Comparison of simultaneous multi-slice readout-segmented EPI and conventional single-shot EPI for diffusion tensor imaging of the ulnar nerve.

PURPOSE: To compare conventional single-shot echo planar imaging (ss-EPI) and simultaneous multi-slice (SMS) readout-segmented EPI (rs-EPI) for magnetic resonance diffusion tensor imaging (DTI) of the ulnar nerve. MATERIALS AND METHODS: This study was approved by the local ethics committee. Ten healthy volunteers (mean age 30.4 ± 4.01 years; range 25-36 years) underwent 3T DTI of the ulnar nerve at the level of the cubital tunnel. DTI was performed based on ss-EPI as well as SMS rs-EPI sequences. Signal-to-noise ratio (SNR), image quality, and DTI parameters in the ulnar nerve (fractional anisotropy, FA; mean diffusivity, MD) were compared between the two sequences by two independent radiologists. RESULTS: Acquisition time was 5:12 min for ss-EPI and 5:18 min for SMS rs-EPI. Between the two sequences, no significant differences were found for derived DTI measures FA (p = 0.11) and MD values (p = 0.93). Compared to conventional ss-EPI, SMS rs-EPI yielded significantly less ghosting artifacts (p = 0.04) but inferior nerve depiction (p = 0.001) and worse overall image quality (p = 0.008). CONCLUSION: SMS rs-EPI is not advantageous over ss-EPI in DTI of the ulnar nerve at the level of the cubital tunnel.

Reduction of BOLD interference in pseudo-continuous arterial spin labeling: towards quantitative fMRI.

Fluctuations in blood-oxygenation level dependent (BOLD) signal and perfusion affect the quantification of changes in cerebral blood flow (CBF), coupled to neuronal activity, in arterial spin labeling (ASL). Subtraction methods for control and labeled MR images (i.e. pair-wise, surround subtraction, and subtraction of sinc-interpolated images), postulated to mitigate this interference in pseudo-continuous ASL (pCASL), were evaluated by comparison with quantitative 15O-water PET. At rest, a good agreement in the CBF values was found between PET and MRI for each of the subtraction methods. Stimulation of the visual system resulted in a regional CBF increase in the occipital lobe, which was detectable in both modalities. Bland-Altman analysis showed a systematic underestimation of the CBF values during activation in MRI. Evaluation of the relative CBF change induced by neuronal stimulation showed good inter-modality agreement for the three subtraction methods. Perfusion data obtained with each subtraction method followed the stimulation paradigm without significant differences in the correlation patterns or in the time lag between stimulation and perfusion response. Comparison to the gold standard confirmed the detectability of a neuronal stimulation pattern by pCASL. The results indicate that the combined use of background suppression and short TE reduces the BOLD-weighting in the pCASL signal.

PET+MR versus PET/CT in the initial staging of head and neck cancer, using a trimodality PET/CT+MR system.

PURPOSE: To compare the diagnostic accuracy of PET+MR with PET/CT in the initial staging of head and neck cancer. MATERIALS AND METHODS: Contrast-enhanced PET/CT+MR was performed in 27 patients with newly diagnosed head and neck cancer. PET/CT and PET+MR were evaluated separately, and the TNM stage and factors influencing treatment were assessed. RESULTS: The TNM staging by PET+MR was comparable to PET/CT (T: p=0.331, N: p=0.453, M: p=0.034). The sensitivity/specificity/accuracy of treatment-influencing factors by PET/CT and PET+MR were 0.68/0.99/0.97, and 1.00/1.00/0.99, respectively. CONCLUSIONS: Whole-body staging with PET+MR yields at least equal diagnostic accuracy as PET/CT in head and neck cancer.

Simultaneous multislice readout-segmented echo planar imaging for accelerated diffusion tensor imaging of the mandibular nerve: A feasibility study.

PURPOSE: To assess the feasibility of diffusion tensor imaging (DTI) using simultaneous multislice (SMS) acquisition with blipped controlled aliasing in parallel imaging (CAIPI) for accelerated readout-segmented echo planar imaging (rs-EPI) of the mandibular nerves. DTI of the mandibular nerves using EPI is challenging due to susceptibility artifacts. Rs-EPI is less prone to artifacts but associated with longer scan durations. MATERIALS AND METHODS: Eight asymptomatic volunteers were imaged at 3T using a 64-channel head/neck coil. Conventional, 2-fold (2xSMS) and 3-fold (3xSMS) slice-accelerated rs-EPI sequences were acquired. Tractography of the mandibular nerves was performed. Signal-to-noise ratio (SNR), fractional anisotropy (FA), mean diffusivity (MD), and number of tracts were calculated. Artifacts were evaluated qualitatively on Likert scales. Parameters were compared statistically. Clinical feasibility of 2xSMS rs-EPI was tested in four patients. RESULTS: SNR was similar for conventional (mean ± SD; 8.55 ± 3.90) and 2xSMS rs-EPI (7.83 ± 3.15) but lower for 3xSMS rs-EPI (5.42 ± 2.93; analysis of variance, P = 0.004). FA was similar for all sequences (rs-EPI, 0.42 ± 0.08; 2xSMS rs-EPI, 0.43 ± 0.08; 3xSMS rs-EPI, 0.44 ± 0.06), while 3xSMS rs-EPI showed lower MD (rs-EPI, 0.0015 ± 0.0003; 2xSMS rs-EPI, 0.0014 ± 0.0001; 3xSMS rs-EPI, 0.0013 ± 0.0003) and lower number of tracts (rs-EPI, 66.56 ± 51.31; 2xSMS rs-EPI, 65.75 ± 55.40; 3xSMS rs-EPI, 37.93 ± 52.42) compared to rs-EPI and 2xSMS rs-EPI. Additionally, 2xSMS rs-EPI was feasible in four clinical patients and provided robust imaging results. CONCLUSION: 2xSMS rs-EPI yielded similar SNR, FA, and MD values compared to conventional rs-EPI at reduced scan time and is feasible in clinical patients. These findings suggest the potential clinical applicability of rs-EPI for DTI of the mandibular nerve. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:663-677.

MR imaging of the temporomandibular joint: comparison between acquisitions at 7.0 T using dielectric pads and 3.0 T.

OBJECTIVES: To qualitatively and quantitatively compare MRI of the temporomandibular joint (TMJ) at 7.0 T using high-permittivity dielectric pads and 3.0 T using a clinical high-resolution protocol. METHODS: Institutional review board-approved study with written informed consent. 12 asymptomatic volunteers were imaged at 7.0 and 3.0 T using 32-channel head coils. High-permittivity dielectric pads consisting of barium titanate in deuterated suspension were used for imaging at 7.0 T. Imaging protocol consisted of oblique sagittal proton density weighted turbo spin echo sequences. For quantitative analysis, pixelwise signal-to-noise ratio maps of the TMJ were calculated. For qualitative analysis, images were evaluated by two independent readers using 5-point Likert scales. Quantitative and qualitative results were compared using t-tests and Wilcoxon signed-rank tests, respectively. RESULTS: TMJ imaging at 7.0 T using high-permittivity dielectric pads was feasible in all volunteers. Quantitative analysis showed similar signal-to-noise ratio for both field strengths (mean ± SD; 7.0 T, 13.02 ± 3.92; 3.0 T, 14.02 ± 3.41; two-sample t-tests, p = 0.188). At 7.0 T, qualitative analysis yielded better visibility of all anatomical subregions of the temporomandibular disc (anterior band, intermediate zone and posterior band) than 3.0 T (Wilcoxon signed-rank tests, p < 0.05, corrected for multiple comparisons). CONCLUSIONS: MRI of the TMJ at 7.0 T using high-permittivity dielectric pads yields superior visibility of the temporomandibular disc compared with 3.0 T.

Prevalence of simple and complex sacral perineural Tarlov cysts in a French cohort of adults and children.

OBJECTIVE: To determine the prevalence of simple and complex sacral perineural Tarlov cysts (TCs) in a cohort of children and adults. MATERIAL AND METHODS: Retrospective observational epidemiological study assessing 1100 consecutive sacral magnetic resonance (MR) studies, including 100 children and adolescents. All patients underwent 1.5T MR imaging with T1 and T2 weighted image acquisitions in sagittal and axial planes. All perineural cysts affecting the sacral nerve roots S1-S4 were quantitatively and qualitatively assessed. RESULTS: Two hundred and sixty-three sacral TCs were found in 132 adult patients (13.2%), with a female predominance (68%). None was found in children. The prevalence of TCs increased with age. The average number of cysts per patient was 2.0±1.2 with a maximum of 6 cysts in a single patient. Most of the cysts (87.5%) showed a homogenous central fluid collection and a parietal course of the nerve fibers. Complex patterns were present in 33 cysts (12.5%) within which 28 cysts showed endocystic crossing of nerve fibers and 5 cysts contained internal septations. Seventy cysts (26.6%) eroded the adjacent bone and 13 cysts (4.9%) extended to the pelvis. CONCLUSION: The prevalence of sacral TCs in our cohort corresponded to 13%, with a female predominance. Interestingly no TCs were found in children or adolescents (<18 years). In relation to the non-negligible percentage of complex cysts with internal septations, or endocystic crossing of nerve fibers, pre-interventional characterization of sacral TCs might help to choose an appropriate procedure in the treatment of rare symptomatic variants.

Kinetic DTI of the cervical spine: diffusivity changes in healthy subjects.

INTRODUCTION: The study aims to assess the influence of neck extension on water diffusivity within the cervical spinal cord. METHODS: IRB approved the study in 22 healthy volunteers. All subjects underwent anatomical MR and diffusion tensor imaging (DTI) at 1.5 T. The cervical cord was imaged in neutral (standard) position and extension. Segmental vertebral rotations were analyzed on sagittal T2-weighted images using the SpineView® software. Spinal cord diffusivity was measured in cross-sectional regions of interests at multiple levels (C1-C5). RESULTS: As a result of non-adapted coil geometry for spinal extension, 10 subjects had to be excluded. Image quality of the remaining 12 subjects was good without any deteriorating artifacts. Quantitative measurements of vertebral rotation angles and diffusion parameters showed good intra-rater reliability (ICC = 0.84-0.99). DTI during neck extension revealed significantly decreased fractional anisotropy (FA) and increased radial diffusivity (RD) at the C3 level and increased apparent diffusion coefficients (ADC) at the C3 and C4 levels (p < 0.01 Bonferroni corrected). The C3/C4 level corresponded to the maximal absolute change in segmental vertebral rotation between the two positions. The increase in RD correlated positively with the degree of global extension, i.e., the summed vertebral rotation angle between C1 and C5 (R = 0.77, p = 0.006). CONCLUSION: Our preliminary results suggest that DTI can quantify changes in water diffusivity during cervical spine extension. The maximal differences in segmental vertebral rotation corresponded to the levels with significant changes in diffusivity (C3/C4). Consequently, kinetic DTI measurements may open new perspectives in the assessment of neural tissue under biomechanical constraints.

68Gallium-DOTATATE PET in meningioma: A reliable predictor of tumor growth rate?

BACKGROUND: DOTATATE-based radionuclides have added new options in the diagnosis and treatment of meningiomas; however, a reliable predictor of tumor growth has still not been established. METHODS: We analyzed 64 meningiomas imaged with (68)Ga-DOTATATE PET. Tumor growth rates were calculated by volumetric analysis of sequential MRI scans. Maximums of standardized uptake values (SUVmax) were correlated with tumor growth and covariates. RESULTS: World Health Organization (WHO) grades I and II meningiomas showed a correlation of SUVmax and tumor growth rate (meningiomas limited to the intracranial compartment: r = 0.757, P < .001, and transosseous growing meningiomas: r = 0.819, P = .024). SUVmax was significantly higher and the slope of the linear regression significantly steeper in transosseous compared with intracranial meningiomas (both P < .001). The association remained significant in multivariate analysis, and the prediction of tumor growth rate was independent of WHO grade. Anaplastic meningiomas showed no significant correlation of SUVmax and tumor growth. CONCLUSIONS: (68)Ga-DOTATATE PET is a reliable predictor of tumor growth in WHO grades I and II meningiomas and provides additional information to conventional cross-sectional imaging modalities. Hence, (68)Ga-DOTATATE PET can assist in selecting the time point for treatment initiation. Furthermore, meningiomas with fast tumor growth and transosseous expansion elicit the highest DOTATATE binding; therefore, they might be especially suited for DOTATATE-based therapy.

Comparison of a 32-channel head coil and a 2-channel surface coil for MR imaging of the temporomandibular joint at 3.0 T.

OBJECTIVE: To quantitatively and qualitatively compare MRI of the temporomandibular joint (TMJ) using a standard TMJ surface coil and a head coil at 3.0 T. METHODS: 22 asymptomatic volunteers were MR imaged using a 2-channel surface coil (standard TMJ coil) and a 32-channel head coil at 3.0 T (Philips Ingenia; Philips Healthcare, Netherlands). Imaging protocol consisted of an oblique sagittal proton density weighted turbo spin echo sequence (repetition time/echo time, 2700/26 ms). For quantitative assessment, a spherical phantom was imaged using the same sequence including a noise scan and a B1+ scan. Signal-to-noise ratio (SNR) maps and B1+ maps were calculated on a voxelwise basis. For qualitative evaluation, all volunteers underwent MRI of both TMJs with the jaw in the closed position. Two independent blinded readers assessed accuracy of TMJ anatomical representation and overall image quality on a 5-point scale. Quantitative and qualitative measurements were compared between coils using t-tests and Wilcoxon signed-rank test, respectively. RESULTS: Quantitative analysis showed similar B1+ and significantly higher SNR for the head coil than the TMJ surface coil. Qualitative analysis showed significantly better visibility and delineation of clinically relevant anatomical structures of the TMJ, including the articular disc, bilaminar zone and lateral pterygoid muscle. Furthermore, better overall image quality was observed for the head coil than for the TMJ surface coil. CONCLUSIONS: A 32-channel head coil is preferable to a standard 2-channel TMJ surface coil when imaging the TMJ at 3.0 T, because it yields higher SNR, thus increasing accuracy of the anatomical representation of the TMJ.

MR neurographic orthopantomogram: Ultrashort echo-time imaging of mandibular bone and teeth complemented with high-resolution morphological and functional MR neurography.

PURPOSE: Panoramical radiographs or cone-beam computed tomography (CT) are the standard-of-care in dental imaging to assess teeth, mandible, and mandibular canal pathologies, but do not allow assessment of the inferior alveolar nerve itself nor of its branches. We propose a new technique for "MR neurographic orthopantomograms" exploiting ultrashort echo-time (UTE) imaging of bone and teeth complemented with high-resolution morphological and functional MR neurography. MATERIALS AND METHODS: The Institutional Review Board approved the study in 10 healthy volunteers. Imaging of the subjects mandibles at 3.0T (Magnetom Skyra, Siemens-Healthcare) using a 64-channel head coil with isotropic spatial resolution for subsequent multiplanar reformatting, was performed. Bone images were acquired using a 3D PETRA sequence (TE, 0.07 msec). Morphological nerve imaging was performed using a dedicated 3D PSIF and 3D SPACE STIR sequence. Functional MR neurography was accomplished using a new accelerated diffusion-tensor-imaging (DTI) prototype sequence (2D SMS-accelerated RESOLVE). Qualitative and quantitative image analysis was performed and descriptive statistics are provided. RESULTS: Image acquisition and subsequent postprocessing into the MR neurographic orthopantomogram by overlay of morphological and functional images were feasible in all 10 volunteers without artifacts. All mandibular bones and mandibular nerves were assessable and considered normal. Fiber tractography with quantitative evaluation of physiological diffusion properties of mandibular nerves yielded the following mean ± SD values: fractional anisotropy, 0.43 ± 0.07; mean diffusivity (mm(2) /s), 0.0014 ± 0.0002; axial diffusivity, 0.0020 ± 0.0002, and radial diffusivity, 0.0011 ± 0.0001. CONCLUSION: The proposed technique of MR neurographic orthopantomogram exploiting UTE imaging complemented with high-resolution morphological and functional MR neurography was feasible and allowed comprehensive assessment of osseous texture and neural microarchitecture in a single examination. J. Magn. Reson. Imaging 2016;44:393-400.

Magnetic Resonance Imaging of the Temporomandibular Joint at 7.0 T Using High-Permittivity Dielectric Pads: A Feasibility Study.

OBJECTIVES: The aims of this study were to show feasibility and to quantitatively and qualitatively evaluate the use of high-permittivity dielectric pads for imaging the temporomandibular joint (TMJ) at 7.0 T. MATERIALS AND METHODS: This study is an institutional review board-approved study with written informed consent. Ten asymptomatic volunteers (20 TMJs) were magnetic resonance imaged using a 32-channel head coil at 7.0 T (Achieva; Philips Healthcare, the Netherlands) with and without high-permittivity dielectric pads consisting of barium titanate in deuterated suspension. Imaging protocol consisted of an oblique sagittal proton density-weighted turbo-spin echo sequence. For quantitative evaluation, B1 maps and voxelwise signal-to-noise ratio (SNR) maps were calculated. For qualitative evaluation, 2 readers assessed the visibility of anatomical structures of the TMJ and overall image quality on a 5-point Likert scale from 1 (excellent visibility) to 5 (not visible) in consensus. Quantitative and qualitative measurements were compared between images acquired with and without pads. RESULTS: Imaging the TMJ using dielectric pads was feasible in all volunteers. The quantitative analysis showed locally higher B1+ and higher SNR in the area covering the TMJ for the scans performed with dielectric pads compared with those without pads (SNR: mean [SD] pads, 12.38 [3.18]; mean [SD] no pads, 6.60 [0.72]). The qualitative analysis showed significantly better visibility and delineation of clinically relevant anatomical structures of the TMJ, including temporomandibular disc, bilaminar zone, mandibular fossa, mandibular condyle, and pterygoid muscle. In addition, observers judged overall image quality as better for images taken with pads compared with those taken without pads (mean [SD] pads, 1.40 [0.50]; mean [SD] no pads, 4.25 [0.78]). CONCLUSIONS: The application of high-permittivity dielectric pads improves the local B1+ field and thus the SNR, optimizing TMJ magnetic resonance imaging at 7.0 T.

Quantitative H2[(15)O]-PET in Pediatric Moyamoya Disease: Evaluating Perfusion before and after Cerebral Revascularization.

BACKGROUND: Moyamoya disease (MMD) is an idiopathic intracranial angiopathy with a progressive spontaneous occlusion of the circle of Willis resulting in repeated ischemia if not diagnosed and treated early, especially in children. Prevention of stroke is achieved by revascularization of the affected cerebral regions. Functional imaging techniques such as H2[(15)O]-Positron emission tomography (PET) allow quantification of cerebral perfusion/blood flow (CBF) and in particular cerebrovascular response after acetazolamide (AZA) challenge. The cerebrovascular reserve (CVR) can then be calculated and used to identify regions at risk of infarct, hence allowing surgery to be specifically targeted and personalized. METHODS: Pediatric patients with diagnosed MMD underwent initial H2[(15)O]-PET scans at baseline and after stimulation with AZA. Indication for surgery was then based collectively on the extent of disease observed clinically and on magnetic resonance imaging, on the arterial territories involved, as seen in angiography and the respective regional CVR observed in PET. Cerebral revascularization surgeries were subsequently performed, tailored to the individual patient. Postoperative assessment of clinical outcome was augmented with follow-up PET (median duration after surgery, 10.4 months). CBF at baseline, after AZA and CVR were compared between presurgery and postsurgery scans in the areas supplied by the major cerebral arteries. RESULTS: Parametric images reflecting CBF, response to AZA and CVR clearly showed deficits in cortical but not subcortical regions or cerebellum. AZA-CBF and CVR deficits were most clear in middle cerebral artery and anterior cerebral artery (ACA) regions. In addition to the clinical symptomatology, angiography, AZA-CBF, and CVR images allowed the laterality of deficits to be clearly visualized for tailored surgery and the indication for targeted ACA or posterior cerebral artery revascularization to be assessed. Comparison of baseline CBF, AZA-CBF, and CVR between presurgery and postsurgery scans in revascularized areas revealed a significant improvement in baseline and AZA-CBF after surgery. Although no significant differences in CVR after revascularization surgery were found, a clear improvement of the deficits apparent in AZA-CBF in revascularized regions was found. CONCLUSIONS: We demonstrate that quantitative H2[(15)O]-PET is a highly useful tool to direct surgical intervention in MMD. Detailed quantitative analysis of CBF changes and CVR after surgery supports a targeted surgical approach.

Regional cerebral blood flow estimated by early PiB uptake is reduced in mild cognitive impairment and associated with age in an amyloid-dependent manner.

Early uptake of [(11)C]-Pittsburgh Compound B (ePiB, 0-6 minutes) estimates cerebral blood flow. We studied ePiB in 13 PiB-negative and 10 PiB-positive subjects with mild cognitive impairment (MCI, n = 23) and 11 PiB-positive and 74 PiB-negative cognitively healthy elderly control subjects (HCS, n = 85) in 6 bilateral volumes of interest: posterior cingulate cortex (PCC), hippocampus (hipp), temporoparietal region, superior parietal gyrus, parahippocampal gyrus (parahipp), and inferior frontal gyrus (IFG) for the associations with cognitive status, age, amyloid deposition, and apolipoprotein E ε4-allele. We observed no difference in ePiB between PiB-positive and -negative subjects and carriers and noncarriers. EPiB decreased with age in PiB-positive subjects in bilateral superior parietal gyrus, bilateral temporoparietal region, right IFG, right PCC, and left parahippocampal gyrus but not in PiB-negative subjects. MCI had lower ePiB than HCS (left PCC, left IFG, and left and right hipp). Lowest ePiB values were found in MCI of 70 years and older, who also displayed high cortical PiB binding. This suggests that lowered regional cerebral blood flow indicated by ePiB is associated with age in the presence but not in the absence of amyloid pathology.

Image registration accuracy of an in-house developed patient transport system for PET/CT+MR and SPECT+CT imaging.

OBJECTIVE: The aim of this study was to investigate the registration accuracy of a newly developed patient shuttle system that can integrate different scanners by patient transfer without repositioning for 'hardware'-based image fusion. We aimed to assess the registration accuracy of image fusion in two different settings: a trimodality PET/CT+MR system and a SPECT+CT system. MATERIALS AND METHODS: In this prospective study, 43 patients underwent either sequential PET/CT and MR (n=31) or sequential SPECT and diagnostic CT (D-CT) (n=12). A side-loading patient shuttle system was used for patient transport. For PET/CT+MR, hardware-only coregistration was performed and then validated with anatomical landmarks on CT and MR. SPECT+D-CT image fusion was performed with external cobalt-57 markers and manual fusion. Registration accuracy was analysed by anatomical landmarks on the attenuation correction CT and the D-CT. RESULTS: For the PET/CT+MR system, the mean offset between original CT and MR images in all 31 patients was 8.1±5.7 mm in the X-axis, 5±4 mm in the Y-axis and 4.9±5.6 mm in the Z-axis. The validation of the cobalt-57 marker-assisted SPECT+D-CT fusion yielded offsets of 0.7±1.7 mm in the X-axis, 2.1±1.7 mm in the Y-axis and 0.8±1.8 mm in the Z-axis. CONCLUSION: Sequential PET/CT+MR and SPECT+D-CT imaging using a dedicated patient shuttle system is feasible, resulting in mean offsets between data sets of 10.7 mm using the gantry laser system and 2.4 mm with fiducial markers.

Whole-body nonenhanced PET/MR versus PET/CT in the staging and restaging of cancers: preliminary observations.

PURPOSE: To assess the diagnostic performance of whole-body non-contrast material-enhanced positron emission tomography (PET)/magnetic resonance (MR) imaging and PET/computed tomography (CT) for staging and restaging of cancers and provide guidance for modality and sequence selection. MATERIALS AND METHODS: This study was approved by the institutional review board and national government authorities. One hundred six consecutive patients (median age, 68 years; 46 female and 60 male patients) referred for staging or restaging of oncologic malignancies underwent whole-body imaging with a sequential trimodality PET/CT/MR system. The MR protocol included short inversion time inversion-recovery ( STIR short inversion time inversion-recovery ), Dixon-type liver accelerated volume acquisition ( LAVA liver accelerated volume acquisition ; GE Healthcare, Waukesha, Wis), and respiratory-gated periodically rotated overlapping parallel lines with enhanced reconstruction ( PROPELLER periodically rotated overlapping parallel lines with enhanced reconstruction ; GE Healthcare) sequences. Primary tumors (n = 43), local lymph node metastases (n = 74), and distant metastases (n = 66) were evaluated for conspicuity (scored 0-4), artifacts (scored 0-2), and reader confidence on PET/CT and PET/MR images. Subanalysis for lung lesions (n = 46) was also performed. Relevant incidental findings with both modalities were compared. Interreader agreement was analyzed with intraclass correlation coefficients and κ statistics. Lesion conspicuity, image artifacts, and incidental findings were analyzed with nonparametric tests. RESULTS: Primary tumors were less conspicuous on STIR short inversion time inversion-recovery (3.08, P = .016) and LAVA liver accelerated volume acquisition (2.64, P = .002) images than on CT images (3.49), while findings with the PROPELLER periodically rotated overlapping parallel lines with enhanced reconstruction sequence (3.70, P = .436) were comparable to those at CT. In distant metastases, the PROPELLER periodically rotated overlapping parallel lines with enhanced reconstruction sequence (3.84) yielded better results than CT (2.88, P < .001). Subanalysis for lung lesions yielded similar results (primary lung tumors: CT, 3.71; STIR short inversion time inversion-recovery , 3.32 [P = .014]; LAVA liver accelerated volume acquisition , 2.52 [P = .002]; PROPELLER periodically rotated overlapping parallel lines with enhanced reconstruction , 3.64 [P = .546]). Readers classified lesions more confidently with PET/MR than PET/CT. However, PET/CT showed more incidental findings than PET/MR (P = .039), especially in the lung (P < .001). MR images had more artifacts than CT images. CONCLUSION: PET/MR performs comparably to PET/CT in whole-body oncology and neoplastic lung disease, with the use of appropriate sequences. Further studies are needed to define regionalized PET/MR protocols with sequences tailored to specific tumor entities.

Contrast-enhanced PET/MR imaging versus contrast-enhanced PET/CT in head and neck cancer: how much MR information is needed?

UNLABELLED: Considering PET/MR imaging as a whole-body staging tool, scan time restrictions in a single body area are mandatory for the cost-effective clinical operation of an integrated multimodality scanner setting. It has to be considered that (18)F-FDG already acts as a contrast agent and that under certain circumstances MR contrast may not yield additional clinically relevant information. The concept of the present study was to understand which portions of the imaging information enhance the sensitivity and specificity of the hybrid examination and which portions are redundant. METHODS: One hundred fifty consecutive patients referred for primary staging or restaging of head and neck cancer underwent sequential whole-body (18)F-FDG PET with CT-based attenuation correction, contrast-enhanced (ce) CT, and conventional diagnostic MR imaging of the head and neck in a trimodality PET/CT-MR system. Assessed were image quality, lesion conspicuity, diagnostic confidence, and the benefit of additional coronal and sagittal imaging planes in cePET/CT, PET/MR imaging with only T2-weighted fat-suppressed images (T2w PET/MR imaging), and cePET/MR imaging. RESULTS: In 85 patients with at least 1 PET-positive lesion, 162 lesions were evaluated. Similar robustness was found for CT and MR image quality. T2w PET/MR imaging performed similarly to (metastatic lymph nodes) or better than (primary tumors) cePET/CT in the morphologic characterization of PET-positive lesions and permitted the diagnosis of necrotic or cystic lymph node metastasis without application of intravenous contrast medium. CePET/MR imaging yielded a higher diagnostic confidence for accurate lesion conspicuity (especially in the nasopharynx and in the larynx), infiltration of adjacent structures, and perineural spread. CONCLUSION: The results of the present study provide evidence that PET/MR imaging can serve as a legitimate alternative to PET/CT in the clinical workup of patients with head and neck cancers. Intravenous MR contrast medium may be applied only if the exact tumor extent or infiltration of crucial structures is of concern (i.e., preoperatively) or if perineural spread is anticipated. In early assessment of the response to therapy, in follow-up examinations, or in a whole-body protocol for non-head and neck tumors, T2w PET/MR imaging may be sufficient for coverage of the head and neck. The additional MR scanning time may instead be used for advanced MR techniques to increase the specificity of the hybrid imaging examination.

Comparison of PET template-based and MRI-based image processing in the quantitative analysis of C11-raclopride PET.

BACKGROUND: Quantitative measures of 11C-raclopride receptor binding can be used as a correlate of postsynaptic D2 receptor density in the striatum, allowing 11C-raclopride positron emission tomography (PET) to be used for the differentiation of Parkinson's disease from atypical parkinsonian syndromes. Comparison with reference values is recommended to establish a reliable diagnosis. A PET template specific to raclopride may facilitate direct computation of parametric maps without the need for an additional MR scan, aiding automated image analysis. METHODS: Sixteen healthy volunteers underwent a dynamic 11C-raclopride PET and a high-resolution T1-weighted MR scan of the brain. PET data from eight healthy subjects was processed to generate a raclopride-specific PET template normalized to standard space. Subsequently, the data processing based on the PET template was validated against the standard magnetic resonance imaging (MRI)-based method in 8 healthy subjects and 20 patients with suspected parkinsonian syndrome. Semi-quantitative image analysis was performed in Montreal Neurological Institute (MNI) and in original image space (OIS) using VOIs derived from a probabilistic brain atlas previously validated by Hammers et al. (Hum Brain Mapp, 15:165-174, 2002). RESULTS: The striatal-to-cerebellar ratio (SCR) of 11C-raclopride uptake obtained using the PET template was in good agreement with the MRI-based image processing method, yielding a Lin's concordance coefficient of 0.87. Bland-Altman analysis showed that all measurements were within the ±1.96 standard deviation range. In all 20 patients, the PET template-based processing was successful and manual volume of interest optimization had no further impact on the diagnosis of PD in this patient group. A maximal difference of <5% was found between the measured SCR in MNI space and OIS. CONCLUSIONS: The PET template-based method for automated quantification of postsynaptic D2 receptor density is simple to implement and facilitates rapid, robust and reliable image analysis. There was no significant difference between the SCR values obtained with either PET- or MRI-based image processing. The method presented alleviates the clinical workflow and facilitates automated image analysis.

18F-FDG-PET/CT for the assessment of the contralateral neck in patients with head and neck squamous cell carcinoma.

OBJECTIVES/HYPOTHESIS: The aim was to compare the value of 18-Fluoro-Deoxyglucose (18F-FDG) positron emission tomography (PET)/computed tomography (CT) regarding contralateral lymph node (LN) metastasis in the neck. STUDY DESIGN: Retrospective analysis of 61 patients staged by 18F-FDG-PET/CT. METHODS: Cytology/histology served as a reference standard. Further, metabolic midline invasion (MI) of the primary tumor and the presence of bilateral LN metastases were assessed. RESULTS: A true positive rate in the ipsilateral neck of 80% versus 65% in the contralateral neck was found (P = 0.067). Median-standardized uptake value (SUV)-max for suspicious LN ipsilaterally was 7.6 versus 5.8 contralaterally (P = 0.038). There was no positive correlation between metabolic MI and bilateral metastasis (P = 0.82). CONCLUSIONS: The rate of true positive detected LN by 18F-FDG-PET/CT is less on the contralateral neck side; therefore, all suspicious LNs should be verified by cytology. A high SUV in the contralateral neck suggests metastatic disease regardless of nodal size. Metabolic MI needs to be addressed carefully as it was not predictive for bilateral LN involvement. LEVEL OF EVIDENCE: 4.

Discrimination and anatomical mapping of PET-positive lesions: comparison of CT attenuation-corrected PET images with coregistered MR and CT images in the abdomen.

PURPOSE: PET/MR has the potential to become a powerful tool in clinical oncological imaging. The purpose of this prospective study was to evaluate the performance of a single T1-weighted (T1w) fat-suppressed unenhanced MR pulse sequence of the abdomen in comparison with unenhanced low-dose CT images to characterize PET-positive lesions. METHODS: A total of 100 oncological patients underwent sequential whole-body (18)F-FDG PET with CT-based attenuation correction (AC), 40 mAs low-dose CT and two-point Dixon-based T1w 3D MRI of the abdomen in a trimodality PET/CT-MR system. PET-positive lesions were assessed by CT and MRI with regard to their anatomical location, conspicuity and additional relevant information for characterization. RESULTS: From among 66 patients with at least one PET-positive lesion, 147 lesions were evaluated. No significant difference between MRI and CT was found regarding anatomical lesion localization. The MR pulse sequence used performed significantly better than CT regarding conspicuity of liver lesions (p < 0.001, Wilcoxon signed ranks test), whereas no difference was noted for extrahepatic lesions. For overall lesion characterization, MRI was considered superior to CT in 40 % of lesions, equal to CT in 49 %, and inferior to CT in 11 %. CONCLUSION: Fast Dixon-based T1w MRI outperformed low-dose CT in terms of conspicuity and characterization of PET-positive liver lesions and performed similarly in extrahepatic tumour manifestations. Hence, under the assumption that the technical issue of MR AC for whole-body PET examinations is solved, in abdominal PET/MR imaging the replacement of low-dose CT by a single Dixon-based MR pulse sequence for anatomical lesion correlation appears to be valid and robust.

PET/MR imaging of bone lesions--implications for PET quantification from imperfect attenuation correction.

PURPOSE: Accurate attenuation correction (AC) is essential for quantitative analysis of PET tracer distribution. In MR, the lack of cortical bone signal makes bone segmentation difficult and may require implementation of special sequences. The purpose of this study was to evaluate the need for accurate bone segmentation in MR-based AC for whole-body PET/MR imaging. METHODS: In 22 patients undergoing sequential PET/CT and 3-T MR imaging, modified CT AC maps were produced by replacing pixels with values of >100 HU, representing mostly bone structures, by pixels with a constant value of 36 HU corresponding to soft tissue, thereby simulating current MR-derived AC maps. A total of 141 FDG-positive osseous lesions and 50 soft-tissue lesions adjacent to bones were evaluated. The mean standardized uptake value (SUVmean) was measured in each lesion in PET images reconstructed once using the standard AC maps and once using the modified AC maps. Subsequently, the errors in lesion tracer uptake for the modified PET images were calculated using the standard PET image as a reference. RESULTS: Substitution of bone by soft tissue values in AC maps resulted in an underestimation of tracer uptake in osseous and soft tissue lesions adjacent to bones of 11.2 ± 5.4% (range 1.5-30.8%) and 3.2 ± 1.7% (range 0.2-4%), respectively. Analysis of the spine and pelvic osseous lesions revealed a substantial dependence of the error on lesion composition. For predominantly sclerotic spine lesions, the mean underestimation was 15.9 ± 3.4% (range 9.9-23.5%) and for osteolytic spine lesions, 7.2 ± 1.7% (range 4.9-9.3%), respectively. CONCLUSION: CT data simulating treating bone as soft tissue as is currently done in MR maps for PET AC leads to a substantial underestimation of tracer uptake in bone lesions and depends on lesion composition, the largest error being seen in sclerotic lesions. Therefore, depiction of cortical bone and other calcified areas in MR AC maps is necessary for accurate quantification of tracer uptake values in PET/MR imaging.