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, Alzheimer's 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.
The aim of this study was to compare the diagnostic accuracy of 18FFDG-PET/MRI with PET/CT for the detection of liver metastases.
32 patients with solid malignancies underwent 18FFDG-PET/CT and ...subsequent PET/MRI of the liver. Two readers assessed both datasets regarding lesion characterization (benign, indeterminate, malignant), conspicuity and diagnostic confidence. An imaging follow-up (mean interval: 185±92 days) and/-or histopathological specimen served as standards of reference. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated for both modalities. Accuracy was determined by calculating the area under the receiver operating characteristic (ROC) curve. Values of conspicuity and diagnostic confidence were compared using Wilcoxon-signed-rank test.
The standard of reference revealed 113 liver lesions in 26 patients (malignant: n = 45; benign: n = 68). For PET/MRI a higher accuracy (PET/CT: 82.4%; PET/MRI: 96.1%; p<0.001) as well as sensitivity (67.8% vs. 92.2%, p<0.01) and NPV (82.0% vs. 95.1%, p<0.05) were observed. PET/MRI offered higher lesion conspicuity (PET/CT: 2.0±1.1 median: 2; range 0-3; PET/MRI: 2.8±0.5 median: 3; range 0-3; p<0.001) and diagnostic confidence (PET/CT: 2.0±0.8 median: 2; range: 1-3; PET/MRI 2.6±0.6 median: 3; range: 1-3; p<0.001). Furthermore, PET/MRI enabled the detection of additional PET-negative metastases (reader 1: 10; reader 2: 12).
PET/MRI offers higher diagnostic accuracy compared to PET/CT for the detection of liver metastases.
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.
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.
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).
Cardiac PET/MR imaging with FDG is feasible and may add complementary information in patients with ischemic heart disease.
The aim of this pilot study was to demonstrate the potential of simultaneously acquired 68-Gallium-DOTA-D-Phe1-Tyr3-octreotide (68Ga-DOTATOC) positron emission tomography/magnetic resonance imaging ...(PET/MRI) in comparison with 68Ga-DOTATOC PET/computed tomography (PET/CT) in patients with known gastroenteropancreatic neuroendocrine tumors (NETs).
Eight patients (4 women and 4 men; mean SD age, 54 17 years; median, 55 years; range 25-74 years) with histopathologically confirmed NET and scheduled 68Ga-DOTATOC PET/CT were prospectively enrolled for an additional integrated PET/MRI scan. Positron emission tomography/computed tomography was performed using a triple-phase contrast-enhanced full-dose protocol. Positron emission tomography/magnetic resonance imaging encompassed a diagnostic, contrast-enhanced whole-body MRI protocol. Two readers separately analyzed the PET/CT and PET/MRI data sets including their subscans in random order regarding lesion localization, count, and characterization on a 4-point ordinal scale (0, not visible; 1, benign; 2, indeterminate; and 3, malignant). In addition, each lesion was rated in consensus on a binary scale (allowing for benign/malignant only). Clinical imaging, existing prior examinations, and histopathology (if available) served as the standard of reference. In PET-positive lesions, the standardized uptake value (SUV max) was measured in consensus. A descriptive, case-oriented data analysis was performed, including determination of frequencies and percentages in detection of malignant, benign, and indeterminate lesions in connection to their localization. In addition, percentages in detection by a singular modality (such as PET, CT, or MRI) were calculated. Interobserver variability was calculated (Cohen's κ). The SUVs in the lesions in PET/CT and PET/MRI were measured, and the correlation coefficient (Pearson, 2-tailed) was calculated.
According to the reference standard, 5 of the 8 patients had malignant NET lesions at the time of the examination. A total of 4 patients were correctly identified by PET/CT, with the PET and CT component correctly identifying 3 patients each. All 5 patients positive for NET disease were correctly identified by PET/MRI, with the MRI subscan identifying all 5 patients and the PET subscan identifying 3 patients. All lesions considered as malignant in PET/CT were equally depicted in and considered using PET/MRI. One liver lesion rated as "indetermined" in PET/CT was identified as metastasis in PET/MRI because of a diffusion restriction in diffusion-weighted imaging. Of the 4 lung lesions characterized in PET/CT, only 1 was depicted in PET/MRI. Of the 3 lymph nodes depicted in PET/CT, only 1 was characterized in PET/MRI. Interobserver reliability was equally very good in PET/CT (κ = 0.916) and PET/MRI (κ = 1.0). The SUV max measured in PET/CT and in PET/MRI showed a strong correlation (Pearson correlation coefficient, 0.996).
This pilot study demonstrates the potential of 68Ga-DOTATOC PET/MRI in patients with gastroenteropancreatic NET, with special advantages in the characterization of abdominal lesions yet certain weaknesses inherent to MRI, such as lung metastases and hypersclerotic bone lesions.
The aim of this study was to investigate and compare the feasibility as well as potential impact of altered magnetic field properties on image quality and potential artifacts of 1.5 Tesla, 3 Tesla ...and 7 Tesla non-enhanced abdominal MRI.
Magnetic Resonance (MR) imaging of the upper abdomen was performed in 10 healthy volunteers on a 1.5 Tesla, a 3 Tesla and a 7 Tesla MR system. The study protocol comprised a (1) T1-weighted fat-saturated spoiled gradient-echo sequence (2D FLASH), (2) T1-weighted fat-saturated volumetric interpolated breath hold examination sequence (3D VIBE), (3) T1-weighted 2D in and opposed phase sequence, (4) True fast imaging with steady-state precession sequence (TrueFISP) and (5) T2-weighted turbo spin-echo (TSE) sequence. For comparison reasons field of view and acquisition times were kept comparable for each correlating sequence at all three field strengths, while trying to achieve the highest possible spatial resolution. Qualitative and quantitative analyses were tested for significant differences.
While 1.5 and 3 Tesla MRI revealed comparable results in all assessed features and sequences, 7 Tesla MRI yielded considerable differences in T1 and T2 weighted imaging. Benefits of 7 Tesla MRI encompassed an increased higher spatial resolution and a non-enhanced hyperintense vessel signal at 7 Tesla, potentially offering a more accurate diagnosis of abdominal parenchymatous and vasculature disease. 7 Tesla MRI was also shown to be more impaired by artifacts, including residual B1 inhomogeneities, susceptibility and chemical shift artifacts, resulting in reduced overall image quality and overall image impairment ratings. While 1.5 and 3 Tesla T2w imaging showed equivalently high image quality, 7 Tesla revealed strong impairments in its diagnostic value.
Our results demonstrate the feasibility and overall comparable imaging ability of T1-weighted 7 Tesla abdominal MRI towards 3 Tesla and 1.5 Tesla MRI, yielding a promising diagnostic potential for non-enhanced Magnetic Resonance Angiography (MRA). 1.5 Tesla and 3 Tesla offer comparably high-quality T2w imaging, showing superior diagnostic quality over 7 Tesla MRI.
Abstract 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 cm3 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.
To evaluate a potential correlation of the maximum standard uptake value (SUVmax) and the minimum apparent diffusion coefficient (ADCmin) in primary and recurrent cervical cancer based on integrated ...PET/MRI examinations.
19 consecutive patients (mean age 51.6 years; range 30-72 years) with histopathologically confirmed primary cervical cancer (n = 9) or suspected tumor recurrence (n = 10) were prospectively enrolled for an integrated PET/MRI examination. Two radiologists performed a consensus reading in random order, using a dedicated post-processing software. Polygonal regions of interest (ROI) covering the entire tumor lesions were drawn into PET/MR images to assess SUVmax and into ADC parameter maps to determine ADCmin values. Pearson's correlation coefficients were calculated to assess a potential correlation between the mean values of ADCmin and SUVmax.
In 15 out of 19 patients cervical cancer lesions (n = 12) or lymph node metastases (n = 42) were detected. Mean SUVmax (12.5 ± 6.5) and ADCmin (644.5 ± 179.7 × 10(-5) mm2/s) values for all assessed tumor lesions showed a significant but weak inverse correlation (R = -0.342, p < 0.05). When subdivided in primary and recurrent tumors, primary tumors and associated primary lymph node metastases revealed a significant and strong inverse correlation between SUVmax and ADCmin (R = -0.692, p < 0.001), whereas recurrent cancer lesions did not show a significant correlation.
These initial results of this emerging hybrid imaging technique demonstrate the high diagnostic potential of simultaneous PET/MR imaging for the assessment of functional biomarkers, revealing a significant and strong correlation of tumor metabolism and higher cellularity in cervical cancer lesions.
The aim of this study was to systematically assess the quantitative and qualitative impact of including point-spread function (PSF) modeling into the process of iterative PET image reconstruction in ...integrated PET/MR imaging.
All measurements were performed on an integrated whole-body PET/MR system. Three substudies were performed: an (18)F-filled Jaszczak phantom was measured, and the impact of including PSF modeling in ordinary Poisson ordered-subset expectation maximization reconstruction on quantitative accuracy and image noise was evaluated for a range of radial phantom positions, iteration numbers, and postreconstruction smoothing settings; 5 representative datasets from a patient population (total n = 20, all oncologic (18)F-FDG PET/MR) were selected, and the impact of PSF on lesion activity concentration and image noise for various iteration numbers and postsmoothing settings was evaluated; and for all 20 patients, the influence of PSF modeling was investigated on visual image quality and number of detected lesions, both assessed by clinical experts. Additionally, the influence on objective metrics such as changes in SUVmean, SUVpeak, SUVmax, and lesion volume was assessed using the manufacturer-recommended reconstruction settings.
In the phantom study, PSF modeling significantly improved activity recovery and reduced the image noise at all radial positions. This effect was measurable only at a high number of iterations (>10 iterations, 21 subsets). In the patient study, again, PSF increased the detected activity in the patient's lesions at concurrently reduced image noise. Contrary to the phantom results, the effect was notable already at a lower number of iterations (>1 iteration, 21 subsets). Lastly, for all 20 patients, when PSF and no-PSF reconstructions were compared, an identical number of congruent lesions was found. The overall image quality of the PSF reconstructions was rated better when compared with no-PSF data. The SUVs of the detected lesions with PSF were substantially increased in the range of 6%-75%, 5%-131%, and 5%-148% for SUVmean, SUVpeak, and SUVmax, respectively. A regression analysis showed that the relative increase in SUVmean/peak/max decreases with increasing lesion size, whereas it increases with the distance from the center of the PET field of view.
In whole-body PET/MR hybrid imaging, PSF-based PET reconstructions can improve activity recovery and image noise, especially at lateral positions of the PET field of view. This has been demonstrated quantitatively in phantom experiments as well as in patient imaging, for which additionally an improvement of image quality could be observed.
In integrated positron emission tomography (PET)/magnetic resonance imaging (MRI), the PET data acquisition is performed simultaneously to the magnetic resonance data acquisition, leaving latitude ...for the duration of PET acquisition time. This establishes emission time as an important parameter in forthcoming PET/MRI protocols because it is one of the key factors determining PET image quality. Thus, the purpose of the current study was to identify optimal duration of PET acquisition time in PET/MRI.
A total of 22 consecutive patients (7 men, 15 women) underwent fluorine-18-labeled fluorodeoxyglucose (18FFDG) PET/MRI after clinical PET/computed tomography. Positron emission tomography/magnetic resonance scans were acquired for 8 minutes per bed position (mpb). Positron emission tomography was extracted to reconstruct images with 2, 4, 6, and 8 mpb for each patient. Visual and quantitative approaches were used to assess image quality and lesion detectability for each image. For image quality, (a) 3 readers independently scored subjective image quality on a 4-point scale and (b) a region-of-interest approach was used to obtain a quantitative estimate of image quality in terms of noise. For lesion detectability, (a) the readers independently counted the number of hypermetabolic lesions and (b) signal-to-noise ratio and contrast-to-noise ratio were computed in a region-of-interest approach. Moreover, the mean and maximal standardized uptake value (SUV mean and SUV max, respectively) of the hypermetabolic lesions was compared across all acquisition times.
For image quality, subjective image quality significantly declined from 8 to 2 mpb (P <; 0.05), with the exception of the difference between 6 and 8 mpb. Image noise increased with shorter imaging duration, ranging from 13% on average in the 8-mpb scans to 23% in the 2-mpb scans (differences were statistically significant for 2 vs 6 mpb, 2 vs 8 mpb, and 4 vs 8 mpb; P <; 0.05). For lesion detectability, 39 hypermetabolic lesions were identified by consensus. There was no difference in detected lesions across all acquisition times. Signal-to-noise ratio and contrast-to-noise ratio were constantly high and did not differ significantly across the acquisition times. The SUV mean and SUV max did not differ significantly across all acquisition times.
Positron emission tomography acquisition times on integrated PET/MRI do not need to exceed usual acquisition times on current PET/computed tomography scanners: Although the PET image quality suffers from short acquisition times, even a duration of 2 mpb permits sufficient lesion detection. Moreover, quantitative measures of tracer uptake are also reasonably precise at short acquisition times.
To evaluate the added value of the application of the liver-specific contrast phase of Gadobenate dimeglumine (Gd-BOPTA) for detection and characterization of liver lesions in 18F-FDG PET/MRI.
41 ...patients with histologically confirmed solid tumors and known / suspected liver metastases or not classifiable lesions in 18F-FDG PET/CT were included in this study. All patients underwent a subsequent Gd-BOPTA enhanced 18F-FDG PET/MRI examination. MRI without liver-specific contrast phase (MRI1), MRI with liver-specific contrast phase (MRI2), 18F-FDG PET/MRI without liver-specific contrast phase (PET/MRI1) and with liver-specific contrast phase (PET/MRI2) were separately evaluated for suspect lesions regarding lesion dignity, characterization, conspicuity and confidence.
PET/MRI datasets enabled correct identification of 18/18 patients with malignant lesions; MRI datasets correctly identified 17/18 patients. On a lesion-based analysis PET/MRI2 provided highest accuracy for differentiation of lesions into malignant and benign lesions of 98% and 100%. Respective values were 95% and 100% for PET/MRI1, 93% and 96% for MRI2 and 91% and 93% for MRI1. Statistically significant higher diagnostic confidence was found for PET/MRI2 and MRI2 datasets compared to PET/MRI1 and MRI1, respectively (p < 0.001).
The application of the liver-specific contrast phase in 18F-FDG PET/MRI further increases the diagnostic accuracy and diagnostic confidence for correct assessment of benign and malignant liver lesions.
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