Acceleration techniques and their impact on arterial input function sampling: Non-accelerated versus view-sharing and compressed sensing sequences.

PURPOSE: The aim was to investigate the variation of the arterial input function (AIF) within and between various DCE MRI sequences. MATERIAL AND METHODS: A dynamic flow-phantom and steady signal reference were scanned on a 3T MRI using fast low angle shot (FLASH) 2d, FLASH3d (parallel imaging factor (P) = P0, P2, P4), volumetric interpolated breath-hold examination (VIBE) (P = P0, P3, P2 × 2, P2 × 3, P3 × 2), golden-angle radial sparse parallel imaging (GRASP), and time-resolved imaging with stochastic trajectories (TWIST). Signal over time curves were normalized and quantitatively analyzed by full width half maximum (FWHM) measurements to assess variation within and between sequences. RESULTS: The coefficient of variation (CV) for the steady signal reference ranged from 0.07-0.8%. The non-accelerated gradient echo FLASH2d, FLASH3d, and VIBE sequences showed low within sequence variation with 2.1%, 1.0%, and 1.6%. The maximum FWHM CV was 3.2% for parallel imaging acceleration (VIBE P2 × 3), 2.7% for GRASP and 9.1% for TWIST. The FWHM CV between sequences ranged from 8.5-14.4% for most non-accelerated/accelerated gradient echo sequences except 6.2% for FLASH3d P0 and 0.3% for FLASH3d P2; GRASP FWHM CV was 9.9% versus 28% for TWIST. CONCLUSION: MRI acceleration techniques vary in reproducibility and quantification of the AIF. Incomplete coverage of the k-space with TWIST as a representative of view-sharing techniques showed the highest variation within sequences and might be less suited for reproducible quantification of the AIF.

Post-contrast acute kidney injury. Part 2: risk stratification, role of hydration and other prophylactic measures, patients taking metformin and chronic dialysis patients : Recommendations for updated ESUR Contrast Medium Safety Committee guidelines.

OBJECTIVES: The Contrast Media Safety Committee (CMSC) of the European Society of Urogenital Radiology (ESUR) has updated its 2011 guidelines on the prevention of post-contrast acute kidney injury (PC-AKI). The results of the literature review and the recommendations based on it, which were used to prepare the new guidelines, are presented in two papers. AREAS COVERED IN PART 2: Topics reviewed include stratification of PC-AKI risk, the need to withdraw nephrotoxic medication, PC-AKI prophylaxis with hydration or drugs, the use of metformin in diabetic patients receiving contrast medium and the need to alter dialysis schedules in patients receiving contrast medium. KEY POINTS: • In CKD, hydration reduces the PC-AKI risk • Intravenous normal saline and intravenous sodium bicarbonate provide equally effective prophylaxis • No drugs have been consistently shown to reduce the risk of PC-AKI • Stop metformin from the time of contrast medium administration if eGFR < 30 ml/min/1.73 m 2 • Dialysis schedules need not change when intravascular contrast medium is given.

Post-contrast acute kidney injury - Part 1: Definition, clinical features, incidence, role of contrast medium and risk factors : Recommendations for updated ESUR Contrast Medium Safety Committee guidelines.

PURPOSE: The Contrast Media Safety Committee (CMSC) of the European Society of Urogenital Radiology (ESUR) has updated its 2011 guidelines on the prevention of post-contrast acute kidney injury (PC-AKI). The results of the literature review and the recommendations based on it, which were used to prepare the new guidelines, are presented in two papers. AREAS COVERED IN PART 1: Topics reviewed include the terminology used, the best way to measure eGFR, the definition of PC-AKI, and the risk factors for PC-AKI, including whether the risk with intravenous and intra-arterial contrast medium differs. KEY POINTS: • PC-AKI is the preferred term for renal function deterioration after contrast medium. • PC-AKI has many possible causes. • The risk of AKI caused by intravascular contrast medium has been overstated. • Important patient risk factors for PC-AKI are CKD and dehydration.

Iodine-based contrast media, multiple myeloma and monoclonal gammopathies: literature review and ESUR Contrast Media Safety Committee guidelines.

OBJECTIVES: Many radiologists and clinicians still consider multiple myeloma (MM) and monoclonal gammopathies (MG) a contraindication for using iodine-based contrast media. The ESUR Contrast Media Safety Committee performed a systematic review of the incidence of post-contrast acute kidney injury (PC-AKI) in these patients. METHODS: A systematic search in Medline and Scopus databases was performed for renal function deterioration studies in patients with MM or MG following administration of iodine-based contrast media. Data collection and analysis were performed according to the PRISMA statement 2009. Eligibility criteria and methods of analysis were specified in advance. Cohort and case-control studies reporting changes in renal function were included. RESULTS: Thirteen studies were selected that reported 824 iodine-based contrast medium administrations in 642 patients with MM or MG, in which 12 unconfounded cases of PC-AKI were found (1.6 %). The majority of patients had intravenous urography with high osmolality ionic contrast media after preparatory dehydration and purgation. CONCLUSIONS: MM and MG alone are not risk factors for PC-AKI. However, the risk of PC-AKI may become significant in dehydrated patients with impaired renal function. Hypercalcaemia may increase the risk of kidney damage, and should be corrected before contrast medium administration. Assessment for Bence-Jones proteinuria is not necessary. KEY POINTS: • Monoclonal gammopathies including multiple myeloma are a large spectrum of disorders. • In monoclonal gammopathy with normal renal function, PC-AKI risk is not increased. • Renal function is often reduced in myeloma, increasing the risk of PC-AKI. • Correction of hypercalcaemia is necessary in myeloma before iodine-based contrast medium administration. • Bence-Jones proteinuria assessment in myeloma is unnecessary before iodine-based contrast medium administration.

Scan time adapted contrast agent injection protocols with low volume for low-tube voltage CT angiography: An in vitro study.

PURPOSE: The aims of this study were twofold. First, we investigated the extent of changes in arterial peak enhancement and changes in the duration of a diagnostic arterial enhancement when small amounts of CA volumes (≤30mL) were administered at varying tube voltages. Second, we investigated how to optimize CA injection protocols for CT-angiography with long scan times at various tube voltages to achieve optimal vascular enhancement at the lowest reasonable CA dose. MATERIALS AND METHODS: Measurements were performed with a custom-made dynamic flow phantom. For CTA protocols with a short scan time, we investigated the effect of various tube voltages (70-120kVp) on the arterial enhancement profile with very small CA volumes (20 and 30mL of Iobitridol 350mg I/mL) at a flow rate of 5mL/s. For CTA protocols with a long scan time, we utilized an optimized multi-bolus technique switching rapidly between 13 "micro-boli" of CA (total, 60mL) and saline (total, 24mL) at a flow rate of 4mL/s. The peak arterial enhancement (PAE) and the time period of diagnostic aortic enhancement ≥200 HU (T200) were analyzed. RESULTS: For the short scan time protocols, a diagnostic peak enhancement was achieved using 20mL of CA at 70 and 80kVp (PAE: 327±10 and 255±15 HU, respectively) or 30mL of CA at 70, 80 and 100kVp (PAE 451±10, 367±9, and 253±15 HU). For the long scan time, the optimized multi-bolus injection protocol extended T200 at 100kVp by 6s (40%) compared to a linear injection protocol (21±1s and 15±1s, respectively; p<0.001). CONCLUSION: Optimized CTA protocols comprising alternations of tube voltage and the CA injection protocol can save radiation doses and CA volumes at the same time.

Gadobutrol in Renally Impaired Patients: Results of the GRIP Study.

OBJECTIVE: The aim of this study was to assess the potential risk of gadobutrol-enhanced magnetic resonance imaging (MRI) in patients with moderate to severe renal impairment for the development of nephrogenic systemic fibrosis (NSF). MATERIALS AND METHODS: We performed a prospective, international, multicenter, open-label study in 55 centers. Patients with moderate to severe renal impairment scheduled for any gadobutrol-enhanced MRI were included. All patients received a single intravenous bolus injection of gadobutrol at a dose of 0.1 mmol/kg body weight. The primary target variable was the number of patients who develop NSF within a 2-year follow-up period. RESULTS: A total of 908 patients were enrolled, including 586 with moderate and 284 with severe renal impairment who are at highest risk for developing NSF. The mean time since renal disease diagnosis was 1.83 and 5.49 years in the moderate and severe renal impairment cohort, respectively. Overall, 184 patients (20.3%) underwent further contrast-enhanced MRI with other gadolinium-based contrast agents within the 2-year follow-up. No patient developed symptoms conclusive of NSF. CONCLUSIONS: No safety concerns with gadobutrol in patients with moderate to severe renal impairment were identified. There were no NSF cases.

Stress examination of flexor tendon pulley rupture in the crimp grip position: a 1.5-Tesla MRI cadaver study.

OBJECTIVE: The objectives of this study were the evaluation of flexor tendon pulley rupture of the fingers in the crimp grip position using magnetic resonance imaging (MRI) and the comparison of the results with MRI in the neutral position in a cadaver study. MATERIALS AND METHODS: MRI in the crimp grip position and in the neutral position was performed in 21 cadaver fingers with artificially created flexor tendon pulley tears (combined pulley rupture, n = 14; single pulley rupture, n = 7). Measurement of the distance between the tendon and bone was performed. Images were evaluated by two readers, first independently and in cases of discrepancy in consensus. Sensitivity and specificity for detecting combined pulley ruptures were calculated. RESULTS: Tendon bone distances were significantly higher in the crimp grip position than in the neutral position. Sensitivity and specificity for detecting combined pulley rupture were 92.86 % and 100 % respectively in the crimp grip position and 78.57 % and 85.71 % respectively in the neutral position. Kappa values for interobserver reliability were 0.87 in the crimp grip position and 0.59 in the neutral position. CONCLUSION: MRI examination in the crimp grip position results in higher tendon bone distances by subjecting the pulleys to a higher strain, which facilitates image evaluation with higher interobserver reliability, higher sensitivity, and higher specificity for combined pulley rupture compared with examination in the neutral position.

Serum creatinine measurements: evaluation of a questionnaire according to the ESUR guidelines.

BACKGROUND: The European Society of Urogenital Radiology (ESUR) propose measurements of serum creatinine levels in patients undergoing contrast-enhanced studies with a high probability of impaired renal function and therefore with a higher risk of CIN and NSF. PURPOSE: To determine whether the recommended questionnaire is able to select these patients. MATERIAL AND METHODS: Over a time period of 10 months the questionnaire was conducted in 1389 patients (725 women, 654 men) before contrast administration for computed tomography (CT) or magnetic resonance imaging (MRI) examination. Serum creatinine (SCr) measurements and calculation of estimated glomerular filtration rate (eGFR) values were performed when one or more answers were positive. Eighty-one patients were excluded due to incomplete data. Statistical evaluation of the questionnaire was done retrospectively. RESULTS: Four hundred and ninety-nine patients (38%) gave one or more positive answers to the questionnaire. Of these, 71 (14%) had an eGFR <60 mL/min/1.73 m(2), 31 (6%) had an eGFR <45 mL/min/1.73 m(2), and five (1%) had an eGFR <30 mL/min/1.73 m(2). Only the question concerning previous renal disease showed a significant correlation to an eGFR <60 mL/min/1.73 m(2) (P < 0.05) and <45 mL/min/1.73 m(2). Slight correlations with some other risk factors (renal disease, family history of renal disease, arterial hypertension with medication, analgetic medication with nephrotoxic drugs) were found for either a threshold of 60 or 45 mL/min/1.73 m(2). In addition, there was a positive correlation with patient age. CONCLUSION: We propose to reduce the questionnaire to a smaller number of risk factors and consider a point-of-care (POC) SCr measurement for all patients aged >70 years without a recent eGFR value while referred for CT. For MRI a SCr measurement is not mandatory while using medium and lowest risk contrast agents.

Integration of the computational fluid dynamics technique with MRI in aortic dissections.

Short-term and long-term prognosis and their determining factors of Type III/Stanford B aortic dissections (TB-AD), which separate the aorta distal at the origin of the subclavian artery into a true lumen and false lumen, have been elusive: One quarter of patients thought to be treated successfully, either by medical or by surgical means, do not survive 3 years. Unfavorable hemodynamic conditions are believed to lead to false lumen pressure increases and complications. A better characterization of TB-AD hemodynamics may therefore impact therapeutic decision making and improve outcome. The large variations in TB-AD morphology and hemodynamics favor a patient-specific approach. Magnetic resonance imaging with its capability to provide high-resolution structural images of the lumen and aortic wall and also to quantify aortic flow and kinetics of an exogenous tracer is a promising clinical modality for developing a deeper understanding of TB-AD hemodynamics in an individual patient. With the information obtained with magnetic resonance imaging, computational fluid dynamics simulations can be performed to augment the image information. Here, an overview of the interplay of magnetic resonance imaging and computational fluid dynamics techniques is given illustrating the synergy of these two approaches toward a comprehensive morphological and hemodynamic characterization of TB-AD.

Detection of suspected placental invasion by MRI: do the results depend on observer' experience?

PURPOSE: To evaluate the diagnostic value of previously described MR features used for detecting suspected placental invasion according to observers' experience. MATERIALS AND METHODS: Our population included 25 pregnant women (mean age 35.16) investigated by prenatal MRI (1.5T, T1- and T2-weighted MR-sequences without i.v. contrast), among them 12 with histopathologically proven placental invasion and 13 women (52%) without placental invasion used as control group. Two senior and two junior radiologists blindly and independently reviewed MR-examinations in view of 6 previously defined MR-features indicating presence and degree of placental invasion (placenta increta, accreta or percreta). For each reader the sensibility, specificity, and receiver operating curve (ROC) were calculated. Interobserver agreements between senior and junior readers were determined. Stepwise logistic regression was performed including the 6 MR-features predictive of placental invasion. RESULTS: Demographics between both groups were statistically equivalent. Overall sensitivity and specificity for placental invasion was 90.9% and 75.0% for seniors and 81.8% and 61.8% for juniors, respectively. The best single MR-feature indicating placental invasion was T2-hypointense placental bands (r(2)=0.28), followed by focally interrupted myometrial border, infiltration of pelvic organs and tenting of the bladder (r(2)=0.36). Interobserver agreement for detecting placental invasion was 0.64 for seniors and 0.41 for juniors, thus substantial and moderate, respectively. Seniors detected placental invasion and depth of infiltration with significantly higher diagnostic certitude than juniors (p=0.0002 and p=0.0282, respectively). CONCLUSION: MRI can be a reliable and reproducible tool for the detection of suspected placental invasion, but the diagnostic value significantly depends on observers' experience.

Nephrogenic systemic fibrosis and gadolinium-based contrast media: updated ESUR Contrast Medium Safety Committee guidelines.

PURPOSE: To update the guidelines of the Contrast Media Safety Committee (CMSC) of the European Society of Urogenital Radiology (ESUR) on nephrogenic systemic fibrosis and gadolinium-based contrast media. AREAS COVERED: Topics reviewed include the history, clinical features and prevalence of nephrogenic systemic fibrosis and the current understanding of its pathophysiology. The risk factors for NSF are discussed and prophylactic measures are recommended. The stability of the different gadolinium-based contrast media and the potential long-term effects of gadolinium in the body have also been reviewed.

Choi response criteria for prediction of survival in patients with metastatic renal cell carcinoma treated with anti-angiogenic therapies.

OBJECTIVE: Anti-angiogenic drugs cause a reduction in tumour density (Choi criteria) first and then in size [Response Evaluation Criteria In Solid Tumours (RECIST)]. The prognostic significance of changes in tumour density in metastatic renal cell carcinoma (mRCC) is unknown and was assessed in this study. METHODS: The prognostic significance of partial response (PR) as opposed to non-response [stable disease (SD) + progressive (PD)] to anti-angiogenic therapy was assessed in patients with mRCC separately for both criteria using the log-rank test and Cox regression models. RESULTS: Both criteria were applied to 35 patients. The response was identical for all eight patients with PR and most patients with PD (10/12) when using the RECIST and Choi criteria. Adding tumour density information, 14 patients with SD were re-categorised as having PR (7), SD (4), and PD (3). Patients with PR (Choi) were progression free significantly longer [hazard ratio (HR) 0.24; 95 % CI 0.10-0.57; P = 0.001] and had better overall survival (HR 0.36; 95 % CI 0.15-0.89; P = 0.026) compared to patients with SD or PD. The predictive value of PR according to RECIST was not statistically significant. CONCLUSIONS: In mRCC, the Choi criteria separate prognostic groups better when compared with RECIST. This may allow early discrimination of patients benefiting from continued treatment.

Remote sonographic interpretation: comparison of standardized video clips to still images.

OBJECTIVE: The aim of our study was to evaluate the role of standardized video clips compared with still images in the diagnostic accuracy of remote sonographic interpretation. METHODS: We compared the remote interpretation of sonographic examinations acquired with a standardized video clip approach to examinations performed with still images alone in 60 patients with various hepatic and extrahepatic pathologies. RESULTS: The use of video clips improved the diagnostic accuracy of sonographic studies interpreted remotely compared with the use of still images (p < 0.0001). The sensitivity, specificity, and positive and negative predictive values increased from 47.3% to 68.3%, 81.8% to 87.8%, 71.5% to 81%, and 63.8% to 74.5%, respectively. CONCLUSIONS: Standardized video clips are easy to obtain, less operator-dependent than still images, and can be transferred to remote sites without loss of important data. We recommend this method in remote interpretation (teleradiology and distant consultation) of sonographic examinations.

Skeletal muscle BOLD MRI: from underlying physiological concepts to its usefulness in clinical conditions.

Blood oxygenation-level dependent (BOLD) MRI has gained particular attention in functional brain imaging studies, where it can be used to localize areas of brain activation with high temporal resolution. To a higher degree than in the brain, skeletal muscles show extensive but transient alterations of blood flow between resting and activation state. Thus, there has been interest in the application of the BOLD effect in studying the physiology of skeletal muscles (healthy and diseased) and its possible application to clinical practice. This review outlines the potential of skeletal muscle BOLD MRI as a diagnostic tool for the evaluation of physiological and pathological alterations in the peripheral limb perfusion, such as in peripheral arterial occlusive disease. Moreover, current knowledge is summarized regarding the complex mechanisms eliciting BOLD effect in skeletal muscle. We describe technical fundaments of the procedure that should be taken into account when performing skeletal muscle BOLD MRI, including the most often applied paradigms to provoke BOLD signal changes and key parameters of the resulting time courses. Possible confounding effects in muscle BOLD imaging studies, like age, muscle fiber type, training state, and drug effects are also reviewed in detail.

Proximal interphalangeal joint volar plate configuration in the crimp grip position.

PURPOSE: To study the configuration of the proximal interphalangeal joint volar plate (VP) in the crimp grip position (metacarpophalangeal joint at 0° to 45° flexion, proximal interphalangeal joint at 90° to 100° flexion, and distal interphalangeal joint at 0° to 10° hyperextension) using magnetic resonance imaging techniques in healthy volunteers and cadaver fingers and to compare the results with histological sections. METHODS: Magnetic resonance imaging was performed on 24 fingers of 8 healthy volunteers and 12 fingers of 4 embalmed cadaver hands in the neutral position and in the crimp grip position. The translation of the VP body relative to the middle phalanx base during finger flexion was measured. In 6 of 12 cadaver specimens, a load of 10 N was applied to the flexor tendons to examine how this would affect the histological VP fiber configuration. RESULTS: When the flexor tendons were under load in the crimp grip position, the volunteers' VP body was translated an average of 3.2 mm, and the cadaver fingers' VP body was translated an average of 3.0 mm, relative to the middle phalanx base in a distal direction. Histological analysis of the crimp grip position revealed reversing fibers in the VP insertion at the base of the middle phalanx when the flexor tendons were under load and the VP body was translated. When no load was applied in the crimp grip position, no translation of the VP body occurred. CONCLUSIONS: This article describes a VP translation in a distal direction relative to the middle phalanx base in the crimp grip position when the flexor tendons are under load. CLINICAL RELEVANCE: A more precise knowledge of the histological properties of the proximal interphalangeal joint VP during finger flexion can be expected to provide greater diagnostic capabilities and can lead to a better comprehension of injuries.

Clinical implications of skeletal muscle blood-oxygenation-level-dependent (BOLD) MRI.

Blood-oxygenation-level-dependent (BOLD) contrast in magnetic resonance (MR) imaging of skeletal muscle mainly depends on changes of oxygen saturation in the microcirculation. In recent years, an increasing number of studies have evaluated the clinical relevance of skeletal muscle BOLD MR imaging in vascular diseases, such as peripheral arterial occlusive disease, diabetes mellitus, and chronic compartment syndrome. BOLD imaging combines the advantages of MR imaging, i.e., high spatial resolution, no exposure to ionizing radiation, with functional information of local microvascular perfusion. Due to intrinsic contrast provoked via changes in hemoglobin oxygen saturation, it is a safe and easy applicable procedure on standard whole-body MR devices. Therefore, BOLD MR imaging of skeletal muscle is a potential new diagnostic tool in the clinical evaluation of vascular, inflammatory, and muscular pathologies. Our review focuses on the current evidence concerning the use of BOLD MR imaging of skeletal muscle under pathological conditions and highlights ways for future clinical and scientific applications.

Blood oxygenation level-dependent (BOLD) MRI of human skeletal muscle at 1.5 and 3 T.

PURPOSE: To evaluate the dependence of skeletal muscle blood oxygenation level-dependent (BOLD) effect and time course characteristics on magnetic field strength in healthy volunteers using an ischemia/reactive hyperemia paradigm. MATERIALS AND METHODS: Two consecutive skeletal muscle BOLD magnetic resonance imaging (MRI) measurements in eight healthy volunteers were performed on 1.5 T and 3.0 T whole-body MRI scanners. For both measurements a fat-saturated multi-shot multiecho gradient-echo EPI sequence was applied. Temporary vascular occlusion was induced by suprasystolic cuff compression of the thigh. T2 time courses were obtained from two different calf muscles and characterized by typical curve parameters. Ischemia- and hyperemia-induced changes in R2 (ΔR2) were calculated for both muscles in each volunteer at the two field strengths. RESULTS: Skeletal muscle BOLD changes are dependent on magnetic field strength as the ratio ΔR2(3.0 T)/ΔR2(1.5 T) was found to range between 1.6 and 2.2. Regarding time course characteristics, significantly higher relative T2 changes were found in both muscles at 3.0 T. CONCLUSION: The present study shows an approximately linear field strength dependence of ΔR2 in the skeletal muscle in response to ischemia and reactive hyperemia. Using higher magnetic fields is advisable for future BOLD imaging studies of peripheral limb pathologies.