was applied to determine the quality of the PET images of both PET/CT and PET/MRI. Agreement between PET/CT and PET/MRI regarding SUVmax and SUVmean was tested using Pearson's product-moment correlation and Bland-Altman analysis. All PET-positive lesions that were visible on PET/CT were also detectable on PET/MRI. The quality of the PET images was comparable in both groups. Median SUVmax and SUVmean of all lesions were significantly lower in PET/MRI than in PET/CT (5.2 vs 6.1, p<0.05 and 2.0 vs 2.6, p<0.001, respectively). Pearson's product-moment correlation indicated highly significant correlations between SUVmax of PET/CT and PET/MRI (R=0.86, p<0.001) as well as between SUVmean of PET/CT and PET/MRI (R=0.81, p<0.001). Bland-Altman analysis revealed lower and upper limits of agreement of -2.77 to 3.64 between SUVmax of PET/CT vs PET/MRI and -1.12 to +2.23 between SUVmean of PET/CT vs PET/MRI. PET image quality of PET/MRI was comparable to that of PET/CT. A highly significant correlation between SUVmax and SUVmean was found. Both SUVmax and SUVmean were significantly lower in [(18)F]choline PET/MRI than in [(18)F]choline PET/CT. Differences of SUVmax and SUVmean might be caused by different techniques of attenuation correction. Furthermore, differences in biodistribution and biokinetics of [(18)F]choline between the subsequent examinations and in the respective organ systems have to be taken into account.

A strategy for multimodal deformable image registration to integrate PET/MR into radiotherapy treatment planning

Background. Combined positron emission tomography (PET)/magnetic resonance imaging (MRI) is highly promising for biologically individualized radiotherapy (RT). Hence, the purpose of this work was to develop an accurate and robust registration strategy to integrate combined PET/MR data into RT treatment planning. Material and methods. Eight patient datasets consisting of an FDG PET/computed tomography (CT) and a subsequently acquired PET/MR of the head and neck (HN) region were available. Registration strategies were developed based on CT and MR data only, whereas the PET components were fused with the resulting deformation field. Following a rigid registration, deformable registration was performed with a transform parametrized by B-splines. Three different optimization metrics were investigated: global mutual information (GMI), GMI combined with a bending energy penalty (BEP) for regularization (GMI+ BEP) and localized mutual information with BEP (LMI+ BEP). Different quantitative registration quality measures were developed, including volumetric overlap and mean distance measures for structures segmented on CT and MR as well as anatomical landmark distances. Moreover, the local registration quality in the tumor region was assessed by the normalized cross correlation (NCC) of the two PET datasets. Results. LMI+ BEP yielded the most robust and accurate registration results. For GMI, GMI+ BEP and LMI+ BEP, mean landmark distances (standard deviations) were 23.9 mm (15.5 mm), 4.8 mm (4.0 mm) and 3.0 mm (1.0 mm), and mean NCC values (standard deviations) were 0.29 (0.29), 0.84 (0.14) and 0.88 (0.06), respectively. Conclusion. Accurate and robust multimodal deformable image registration of CT and MR in the HN region can be performed using a B-spline parametrized transform and LMI+ BEP as optimization metric. With this strategy, biologically individualized RT based on combined PET/MRI in terms of dose painting is possible.

Integrated Whole-Body PET/MR Hybrid Imaging

Integrated whole-body positron emission tomography (PET)/magnetic resonance (MR) scanners have recently been introduced and potentially offer new possibilities in hybrid imaging of oncologic patients. Integration of PET in a whole-body MR system requires new PET detector technology and new approaches to attenuation correction of PET data based on MR imaging. The aim of this study was to evaluate the clinical performance and image quality parameters of integrated whole-body PET/MR hybrid imaging in intraindividual comparison with PET/CT in oncologic patients. Eighty patients underwent a single-injection, dual-imaging protocol including whole-body PET/computed tomography (CT) and subsequent whole-body PET/MR hybrid imaging. Positron emission tomography/computed tomography was performed after adequate resting time (73 ± 13 minutes post injectionem of 227 ± 52.7 MBq Fluor-18-Fluordesoxyglucose, 3 minutes of acquisition time for each of 7 bed positions), followed by PET/MR (172 ± 33 minutes post injectionem, 10 minutes acquisition time for each of 4 bed positions). Positron emission tomographic data for both modalities were reconstructed iteratively. Two observers evaluated the following parameters: qualitative correlation of tracer-avid lesions in PET/CT versus PET/MR and PET image quality of PET/CT versus PET/MR. Magnetic resonance image quality of standard sequences (T1-weighted, T2-weighted), performance of the Dixon sequence for MR-based attenuation correction in comparison with corresponding T1-weighted images, artifacts in PET/MR data, and spatial coregistration of PET and MR data were evaluated by another observer. In 70 of the 80 patients, both image data sets were complete. In these patients, 192 tracer-avid lesions were identified on PET/CT; 195, on PET/MR. A total of 187 lesions were identified concordantly by both modalities, and this corresponds to an agreement rate of 97.4%. The overall PET image quality was rated good to excellent for PET from PET/CT (12/28, excellent, 42.9%; 16/28, good, 57.1%; 0/28, poor, 0.0%) and slightly superior compared with PET from PET/MR, which was rated good (3/28, excellent, 10.7%; 20/28, good, 71.4%; 5/28, poor, 17.9%) in a subset of 28 patients. The overall image quality of the MR image data sets in all 70 of the 80 patients was rated excellent (260/280, excellent, 92.8%; 15/280, good, 5.4%; 5/280, poor, 1.8%). The Dixon sequence and conversion to μ-maps for MR-based attenuation correction provided robust tissue segmentation in all 280 bed positions of the acquired PET/MR data. No artifacts such as elevated noise and radiofrequency disturbances related to hardware cross talk between the PET and MR components in the hybrid system could be detected in the MR images. No major spatial mismatches between PET and MR data were detected. Integrated PET/MR hybrid imaging is feasible in a clinical setting with similar detection rates as those of PET/CT. Attenuation correction can be performed sufficiently with Dixon sequences, although bone is disregarded. The administration of specific radiotracers and dedicated imaging sequences will foster this hybrid imaging modality in various indications.

Simultaneous 18F Choline Positron Emission Tomography/Magnetic Resonance Imaging of the Prostate

The purposes of this study were to evaluate the feasibility of simultaneous 18F choline positron emission tomography (PET) and magnetic resonance imaging (MRI) of the prostate and to present the first clinical results of the method. From March 2012 to October 2012, a total of 15 consecutive patients were examined with simultaneous 18F choline PET/MRI. At the time of the examination, 8 patients had histologically proven prostate cancer, 2 patients had repeated prostate biopsies with negative results, and 5 patients had suspected prostate cancer with an elevated or rising prostate specific antigene level but did not have a prostate biopsy. Sequence protocol comprised T2-weighted high-resolution images and diffusion-weighted images of the prostate in addition to PET imaging. Image quality was assessed by 2 radiologists, and the PET images were evaluated qualitatively and quantitatively. Simultaneous PET/MRI of the prostate was accomplished successfully in all patients. The method proved to be robust without technical failure, and the image quality was rated to be diagnostic in all examinations except in 1 diffusion-weighted imaging (DWI) data set that was judged to be nondiagnostic because of susceptibility artifacts. High-resolution T2-weighted images allowed exact correlation of elevated focal or diffuse choline uptake to suspicious T2-weighted lesions of the prostate. A high accordance was found between PET and DWI. However, PET-positive lesions were found in 3 patients wherein DWI did not indicate tumor in suspicious T2-weighted lesions. Simultaneous positron emission tomography/magnetic resonance imaging of the prostate has the advantage of combining high-resolution prostate images, functional studies, and metabolic/molecular imaging. The PET component adds diagnostic confidence to the MRI-based parameters in identifying and localizing tumor in the prostate.

Does positron emission tomography data acquisition impact simultaneous diffusion-weighted imaging in a whole-body PET/MRI system?

ObjectivesThe purpose of this study was to test whether the acquisition of positron emission tomography (PET) does interfere with simultaneous diffusion weighted imaging (DWI) in an integrated whole-body PET/MRI system. Material and methodsFourteen consecutive oncological patients (9 men, 5 women; age 54±13 years ([mean±standard deviation]) scheduled for routine [18F]-FDG PET/CT were prospectively enrolled. For DWI, an echo planar imaging (EPI) sequence (b=0–500–1000s/mm2) was acquired twice on an integrated whole-body 3T PET/MRI system in each patient; first with simultaneous PET acquisition and a second time with the PET component switched off. The apparent diffusion coefficient (ADC) and the signal-to-noise ratio at b=1000s/mm2 (SNR) of the myocardium, paraspinal muscle, liver, spleen, renal cortex and tumor tissue (if present) were measured. In addition, the coefficient of variation (CV) of ADC values was calculated. Student's t-test for paired samples was performed to test for differences of the mean ADC, ADC CV and SNR between DWI with and without simultaneous PET acquisition. ResultsThere were no significant differences of the ADC [(mean±standard deviation)] between the DWI acquisitions with and without simultaneous PET acquisition for the myocardium (2572±441×10−6mm2/s and 2586±376×10−6mm2/s, respectively) (P=0.817), paraspinal muscle (1279±254×10−6mm2/s vs. 1219±181×10−6mm2/s) (P=0.318), liver (1245±158×10−6mm2/s vs. 1254±171×10−6mm2/s) (P=0.848), spleen (980±122×10−6mm2/s vs. 1000±187×10−6mm2/s) (P=0.676) and renal cortex (1951±226×10−6mm2/s vs. 1930±273×10−6mm2/s) (P=0.730). Mean ADC of lymph node metastases (n=6) did not differ between with PET acquisition (853±174×10−6mm2/s) and without simultaneous PET (865±170×10−6mm2/s) (P=0.675). There were no significant differences between the CV of ADC values or the SNR values measured in DWI datasets that were acquired with or without simultaneous PET for any evaluated organ site. ConclusionThe simultaneous acquisition of DWI and PET on an integrated PET/MRI system does not impact ADC quantification of normal and tumor tissue and does not alter SNR. This knowledge provides a basis for the use of simultaneous multiparametric PET/MRI comprising DWI in diagnostic imaging and quantitative tumor therapy monitoring using repeated ADC measurements.

Reply to A. Aouba et al

The main issue of our case report is that Erdheim-Chester disease (ECD) clinically presents most commonly with bone and joint pain. We would again like to stress that technetium-99 bone scintigraphy has an important role to identify ECD in an early phase of the disease. Most diagnoses of ECD are made serendipitously. In their reply, Aouba et al compare stand-alone [F] fluorodeoxyglucose ([F]FDG) positron emission tomography (PET) results with computed tomography (CT) scan results. This may be a somewhat obsolete discussion; a hybrid PET/CT delivers the advantage of the synergy of the anatomic and metabolic information. As in any disease, in ECD metabolic changes precede the anatomic changes, creating a higher sensitivity in early stages of the disease. The PET component of a hybrid PET/CT camera is very useful in identifying subtle lesions on CT images that would otherwise be missed. In the wide clinical range that a patient with ECD may present, our patient has the indolent and isolated bone involvement, and not a more systemic and potentially life-threatening form. The irregular mildly increased uptake in the basal field of the right lung and in the lingual of the left lung was, together with the CT findings, indicative of transient infiltrative changes caused by a banal lung infection (Fig 1A). A control CT of the thorax 1 month later showed normalized images. A repeated [F]FDG PET/CT 1 year after diagnosis revealed no lung abnormalities or any other pathology suggestive of extraskeletal involvement of ECD (Fig 1B). The characteristic symmetric pathologic uptake in both distal femurs and both proximal tibiae did not show progression. We would like to thank Aouba et al for their suggestion to use anakinra for the treatment of extra-skeletal involvement of ECD. Because our patient has no extraskeletal involvement, neither anakinra, imatinib mesylate, nor any other systemic therapy is indicated.