Felix Nensa

Hybrid PET/MR Imaging of the Heart: Feasibility and Initial Results

PURPOSE To assess the feasibility of hybrid imaging of the heart with fluorine 18 fluorodeoxyglucose (FDG) on an integrated 3-T positron emission tomography (PET)/magnetic resonance (MR) imaging system. MATERIALS AND METHODS The present study was approved by the local institutional review board. Written informed consent was obtained from all patients before imaging. Twenty consecutive patients with myocardial infarction (n = 20) underwent cardiac PET/MR imaging examination. Ten patients underwent additional cardiac PET/computed tomography (CT) before PET/MR. Two-dimensional half-Fourier acquisition single-shot turbo spin-echo sequences, balanced steady-state free precession cine sequences, two-dimensional turbo inversion-recovery magnitude T2-weighted sequences, and late gadolinium-enhanced (LGE) segmented two-dimensional inversion-recovery turbo fast low-angle shot sequences were performed. According to the 17-segment model, PET tracer uptake, wall motion, and late gadolinium enhancement were visually assessed for each segment on a binary scale, and categorical intermethod agreement was calculated by using the Cohen κ. The maximum standardized uptake value was measured in corresponding myocardial locations on PET/CT and PET/MR images. RESULTS Agreement was substantial over all patients and segments between PET and LGE images (κ = 0.76) and between PET and cine images (κ = 0.78). In 306 segments, 97 (32%) were rated as infarcted on PET images, compared with 93 (30%) rated as infarcted on LGE images and with 90 (29%) rated as infarcted on cine images. In a subgroup of patients (n = 10) with an additional PET/CT scan, no significant difference in myocardial tracer uptake between PET/CT and PET/MR images was found (paired t test, P = .95). CONCLUSION Cardiac PET/MR imaging with FDG is feasible and may add complementary information in patients with ischemic heart disease.

Standardized uptake values for [18F] FDG in normal organ tissues: Comparison of whole-body PET/CT and PET/MRI

PURPOSE To compare maximum and mean standardized uptake values (SUVmax/mean) of normal organ tissues derived from [(18)F]-fluoro-desoxyglucose (FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) using MR attenuation correction (MRAC) (DIXON-based 4-segment μ-map) with [(18)F]-FDG positron emission tomography/computed tomography (PET/CT) using CT-based attenuation correction (CTAC). METHODS AND MATERIALS In 25 oncologic patients (15 men, 10 women; age 57 ± 13 years) after routine whole-body FDG-PET/CT (60 min after injection of 290 ± 40 MBq [(18)F]-FDG) a whole-body PET/MRI was performed (Magnetom Biograph mMR, Siemens Healthcare, Erlangen, Germany). Volumes of interest of 1.0 cm(3) were drawn in 7 physiological organ sites in MRAC-PET and the corresponding CTAC-PET images manually. Spearman correlation coefficients were calculated to compare MRAC- and CTAC based SUV values; Wilcoxon-Matched-Pairs signed ranks test was performed to test for potential differences. RESULTS The mean delay between FDG-PET/CT and PET/MRI was 92 ± 18 min. Excellent correlations of SUV values were found for the heart muscle (SUVmax/mean: R=0.97/0.97); reasonably good correlations were found for the liver (R=0.65/0.72), bone marrow (R=0.42/0.41) and the SUVmax of the psoas muscle (R=0.41). For subcutaneous fat, the correlation coefficient was 0.66 for SUVmean (p<0.05). Correlations between MRAC and CTAC were non-significant for SUVmean of the psoas muscle, SUVmax of subcutaneous fat, SUVmax and SUVmean of the lungs, SUVmax and SUVmean of the blood-pool. The median SUVmax and SUVmean in MRAC-PET were lower than the respective CTAC values in all organs (p<0.05) but heart (SUVmax) and the bone marrow (SUVmean). CONCLUSION In conclusion, in oncologic patients examined with PET/CT and PET/MRI SUVmax and SUVmean values generally correlate well in normal organ tissues, except the lung, subcutaneous fat and the blood pool. SUVmax and SUVmean derived from PET/MRI can be used reliably in clinical routine.

Depiction and characterization of liver lesions in whole body [18F]-FDG PET/MRI

OBJECTIVES To assess the value of PET/MRI with [(18)F]-FDG using a whole body protocol for the depiction and characterization of liver lesions in comparison to PET/CT. METHODS 70 patients (31 women, 39 men) with solid tumors underwent [(18)F]-FDG PET/CT and followed by an additional PET/MRI using an integrated scanner. Two readers rated the datasets (PET/CT; PET/MRI) regarding conspicuity of hepatic lesions (4-point ordinal scale) and diagnostic confidence (5-point ordinal scale). Median scores for lesion conspicuity and diagnostic confidence were compared using Wilcoxons rank sum test. Prior examinations, histopathology and clinical follow-up (116 ± 54 days) served as standard of reference. RESULTS 36 of 70 (51%) patients showed liver lesions. Using PET/CT and PET/MRI all patients with liver metastases could correctly be identified. A total of 97 lesions were found (malignant n=26; benign n=71). For lesion conspicuity significantly higher scores were obtained for PET/MRI in comparison to PET/CT (p<0.001). Significantly better performance for diagnostic confidence was observed in PET/MRI, both for malignant as for benign lesions (p<0.001). CONCLUSIONS PET/MRI, even in the setting of a whole body approach, provides higher lesion conspicuity and diagnostic confidence compared to PET/CT and may therefore evolve as an attractive alternative in oncologic imaging.

Simultaneous 18F choline positron emission tomography/magnetic resonance imaging of the prostate: initial results.

PurposeThe 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. Materials and MethodsFrom 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. ResultsSimultaneous 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. ConclusionsSimultaneous 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.

Integrated 18F-FDG PET/MR Imaging in the Assessment of Cardiac Masses: A Pilot Study

The objective of the present study was to evaluate whether integrated 18F-FDG PET/MR imaging could improve the diagnostic workup in patients with cardiac masses. Methods: Twenty patients were prospectively assessed using integrated cardiac 18F-FDG PET/MR imaging: 16 patients with cardiac masses of unknown identity and 4 patients with cardiac sarcoma after surgical therapy. All scans were obtained on an integrated 3-T PET/MR device. The MR protocol consisted of half Fourier acquisition single-shot turbo spin-echo sequence, cine, and T2-weighted images as well as T1-weighted images before and after injection of gadobutrol. PET data were acquired simultaneously with the MR scan after injection of 199 ± 58 MBq of 18F-FDG. Patients were prepared with a high-fat, low-carbohydrate diet in a period of 24 h before the examination, and 50 IU/kg of unfractionated heparin were administered intravenously 15 min before 18F-FDG injection. Results: Cardiac masses were diagnosed as follows: metastases, 3; direct tumor infiltration via pulmonary vein, 1; local relapse of primary sarcoma after surgery, 2; Burkitt lymphoma, 1; scar/patch tissue after surgery of primary sarcoma, 2; myxoma, 4; fibroelastoma, 1; caseous calcification of mitral annulus, 3; and thrombus, 3. The maximum standardized uptake value (SUVmax) in malignant lesions was significantly higher than in nonmalignant cases (13.2 ± 6.2 vs. 2.3 ± 1.2, P = 0.0004). When a threshold of 5.2 or greater was used, SUVmax was found to yield 100% sensitivity and 92% specificity for the differentiation between malignant and nonmalignant cases. T2-weighted hyperintensity and contrast enhancement both yielded 100% sensitivity but a weak specificity of 54% and 46%, respectively. Morphologic tumor features as assessed by cine MR imaging yielded 86% sensitivity and 92% specificity. Consent interpretation using all available MR features yielded 100% sensitivity and 92% specificity. A Boolean ‘AND’ combination of an SUVmax of 5.2 or greater with consent MR image interpretation improved sensitivity and specificity to 100%. Conclusion: In selected patients, 18F-FDG PET/MR imaging can improve the noninvasive diagnosis and follow-up of cardiac masses.

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

PurposeThe aim of this study was to evaluate the positron emission tomography (PET) component of [18F]choline PET/MRI and compare it with the PET component of [18F]choline PET/CT in patients with histologically proven prostate cancer and suspected recurrent prostate cancer.MethodsThirty-six patients were examined with simultaneous [18F]choline PET/MRI following combined [18F]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.ResultsAll 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.ConclusionPET 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 [18F]choline PET/MRI than in [18F]choline PET/CT. Differences of SUVmax and SUVmean might be caused by different techniques of attenuation correction. Furthermore, differences in biodistribution and biokinetics of [18F]choline between the subsequent examinations and in the respective organ systems have to be taken into account.

Clinical applications of PET/MRI: current status and future perspectives.

Fully integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) scanners have been available for a few years. Since then, the number of scanner installations and published studies have been growing. While feasibility of integrated PET/MRI has been demonstrated for many clinical and preclinical imaging applications, now those applications where PET/MRI provides a clear benefit in comparison to the established reference standards need to be identified. The current data show that those particular applications demanding multiparametric imaging capabilities, high soft tissue contrast and/or lower radiation dose seem to benefit from this novel hybrid modality. Promising results have been obtained in whole-body cancer staging in non-small cell lung cancer and multiparametric tumor imaging. Furthermore, integrated PET/MRI appears to have added value in oncologic applications requiring high soft tissue contrast such as assessment of liver metastases of neuroendocrine tumors or prostate cancer imaging. Potential benefit of integrated PET/MRI has also been demonstrated for cardiac (i.e., myocardial viability, cardiac sarcoidosis) and brain (i.e., glioma grading, Alzheimers disease) imaging, where MRI is the predominant modality. The lower radiation dose compared to PET/computed tomography will be particularly valuable in the imaging of young patients with potentially curable diseases.However, further clinical studies and technical innovation on scanner hard- and software are needed. Also, agreements on adequate refunding of PET/MRI examinations need to be reached. Finally, the translation of new PET tracers from preclinical evaluation into clinical applications is expected to foster the entire field of hybrid PET imaging, including PET/MRI.

Correlation of the Apparent Diffusion Coefficient (ADC) with the Standardized Uptake Value (SUV) in Hybrid 18F-FDG PET/MRI in Non-Small Cell Lung Cancer (NSCLC) Lesions: Initial Results

PURPOSE To compare the apparent diffusion coefficient (ADC) in non-small cell lung cancer lesions with standardized uptake values (SUV) derived from combined 18F-fluoro-deoxy-glucose-positron emission tomography/magnetic resonance imaging (FDG-PET/MRI) and those derived from FDG-PET/CT. MATERIALS AND METHODS In 18 consecutive patients with histologically proven NSCLC (17 men, 1 woman; mean age, 61 ± 12 years), whole-body FDG-PET/MRI was performed after whole-body FDG-PET/CT. Regions of interest (ROI) encompassing the entire primary tumor were drawn into FDG-PET/CT and FDG-PET/MR images to determine the maximum and mean standardized uptake value (SUVmax; SUVmean) and into ADC parameter maps to assess mean ADC values. Pearsons correlation coefficients were calculated to compare SUV and ADC values. RESULTS The SUVmax of NSCLC was 12.3 ± 4.8 [mean ±SD], and the SUVmean was 7.2 ± 2.8 as assessed by FDG-PET/MRI. The SUVmax and SUVmean derived from FDG-PET/CT and FDG-PET/MRI correlated well (R = 0.93; p < 0.001 and R = 0.92; p < 0.001, respectively). The ADCmean of the pulmonary tumors was 187.9 ± 88.8 × 10-5 mm²/s [mean ± SD]. The ADCmean exhibited a significant inverse correlation with the SUVmax (R = -0.72; p < 0.001) as well as with the SUVmean assessed by FDG-PET/MRI (R = -0.71; p < 0.001). CONCLUSION This simultaneous PET/MRI study corroborates the assumed significant inverse correlation between increased metabolic activity on FDG-PET and restricted diffusion on DWI in NSCLC.Citation Format:

Hybrid MRI/PET of the heart: a new complementary imaging technique for simultaneous acquisition of MRI and PET data

The authors certify that they have no commercial associations that may pose a conflict of interests in connection with the submitted article. A 55-year-old man with acute ST-segment elevating myocardial infarction and thrombotic occlusion of the left circumflex artery (LCX) had undergone percutaneous transluminal coronary angioplasty and coronary stenting 6 h after the onset of symptoms. Five days later, a combined 18F-fluorodeoxyglucose (18F-FDG) magnetic resonance imaging (MRI)/positron emission tomography (PET) examination of …

Silent Cerebral Ischemia After Thoracic Endovascular Aortic Repair: A Neuroimaging Study

BACKGROUND The risk of clinically apparent, periprocedural stroke after thoracic endovascular aortic repair (TEVAR) due to dislodgement and embolization of aortic debris from intravascular manipulation of guidewires, catheters, and large-bore delivery systems ranges between 2% and 6% and has been associated with increased postoperative mortality. The rate of clinically silent cerebral ischemia is yet unknown, but may be even higher. METHODS Nineteen patients (13 male, 6 female) who underwent TEVAR were included into this descriptive study. Periprocedural apparent and silent cerebral ischemia was assessed by daily clinical neurologic assessment and serial cerebral diffusion-weighted magnetic resonance imaging (DW-MRI) at baseline and 5 days (median, interquartile range: 3.5) after the procedure. RESULTS The TEVAR was successful in all patients without immediate clinically apparent neurologic deficits. Postinterventional cerebral DW-MRI detected a total of 29 new foci of restricted diffusion in 12 of 19 TEVAR patients (63%). Lesions were usually multiple (1 to 6 lesions per patient) and ranged in size between 15 mm3 and 300 mm3; 16 lesions were found in the left hemisphere, 13 lesions in the right hemisphere. Overstenting of the left subclavian artery was performed in 8 cases, but was not associated with lateralization of lesions. There were no additional apparent neurologic events during the in-hospital period. CONCLUSIONS Thoracic endovascular aortic repair resulted in a high incidence of new foci of restricted diffusion on cerebral DW-MRI in a pattern suggestive of periprocedural embolization. Although multiple lesions per patients were found, these lesions were not associated with apparent neurologic deficits during the in-hospital period. Further developments in TEVAR should be directed toward reducing the risk of periprocedural cerebral embolization.