Jeremy D. Collins

Safety of gadolinium contrast angiography in patients with chronic renal insufficiency

OBJECTIVE To prevent iodinated contrast medium-induced nephrotoxicity, gadolinium has been used increasingly for magnetic resonance angiography (MRA) or conventional digital subtraction angiography (DSA) to visualize arterial anatomy in patients undergoing vascular surgery who are considered at high risk because of chronic renal insufficiency. We assessed the safety of gadolinium-based contrast medium as a substitute for iodinated contrast medium-enhanced examinations. We determined the incidence of gadolinium-induced nephrotoxicity in a clinical setting and searched for contributing risk factors. Patients and methods In a single-center retrospective study from December 1999 to January 2001, 218 inpatients underwent MRA and 42 inpatients underwent DSA, with gadolinium as the sole contrast agent. Patient comorbid conditions, indications for vascular imaging, contrast dose, urine output, baseline and post-procedure serum creatinine concentration (SCr), and outcome were recorded for all patients in whom gadolinium-induced renal failure developed. RESULTS Of 260 patients who received gadolinium-based contrast agents, at a dose of 0.25 mmol/kg or more, 195 patients (75%) had pre-test baseline chronic renal insufficiency. In 7 of 195 patients (3.5%) acute renal failure developed after gadolinium-based contrast medium administration, for MRA (n = 153) in 3 patients (1.9%) and DSA (n = 42) in 4 patients (9.5%). Average baseline SCr in the 195 patients with chronic renal insufficiency was 38.2 +/- 1.6 mL/min/1.73 m(2), and in the 7 patients in whom acute renal failure developed, baseline SCr was 32.5 +/- 7.8 mL/min/1.73 m(2) (P =.33). Respective intravenous and intra-arterial gadolinium doses in these 7 patients ranged from 0.31 to 0.41 mmol/kg for MRA and 0.27 to 0.42 mmol/kg for DSA. Acute renal failure did not develop in any of 65 patients with normal baseline SCr. CONCLUSION Despite reports of negligible nephrotoxicity, rarely gadolinium-based contrast agents can cause acute renal failure in patients with underlying chronic renal insufficiency. Estimation of creatinine clearance alone does not enable prediction of which patients are likely to have acute renal failure. Patients at high-risk should be identified, and prophylactic measures should be taken to reduce the risk for nephrotoxicity.

Bicuspid Aortic Cusp Fusion Morphology Alters Aortic Three-Dimensional Outflow Patterns, Wall Shear Stress, and Expression of Aortopathy

Background— Aortic 3-dimensional blood flow was analyzed to investigate altered ascending aorta (AAo) hemodynamics in bicuspid aortic valve (BAV) patients and its association with differences in cusp fusion patterns (right-left, RL versus right-noncoronary, RN) and expression of aortopathy. Methods and Results— Four-dimensional flow MRI measured in vivo 3-dimensional blood flow in the aorta of 75 subjects: BAV patients with aortic dilatation stratified by leaflet fusion pattern (n=15 RL-BAV, mid AAo diameter=39.9±4.4 mm; n=15 RN-BAV, 39.6±7.2 mm); aorta size controls with tricuspid aortic valves (n=30, 41.0±4.4 mm); healthy volunteers (n=15, 24.9±3.0 mm). Aortopathy type (0–3), systolic flow angle, flow displacement, and regional wall shear stress were determined for all subjects. Eccentric outflow jet patterns in BAV patients resulted in elevated regional wall shear stress (P<0.0125) at the right-anterior walls for RL-BAV and right-posterior walls for RN-BAV in comparison with aorta size controls. Dilatation of the aortic root only (type 1) or involving the entire AAo and arch (type 3) was found in the majority of RN-BAV patients (87%) but was mostly absent for RL-BAV patients (87% type 2). Differences in aortopathy type between RL-BAV and RN-BAV patients were associated with altered flow displacement in the proximal and mid AAo for type 1 (42%–81% decrease versus type 2) and distal AAo for type 3 (33%–39% increase versus type 2). Conclusions— The presence and type of BAV fusion was associated with changes in regional wall shear stress distribution, systolic flow eccentricity, and expression of BAV aortopathy. Hemodynamic markers suggest a physiological mechanism by which the valve morphology phenotype can influence phenotypes of BAV aortopathy.

Valve-Related Hemodynamics Mediate Human Bicuspid Aortopathy: Insights From Wall Shear Stress Mapping

BACKGROUND Suspected genetic causes for extracellular matrix (ECM) dysregulation in the ascending aorta in patients with bicuspid aortic valves (BAV) have influenced strategies and thresholds for surgical resection of BAV aortopathy. Using 4-dimensional (4D) flow cardiac magnetic resonance imaging (CMR), we have documented increased regional wall shear stress (WSS) in the ascending aorta of BAV patients. OBJECTIVES This study assessed the relationship between WSS and regional aortic tissue remodeling in BAV patients to determine the influence of regional WSS on the expression of ECM dysregulation. METHODS BAV patients (n = 20) undergoing ascending aortic resection underwent pre-operative 4D flow CMR to regionally map WSS. Paired aortic wall samples (i.e., within-patient samples obtained from regions of elevated and normal WSS) were collected and compared for medial elastin degeneration by histology and ECM regulation by protein expression. RESULTS Regions of increased WSS showed greater medial elastin degradation compared to adjacent areas with normal WSS: decreased total elastin (p = 0.01) with thinner fibers (p = 0.00007) that were farther apart (p = 0.001). Multiplex protein analyses of ECM regulatory molecules revealed an increase in transforming growth factor β-1 (p = 0.04), matrix metalloproteinase (MMP)-1 (p = 0.03), MMP-2 (p = 0.06), MMP-3 (p = 0.02), and tissue inhibitor of metalloproteinase-1 (p = 0.04) in elevated WSS regions, indicating ECM dysregulation in regions of high WSS. CONCLUSIONS Regions of increased WSS correspond with ECM dysregulation and elastic fiber degeneration in the ascending aorta of BAV patients, implicating valve-related hemodynamics as a contributing factor in the development of aortopathy. Further study to validate the use of 4D flow CMR as a noninvasive biomarker of disease progression and its ability to individualize resection strategies is warranted.

Evaluation of Peripheral Arterial Disease with Nonenhanced Quiescent-Interval Single-Shot MR Angiography

PURPOSE To assess the diagnostic performance of quiescent-interval single-shot (QISS) magnetic resonance (MR) angiography, a nonenhanced two-dimensional electrocardiographically gated single-shot balanced steady-state free precession examination for the evaluation of symptomatic chronic lower limb ischemia. MATERIALS AND METHODS For this prospective institutional review board-approved, HIPAA-compliant study, the institutional review board waived the requirement for informed patient consent. The QISS nonenhanced MR angiography technique was evaluated in a two-center trial involving 53 patients referred for lower extremity MR angiography for suspected or known chronic peripheral arterial disease (PAD), with contrast material-enhanced MR angiography serving as the noninvasive reference standard. The accuracy of stenosis assessments performed with the nonenhanced MR angiography sequence was evaluated relative to the reference standard. Per-segment, per-region, and per-limb sensitivities and specificities were calculated, and assessments were considered correct only if they were in exact agreement with the reference standard-derived assessments. Generalized estimating equation (GEE) modeling with use of an unstructured binomial logit analysis was used to account for clustering of multiple measurements per case. The sensitivity and specificity of QISS MR angiography for the determination of nonsignificant (<50%) versus significant (50%-100%) stenosis were compared with the sensitivity and specificity of the reference standard. RESULTS The diagnostic performance of nonenhanced MR angiography was found to be nearly equivalent to the diagnostic performances of contrast-enhanced MR angiography and digital subtraction angiography. Non-GEE segment-based analysis revealed that for the two reviewers, nonenhanced MR angiography had sensitivities of 89.7% (436 of 486 segments) and 87.0% (423 of 486 segments) and specificities of 96.5% (994 of 1030 segments) and 94.6% (973 of 1028 segments). CONCLUSION QISS nonenhanced MR angiography offers an alternative to currently used imaging tests for symptomatic chronic lower limb ischemia, for which the administration of iodinated or gadolinium-based contrast agents is contraindicated.

Cardiac Magnetic Resonance T2 Mapping in the Monitoring and Follow-up of Acute Cardiac Transplant Rejection A Pilot Study

Background—Acute rejection is a major factor impacting survival in the first 12 months after cardiac transplantation. Transplant monitoring requires invasive techniques. Cardiac magnetic resonance (CMR), noninvasive testing, has been used in monitoring heart transplants. Prolonged T2 relaxation has been related to transplant edema and possibly rejection. We hypothesize that prolonged T2 reflects transplant rejection and that quantitative T2 mapping will concur with the pathological and clinical findings of acute rejection. Methods and Results—Patients were recruited within the first year after transplantation. Biopsies were graded according to the International Society for Heart Lung Transplant system for cellular rejection with immunohistochemistry for humoral rejection. Rejection was also considered if patients presented with signs and symptoms of hemodynamic compromise without biopsy evidence of rejection who subsequently improved with treatment. Patients underwent a novel single-shot T2-prepared steady-state free precession 4-chamber and 3 short axis sequences and regions of interest were drawn overlying T2 maps by 2 independent blinded reviewers. A total of 74 (68 analyzable) CMRs T2 maps in 53 patients were performed. There were 4 cellular, 2 humoral, and 2 hemodynamic rejection cases. The average T2 relaxation time for grade 0R (n=46) and grade 1R (n=17) was 52.5±2.2 and 53.1±3.3 ms (mean±SD), respectively. The average T2 relaxation for grade 2R (n=3) was 59.6±3.1 ms and 3R (n=1) was 60.3 ms (all P value <0.05 compared with controls). The T2 average in humoral rejection cases (n=2) was 59.2±3.3 ms and the hemodynamic rejection (n=2) was 61.1±1.8 ms (P<0.05 versus controls). The average T2 relaxation time for all-cause rejection versus no rejection is 60.1±2.1 versus 52.8±2.7 ms (P<0.05). All rejection cases were rescanned 2.5 months after treatment and demonstrated T2 normalization with average of 51.4±1.6 ms. No difference was found in ventricular function between nonrejection and rejection patients, except in ventricular mass 107.8±10.3 versus 127.5±10.4 g (P < 0.05). Conclusions—Quantitative T2 mapping offers a novel noninvasive tool for transplant monitoring, and these initial findings suggest potential use in characterizing rejections. Given the limited numbers, a larger multi-institution study may help elucidate the benefits of T2 mapping as an adjunctive tool in routine monitoring of cardiac transplants.

k-t GRAPPA accelerated four-dimensional flow MRI in the aorta: effect on scan time, image quality, and quantification of flow and wall shear stress.

The purpose of this study was to evaluate the utility of k‐t parallel imaging for accelerating aortic four‐dimensional (4D)‐flow MRI. The aim was to systematically investigate the impact of different acceleration factors and number of coil elements on acquisition time, image quality and quantification of hemodynamic parameters.

Viscous energy loss in the presence of abnormal aortic flow

To present a theoretical basis for noninvasively characterizing in vivo fluid‐mechanical energy losses and to apply it in a pilot study of patients known to express abnormal aortic flow patterns.

Peripheral arterial disease in a symptomatic diabetic population: prospective comparison of rapid unenhanced MR angiography (MRA) with contrast-enhanced MRA.

OBJECTIVE The joint guidelines of the American College of Cardiology and American Heart Association support the use of contrast-enhanced MR angiography (CEMRA) to diagnose the location and degree of stenosis in patients with known or suspected peripheral arterial disease (PAD). The high prevalence of chronic renal impairment in diabetic patients with PAD and the need for high doses of gadolinium-based contrast agents place them at risk for nephrogenic systemic fibrosis. The purpose of our study was to evaluate the accuracy of the rapid technique of quiescent-interval single-shot (QISS) unenhanced MR angiography (MRA) compared with CEMRA for the diagnosis in diabetic patients referred with symptomatic chronic PAD. SUBJECTS AND METHODS This prospective two-center study evaluated 25 consecutive diabetic patients with documented or suspected symptomatic PAD. Both centers used identical imaging protocols. Images were independently analyzed by two radiologists. A subgroup analysis was performed of patients who were also assessed with digital subtraction angiography (DSA) as part of the standard-of-care protocol before revascularization. RESULTS For this study, 775 segments were analyzed. On a per-segment basis, the mean values of the diagnostic accuracy of unenhanced MRA compared with reference CEMRA for two reviewers, reviewers 1 and 2, were as follows: sensitivity, 87.4% and 92.1%; specificity, 96.8% and 96.0%; positive predictive value, 90.8% and 94.0%; and negative predictive value, 95.5% and 94.6%. Substantial agreement was found when overall DSA results were compared with QISS unenhanced MRA (κ = 0.68) and CEMRA (κ = 0.63) in the subgroup of patients who also underwent DSA. There was almost perfect agreement between the two readers for stenosis scores, with Cohens kappa values being greater than 0.80 for both MRA techniques. CONCLUSION The results of our study indicate that QISS unenhanced MRA is an accurate noncontrast alternative to CEMRA for showing clinically significant arterial disease in patients with diabetes with symptomatic PAD.

A methodology to detect abnormal relative wall shear stress on the full surface of the thoracic aorta using four-dimensional flow MRI

To compute cohort‐averaged wall shear stress (WSS) maps in the thoracic aorta of patients with aortic dilatation or valvular stenosis and to detect abnormal regional WSS.

Cancer concepts and principles: Primer for the interventional oncologist - Part i

A sophisticated understanding of the rapidly changing field of oncology, including a broad knowledge of oncologic disease and the therapies available to treat them, is fundamental to the interventional radiologist providing oncologic therapies, and is necessary to affirm interventional oncology as one of the four pillars of cancer care alongside medical, surgical, and radiation oncology. The first part of this review intends to provide a concise overview of the fundamentals of oncologic clinical trials, including trial design, methods to assess therapeutic response, common statistical analyses, and the levels of evidence provided by clinical trials.