Abdominal vessel depiction on virtual triphasic spectral detector CT: initial clinical experience.

PURPOSE: To evaluate vessel assessment in virtual monoenergetic images (VMI40keV) and virtual-non-contrast images (VNC) derived from venous phase spectral detector computed tomography (SDCT) acquisitions in comparison to arterial phase and true non-contrast (TNC) images. METHODS: Triphasic abdominal SDCT was performed in 25 patients including TNC, arterial and venous phase. VMI40keV and VNC were reconstructed from the venous phase and compared to conventional arterial-phase images (CIart), TNC and conventional venous-phase images (CIven). Vessel contrast and virtual contrast removal were analyzed with region-of-interest-based measurements and in a qualitative assessment. RESULTS: Quantitative analysis revealed no significant attenuation differences between TNC and VNC in arterial vessels (p-range 0.07-0.47) except for the renal artery (p = 0.011). For venous vessels, significant differences between TNC and VNC were found for all veins (p < 0.001) except the inferior vena cava (p = 0.26), yet these differences remained within a 10 HU range in most patients. No significant attenuation differences were found between CIart/VMI40keV in arterial vessels (p-range 0.06-0.86). Contrast-to-noise ratio provided by VMI40keV and CIart was equivalent for all arterial vessels assessed (p-range 0.14-0.91). Qualitatively, VMI40keV showed similar enhancement of abdominal and pelvic arteries as CIart and VNC were rated comparable to TNC. CONCLUSION: Our study suggests that VNC and VMI40keV derived from single venous-phase SDCT offer comparable assessment of major abdominal vessels as provided by routine triphasic examinations, if no dynamic contrast information is required.

Renal cystic lesions characterization using spectral detector CT (SDCT): Added value of spectral results.

OBJECTIVES: To evaluate the added value of spectral results derived from Spectral Detector CT (SDCT) to the characterization of renal cystic lesions (RCL). METHODS: This retrospective study was approved by the local Institutional review board. 70 consecutive patients who underwent abdominopelvic SDCT and had at least one RCL were included. 84 RCL were categorized as simple, complex or neoplastic based on attenuation values on single-phase post-contrast images. Attenuation values were measured in each lesion on standard conventional CT images (stCI) and virtual monoenergetic images of 40keV and 100keV. A spectral curve slope was calculated and intra lesional iodine concentration (IC) was measured using iodine-density maps. Reference standard was established using histopathologic correlation, prior and follow-up imaging. Analysis of variance (ANOVA) was used to compare between the groups. RESULTS: Mean attenuation values for benign simple and complex RCL differed significantly (42 ± 16 vs 8 ± 3 HU; p < 0.001). IC was almost identical in benign simple and complex RCL (0.23 ± 0.04 mg ml-1 vs 0.24 ± 0.04 mg ml-1), while IC in neoplastic RCL was significantly higher (2.10 ± 0.08 mg ml-1 ; p < 0.001). The mean spectral curve slope did not differ significantly between simple and complex RCL (0.30 ± 0.03 vs 0.33 ± 0.05) but was significantly higher in neoplastic RCL (2.60 ± 0.10; p < 0.001). CONCLUSIONS: Spectral results of SDCT are highly promising in distinguishing benign complex RCL from enhancing neoplastic RCL based on single-phase post-contrast imaging only. ADVANCES IN KNOWLEDGE: SDCT can assist in differentiating between benign complex and neoplastic renal cystic lesions.

UTE-mDixon-based thorax synthetic CT generation.

PURPOSE: Accurate photon attenuation assessment from MR data remains an unmet challenge in the thorax due to tissue heterogeneity and the difficulty of MR lung imaging. As thoracic tissues encompass the whole physiologic range of photon absorption, large errors can occur when using, for example, a uniform, water-equivalent or a soft-tissue-only approximation. The purpose of this study was to introduce a method for voxel-wise thoracic synthetic CT (sCT) generation from MR data attenuation correction (AC) for PET/MR or for MR-only radiation treatment planning (RTP). METHODS: Acquisition: A radial stack-of-stars combining ultra-short-echo time (UTE) and modified Dixon (mDixon) sequence was optimized for thoracic imaging. The UTE-mDixon pulse sequence collects MR signals at three TE times denoted as UTE, Echo1, and Echo2. Three-point mDixon processing was used to reconstruct water and fat images. Bias field correction was applied in order to avoid artifacts caused by inhomogeneity of the MR magnetic field. ANALYSIS: Water fraction and R2* maps were estimated using the UTE-mDixon data to produce a total of seven MR features, that is UTE, Echo1, Echo2, Dixon water, Dixon fat, Water fraction, and R2*. A feature selection process was performed to determine the optimal feature combination for the proposed automatic, 6-tissue classification for sCT generation. Fuzzy c-means was used for the automatic classification which was followed by voxel-wise attenuation coefficient assignment as a weighted sum of those of the component tissues. Performance evaluation: MR data collected using the proposed pulse sequence were compared to those using a traditional two-point Dixon approach. Image quality measures, including image resolution and uniformity, were evaluated using an MR ACR phantom. Data collected from 25 normal volunteers were used to evaluate the accuracy of the proposed method compared to the template-based approach. Notably, the template approach is applicable here, that is normal volunteers, but may not be robust enough for patients with pathologies. RESULTS: The free breathing UTE-mDixon pulse sequence yielded images with quality comparable to those using the traditional breath holding mDixon sequence. Furthermore, by capturing the signal before T2* decay, the UTE-mDixon image provided lung and bone information which the mDixon image did not. The combination of Dixon water, Dixon fat, and the Water fraction was the most robust for tissue clustering and supported the classification of six tissues, that is, air, lung, fat, soft tissue, low-density bone, and dense bone, used to generate the sCT. The thoracic sCT had a mean absolute difference from the template-based (reference) CT of less than 50 HU and which was better agreement with the reference CT than the results produced using the traditional Dixon-based data. CONCLUSION: MR thoracic acquisition and analyses have been established to automatically provide six distinguishable tissue types to generate sCT for MR-based AC of PET/MR and for MR-only RTP.

Diagnostic Accuracy of a Rapid Biparametric MRI Protocol for Detection of Histologically Proven Prostate Cancer.

OBJECTIVE: To evaluate the performance of a rapid, low cost, noncontrast MRI examination as a secondary screening tool in detection of clinically significant prostate cancer. METHODS: In this prospective single institution study, 129 patients with elevated prostate-specific antigen levels or abnormal digital rectal examination findings underwent MRI with an abbreviated biparamatric MRI protocol consisting of high-resolution axial T2- and diffusion-weighted images. Index lesions were classified according to modified Prostate Imaging - Reporting and Data System (mPI-RADS) version 2.0. All patients underwent standard transrectal ultrasound-guided biopsy after MRI with the urologist being blinded to MRI results. Subsequently, all patients with suspicious lesions (mPI-RADS 3, 4, or 5) underwent cognitively guided targeted biopsy after discussion of MRI results with the urologist. Sensitivity and negative predictive value for identification of clinically significant prostate cancer (Gleason score 3+4 and above) were determined. RESULTS: Rapid biparametric MRI discovered 176 lesions identified in 129 patients. Rapid MRI detected clinically significant cancers with a sensitivity of 95.1% with a negative predictive value of 95.1% and positive predictive value of 53.2%, leading to a change in management in 10.8% of the patients. False negative rate of biparametric (bp) MRI was 4.7%. CONCLUSION: We found that a bp-MRI examination can detect clinically significant lesions and changed patient management in 10.8% of the patients. A rapid MRI protocol can be used as a useful secondary screening tool in men presenting with suspicion of prostate cancer.

(18F)-FDG-PET/MRI of unicentric retroperitoneal Castleman disease in a pediatric patient.

Castleman disease (CD) is a rare lymphoproliferative disorder of unknown etiology that may occur anywhere in the lymphatic system. Imaging plays an important role in detecting and staging this disease. Positron Emission Tomography/Magnetic Resonance Imaging (PET/MRI) combines the metabolic information derived from nuclear medical imaging with the high soft tissue resolution from MRI. We review the features of CD in standard diagnostic imaging, analyze the specific imaging findings of CD in FDG-PET/MRI and discuss a potential benefit of PET/MRI based on the case of a 15-year-old female patient with retroperitoneal CD.

Magnetic resonance enterography/enteroclysis in acquired small bowel diverticulitis and small bowel diverticulosis.

PURPOSE: Small bowel (SB) diverticulosis is a rare disorder that may entail serious complications, including SB diverticulitis. Both are often missed in imaging. Magnetic resonance enterography/enteroclysis (MRE) is increasingly used to assess SB disease; awareness of the appearance of SB diverticulitis is essential to ensure appropriate management. Our aim was to systematically describe imaging characteristics of SB diverticulosis and diverticulitis in MRE. METHODS: This retrospective, HIPAA-compliant study identified 186 patients with suspected SB diverticulosis/diverticulitis in medical databases of two tertiary medical centres between 2005 and 2011. Patients with surgically confirmed diagnoses of SB diverticulosis/diverticulitis were included. Two observers analyzed MR images for the presence, location, number, and size of diverticula, wall thickness, and mural and extramural patterns of inflammation. RESULTS: Seven patients were recruited. MRI analysis showed multiple diverticula in all (100 %). Diverticular size ranged from 0.5 to 6 cm. Prevalence of diverticula was higher in the proximal than the distal SB (jejunum 86 %, ileum 57 %, distal ileum43%). Diverticulitis occurred in 3/7 patients (43 %) showing asymmetric bowel wall thickening and focal mesenteric inflammation. CONCLUSION: SB diverticulitis demonstrates characteristic MRE imaging features to distinguish this rare disorder from more common diseases. Asymmetric, focal mesenteric and mural inflammation and presence of multiple diverticula are keys to diagnosis. KEY POINTS: • Small bowel diverticulosis and diverticulitis is rare and often missed in imaging • Acquired small bowel diverticula are variable in size and number • Small bowel diverticulitis demonstrates characteristic features on MR enterography/enteroclysis • A focal or segmental asymmetric small bowel inflammation should prompt the search for diverticula.

Generation of brain pseudo-CTs using an undersampled, single-acquisition UTE-mDixon pulse sequence and unsupervised clustering.

PURPOSE: MR-based pseudo-CT has an important role in MR-based radiation therapy planning and PET attenuation correction. The purpose of this study is to establish a clinically feasible approach, including image acquisition, correction, and CT formation, for pseudo-CT generation of the brain using a single-acquisition, undersampled ultrashort echo time (UTE)-mDixon pulse sequence. METHODS: Nine patients were recruited for this study. For each patient, a 190-s, undersampled, single acquisition UTE-mDixon sequence of the brain was acquired (TE = 0.1, 1.5, and 2.8 ms). A novel method of retrospective trajectory correction of the free induction decay (FID) signal was performed based on point-spread functions of three external MR markers. Two-point Dixon images were reconstructed using the first and second echo data (TE = 1.5 and 2.8 ms). R2(∗) images (1/T2(∗)) were then estimated and were used to provide bone information. Three image features, i.e., Dixon-fat, Dixon-water, and R2(∗), were used for unsupervised clustering. Five tissue clusters, i.e., air, brain, fat, fluid, and bone, were estimated using the fuzzy c-means (FCM) algorithm. A two-step, automatic tissue-assignment approach was proposed and designed according to the prior information of the given feature space. Pseudo-CTs were generated by a voxelwise linear combination of the membership functions of the FCM. A low-dose CT was acquired for each patient and was used as the gold standard for comparison. RESULTS: The contrast and sharpness of the FID images were improved after trajectory correction was applied. The mean of the estimated trajectory delay was 0.774 µs (max: 1.350 µs; min: 0.180 µs). The FCM-estimated centroids of different tissue types showed a distinguishable pattern for different tissues, and significant differences were found between the centroid locations of different tissue types. Pseudo-CT can provide additional skull detail and has low bias and absolute error of estimated CT numbers of voxels (-22 ± 29 HU and 130 ± 16 HU) when compared to low-dose CT. CONCLUSIONS: The MR features generated by the proposed acquisition, correction, and processing methods may provide representative clustering information and could thus be used for clinical pseudo-CT generation.

Comparison of hybrid FDG PET/MRI compared with PET/CT in colorectal cancer staging and restaging: a pilot study.

PURPOSE: We report our initial clinical experience from a pilot study to compare the diagnostic accuracy of hybrid PET/MRI with PET/CT in colorectal cancer and discuss potential PET/MRI workflow solutions for colorectal cancer. METHODS: Patients underwent both FDG PET/CT and PET/MRI (Ingenuity TF PET/MRI, Philips Healthcare) for rectal cancer staging or colorectal cancer restaging. The PET acquisition of PET/MRI was similar to that of PET/CT whereas the MRI protocol was selected individually based on the patient's medical history. One nuclear medicine physician reviewed the PET/CT studies and one radiologist reviewed the PET/MRI studies independently. The diagnostic accuracy of each modality was determined in consensus, using available medical records as a reference. RESULTS: Of the 12 patients enrolled, two were for initial staging and ten for restaging. The median scan delay between the two modalities was 60 min. The initial imaging was PET/CT in nine patients and PET/MRI in three patients. When PET/CT was performed first, the SUV values of the 16 FDG avid lesions were greater at PET/MRI than at PET/CT. In contrast, when PET/MRI was performed first, the SUV values of the seven FDG avid lesions were greater at PET/CT than at PET/MRI. PET/MRI provided more detailed T staging than PET/CT. On a per-patient basis, with both patient groups combined for the evaluation of N and M staging/restaging, the true positive rate was 5/7 (71%) for PET/CT and 6/7 (86%) for PET/MRI, and true negative rate was 5/5 (100%) for both modalities. On a per-lesion basis, PET/CT identified 26 of 29 (90%) tumor lesions that were correctly detected by PET/MRI. Our proposed workflow allows for comprehensive cancer staging including integrated local and whole-body assessment. CONCLUSIONS: Our initial experience shows a high diagnostic accuracy of PET/MRI in T staging of rectal cancer compared with PET/CT. In addition, PET/MRI shows at least comparable accuracy in N and M staging as well as restaging to PET/CT. However, the small sample size limits the generalizability of the results. It is expected that PET/MRI would yield higher diagnostic accuracy than PET/CT considering the high soft tissue contrast provided by MRI compared with CT, but larger studies are necessary to fully assess the benefit of PET/MRI in colorectal cancer.

Clinical oncologic applications of PET/MRI: a new horizon.

Positron emission tomography/magnetic resonance imaging (PET/MRI) leverages the high soft-tissue contrast and the functional sequences of MR with the molecular information of PET in one single, hybrid imaging technology. This technology, which was recently introduced into the clinical arena in a few medical centers worldwide, provides information about tumor biology and microenvironment. Studies on indirect PET/MRI (use of positron emission tomography/computed tomography (PET/CT) images software fused with MRI images) have already generated interesting preliminary data to pave the ground for potential applications of PET/MRI. These initial data convey that PET/MRI is promising in neuro-oncology and head & neck cancer applications as well as neoplasms in the abdomen and pelvis. The pediatric and young adult oncology population requiring frequent follow-up studies as well as pregnant woman might benefit from PET/MRI due to its lower ionizing radiation dose. The indication and planning of therapeutic interventions and specifically radiation therapy in individual patients could be and to a certain extent are already facilitated by performing PET/MRI. The objective of this article is to discuss potential clinical oncology indications of PET/MRI.

Effects of infliximab therapy on transmural lesions as assessed by magnetic resonance enteroclysis in patients with ileal Crohn's disease.

BACKGROUND AND AIMS: Anti TNF therapy induces mucosal healing in patients with Crohn's disease, but the effects on transmural inflammation in the ileum are not well understood. Magnetic resonance-enteroclysis (MRE) offers excellent imaging of transmural and peri-enteric lesions in Crohn's ileitis and we aimed to study its responsiveness to anti TNF therapy. METHODS: In this multi-center prospective trial, anti TNF naïve patients with ileal Crohn's disease and with increased CRP and contrast enhanced wall thickening received infliximab 5 mg/kg at weeks 0, 2 and 6, and q8 weeks maintenance MRE was performed at baseline, 2 weeks and 6 months and assessed based on a predefined MRE score of severity in ileal Crohn's Disease. RESULTS: Twenty patients were included; of those, 18 patients underwent MRE at week 2 and 15 patients at weeks 2 and 26 as scheduled. Inflammatory components of the MRE index decreased by ≥2 points and by ≥50% at week 26 (primary endpoint) in 40% and 32% of patients (per protocol and intention to treat analysis, respectively). The MRE index improved in 44% at week 2 and in 80% at week 26. Complete absence of inflammatory lesions was observed in 0/18 at week 2 and 13% (2/15) at week 26. The obstructive elements did not change. Clinical and CRP improvement occurred as early as wk 2, but only CDAI correlated with the MRE index. CONCLUSION: Improvement of MRE occurs from 2 weeks after infliximab therapy onwards and correlates with clinical response but normalization of MRE is rare.

MR lymphangiography at 3.0 T: correlation with lymphoscintigraphy.

PURPOSE: To prospectively compare findings of magnetic resonance (MR) lymphangiography with those of lymphoscintigraphy, evaluate the pattern and delay of lymphatic drainage, compare typical findings, and investigate discrepancies between the techniques. MATERIALS AND METHODS: This prospective study was performed according to the Declaration of Helsinki and was approved by the local ethics committee. Thirty consecutive patients with uni- or bilateral lymphedema and lymph vessel transplants of the lower extremities were examined with 3.0-T fat-saturated three-dimensional gradient-echo MR after gadopentetate dimeglumine injection. Results of all examinations were correlated with corresponding results of lymphoscintigraphy examinations. Results of both techniques were separately reviewed in consensus by a radiologist and a nuclear physician, who rated delay and pattern of drainage, number of enhancing levels, and quality of conspicuity of the depiction of lymph nodes and lymph vessels. Sensitivity and specificity were calculated by using combined results of both techniques and clinical presentation findings as reference standard. Correlation was calculated with weighted k coefficients. RESULTS: Weak lymphatic drainage at lymphoscintigraphy correlated with lymphangiectasia at MR lymphangiography (13 of 33 affected extremities). Lymph vessels were clearly visualized with MR lymphangiography (five of 24 affected extremities), while they were not detectable with lymphoscintigraphy. Depiction of inguinal lymph nodes was clearer with lymphoscintigraphy (five of 60 extremities). Correlation of both techniques was excellent for delay (κ=0.93) and pattern (κ=0.84) of drainage, good for depiction of lymph nodes (κ=0.67) and number of enhancing levels (κ=0.77), and moderate for depiction of lymph vessels (κ=0.50). Sensitivity and specificity for delay and pattern of drainage were concordant, whereas MR lymphangiography showed a higher sensitivity for lymph vessel abnormalities (100% vs 79%) and lower specificity for lymph node abnormalities (78% vs 100%). CONCLUSION: Imaging findings of MR lymphangiography and lymphoscintigraphy show a clear concordance. With lymphoscintigraphy, better visualization of inguinal lymph nodes was achieved, whereas with MR lymphangiography, better depiction of lymph vessels and morphologic features of lymph vessel abnormalities were achieved.

Fluid-fluid level in hepatic metastases: a characteristic sign of metastases of neuroendocrine origin.

OBJECTIVES: The aim of this study is to determine MRI characteristics which indicate liver metastases of neuroendocrine tumors (NET) rather than metastases of other origin (non-NET). METHODS: Sixty-nine patients with histopathologically proven liver metastases from NET and 69 patients with known liver metastases of other origin underwent MRI of the liver using a 1.5 T MR-scanner. Two board certified radiologists assessed presence of fluid-fluid-levels, number and distribution pattern, signal intensity (SI) characteristics, lesion homogeneity, presence of central necrosis and intratumoral hemorrhage in T2w and T1w non-contrast imaging. A multivariate logistic regression analysis was performed to determine the independent association of image findings and occurrence of NET. RESULTS: Fluid-fluid-levels were identified in 19/69 of patients with NET-metastases, and in none of the patients in the control group (p<0.0001). Hyperintense SI in T1w imaging, markedly hyperintense SI in T2w imaging, a disseminated distribution pattern and intratumoral hemorrhage were indicative of NET metastases (p<0.05). After statistical adjustment for all significant MRI findings, fluid-fluid-levels (OR: 17.6, 95% CI: 1.9-166.5), strongly hyperintense SI in T2w (OR: 4.7, 95% CI: 1.8-12.7) and a disseminated distribution pattern (OR: 2.9, 95% CI: 1.1-7.4) were independent predictors for NET metastases. CONCLUSIONS: The presence of fluid-fluid-levels is highly indicative of NET liver metastases and can be used as an independent predictor to distinguish them from metastases of other origin.

Chromogranin a as serum marker for gastroenteropancreatic neuroendocrine tumors: a single center experience and literature review.

The aim of this study was to assess the clinical sensitivities of the tumor markers chromogranin A (CgA), urinary 5-hydroxyindoleacetic acid (5-HIAA) and alkaline phosphatase (AP) in neuroendocrine tumors (NETs) of the GastroEnteroPancreatic-(GEP-) system depending on tumor primary location and metastatic spread. In a retrospective single-center series, sensitivities were evaluated in serum samples from 110 patients with midgut (n = 62) and pancreatic (n = 48) NETs. CgA levels were analyzed by a commercially-available immunoradiometric assay (CIS-bio) during routine follow-up in the years 2000-2009. CgA showed a higher sensitivity for midgut (68%) than pancreatic (54%) NETs. A higher CgA sensitivity and significantly higher median CgA values were found in patients with liver metastases than in those without, and in patients with hepatic and additionally extra-hepatic metastases than in those with hepatic and nodal metastases alone, respectively. We found an overall sensitivity for elevated 5HIAA excretion of 69% for midgut NETs and a significant correlation between median CgA and 5-HIAA values. The sensitivity of AP and the correlations of AP/CgA-data-pairs were low in both midgut and pancreatic NETs, although highest for metastatic pancreatic NETs. The sensitivity of CgA measurement depends on the NET primary location and spread of disease. 5-HIAA and CgA showed comparable sensitivity in midgut NETs, while AP does not seem to be useful as a tumor marker in GEP-NETs.

Diffusion tensor imaging (DTI) of the kidney at 3 tesla-feasibility, protocol evaluation and comparison to 1.5 Tesla.

PURPOSE: The purpose of this study was to evaluate the feasibility of diffusion tensor imaging of the kidney at a field strength of 3T. We assessed fractional anisotropy (FA) and apparent diffusion coefficients (ADC) of various acquisition protocols and determined the reproducibility of these measurements. FA, ADC, signal-to-noise ratios (SNR), and contrast-to-noise ratios (CNR) were compared with those acquired at 1.5T. MATERIAL AND METHODS: Ten healthy volunteers were examined with a respiratory-triggered echo-planar imaging sequence (TR: 1800 ms, TE: 58 ms, b = 0, 300 s/mm(2)) on a 3-Tesla whole-body MR scanner. Protocol variations included diffusion measurements during free-breathing, in 6 or 12 directions, and an additional b-value of 50 s/mm(2). A breath-hold protocol was also integrated (TR: 820 ms, TE: 58 ms, b = 0, 300 s/mm(2)). Measurements with 2 b-values and 6 diffusion directions were also acquired at 1.5 T. SNR was calculated with the difference-image method. Statistical analysis was performed with Wilcoxon signed-rank tests. Intrareader correlation was assessed with weighted kappa coefficients and reproducibility with the root-mean-square-average and the Bland-Altman-method. RESULTS: At 3T, SNR of cortex and medulla and CNR of cortex/medulla were significantly higher than at 1.5T, leading to improved corticomedullary discrimination. There were no significant FA- and ADC differences with 2 b-values and 6 diffusion directions between measurements at 1.5T and 3T. FA of the medulla was significantly higher than that of the cortex in all measurements. Tractography visualized a typical radial diffusion direction in the medulla. Best image quality was achieved with a respiratory triggered protocol with 12 acquisition directions. Measurements with 3 b-values led to decreased ADCs. Acquisition in 12 directions resulted in decreased cortical FA. FA and ADC of breath-hold and free-breathing acquisitions were significantly higher than that of the respiratory-triggered protocol. Intrareader correlation ranged from kappa 0.60 to 0.96. Variance of the respiratory-triggered protocol was smaller than that of breath-hold and free-breathing protocols. Variance was highest for medullary FA in all protocols with reproducibility coefficients ranging from 0.36 to 0.46. CONCLUSION: Diffusion tensor imaging of the kidney at 3T is feasible and yields significantly higher SNR and CNR. FA and ADCs do not significantly differ from 1.5T. Number of b-values influences ADC-values. Acquisitions in 12 directions provide lower cortical FA-values. We recommend a respiratory-triggered protocol because of improved image quality and reproducibility.

Measuring perfusion and permeability in renal cell carcinoma with dynamic contrast-enhanced MRI: a pilot study.

PURPOSE: To retrospectively assess an improved quantitative methodology with separate assessment of perfusion and permeability for characterization of primary renal cell carcinoma (RCC) and monitoring antiangiogenic treatment. MATERIALS AND METHODS: Fifteen RCC patients before surgery, 6 RCC patients before and after neoadjuvant antiangiogenic therapy, and 15 patients without renal disease underwent dynamic contrast-enhanced (DCE)-MRI of the kidney with integrated retrospective respiratory triggering and an individual arterial input function. Tracer kinetic analysis was performed with a two-compartment-filtration-model for the kidney data and a two-compartment-exchange-model for the tumor data, providing four independent parameters: the perfusion-parameters plasma flow (F(P)) and plasma volume (V(P)), and the permeability-parameters extraction flow (F(E)) and extravascular-extracellular volume (V(E)). RESULTS: In tumors F(P) and F(E) were significantly lower than in normal kidneys. Tracer kinetic analysis displayed hemodynamic alteration caused by vessel infiltration or necrosis. Papillary RCC could be differentiated from clear-cell variants by a distinct perfusion pattern. In antiangiogenically treated RCC V(E) was not significantly decreased, while the perfusion parameters V(P) and F(P) were significantly diminished. CONCLUSION: DCE-MRI with integrated motion compensation enables evaluation of primary RCC and detects distinct perfusion patterns. Quantification with a two-compartment-exchange-model produces a separate perfusion- and permeability characterization and may become a diagnostic tool to monitor antiangiogenic treatment.

Benefits and challenges in bowel MR imaging at 3.0 T.

Abdominal imaging at 3.0 T has shown to be challenging because of a number of artifacts and effects related to the physics at higher field strength. For bowel imaging at 3.0 T, artifacts due to magnetic field inhomogeneities, standing waves, increased susceptibility, and greater chemical shift effects are of particular concern because they are likely to affect the assessment of relevant structures and counterbalance the benefits of higher signal-to-noise ratio. Regarding small- and large-bowel magnetic resonance imaging, the benefits of higher field strengths translate mainly in better contrast-to-noise ratio of contrast-enhanced T1-weighted gradient echo and T2-weighted imaging, whereas steady-state free precession sequences seem to suffer from serious degradation of image quality. The present article summarizes the technical challenges in bowel imaging at 3.0 T, provides an overview of performance compared with 1.5 T in small- and large-bowel diseases including the rectum, and revises the current literature.

Use of 3.0-T MR imaging for evaluation of the abdomen.

The most important advantage of 3.0-T magnetic resonance (MR) imaging systems is their increased signal-to-noise ratio (SNR) compared with 1.5-T systems. The higher SNR can be used to shorten acquisition time, achieve higher spatial resolution, or a combination of the two, thereby improving image quality and clinical diagnosis. In fact, 3.0-T MR imaging systems have already proved superior to 1.5-T systems in neuroradiologic and musculoskeletal applications. In the abdomen, 3.0-T MR imaging is uniquely beneficial for techniques such as enhanced and nonenhanced hepatic imaging, diffusion-weighted imaging, angiography, MR pancreatography, and colonography. Admittedly, 3.0-T abdominal imaging has important technical limitations, such as standing wave artifact, chemical shift artifact, susceptibility artifact, and safety issues such as increased energy deposition within the patient's body. Furthermore, 3.0-T abdominal MR imaging is still in the early stages of development and requires substantial modifications of the pulse sequences and hardware components used for 1.5-T imaging. Nevertheless, the ability to obtain physiologic and functional information within reasonably short acquisition times with 3.0-T abdominal MR imaging bodies well for the future of this imaging technique.

MRI of the knee at 3T: first clinical results with an isotropic PDfs-weighted 3D-TSE-sequence.

PURPOSE: To clinically evaluate MRI of the knee using a highly resolved isotropic fat-saturated (fs) proton-density weighted 3D-TSE-sequence (SPACE) at 3T. MATERIALS AND METHODS: Imaging was performed on a 3T-scanner (Magnetom TRIO). For technical evaluation, sagittally orientated SPACE-datasets (repetition-time [TR], 1200 milliseconds/[TE], 30 milliseconds/voxel-size, 0.5 mm3/acquisition time, 10:35 minutes) were acquired from the dominant knee of 10 healthy volunteers. In the 3 major anatomic planes, 0.5, 1, and 2 mm thick reconstructions were performed. Signal-to-noise (SNR), SNR-efficiency, contrast-to-noise (CNR) ratios, and anatomic detail visualization were compared with a state-of-the-art 2D-TSE-sequence in 3 imaging planes (TR, 3200 milliseconds/TE, 30 milliseconds/acquisition time, 12:34 minutes). Sixty patients with cartilage and meniscus pathologies were examined with these techniques. Patient SPACE-datasets were assessed in 1-mm thick reconstructions. Arthroscopical correlation was available for 18 patients. Lesion detection and diagnostic confidence were assessed by 2 radiologists independently. Statistical analysis was performed using 95% confidence intervals, Wilcoxon signed rank tests, and Weighted-kappa. RESULTS: SNR-efficiency of SPACE was 4 to 5 times higher than for 2D-TSE-sequences. SNR and CNR of 1-mm thick SPACE-reconstructions were comparable to 2D-TSE-sequences and provided superior visualization of small structures such as meniscal roots.Correlation with arthroscopy did not show significant differences between 2D- and 3D-sequences. One reader detected significantly more cartilage abnormalities with the 2D-TSE-sequence (131 vs. 151, P = 0.04), probably because of an unfamiliar fluid/cartilage contrast. Diagnostic confidence was significantly higher for meniscus abnormalities for SPACE for 1 reader. Intersequence-correlation was excellent (kappa = 0.82-0.92). Interreader-correlation was good to excellent (kappa = 0.71-0.80), intrareader-correlation was excellent (kappa = 0.90-0.92) for both sequences. CONCLUSIONS: Time-efficient 3D-TSE-imaging of the knee at 3T is feasible with adequate SNR and CNR and excellent anatomic detail visualization. Detection and visualization of meniscus and cartilage pathologies is comparable to standard 2D-TSE-sequences. 3D-TSE-sequences with consecutive multiplanar reconstruction may become a valuable component of future knee-MRI protocols.

MR-lymphangiography at 3.0 T--a feasibility study.

The purpose of this study was to establish and evaluate contrast-enhanced MR-lymphangiography (MRL) at 3.0 T for detection and visualization of abnormalities of the peripheral lymphatic system. Sixteen patients were examined with a highly resolved isotropic T1w-3D-GRE-(FLASH) sequence (TR 3.76 ms/TE 1.45 ms/FA 30 degrees /voxel-size 0.8 x 0.8 x 0.8 mm(3)) at 3T after intracutaneous injection of gadolinium-diethylene-triamine-pentaacetic-acid. Two radiologists evaluated overall image quality, contrast between lymph vessels and background tissue, venous contamination, visualized levels, and fat-saturation-homogeneity on 3D maximum-intensity projections. Overall image quality was good to excellent, and all examinations were diagnostic except one, where contrast medium was injected subcutaneously instead of intracutaneously. Overall image quality was good to excellent in 12/16 cases, depiction of lymph vessels was good to excellent in 15/16 cases. Venous contamination was always present, but diagnostically problematical in only one case. Instant lymphatic drainage was observed in unaffected extremities, reaching the pelvic level after approximately 10 min. Lymphatic drainage was considerably delayed in lymphedematous extremities. Ectatic lymph vessels, entrapment, and diffuse drainage of contrast medium correlated with impaired lymphatic drainage. In conclusion, MRL at 3.0 T provides very high spatial resolution and anatomical detail of normal and abnormal peripheral lymph vessels. MRL may thus become a valuable tool for microsurgical treatment planning and monitoring.