Thorsten A. Bley

Time-resolved 3D MR velocity mapping at 3T: Improved navigator-gated assessment of vascular anatomy and blood flow

To evaluate an improved image acquisition and data‐processing strategy for assessing aortic vascular geometry and 3D blood flow at 3T.

Fat and water magnetic resonance imaging

A wide variety of fat suppression and water–fat separation methods are used to suppress fat signal and improve visualization of abnormalities. This article reviews the most commonly used techniques for fat suppression and fat–water imaging including 1) chemically selective fat suppression pulses “FAT‐SAT”; 2) spatial‐spectral pulses (water excitation); 3) short inversion time (TI) inversion recovery (STIR) imaging; 4) chemical shift based water–fat separation methods; and finally 5) fat suppression and balanced steady‐state free precession (SSFP) sequences. The basic physical background of these techniques including their specific advantages and disadvantages is given and related to clinical applications. This enables the reader to understand the reasons why some fat suppression methods work better than others in specific clinical settings. J. Magn. Reson. Imaging 2010;31:4–18.

Imaging for large-vessel vasculitis

Purpose of reviewUltrasonography, MRI, and PET are increasingly studied in large-vessel vasculitis. They have broadened our knowledge on these disorders and have a place in the diagnostic approach of these patients. Recent findingsTemporal artery ultrasonography can be used to guide the surgeon to that artery segment with the clearest ‘halo’ sign to perform a biopsy, or in experienced hands can even replace biopsy. The distal subclavian, axillary, and brachial arteries can also be examined. High-resolution MRI depicts superficial cranial and extracranial involvement patterns in giant cell arteritis (GCA). Contrast enhancement is prominent in active inflammation and decreases under successful steroid therapy. Presence of aortic complications such as aneurysm or dissection can be ruled out within the same investigation. Large thoracic vessel FDG-uptake is seen in the majority of patients with GCA, especially at the subclavian arteries and the aorta. FDG-PET cannot predict which patients are bound to relapse, and once steroids are started, interpretation is hazardous, which makes its role in follow-up uncertain. Increased thoracic aortic FDG-uptake at diagnosis of GCA may be a bad prognostic factor for later aortic dilatation. In patients with isolated polymyalgia rheumatica – who have less intense vascular FDG uptake – symptoms are caused by inflammation around the shoulders, hips, and spine. SummaryUltrasonography, MRI, and PET remain promising techniques in the scientific and clinical approach of large-vessel vasculitis.

Diagnostic value of high-resolution MR imaging in giant cell arteritis.

BACKGROUND AND PURPOSE: Clinical indications of giant cell arteritis may be unspecific, and noninvasive diagnosis is often difficult. This study investigated the hypothesis that high-resolution MR imaging of the superficial cranial arteries is a noninvasive imaging technique that can detect the occurrence of giant cell arteritis. MATERIALS AND METHODS: Contrast-enhanced, high-resolution MR imaging was performed on 64 consecutive patients with suspected giant cell arteritis. Mural thickness, lumen diameter, and a mural contrast enhancement score were assessed with T1-weighted spin-echo images with submillimeter in-plane spatial resolution. The final rheumatologists diagnosis according to the clinical criteria of the American College of Rheumatology including laboratory tests and results of temporal artery biopsies from 32 patients was used as a “gold standard” for the evaluation of the MR imaging findings. RESULTS: All of the examinations provided diagnostic image quality. Evaluation of the mural inflammatory MR imaging signs for diagnosing vasculitis resulted in a sensitivity of 80.6% and a specificity of 97.0%. In comparison, histology results alone showed a sensitivity of 77.8% and specificity of 100%. The mean wall thickness increased significantly from 0.39 mm (±0.18 mm) to 0.74 mm (±0.32 mm; P < .001), and the lumen diameter decreased significantly from 0.84 mm (±0.29 mm) to 0.65 mm (±0.38 mm; P < .05) for patients with giant cell arteritis. CONCLUSION: Contrast-enhanced, high-resolution MR imaging allows noninvasive assessment of mural inflammation in giant cell arteritis with good diagnostic certainty. Measures of mural thickening and contrast enhancement can be obtained in these small vessels and provide valuable vasculitic MR imaging findings.

EULAR points to consider in the development of classification and diagnostic criteria in systemic vasculitis

Objectives The systemic vasculitides are multiorgan diseases where early diagnosis and treatment can significantly improve outcomes. Robust nomenclature reduces diagnostic delay. However, key aspects of current nomenclature are widely perceived to be out of date, these include disease definitions, classification and diagnostic criteria. Therefore, the aim of the present work was to identify deficiencies and provide contemporary points to consider for the development of future definitions and criteria in systemic vasculitis. Methods The expert panel identified areas of concern within existing definitions/criteria. Consequently, a systematic literature review was undertaken looking to address these deficiencies and produce ‘points to consider’ in accordance with standardised European League Against Rheumatism (EULAR) operating procedures. In the absence of evidence, expert consensus was used. Results There was unanimous consensus for re-evaluating existing definitions and developing new criteria. A total of 17 points to consider were proposed, covering 6 main areas: biopsy, laboratory testing, diagnostic radiology, nosology, definitions and research agenda. Suggestions to improve and expand current definitions were described including the incorporation of anti-neutrophil cytoplasm antibody and aetiological factors, where known. The importance of biopsy in diagnosis and exclusion of mimics was highlighted, while equally emphasising its problems. Thus, the role of alternative diagnostic tools such as MRI, ultrasound and surrogate markers were also discussed. Finally, structures to develop future criteria were considered. Conclusions Limitations in current classification criteria and definitions for vasculitis have been identified and suggestions provided for improvement. Additionally it is proposed that, in combination with the updated evidence, these should form the basis of future attempts to develop and validate revised criteria and definitions of vasculitis.

4D phase contrast MRI at 3 T: effect of standard and blood-pool contrast agents on SNR, PC-MRA, and blood flow visualization.

Time‐resolved phase contrast (PC) MRI with velocity encoding in three directions (flow‐sensitive four‐dimensional MRI) can be employed to assess three‐dimensional blood flow in the entire aortic lumen within a single measurement. These data can be used not only for the visualization of blood flow but also to derive additional information on vascular geometry with three‐dimensional PC MR angiography (MRA). As PC‐MRA is sensitive to available signal‐to‐noise ratio, standard and novel blood pool contrast agents may help to enhance PC‐MRA image quality. In a group of 30 healthy volunteers, the influence of different contrast agents on vascular signal‐to‐noise ratio, PC‐MRA quality, and subsequent three‐dimensional stream‐line visualization in the thoracic aorta was determined. Flow‐sensitive four‐dimensional MRI data acquired with contrast agent provided significantly improved signal‐to‐noise ratio in magnitude data and noise reduction in velocity data compared to measurements without contrast media. The agreement of three‐dimensional PC‐MRA with reference standard contrast‐enhanced MRA was good for both contrast agents, with improved PC‐MRA performance for blood pool contrast agent, particularly for the smaller supra‐aortic branches. For three‐dimensional flow visualization, a trend toward improved results for the data with contrast agent was observed. Magn Reson Med, 2010.

Repeatability of magnetic resonance elastography for quantification of hepatic stiffness.

To determine the sources of variability of MRE hepatic stiffness measurements using healthy volunteers and patients and to calculate the minimum change required for statistical significance. Hepatic stiffness measured with magnetic resonance elastography (MRE) has demonstrated tremendous potential as a noninvasive surrogate of hepatic fibrosis, although the underlying repeatability of MRE for longitudinal tracking of liver disease has not been documented.

Time-resolved, 3-dimensional magnetic resonance flow analysis at 3 T: visualization of normal and pathological aortic vascular hemodynamics.

Flow-sensitive 3-dimensional magnetic resonance imaging at 3 T and advanced 3-dimensional visualization were used to visualize local and global vascular hemodynamics in the thoracic aorta. In patients with pathological geometric alterations of the thoracic aorta, this technique revealed considerable changes in local blood flow characteristics, compared with normal volunteers. Specifically, relatively small geometric changes, such as a partially thrombosed aortic arch or a mild aneurysm of the ascending aorta, resulted in major disturbances of local blood flow patterns within and even further downstream to the pathology.

Comparison of duplex sonography and high-resolution magnetic resonance imaging in the diagnosis of giant cell (temporal) arteritis

OBJECTIVE To compare the diagnostic performance of high-resolution magnetic resonance imaging (MRI) and color-coded duplex sonography (CCDS) in patients with giant cell (temporal) arteritis (GCA). METHODS Results of high-resolution MRI and CCDS in 59 patients with suspected GCA were compared with the final clinical diagnosis (based on the American College of Rheumatology GCA criteria and a 6-month followup study). Sensitivity, specificity, and positive and negative predictive values (PPV, NPV) were calculated for each method. In 41 of the patients, imaging results were also compared with the findings of a temporal artery (TA) biopsy. RESULTS Thirty-six of the 59 patients (61%) were ultimately diagnosed as having GCA. Sensitivity of high-resolution MRI and CCDS was 69% and 67%, respectively, specificity was 91% and 91%, PPV was 93% and 92%, and NPV was 66% and 64%, respectively. TA biopsy findings were positive in 24 of the 41 biopsied patients (59%). Sensitivity of high-resolution MRI and CCDS compared with TA biopsy was 83% and 79%, respectively, specificity was 71% and 59%, PPV was 80% and 73%, and NPV was 75% and 67%, respectively. The differences between high-resolution MRI and CCDS were not significant. CONCLUSION The diagnostic power of high-resolution MRI and CCDS in detecting GCA was comparable. Either of these noninvasive techniques may have value in the evaluation of patients with suspected GCA, and decisions regarding which technique to use may depend on the clinical setting.

Endovascular Abdominal Aortic Aneurysm Repair: Nonenhanced Volumetric CT for Follow-up

PURPOSE To evaluate the clinical usefulness of volumetric analysis at nonenhanced computed tomography (CT) as the sole method with which to follow up endovascular abdominal aortic aneurysm repair (EVAR) and to identify endoleaks causing more than 2% volumetric increase from the previous volume determination. MATERIALS AND METHODS The study had institutional review board approval. Images were reviewed retrospectively in a HIPAA-compliant manner for 230 CT studies in 70 patients (11 women, 59 men; mean age, 74 years) who underwent EVAR. The scannning protocol consisted of three steps: (a) contrast material-enhanced CT angiography before endovascular stent placement, (b) contrast-enhanced CT angiography 0-3 months after repair to depict immediate complications, and (c) nonenhanced CT at 3, 6, and 12 months after repair. At each follow-up visit, immediate aortic volume analysis was performed. If the interval volumetric change was 2% or less, no further imaging was performed. If the volume increased by more than 2% on the nonenhanced CT image, contrast-enhanced CT angiography was performed immediately to identify the suspected endoleak. Confidence intervals (CIs) were obtained by using bootstrapping to account for repeated measurements in the same patients. RESULTS Mean volume decrease was -3.2% (95% CI: -4.7%, -1.9%) in intervals without occurrence of a clinically relevant endoleak (n = 183). Types I and III high-pressure endoleaks (n = 10) showed a 10.0% (95% CI: 5.0%, 18.2%) interval volumetric increase. Type II low-pressure endoleaks (n = 37) showed a 5.4% (95% CI: 4.6%, 6.2%) interval volumetric increase. Endoleaks associated with minimal aortic volume increase of less than 2% did not require any intervention. This protocol reduced radiation exposure by approximately 57%-82% in an average-sized patient. CONCLUSION Serial volumetric analysis of aortic aneurysm with nonenhanced CT serves as an adequate screening test for endoleak, causing volumetric increase of more than 2% from the volume seen at the previous examination.