Spatial-temporal perfusion patterns of the human liver assessed by pseudo-continuous arterial spin labeling MRI.

PURPOSE: To investigate the capabilities of a modern pseudo-continuous arterial spin labeling (PCASL) technique for non-invasive assessment of the temporal and spatial distribution of the liver perfusion in healthy volunteers on a clinical MR system at 3T. MATERIALS AND METHODS: A 2D-PCASL multi-slice echo planar imaging sequence was adapted to the specific conditions in liver: a) labeling by PCASL was optimized to the flow characteristics in the portal vein, b) background suppression was applied for reduction of motion related artifacts, c) post labeling delays (PLDs) were varied over a large range (0.7-3.5s) in order to get better insight in the temporal and spatial distribution of tagged blood in the liver, and d) a special timed-breathing protocol was used allowing for recording of 16 to 18 label-control image pairs and a reference M0 image for each of 4 to 6 slices within approx. 5min for one PLD. RESULTS: Measurements with multiple PLDs showed dominating perfusion signal in macroscopic blood vessels for PLDs up to 1.5 s, whereas pure liver parenchyma revealed maximum perfusion signal for a PLD of approx. 2 s, and detectable signal up to PLDs of 3.5 s. Data fitting to a perfusion model for liver provided a mean global perfusion of 153±15ml/100g/min and a mean transit time of 1938±332ms in liver parenchyma. Measurements with a single PLD of 2 s demonstrated that portal-venous and arterial perfusion components can be measured separately by two measurements with two different positions of the labeling plane (one for labeling of the global hepatopetal blood flow and one for selective labeling of the portal blood flow only). Relative contribution of blood from the hepatic artery to the global liver perfusion, the hepatic perfusion index (HPI), amounted to approx. 23%. CONCLUSION: Modern and adapted protocols for assessment of liver perfusion by PCASL have the potential to provide perfusion and blood transit time maps in reasonable acquisition time.

Fast non-enhanced abdominal examination protocols in PET/MRI for patients with neuroendocrine tumors (NET): comparison to multiphase contrast-enhanced PET/CT.

PURPOSE: To evaluate fast non-enhanced protocols for abdominal PET/MRI in comparison to contrast-enhanced PET/CT with somatostatin receptor (SSR)-specific radiotracers regarding effectiveness of lesion detection in NET patients. METHODS: This was a retrospective analysis of 29 patients (12 male, 57 ± 13 years) who underwent PET/CT and subsequently PET/MRI at the same day. Two readers evaluated independently four PET/MRI setups: (I) PET + T2 Half Fourier Acquisition Single Shot Turbo Spin Echo (T2 HASTE), (II) PET + T2 HASTE + T2-weighted spin-echo sequence (T2 TSE), III) PET + T2 HASTE + Diffusion Weighted Imaging (DWI) and (IV) PET + T2 HASTE + T2 TSE + DWI. A consensus reading of PET/MRI and PET/CT including follow-up examinations served as the reference standard for lesion-based analysis. Lesion sizes were assessed. RESULTS: Setup IV provided comparable overall detection rates as PET/CT in both readers: PET/MRI 91.5%/92.9% versus 89.7% in PET/CT. In liver and bone lesions (mean diameter: 1.9 and 1.5 cm), PET/MRI was equal or superior to PET/CT: 98%/98% versus 85% in PET/CT; 100%/95% versus 100% in PET/CT, but inferior in pancreatic lesions, small bowel lesions and lymph node metastases (mean diameter: 1.3, 0.5 and 1.8 cm). CONCLUSION: A non-enhanced MR protocol comprising T2 HASTE, T2 TSE and DWI for SSR-PET/MRI seems to provide comparable effectiveness in lesions detection as multiphase contrast-enhanced PET/CT. It might, therefore, serve as valid alternative, e.g., for follow-up examinations in patients with unresectable NET and kidney failure.

Simultaneous multislice diffusion-weighted imaging in whole-body positron emission tomography/magnetic resonance imaging for multiparametric examination in oncological patients.

OBJECTIVES: The aim of this study was to compare the diagnostic performance of simultaneous multislice diffusion-weighted imaging (DWI-SMS) with that of standard DWI (DWI-STD) in whole-body 3-T PET/MRI examination protocols in oncological patients. METHODS: In a phantom study, we evaluated the apparent diffusion coefficients (ADC) from the two techniques. In ten volunteers, we assessed ADC values in different organs. In 20 oncological patients, we evaluated subjective image quality (Likert scale, 5 indicating excellent) and artefacts in different body regions. We also rated the conspicuity and acquired the ADC values of PET-positive tumorous lesions. RESULTS: The scan time for the whole-body DWI-SMS examinations was 40% shorter than the scan time for the DWI-STD examinations (84 s vs. 140 s per table position). The phantom and volunteer studies showed lower ADC values from DWI-SMS in the liver and muscle (psoas muscle 1.4 vs. 1.3). In patients, DWI-SMS provided poorer subjective image quality in the thoracoabdominal region (3.0 vs. 3.8, p = 0.02) and overall more artefacts (138 vs. 105). No significant differences regarding conspicuity and ADC values of lesions were found. CONCLUSIONS: DWI-SMS seems to provide reliable conspicuity and ADC values of tumorous lesions similar to those provided by DWI-STD. Therefore, although providing poorer image quality in certain regions, DWI-SMS can clearly reduce PET/MRI scan times in oncological patients. KEY POINTS: • DWI-SMS can reduce PET/MRI scan times in oncological patients. • DWI-SMS provides reliable ADC values and good lesion conspicuity similar to those provided by DWI-STD. • DWI-SMS may provide poorer image quality in regions with low signal.

Characterization of Severe Arterial Phase Respiratory Motion Artifact on Gadoxetate Disodium-Enhanced MRI - Assessment of Interrater Agreement and Reliability.

PURPOSE: To assess the interrater agreement and reliability of experienced abdominal radiologists in the characterization and grading of arterial phase gadoxetate disodium-related respiratory motion artifact on liver MRI. MATERIALS AND METHODS: This prospective multicenter study was initiated by the working group for abdominal imaging within the German Roentgen Society (DRG), and approved by the local IRB of each participating center. 11 board-certified radiologists independently reviewed 40 gadoxetate disodium-enhanced liver MRI datasets. Motion artifacts in the arterial phase were assessed on a 5-point scale. Interrater agreement and reliability were calculated using the intraclass correlation coefficient (ICC) and Kendall coefficient of concordance (W), with p < 0.05 deemed significant. RESULTS: The ICC for interrater agreement and reliability were 0.983 (CI 0.973 - 0.990) and 0.985 (CI 0.978 - 0.991), respectively (both p < 0.0001), indicating excellent agreement and reliability. Kendall's W for interrater agreement was 0.865. A severe motion artifact, defined as a mean motion score ≥ 4 in the arterial phase was observed in 12 patients. In these specific cases, a motion score ≥ 4 was assigned by all readers in 75 % (n = 9/12 cases). CONCLUSION: Differentiation and grading of arterial phase respiratory motion artifact is possible with a high level of inter-/intrarater agreement and interrater reliability, which is crucial for assessing the incidence of this phenomenon in larger multicenter studies. KEY POINTS: · Inter- and intrarater agreement for motion artifact scoring is excellent among experienced readers.. · Interrater reliability for motion artifact scoring is excellent among experienced readers.. · Characterization of severe motion artifacts proved feasible in this multicenter study.. CITATION FORMAT: · Ringe KI, Luetkens JA, Fimmers R et al. Characterization of Severe Arterial Phase Respiratory Motion Artifact on Gadoxetate Disodium-Enhanced MRI - Assessment of Interrater Agreement and Reliability. Fortschr Röntgenstr 2017; 190: 341 - 347.

Scan time reduction in diffusion-weighted imaging of the pancreas using a simultaneous multislice technique with different acceleration factors: How fast can we go?

OBJECTIVES: To investigate the feasibility of simultaneous multislice-accelerated diffusion-weighted imaging (sms-DWI) of the pancreas with different acceleration factors and its influence on image quality, acquisition time and apparent diffusion coefficients (ADCs) in comparison to conventional sequences. METHODS: DWI of the pancreas was performed at 1.5T in ten healthy volunteers and 20 patients with sms-accelerated echo-planar DWI using two different sms-acceleration factors of 2 and 3 (sms2/3-DWI). These DWI sequences were compared to conventional DWI (c-DWI) in terms of image quality parameters (5-point Likert scale) and ADC measurements. RESULTS: c-DWI and sms2-DWI offered equivalently high overall image quality (4 [1; 5]) with scan time reduction to one-third (c-DWI: 173 s, sms2-DWI: 56 s). Sms3-DWI showed significantly poorer overall image quality (3 [1; 5]; p < 0.0001). ADC values were significantly lower in sms3-DWI compared to c-DWI in the pancreatic body and tail (body: c-DWI 1.4 x 10-3 mm2/s, sms3-DWI 1.0 x 10-3 mm2/s, p = 0.028; tail: c-DWI 1.3 x 10-3 mm2/s and sms3-DWI 1.0 x 10-3 mm2/s, p = 0.014). CONCLUSIONS: Accelerated multislice DWI of the pancreas offers high image quality with a substantial reduction of acquisition time. Lower ADC values in multislice DWI should be considered in diagnostic reading. KEY POINTS: • Simultaneous multislice-accelerated diffusion-weighted imaging (sms-DWI) promises scan time minimisation. • Sms-DWI of the pancreas offers diagnostic image quality in volunteers and patients. • Sms-DWI with an acceleration factor of 2 offers high image quality. • Higher acceleration factors in sms-DWI do not provide sufficient diagnostic image quality. • ADC values may be lower in sms-DWI.

SUV-quantification of physiological lung tissue in an integrated PET/MR-system: Impact of lung density and bone tissue.

PURPOSE: The aim of the study was to investigate the influence of lung density changes as well as bone proximity on the attenuation correction of lung standardized uptake values (SUVs). METHODS AND MATERIALS: 15 patients with mostly oncologic diseases were examined in 18F-FDG-PET/CT and subsequently in a fully integrated PET/MR scanner. From each PET dataset acquired in PET/MR, four different PET reconstructions were computed using different attenuation maps (µ-maps): i) CT-based µ-map (gold standard); ii) CT-based µ-map in which the linear attenuation coefficients (LAC) of the lung tissue was replaced by the lung LAC from the MR-based segmentation method; iii) based on reconstruction ii), the LAC of bone structures was additionally replaced with the LAC from the MR-based segmentation method; iv) the vendor-provided MR-based µ-map (segmentation-based method). Those steps were performed using MATLAB. CT Hounsfield units (HU) and SUVmean was acquired in different levels and regions of the lung. Relative differences between the differently corrected PETs were computed. RESULTS: Compared to the gold standard, reconstruction ii), iii) and iv) led to a relative underestimation of SUV in the posterior regions of -9.0%, -13.4% and -14.0%, respectively. Anterior and middle regions were less affected with an overestimation of about 6-8% in reconstructions ii)-iv). CONCLUSION: It could be shown that both, differences in lung density and the vicinity of bone tissue in the µ-map may have an influence on SUV, mostly affecting the posterior lung regions.

[Dentogene Focus as a Rare Cause of Necrotizing Fasciitis]. / Dentogener Fokus als Ursache für eine nekrotisierende Fasziitis.

History and clinical findings We elaborate the case of a 72-year-old patient who presented with a painful swelling of the lower jaw in the emergency unit. Investigations and diagnosis In the clinical examination and the CT scan, a widespread cervical emphysema was found which raised suspicion for the presence of a necrotizing fasciitis of the head and neck due to aerogenic infection. Close spatial vicinity to the teeth of the left upper and lower jaw was present, so that the necrotizing fasciitis was assumed to be odontogenic. Treatment and course Based on the clinical presentation and the imaging findings the diagnosis of necrotizing fasciitis in the sense of a possible infection with gas building bacteria accompanying with an infection of the mediastinum was made. Immediately performed therapy included sternotomy and extended surgical debridement of necrosis. Conclusion The presented case emphasizes that necrotizing fasciitis due to gas-producing infections should be considered as a differential diagnosis for cervical soft tissue emphysema for which an odontogenic focus is the most common cause. Rapid diagnosis is essential for successful treatment consisting of immediate surgical debridement and intravenous antibiotics.

Feasibility of self-gated isotropic radial late-phase MR imaging of the liver.

OBJECTIVE: To evaluate feasibility of a 3D-isotropic self-gated radial volumetric interpolated breath-hold examination (VIBE) for late-phase MRI of the liver. MATERIAL AND METHODS: 70 patients were included and underwent liver MRI at 1.5 T. Depending on the diagnosis, either Gd-EOB-DTPA (35 patients) or gadobutrol (35 patients) were administered. During late (gadobutrol) or hepatocyte-specific phase (Gd-EOB-DTPA), a radial prototype sequence was acquired and reconstructed using (1) self-gating with 40 % acceptance (rVIBE40); (2) with 100 % acceptance of the data (rVIBE100) and compared to Cartesian VIBE (cVIBE). Images were assessed qualitatively (image quality, lesion conspicuity, artefacts; 5-point Likert-scale: 5 = excellent; two independent readers) and quantitatively (coefficient-of-variation (CV); contrast-ratio) in axial and coronal reformations. RESULTS: In eight cases only rVIBE provided diagnostic image quality. Image quality of rVIBE40 was rated significantly superior (p < 0.05) in Gd-EOB-DTPA-enhanced and coronal reformatted examinations as compared to cVIBE. Lesion conspicuity was significantly improved (p < 0.05) in coronal reformatted Gd-EOB-DTPA-enhanced rVIBE40 in comparison to cVIBE. CV was higher in rVIBE40 as compared to rVIBE100/cVIBE (p < 0.01). Gadobutrol-enhanced rVIBE40 and cVIBE showed higher contrast-ratios than rVIBE100 (p < 0.001), whereas no differences were found in Gd-EOB-DTPA-enhanced examinations. CONCLUSION: Self-gated 3D-isotropic rVIBE provides significantly superior image quality compared to cVIBE, especially in multiplanar reformatted and Gd-EOB-DTPA-enhanced examinations. KEY POINTS: • Radial VIBE acquisition reduces motion artefacts. • Gd-EOB-DTPA-enhanced scans provide improved image quality. • Non-diagnostic liver MRI examinations may be reduced by radial k-spaces sampling.

Diagnosing Lung Nodules on Oncologic MR/PET Imaging: Comparison of Fast T1-Weighted Sequences and Influence of Image Acquisition in Inspiration and Expiration Breath-Hold.

OBJECTIVE: First, to investigate the diagnostic performance of fast T1-weighted sequences for lung nodule evaluation in oncologic magnetic resonance (MR)/positron emission tomography (PET). Second, to evaluate the influence of image acquisition in inspiration and expiration breath-hold on diagnostic performance. MATERIALS AND METHODS: The study was approved by the local Institutional Review Board. PET/CT and MR/PET of 44 cancer patients were evaluated by 2 readers. PET/CT included lung computed tomography (CT) scans in inspiration and expiration (CTin, CTex). MR/PET included Dixon sequence for attenuation correction and fast T1-weighted volumetric interpolated breath-hold examination (VIBE) sequences (volume interpolated breath-hold examination acquired in inspiration [VIBEin], volume interpolated breath-hold examination acquired in expiration [VIBEex]). Diagnostic performance was analyzed for lesion-, lobe-, and size-dependence. Diagnostic confidence was evaluated (4-point Likert-scale; 1 = high). Jackknife alternative free-response receiver-operating characteristic (JAFROC) analysis was performed. RESULTS: Seventy-six pulmonary lesions were evaluated. Lesion-based detection rates were: CTex, 77.6%; VIBEin, 53.3%; VIBEex, 51.3%; and Dixon, 22.4%. Lobe-based detection rates were: CTex, 89.6%; VIBEin, 58.3%; VIBEex, 60.4%; and Dixon, 31.3%. In contrast to CT, inspiration versus expiration did not alter diagnostic performance in VIBE sequences. Diagnostic confidence was best for VIBEin and CTex and decreased in VIBEex and Dixon (1.2 ± 0.6; 1.2 ± 0.7; 1.5 ± 0.9; 1.7 ± 1.1, respectively). The JAFROC figure-of-merit of Dixon was significantly lower. All patients with malignant lesions were identified by CTex, VIBEin, and VIBEex, while 3 patients were false-negative in Dixon. CONCLUSION: Fast T1-weighted VIBE sequences allow for identification of patients with malignant pulmonary lesions. The Dixon sequence is not recommended for lung nodule evaluation in oncologic MR/PET patients. In contrast to CT, inspiration versus expiratory breath-hold in VIBE sequences was less crucial for lung nodule evaluation but was important for diagnostic confidence.

Diffusion-weighted imaging in the assessment of prostate cancer: Comparison of zoomed imaging and conventional technique.

PURPOSE: To compare reduced field-of-view (zoomed) diffusion-weighted imaging (DWI) and conventional DWI in the evaluation of prostate cancer with respect to lesion detection, image quality and alignment accuracy. MATERIAL AND METHODS: The study was carried out in accordance with the Declaration of Helsinki and was approved by the institutional review board. Image data of 29 histology-proven prostate cancer lesions in 15 patients were evaluated. All patients underwent both conventional DWI and zoomed DWI at 3T. Zoomed DWI and conventional DWI sequences were analysed qualitatively and quantitatively. Subjective image quality, visual distortion and presence of artefacts were rated on a 5-point Likert scale (1=excellent) by two readers in consensus. Lesion conspicuity, sensitivity and specificity in lesion detection were evaluated and compared for both DWI sequences using ROC curves and area under the curve (AUC). To analyze the geographic distortion in DWI the alignment accuracy of prostate and lesions was measured in three spatial dimensions referring to the T2-weighted anatomical images as reference. In a region of interest (ROI) evaluation, ADC values were measured in prostate tissue and malignant lesions. Comparison of qualitative and quantitative parameters was performed using Wilcoxon test with subsequent Bonferroni correction. RESULTS: Subjective image quality was rated significantly higher in zoomed DWI compared to conventional DWI (2.1±0.9 vs. 2.7±0.9; p=0.0375). Visual distortion and artefacts were reduced in zoomed DWI without reaching statistical significance (1.8±0.7 vs. 2.4±1.0 and 2.1±1.0 vs. 2.5±1.0). Sensitivity and specificity of zoomed and conventional DWI were not significantly different. Zoomed DWI had a slightly higher AUC compared to conventional DWI without significant difference (0.82 versus 0.78; p=0.0576). Lesion conspicuity did not significantly differ between zoomed DWI and conventional DWI (1.8±0.8 vs. 1.9±1.0; p=0.8523). The alignment accuracy of zoomed DWI was significantly higher regarding both the prostate gland and lesions (deviation of outer contours of lesions in sagittal plane: 3±4mm vs. 5±3mm; p=0.0008). ADC tended to be higher in zoomed DWI without statistical significance (ADCmean in peripheral zone: 1.7±0.2×10(-3)mm(2)/s vs. 1.5±0.4×10(-3)mm(2)/s; ADCmean in lesion: 1.0±0.71×10(-3)mm(2)/s vs. 0.8±0.2×10(-3)mm(2)/s). CONCLUSIONS: Zoomed technique offers improved image quality for diffusion-weighted imaging of the prostate with reduced image distortion both for the whole gland as well as for cancer lesions and at least comparable diagnostic performance. The zoomed technique could be useful for multiparametric tissue characterization but also for biopsy and radiation therapy planning.

Scan time minimization in hepatic diffusion-weighted imaging: evaluation of the simultaneous multislice acceleration technique with different acceleration factors and gradient preparation schemes.

OBJECTIVE: To evaluate simultaneous multislice (sms) accelerated diffusion-weighted imaging (DWI) of the liver in comparison to conventional sequences. MATERIALS AND METHODS: Ten volunteers underwent DWI of the liver at 1.5 T. Four different sms-accelerated sequences with monopolar and bipolar gradient preparation (MP, BP) and acceleration factors 2 and 3 (sms2-DWI, sms3-DWI) were compared to conventional DWI (c-DWI). Image quality criteria rated on a 5-point Likert scale (5 = excellent), image quality sum scores (maximum 120), and ADC were compared using Friedman test and Dunn-Bonferroni post hoc test. Bland-Altman plots were calculated for ADC comparison. p values <0.05 were considered significant. RESULTS: Sms2-DWI offered scan time minimization of 67 % without significant difference in image quality (sum score: sms2-DWI MP/BP: 97 ± 8/92 ± 9; c-DWI MP/BP: 99 ± 8/97 ± 8). Sms3-DWI offered slight additional scan time minimization with significantly inferior image quality (sum score: sms3-DWI MP/BP: 75 ± 14/69 ± 14; p < 0.001). MP preparation provided slightly higher image quality in sms-DWI without statistical significance. ADC in sms-DWI were significantly lower (sms2-DWI MP 1.01 × 10(-3) mm(2)/s; c-DWI MP 1.20 × 10(-3) mm(2)/s; p < 0.001). CONCLUSION: Sms2-DWI provides considerable scan time minimization without significant shortcomings in image quality. Sms3-DWI provides significantly inferior image quality without further scan time minimization. Potentially lower ADC in sms-DWI should be considered in clinical routine.

Simultaneous multislice diffusion-weighted MRI of the liver: Analysis of different breathing schemes in comparison to standard sequences.

PURPOSE: To systematically evaluate image characteristics of simultaneous-multislice (SMS)-accelerated diffusion-weighted imaging (DWI) of the liver using different breathing schemes in comparison to standard sequences. MATERIALS AND METHODS: DWI of the liver was performed in 10 healthy volunteers and 12 patients at 1.5T using an SMS-accelerated echo planar imaging sequence performed with respiratory-triggering and free breathing (SMS-RT, SMS-FB). Standard DWI sequences served as reference (STD-RT, STD-FB). Reduction of scan time by SMS-acceleration was measured. Image characteristics of SMS-DWI and STD-DWI with both breathing schemes were analyzed quantitatively (apparent diffusion coefficient [ADC], signal-to-noise ratio [SNR]) and qualitatively (5-point Likert scale, 5 = excellent). Qualitative and quantitative parameters were compared using Friedman test and Dunn-Bonferroni post-hoc method with P-values < 0.05 considered statistically significant. RESULTS: SMS-DWI provided diagnostic image quality in volunteers and patients both with RT and FB with a reduction of scan time of 70% (0:56 vs. 3:20 min in FB). Overall image quality did not significantly differ between FB and RT acquisition in both STD and SMS sequences (median STD-RT 5.0, STD-FB 4.5, SMS-RT: 4.75; SMS-FB: 4.5; P = 0.294). SNR in the right hepatic lobe was comparable between the four tested sequences. ADC values were significantly lower in SMS-DWI compared to STD-DWI irrespective of the breathing scheme (1.2 ± 0.2 × 10(-3) mm(2) /s vs. 1.0 ± 0.2 × 10(-3) mm(2) /s; P < 0.001). CONCLUSION: SMS-acceleration provides considerable scan time reduction for hepatic DWI with equivalent image quality compared to the STD technique both using RT and FB. Discrepancies in ADC between STD-DWI and SMS-DWI need to be considered when transferring the SMS technique to clinical routine reading. J. MAGN. RESON. IMAGING 2016;44:865-879.

Optimized Fast Dynamic Contrast-Enhanced Magnetic Resonance Imaging of the Prostate: Effect of Sampling Duration on Pharmacokinetic Parameters.

OBJECTIVE: The aim of this study was to evaluate the effect of sampling duration on pharmacokinetic parameters from dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) and their diagnostic accuracy regarding the detection of potentially malignant prostate lesions. MATERIALS AND METHODS: Sixty-six consecutive male patients (mean [SD] age, 65.4 [10.8] years) with clinically suspected prostate cancer were included. All patients underwent multiparametric MRI of the prostate (T2-weighted imaging, diffusion-weighted imaging, and DCE-MRI) on a 3 T MRI scanner. Patients were divided into 2 groups depending on the prostate imaging reporting and data system (PI-RADS) score of the detected lesions (group A: PI-RADS ≤3, n = 32; group B: PI-RADS >3, n = 34). In all patients, DCE-MRI was performed using a CAIPIRINHA-Dixon-TWIST volume interpolated breath-hold examination sequence (spatial resolution, 3 × 1.2 × 1.2 mm; temporal resolution, 5 seconds; total sampling duration, 4:10 minutes [250 seconds]) with body weight-adapted administration of contrast agent (gadobutrol, Bayer Healthcare, Berlin, Germany). Five DCE-MRI series with different acquisition durations ranging from 50 to 250 seconds were retrospectively generated from the original data sets. Pharmacokinetic parameters (ie, Ktrans, Kep, Ve, and iAUC60) were calculated for the different sampling durations using the Tofts model. Both lesion groups and all 5 DCE-MRI series were compared regarding pharmacokinetic parameters. Diagnostic accuracy for the detection of potentially malignant lesions was calculated for all 5 series using receiver operating characteristic analysis. RESULTS: For all 5 series, Ktrans, Kep, and iAUC60 in patient group B were significantly higher than the respective parameters in patient group A (all P ≤ 0.008). In both groups, Ktrans, Kep, and iAUC60 remained constant at 200 and 150 seconds acquisition duration and did not significantly differ from parameters estimated from the original data sets (250 seconds; all P ≥ 0.310). Ve did not differ significantly between the 2 groups (P ≥ 0.337) and acquisition time did not have a significant effect on this parameter (P ≥ 0.275). Receiver operating characteristic analyses showed consistent diagnostic accuracy for the different series; only diagnostic accuracy of Kep decreased with lowered sampling duration, showing lowest accuracy for the 50-second series (0.682; 95% confidence interval, 0.553-0.811). CONCLUSIONS: Using fast optimized DCE-MRI of the prostate, a minimum sampling duration of 150 seconds is required for sufficient pharmacokinetic parameter estimates, providing a high diagnostic accuracy regarding the discrimination between benign and potentially malignant lesions.

Imaging of Cholangiocarcinoma.

Cholangiocarcinoma (CC) is the second most common primary hepatobiliary tumour, and it is increasing in incidence. Imaging characteristics, behaviour, and therapeutic strategies in CC differ significantly, depending on the morphology and location of the tumour. In cross-sectional imaging, CCs can be classified according to the growth pattern (mass-forming, periductal infiltrating, intraductal) and the location (intrahepatic, perihilar, extrahepatic/distal). The prognosis of CC is unfavourable and surgical resection is the only curative treatment option; thus, early diagnosis (also in recurrent disease) and accurate staging including the evaluation of lymph node involvement and vascular infiltration is crucial. However, the diagnostic evaluation of CC is challenging due to the heterogeneous nature of the tumour. Diagnostic modalities used in the imaging of CC include transabdominal ultrasound, endosonography, computed tomography, magnetic resonance imaging with cholangiopancreatography, and hybrid imaging such as positron emission tomography/computed tomography. In this review, the potential of cross-sectional imaging modalities in primary staging, treatment monitoring, and detection of recurrent disease will be discussed.

Feasibility of CAIPIRINHA-Dixon-TWIST-VIBE for dynamic contrast-enhanced MRI of the prostate.

PURPOSE: To evaluate the feasibility of a CAIPIRINHA-Dixon-TWIST (CDT)-VIBE sequence for improving image quality and temporal resolution in dynamic contrast-enhanced MRI (DCE-MRI) of the prostate. MATERIAL AND METHODS: 44 male patients (age 63.9 ± 8.9 years) with clinically suspected prostate cancer underwent DCE-MRI at a 3T MRI scanner (Magnetom Skyra, Siemens Healthcare, Erlangen, Germany) using a CDT-VIBE sequence (spatial resolution=3×1.2×1.2mm(3), temporal resolution=5s, total scan duration=4:10 min) with body-weight-adapted administration of contrast agent (Gadobutrol, Bayer Healthcare, Berlin, Germany). To investigate effects on image quality, the same sequence was acquired three times per patient during the late phase: 1. with the same protocol as in the arterial phase (VS5), 2. without view-sharing (no view-sharing, NVS) using a 2-fold CAIPIRINHA acceleration R=2 (temporal resolution=15s, NVS15) and 3. NVS using a 6-fold CAIPIRINHA acceleration R=6 (temporal resolution=5s, NVS5). SNR and CNR were evaluated with the subtraction method. Image quality of the three sequences (VS5, NVS15, NVS5) was subjectively assessed by 2 blinded radiologists using a 5-point Likert scale (5 being excellent). Perfusion profiles of visually normal prostate and of malignant lesions as characterized by Wash-In, Wash-Out, time-to-peak (TTP) and initial area under the curve (iAUC) from the original datasets (temporal resolution=5s) and from datasets with a downsampled temporal resolution (15s) were compared. RESULTS: In 20 of 44 included patients, potentially malignant lesions were identified in which 16 had histologically confirmed prostate cancer. SNR was highest for VS5 and NVS15, and lowest for NVS5 (p <.001). Concordantly, subjective image quality was comparable for VS5 and NVS15 (sum score 23.20 ± 1.03 vs 23.53 ± 1.34) and significantly lower for NVS5 (sum score 9.83 ± 2.32; p<.001). Perfusion parameters of macroscopically normal prostate tissue and suspect lesions differed significantly between original datasets and datasets with simulated lower temporal resolution, with the latter showing higher Wash-In (p=.002), lower Wash-Out (p=.003), higher Time-to-Peak (p<.001) and lower iAUC (p<.001). CONCLUSION: CDT-VIBE can be readily exploited for DCE-MRI of the prostate preserving the diagnostic image quality while providing high temporal resolution for quantitative diagnostic assessment of enhancement curves in malignant lesions.

Combined unsupervised-supervised classification of multiparametric PET/MRI data: application to prostate cancer.

Multiparametric medical imaging data can be large and are often complex. Machine learning algorithms can assist in image interpretation when reliable training data exist. In most cases, however, knowledge about ground truth (e.g. histology) and thus training data is limited, which makes application of machine learning algorithms difficult. The purpose of this study was to design and implement a learning algorithm for classification of multidimensional medical imaging data that is robust and accurate even with limited prior knowledge and that allows for generalization and application to unseen data. Local prostate cancer was chosen as a model for application and validation. 16 patients underwent combined simultaneous [(11) C]-choline positron emission tomography (PET)/MRI. The following imaging parameters were acquired: T2 signal intensities, apparent diffusion coefficients, parameters Ktrans and Kep from dynamic contrast-enhanced MRI, and PET standardized uptake values (SUVs). A spatially constrained fuzzy c-means algorithm (sFCM) was applied to the single datasets and the resulting labeled data were used for training of a support vector machine (SVM) classifier. Accuracy and false positive and false negative rates of the proposed algorithm were determined in comparison with manual tumor delineation. For five of the 16 patients rates were also determined in comparison with the histopathological standard of reference. The combined sFCM/SVM algorithm proposed in this study revealed reliable classification results consistent with the histopathological reference standard and comparable to those of manual tumor delineation. sFCM/SVM generally performed better than unsupervised sFCM alone. We observed an improvement in accuracy with increasing number of imaging parameters used for clustering and SVM training. In particular, including PET SUVs as an additional parameter markedly improved classification results. A variety of applications are conceivable, especially for imaging of tissues without easily available histopathological correlation.

Multiparametric analysis of bone marrow in cancer patients using simultaneous PET/MR imaging: Correlation of fat fraction, diffusivity, metabolic activity, and anthropometric data.

BACKGROUND: To analyze the regional composition of bone marrow (BM) in correlation with metabolic activity and diffusivity using simultaneous positron emission tomography (PET)/MRI. METHODS: Retrospective analysis of 18F-FDG-PET/MR scans of 110 patients was performed. A three-dimensional gradient-echo sequence with Dixon-based fat-water separation was used for fat quantification. Dixon images, diffusion-weighted images (DWI) and 18F-FDG-PET were co-registered. Mean values of fat fraction (FF), standardized uptake value (SUV), and apparent diffusion coefficient (ADC) of BM were measured in different anatomical regions. Correlation of FF, SUV, and ADC and association of BM fat content and metabolic activity with anthropometric data was analyzed (Pearson). BM fat content and metabolic activity was compared in patients with and without chemotherapy (t-test). RESULTS: Regional differences in BM were found with highest fat content (93 ± 8%) and lowest ADC (0.22 ± 0.18 × 10(-3) mm(2) /s) in the peripheral skeleton and highest SUV in the spine (1.77 ± 0.6). There was a significant inverse correlation between FF and SUV (r = -0.73; P < 0.0001) and a significant inverse correlation between FF and ADC (r = -0.62; P < 0.0001). In patients with chemotherapy, a tendency to higher fat content and lower metabolic activity was observed in the proximal skeleton, although no statistical significance was reached. CONCLUSION: BM shows distinct regional variations in FF, SUV, and ADC. The inverse correlation of FF and SUV in BM suggests that BM adipose tissue does not have a comparable high metabolic activity as brown adipose tissue.

Segmentation-based attenuation correction in positron emission tomography/magnetic resonance: erroneous tissue identification and its impact on positron emission tomography interpretation.

OBJECTIVES: The objective of this study was to evaluate the frequency and characteristics of artifacts in segmentation-based attenuation correction maps (µ-maps) of positron emission tomography/magnetic resonance (PET/MR) and their impact on PET interpretation and the standardized uptake value (SUV) quantification in normal tissue and lesions. MATERIALS AND METHODS: The study was approved by the local institutional review board. Attenuation maps of 100 patients with PET/MR and preceding PET/computed tomography examination were retrospectively inspected for artifacts (tracers: 2-deoxy-2-[¹8F]fluoro-D-glucose (¹8F-FDG), ¹¹C-Choline, 68Ga-DOTATOC, 68Ga-DOTATATE, ¹¹C-Methionine). The artifacts were subdivided into 9 different groups on the basis of their localization and appearance. The impact of µ-map artifacts in normal tissue and lesions on PET interpretation was evaluated qualitatively via visual analysis in synopsis with the non-attenuation-corrected (NAC) PET as well as quantitatively by comparing the SUV in artifact regions to reference regions. RESULTS: Attenuation map artifacts were found in 72% of the head/neck data sets, 61% of the thoracic data sets, 25% of the upper abdominal data sets, and 26% of the pelvic data sets. The most frequent localizations of the overall 276 artifacts were around metal implants (16%), in the lungs (19%), and outer body contours (31%). Twenty-one percent of all PET-avid lesions (38 of 184 lesions) were affected by artifacts in the majority without further consequences for visual PET interpretation. However, 9 PET-avid lung lesions were masked owing to µ-map artifacts and, thus, were only detectable on the NAC PET or additional MR imaging sequences. Quantitatively, µ-map artifacts led to significant SUV changes in areas with erroneous assignment of air instead of soft tissue (ie, metal artifacts) and of soft tissue instead of lung. Nevertheless, no change in diagnosis would have been caused by µ-map artifacts. CONCLUSIONS: Attenuation map artifacts that occur in a considerable percentage of PET/MR data sets have the potential to falsify PET quantification and visual PET interpretation. Nevertheless, on the basis of the present data, in the clinical interpretation setup, no changes in diagnosis due to µ-map artifacts may occur, especially when the µ-maps are checked for artifacts and PET/MR is read in synopsis with the NAC PET, if artifacts are present.