The value of true-FISP sequence added to conventional gadolinium-enhanced MRA of abdominal aorta and its major branches

Safe Follow-Up after Endovascular Aortic Repair with Unenhanced MRI: The SAFEVAR Study

We aimed to investigate whether unenhanced magnetic resonance imaging (MRI) could represent a safe and highly sensitive tool for endoleak screening in patients treated with endovascular aneurysm repair (EVAR) using computed tomography angiography (CTA) as a reference standard. Patients who underwent CTA for EVAR follow-up at our institution were prospectively enrolled. All MRI examinations were performed with a 1.5 T unit. The true-FISP and HASTE sequences of the MRI scans were assessed for the presence of hyperintensity within the aneurysm sac outside the graft, whereas phase-contrast through-plane sequences were used for blood flow quantification. We included 45 patients, 5 (11%) of whom were female. The median age was 73 years (IQR 68−78 years). Among our patients, 19 (42%) were positive for endoleaks at CTA, of whom 13 (68%) had type II endoleaks and 6 (32%) had type I endoleaks. There were no significant differences in age, sex, aneurysm type, prosthesis type, or contrast-to-noise ratio between hyperintensity and thrombus between patients with and without endoleaks (p > 0.300). The combined evaluation of true-FISP and HASTE yielded 100% sensitivity (95% CI: 79−100%) and 19% specificity (95% CI: 7−40%). Patients with a positive CTA had a median thrombus flow of 0.06 L/min (IQR 0.03−0.23 L/min), significantly greater than that of patients with a negative CTA (p = 0.007). Setting a threshold at 0.01 L/min, our MRI protocol yielded 100% sensitivity, 56% specificity, and an AUC of 0.76 (95% CI 0.60−0.91). In conclusion, unenhanced MRI has perfect sensitivity for endoleak detection, although with subpar specificity that could be improved with phase-contrast flow analysis.

Non-contrast MR angiography using three-dimensional balanced steady-state free-precession imaging for evaluation of stenosis in the celiac trunk and superior mesenteric artery: a preliminary comparative study with computed tomography angiography

OBJECTIVE

Although non-contrast MR angiography (NC-MRA) is well established for the evaluation of renal artery stenosis, its usefulness in the evaluation of other abdominal aortic branches remains to be studied. This study aimed at evaluating the image quality and diagnostic accuracy of NC-MRA using a three-dimensional balanced steady-state free-precession sequence in identifying stenosis in the celiac trunk (CTR) and superior mesenteric artery (SMA) as compared with CT angiography (CTA) as the reference standard.

METHODS

41 patients underwent both NC-MRA and CTA of the abdominal aorta. Two radiologists analyzed the quality of the images (diagnostic vs non-diagnostic) and the performance (accuracy, sensitivity and specificity) of NC-MRA for the identification of arterial stenosis. Kappa tests were used to determine the interobserver agreement and the intermethod agreement between NC-MRA and CTA.

RESULTS

NC-MRA provided diagnostic quality images of the CTR and SMA in 87.8% and 90.2% of cases, respectively, with high interobserver agreement (kappa 0.95 and 0.80, respectively). For stenosis assessment, NC-MRA had a sensitivity of 100%, a positive-predictive value of 50% and a negative-predictive value of 100% for both segments, with accuracies of 88.8% for the CTR and 94.5% for the SMA.

CONCLUSION

NC-MRA is an accurate method for detecting stenosis in the CTR and SMA. Advances in knowledge: Data from this study suggest that MR angiography with balanced steady-state free-precession sequence is a viable non-contrast alternative for stenosis evaluation of these branches in patients for whom a contrast-enhanced examination is contraindicated.

Carbon dioxide (CO2) angiography as an option for endovascular abdominal aortic aneurysm repair (EVAR) in patients with chronic kidney disease (CKD)

To assess feasibility, efficacy and safety of carbon dioxide (CO₂) digital subtraction angiography (DSA) to guide endovascular aneurysm repair (EVAR) in a cohort of patients with chronic kidney disease (CKD). After Ethical Committee approval, the records of 13 patients (all male, mean age 74.6 ± 8.0 years) with CKD, who underwent EVAR to exclude an abdominal aortic aneurysm (AAA) under CO₂ angiography guidance, were reviewed. The AAA to be excluded had a mean diameter of 52.0 ± 8.0 mm. CO₂ angiography was performed by automatic (n = 7) or hand (n = 6) injection. The endograft was correctly placed and the AAA was excluded in all cases, without any surgical conversions. Two patients (15.4%) had an endoleak: one type-Ia, detected by CO₂-DSA and effectively treated with prosthesis dilatation; one type-III, detected by CO₂-DSA, confirmed using 10 ml of ICM, and conservatively managed. In one patient, CO₂ angiograms were considered of too low quality for guiding the procedure and 200 ml of ICM were administered. Overall, 11 patients (84.6%) underwent a successful EVAR under the guidance of the sole CO₂ angiography. No patients suffered from major complications, including those typically CO₂-related. Two patients suffered from abdominal pain during the procedure secondary to a transient splanchnic perfusion's reduction due to CO₂, and one patient had a worsening of renal function probably caused by a cholesterol embolization during the procedure. In patients with CKD, EVAR under CO₂ angiography guidance is feasible, effective, and safe.

Computed tomography angiography and magnetic resonance angiography imaging of the mesenteric vasculature

Computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are highly accurate cross-sectional vascular imaging modalities that have almost completely replaced diagnostic catheter angiography for the evaluation of the mesenteric vasculature. CTA is the technique of choice when evaluating patients with suspected mesenteric ischemia; it permits to differentiate between occlusive and nonocclusive etiologies, to evaluate indirect signs of bowel ischemia, and in some instances, to provide alternative diagnoses. MRA has the advantage of not using ionizing radiation and iodinated contrast agents and can be appropriate in the nonacute setting. Both CTA and MRA are suitable for the assessment of patients with suspected chronic mesenteric ischemia, allowing to evaluate the degree of atherosclerotic steno-occlusive disease and the existence of collateral circulation, as well as other nonatherosclerotic vascular pathologies such as fibromuscular dysplasia and median arcuate ligament syndrome. CTA provides excellent depiction of visceral aneurysms and has an important role to plan therapy for both occlusive and aneurysmal diseases and in the follow-up of patients after open or endovascular mesenteric revascularization procedures. This article provides an introduction to the CTA and MRA imaging protocol to study the mesenteric vasculature, the imaging findings in patients presenting with acute and chronic mesenteric ischemia and visceral aneurysms, and the value of these imaging techniques for therapy planning and follow-up.

Detection of pancreatic ductal adenocarcinoma in mice by ultrasound imaging of thymocyte differentiation antigen 1

BACKGROUND & AIMS

Early detection of pancreatic ductal adenocarcinoma (PDAC) allows for surgical resection and increases patient survival times. Imaging agents that bind and amplify the signal of neovascular proteins in neoplasms can be detected by ultrasound, enabling accurate detection of small lesions. We searched for new markers of neovasculature in PDAC and assessed their potential for tumor detection by ultrasound molecular imaging.

METHODS

Thymocyte differentiation antigen 1 (Thy1) was identified as a specific biomarker of PDAC neovasculature by proteomic analysis. Up-regulation in PDAC was validated by immunohistochemical analysis of pancreatic tissue samples from 28 healthy individuals, 15 with primary chronic pancreatitis tissues, and 196 with PDAC. Binding of Thy1-targeted contrast microbubbles was assessed in cultured cells, in mice with orthotopic PDAC xenograft tumors expressing human Thy1 on the neovasculature, and on the neovasculature of a genetic mouse model of PDAC.

RESULTS

Based on immunohistochemical analyses, levels of Thy1 were significantly higher in the vascular of human PDAC than chronic pancreatitis (P = .007) or normal tissue samples (P < .0001). In mice, ultrasound imaging accurately detected human Thy1-positive PDAC xenografts, as well as PDACs that express endogenous Thy1 in genetic mouse models of PDAC.

CONCLUSIONS

We have identified and validated Thy1 as a marker of PDAC that can be detected by ultrasound molecular imaging in mice. The development of a specific imaging agent and identification of Thy1 as a new biomarker could aid in the diagnosis of this cancer and management of patients.

The evolving role of cardiac imaging in percutaneous valvular intervention

Surgical therapies have represented the primary evidence-based intervention to alter the natural history of valvular heart disease (VHD), however, the increasing incidence of patients at high surgical risk due to age and related co-morbid conditions has given rise to the need for alternative strategies. Thus, percutaneous approaches to VHD therapy have emerged as an important therapeutic option. Cardiovascular imaging plays a critical role in patient screening for percutaneous valvular interventions, during the procedure itself, and as part of follow-up for the identification of implant success/failure and complications. The technical demands on imaging in this context are highly specific. Although imaging has a significant role in the broader evaluation of valvular heart disease mechanism and severity, the purpose of this paper is to summarise the particular goals of cardiovascular imaging in the work-up for, during, and in the follow-up of percutaneous valvular intervention.

Non-contrast MR imaging for detecting endoleak after abdominal endovascular aortic repair

Our aim was to investigate the possibility of ruling out endoleak after endovascular aortic repair (EVAR) of abdominal aortic aneurysm (AAA) using non-contrast MRI. Twenty-three patients (20 males, aged 73 ± 8 years) with an EVAR-treated AAA underwent 1.5-T MRI using axial, coronal and sagittal oblique true-FISP sequences. Two blinded and independent readers with 4 (R1) and 2 (R2) years of experience evaluated these images considering an area of even less than 5 mm in diameter with a signal intensity higher than that of normal muscles visible in the excluded aneurysmal sac as a sign of potential endoleak. The final assessment, mainly based on MR angiography and previous examinations, served as reference standard. Out of 23 patients, 13 (57%) were negative for endoleak at final assessment, while the remaining 10 (43%) were positive, with the following type distribution: Ia (n = 4), Ib (n = 2), II (n = 3), and III (n = 1). Sensitivity was 10/10 (100%; CI 95% 69-100%), specificity 7/13 (54%; 25-81%), accuracy 17/23 (74%; 52-90%), PPV 10/16 (63%; 35-85%) and NPV 7/7 (100%; 59-100%) for R1; 9/10 (90%; 56-100%), 8/13 (62%; 32-86%), 17/23 (74%; 52-90%), 9/14 (64%; 35-8%), and 8/9 (89%; 52-100%) for R2, respectively. Inter-reader Cohen κ was 0.810. A negative non-contrast true-FISP MR study can be used to rule out endoleak after EVAR of AAA. This hypothesis may contribute to the reduction of ionizing radiation exposure and contrast material administration for monitoring patients with an EVAR-treated AAA.

Vascular staging of renal and adrenal malignancies with a noncontrast enhanced steady state free precession technique

PURPOSE

To compare a noncontrast enhanced balanced steady state free precession (bSSFP) MRI technique with a conventional dynamic contrast-enhanced (DCE) three-dimensional (3D) spoiled gradient recalled echo (SPGR) imaging in the vascular staging of renal and adrenal malignancies.

MATERIALS AND METHODS

Sixty-three MRIs with both bSSFP and DCE acquisitions performed for initial staging of renal and adrenal malignancies were retrospectively evaluated for presence and extent of thrombus in the renal veins and inferior vena cava (IVC). Thrombus characterization was also evaluated. DCE imaging was used as the standard-of-reference. Histopathology was available in 46 of 63 cases as an additional external standard.

RESULTS

There is very good agreement between bSSFP and DCE imaging for determining the presence or absence of thrombus in the renal veins (r = 0.95; P < 0.0001) and IVC (r = 0.91; P < 0.0001). BSSFP is less successful at distinguishing bland from tumor thrombus.

CONCLUSION

Noncontrast enhanced bSSFP is an acceptable alternative to DCE imaging for vascular staging of locally advanced renal/adrenal malignancies, with somewhat limited ability to distinguish bland from tumor thrombus.

3D whole-heart coronary MR angiography at 1.5T in healthy volunteers: comparison between unenhanced SSFP and Gd-enhanced FLASH sequences

Objective

To validate the optimal cardiac phase and appropriate acquisition window for three-dimensional (3D) whole-heart coronary magnetic resonance angiography (MRA) with a steady-state free precession (SSFP) sequence, and to compare image quality between SSFP and Gd-enhanced fast low-angle shot (FLASH) MR techniques at 1.5 Tesla (T).

Materials and Methods

Thirty healthy volunteers (M:F = 25:5; mean age, 35 years; range, 24-54 years) underwent a coronary MRA at 1.5T. 3D whole-heart coronary MRA with an SSFP was performed at three different times: 1) at end-systole with a narrow (120-msec) acquisition window (ESN), 2) mid-diastole with narrow acquisition (MDN); and 3) mid-diastole with wide (170-msec) acquisition (MDW). All volunteers underwent a contrast enhanced coronary MRA after undergoing an unenhanced 3D true fast imaging with steady-state precession (FISP) MRA three times. A contrast enhanced coronary MRA with FLASH was performed during MDN. Visibility of the coronary artery and image quality were evaluated for 11 segments, as suggested by the American Heart Association. Image quality was scored by a five-point scale (1 = not visible to 5 = excellent). The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were evaluated at the proximal coronary arteries.

Results

The SSFP sequence rendered higher visibility coronary segments, higher image quality, as well as higher SNR and CNR than the Gd-enhanced FLASH technique at 1.5T (p < 0.05). The visibility of coronary segments, image quality, SNR and CNR in the ESN, MDN and MDW with SSFP sequence did not differ significantly.

Conclusion

An SSFP sequence provides an excellent method for the 3D whole-heart coronary MRA at 1.5T. Contrast enhanced coronary MRA using the FLASH sequence does not help improve the visibility of coronary segments, image quality, SNR or CNR on the 3D whole-heart coronary MRA.