Felix P. Kuhn

Contrast-Enhanced PET/MR Imaging Versus Contrast-Enhanced PET/CT in Head and Neck Cancer: How Much MR Information Is Needed?

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 18F-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 18F-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.

Coronary artery calcium scoring: Influence of adaptive statistical iterative reconstruction using 64-MDCT

OBJECTIVE Assessment of coronary artery calcification is increasingly used for cardiovascular risk stratification. We evaluated the reliability of calcium-scoring results using a novel iterative reconstruction algorithm (ASIR) on a high-definition 64-slice CT scanner, as such data is lacking. METHODS AND RESULTS In 50 consecutive patients Agatston scores, calcium mass and volume score were assessed. Comparisons were performed between groups using filtered back projection (FBP) and 20-100% ASIR algorithms. Calcium score was measured in the coronary arteries, signal and noise were measured in the aortic root and left ventricle. In comparison with FBP, use of 20%, 40%, 60%, 80%, and 100% ASIR resulted in reduced image noise between groups (7.7%, 18.8%, 27.9%, 39.86%, and 48.56%, respectively; p<0.001) without difference in signal (p=0.60). With ASIR algorithms Agatston coronary calcium scoring significantly decreased compared with FBP algorithms (837.3 ± 130.3; 802.2 ± 124.9, 771.5 ± 120.7; 744.7 ± 116.8, 724.5 ± 114.2, and 709.2 ± 112.3 for 0%, 20%, 40%, 60%, 80%, and 100% ASIR, respectively, p<0.001). Volumetric score decreased in a similar manner (p<0.001) while calcium mass remained unchanged. Mean effective radiation dose was 0.81 ± 0.08 mSv. CONCLUSION ASIR results in image noise reduction. However, ASIR image reconstruction techniques for HDCT scans decrease Agatston coronary calcium scores. Thus, one needs to be aware of significant changes of the scoring results caused by different reconstruction methods.

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.

Clinical Positron Emission Tomography/Magnetic Resonance Imaging Applications

Although clinical positron emission tomography (PET)/computed tomography (CT) applications were obvious and have completely replaced PET in oncology, clinical applications of PET/magnetic resonance (MR) are currently not clearly defined. This is due to the lack of clinical data, which is mainly because PET/MR technology is not clinically mature at this point. Open issues are technical and concern ease of obtaining PET attenuation correction maps, dealing with, for example, MR surface coil metal in the PET field-of-view and appropriate workflows leading to a cost-effective examination. All issues can be circumvented by using a shuttle-connected PET/CT-MR system, but the penalty is that simultaneous PET and MR imaging are not possible and potential motion between examinations may occur. Clinically, some systems installed worldwide start to have a reasonable bulk of clinical data. Preliminary results suggest that in oncology, PET/MR may have advantages over PET/CT in head and neck imaging. In liver imaging, more PET-positive lesions are seen on MR than on CT, but that does not mean that PET/MR is superior to PET/CT. Possibly in some settings where a contrast-enhanced PET/CT is needed to be diagnostic, PET/MR can be done without contrast media. Although PET/CT has virtually no role in brain imaging, this may be an important domain for PET/MR, particularly in dementia imaging. The role of PET/MR in the heart is as yet undefined, and much research will have to be done to elucidate this role. At this point, it is also not clear where the simultaneity afforded by a fully integrated PET/MR is really needed. Sequential data acquisition even on separate systems and consecutive software image fusion may well be appropriate. With the increasing installed base of systems, clinical data will be forthcoming and define more clearly where there is clinical value in PET/MR at an affordable price.

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.

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

BackgroundQuantitative 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.MethodsSixteen 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).ResultsThe 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.ConclusionsThe 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

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.

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.

Diffusion Tensor Imaging of Lumbar Nerve Roots: Comparison Between Fast Readout-Segmented and Selective-Excitation Acquisitions.

ObjectivesThe aim of this study was to compare the quality of recently emerged advanced diffusion tensor imaging (DTI) techniques with conventional single-shot echo-planar imaging (EPI) in a functional assessment of lumbar nerve roots. Materials and MethodsThe institutional review board approved the study including 12 healthy volunteers. Diffusion tensor imaging was performed at 3 T (MAGNETOM Skyra; Siemens Healthcare) with b-values of 0 and 700 s/mm2 and an isotropic spatial resolution for subsequent multiplanar reformatting. The nerve roots L2 to S1 were imaged in coronal orientation with readout-segmented EPI (rs-DTI) and selective-excitation EPI (sTX-DTI) with an acquisition time of 5 minutes each, and in axial orientation with single-shot EPI (ss-DTI) with an acquisition time of 12 minutes (scan parameters as in recent literature). Two independent readers qualitatively and quantitatively assessed image quality. ResultsThe interobserver reliability ranged from “substantial” to “almost perfect” for all examined parameter and all 3 sequences (&kgr; = 0.70–0.94). Overall image quality was rated higher, and artifact levels were scored lower for rs-DTI and sTX-DTI than for ss-DTI (P = 0.007–0.027), while fractional anisotropy and signal-to-noise ratio values were similar for all sequences (P ≥ 0.306 and P ≥ 0.100, respectively). Contrast-to-noise ratios were significantly higher for rs-DTI and ss-DTI than for sTX-DTI (P = 0.004–0.013). ConclusionsDespite shorter acquisition times, rs-DTI and sTX-DTI produced images of higher quality with smaller geometrical distortions than the current standard of reference, ss-DTI. Thus, DTI acquisitions in the coronal plane, requiring fewer slices for full coverage of exiting nerve roots, may allow for functional neurography in scan times suitable for routine clinical practice.

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

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.