Evaluation of Renal Fibrosis Using Magnetization Transfer Imaging at 1.5T and 3T in a Porcine Model of Renal Artery Stenosis

Renal fibrosis is an important marker in the progression of chronic kidney disease, and renal biopsy is the current reference standard for detecting its presence. Currently, non-invasive methods have only been partially successful in detecting renal fibrosis. Magnetization transfer imaging (MTI) allows estimates of renal fibrosis but may vary with scanning conditions. We hypothesized that MTI-derived renal fibrosis would be reproducible at 1.5T and 3T MRI and over time in fibrotic kidneys. Fifteen pigs with unilateral renal artery stenosis (RAS, n = 9) or age-matched sham controls (n = 6) underwent MTI-MRI at both 1.5T and 3T 6 weeks post-surgery and again 4 weeks later. Magnetization transfer ratio (MTR) measurements of fibrosis in both kidneys were compared between 1.5T and 3T, and the reproducibility of MTI at the two timepoints was evaluated at 1.5T and 3T. MTR at 3T with 600 Hz offset frequency successfully distinguished between normal, stenotic, and contralateral kidneys. There was excellent reproducibility of MTI at 1.5T and 3T over the two timepoints and no significant differences between MTR measurements at 1.5T and 3T. Therefore, MTI is a highly reproducible technique which is sensitive to detect changes in fibrotic compared to normal kidneys in the RAS porcine model at 3T.

Reliable Assessment of Swine Renal Fibrosis Using Quantitative Magnetization Transfer Imaging

OBJECTIVES

Quantitative magnetization transfer (qMT) is useful for measurement of murine renal fibrosis at high and ultrahigh field strengths. However, its utility at clinical field strengths and in human-like kidneys remains unknown. We tested the hypothesis that qMT would successfully detect fibrosis in swine kidneys with unilateral renal artery stenosis (RAS) at 3.0 T.

METHODS

The qMT protocol is composed of MT scans with variable flip angles and offset frequencies, and of B0, B1, and T1 mapping. Pigs were scanned 10 weeks after RAS or control. A 2-pool model was used to fit the bound pool fraction f of the renal cortex (CO) and outer medulla (OM). Then qMT-derived f in 5 normal and 10 RAS pigs was compared with histological fibrosis determined using Masson's trichrome staining and to renal perfusion assessed with computed tomography.

RESULTS

The qMT 2-pool model provided accurate fittings of data collected on swine kidneys. Stenotic kidneys showed significantly elevated f in both the CO (9.8% ± 2.7% vs 6.4% ± 0.9%, P = 0.002) and OM (7.6% ± 2.2% vs 4.7% ± 1.1%, P = 0.002), as compared with normal kidneys. Histology-measured renal fibrosis and qMT-derived f correlated directly in both the cortex (Pearson correlation coefficient r = 0.93, P < 0.001) and OM (r = 0.84, P = 0.002), and inversely with stenotic kidney perfusion (r = 0.85, P = 0.002).

CONCLUSIONS

This study demonstrates the feasibility of qMT for measuring fibrosis in human-like swine kidneys, and the association between tissue macromolecule content and renal perfusion. Therefore, qMT may be useful as a tool for noninvasive assessment of renal fibrosis in subjects with RAS at clinical field strengths.

Multisystem IgG4-related disease involving the abdomen and coronary arteries and causing chronic abdominal pain

IgG4-related disease was originally discovered in patients with autoimmune pancreatitis accompanied by elevated serum IgG4 levels and has subsequently been described in almost every organ system. IgG4-related disease presents with a variety of symptoms according to the organ affected and may be accompanied by serious complications such as organ dysfunction associated with IgG4-positive cell proliferation. We report a case of IgG4-related abdominal disease in a patient who also had involvement of the coronary artery.

Magnetization Transfer Imaging Predicts Porcine Kidney Recovery After Revascularization of Renal Artery Stenosis

MATERIALS AND METHODS

Stenotic kidney (STK) and contralateral kidney magnetization transfer ratios (MTRs; Mt/M0) were measured at 3.0-T magnetic resonance imaging, at offset frequencies of 600 and 1000 Hz, before and 1 month post-PTRA in 7 RVD pigs. Stenotic kidney MTR was correlated to renal perfusion, renal blood flow (RBF), and glomerular filtration rate (GFR), determined using multidetector computed tomography and with ex vivo renal fibrosis (trichrome staining). Untreated RVD (n = 6) and normal pigs (n = 7) served as controls.

RESULTS

Renovascular disease induced hypertension and renal dysfunction. Blood pressure and renal perfusion were unchanged post-PTRA, but GFR and RBF increased. Baseline cortical STK-MTR predicted post-PTRA renal perfusion and RBF, and MTR changes associated inversely with changes in perfusion and normalized GFR. Stenotic kidney MTR at 600 Hz showed closer association with renal parameters, but both frequencies predicted post-PTRA cortical fibrosis.

CONCLUSIONS

Renal STK-MTR, particularly at 600 Hz offset, is sensitive to hemodynamic changes after PTRA in swine RVD and capable of noninvasively predicting post-PTRA kidney perfusion, RBF, and fibrosis. Therefore, STK-MTR may be a valuable tool to predict renal hemodynamic and functional recovery, as well as residual kidney fibrosis after revascularization in RVD.

Peristenotic Collateral Circulation in Atherosclerotic Renovascular Disease: Association With Kidney Function and Response to Treatment

The significance of peristenotic collateral circulation (PCC) development around a stenotic renal artery is unknown. We tested the hypothesis that PCC is linked to loss of kidney function and recovery potential in patients with atherosclerotic renovascular disease (ARVD). Thirty-four patients with ARVD were assigned to medical-therapy with or without revascularization based on clinical indications. The PCC was visualized using multidetector computed tomography and defined relative to segmental arteries in patients with essential hypertension. PCC number before and 3 months after treatment was correlated with various renal parameters. Thirty-four stenotic kidneys from 30 patients were analyzed. PCC number correlated inversely with kidney volume. ARVD-stenotic kidneys with baseline PCC (collateral ARVD [C-ARVD], n=13) associated with elevated 24-hour urine protein and stenotic kidney vein level of tumor necrosis factor-α, lower single-kidney volume and blood flow, and greater hypoxia than in stenotic kidneys with no PCC (no collateral ARVD [NC-ARVD], n=17). Revascularization (but not medical-therapy alone) improved stenotic kidney function and reduced inflammation in both NC-ARVD and C-ARVD. In C-ARVD, revascularization also increased stenotic kidney volume, blood flow, and oxygenation to levels comparable to NC-ARVD, and induced PCC regression. However, revascularization improved systolic blood pressure, plasma renin activity, and filtration fraction only in NC-ARVD. Therefore, patients with C-ARVD have greater kidney dysfunction, atrophy, hypoxia, and inflammation compared with patients with NC-ARVD, suggesting that PCC does not effectively protect the stenotic kidney in ARVD. Renal artery revascularization improved in C-ARVD stenotic kidney function, but not hypertension or renin-angiotensin system activation. These observations may help direct management of patients with ARVD.

MRI feature tracking strain is prognostic for all-cause mortality in AL amyloidosis

OBJECTIVES

Cardiac involvement is a major determinate of mortality in light chain (AL) amyloidosis. Cardiac magnetic resonance imaging (MRI) feature tracking (FT) strain is a new method for measuring myocardial strain. This study retrospectively evaluated the association of MRI FT strain with all-cause mortality in AL amyloidosis.

MATERIALS AND METHODS

Seventy-six patients with newly diagnosed AL amyloidosis underwent cardiac MRI. 75 had images suitable for MRI FT strain analysis. MRI delayed enhancement, morphologic and functional evaluation, cardiac biomarker staging and transthoracic echocardiography were also performed. Subjects' charts were reviewed for all-cause mortality. Cox proportional hazards analysis was used to evaluate survival in univariate and multivariate analysis.

RESULTS

There were 52 deaths. Median follow-up of surviving patients was 1.7 years. In univariate analysis, global radial (Hazard Ratio (HR) = 0.95, p <.01), circumferential (HR = 1.09, p < .01) and longitudinal (HR = 1.08, p < .01) strain were associated with all-cause mortality. In separate multivariate models, radial (HR = 0.96, p = .02), circumferential (HR = 1.09, p = .03) and longitudinal strain (HR = 1.07, p = .04) remained prognostic when combined with presence of biomarker stage 3.

CONCLUSIONS

MRI FT strain is associated with all-cause mortality in patients with AL amyloidosis.

Phase 2a Clinical Trial of Mitochondrial Protection (Elamipretide) During Stent Revascularization in Patients With Atherosclerotic Renal Artery Stenosis

BACKGROUND

Atherosclerotic renal artery stenosis reduces renal blood flow (RBF) and amplifies stenotic kidney hypoxia. Revascularization with percutaneous transluminal renal angioplasty (PTRA) and stenting often fails to recover renal function, possibly because of ischemia/reperfusion injury developing after PTRA. Elamipretide is a mitochondrial-targeted peptide that binds to cardiolipin and stabilizes mitochondrial function. We tested the hypothesis that elamipretide plus PTRA would improve renal function, oxygenation, and RBF in patients with atherosclerotic renal artery stenosis undergoing PTRA.

METHODS AND RESULTS

Inpatient studies were performed in patients with severe atherosclerotic renal artery stenosis scheduled for PTRA. Patients were treated before and during PTRA with elamipretide (0.05 mg/kg per hour intravenous infusion, n=6) or placebo (n=8). Stenotic kidney cortical/medullary perfusion and RBF were measured using contrast-enhanced multidetector CT, and renal oxygenation by 3-T blood oxygen level-dependent magnetic resonance imaging before and 3 months after PTRA. Age and basal glomerular filtration rate did not differ between groups. Blood oxygen level-dependent imaging demonstrated increased fractional hypoxia 24 hours after angiography and stenting in placebo (+47%) versus elamipretide (-6%). These were reverted to baseline 3 months later. Stenotic kidney RBF rose (202±29-262±115 mL/min; P=0.04) 3 months after PTRA in the elamipretide-treated group only. Over 3 months, systolic blood pressure decreased, and estimated glomerular filtration rate increased (P=0.003) more in the elamipretide group than in the placebo group (P=0.11).

CONCLUSIONS

Adjunctive elamipretide during PTRA was associated with attenuated postprocedural hypoxia, increased RBF, and improved kidney function in this pilot trial. These data support a role for targeted mitochondrial protection to minimize procedure-associated ischemic injury and to improve outcomes of revascularization for human atherosclerotic renal artery stenosis.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT01755858.

Magnetic Resonance Imaging and Computed Tomography of Cardiac Masses and Pseudomasses in the Atrioventricular Groove

The atrioventricular (AV) groove constitutes the anatomic space separating the atria and ventricles. The AV groove is often difficult to visualize at echocardiography, and suspected lesions can be further assessed with cardiac computed tomography or magnetic resonance imaging. AV groove lesions may originate from within the AV groove or extend into this space from adjacent structures. The differential diagnosis for AV groove lesions is often wide, but a precise diagnosis can sometimes be made. This pictorial essay illustrates the magnetic resonance imaging and computed tomography appearance of common and uncommon AV groove lesions, and attempts to provide a logical framework for differential diagnosis when confronted with a known or suspected lesion at cross-sectional imaging.

Time-resolved contrast-enhanced MR angiography with single-echo Dixon fat suppression

PURPOSE

Dixon-based fat suppression has recently gained interest for dynamic contrast-enhanced MRI, but multi-echo techniques require longer scan times and reduce temporal resolution compared to single-echo alternatives without fat suppression. The purpose of this work is to demonstrate accelerated single-echo Dixon imaging with high spatial and temporal resolution.

THEORY AND METHODS

Real-valued water and fat images can be obtained from a single measurement if the shared initial phase and that due to ΔB0 are assumed known a priori. An expression for simultaneous sensitivity encoding (SENSE) unfolding and fat-water separation is derived for the general undersampling case, and simplified under the special case of uniform Cartesian undersampling. In vivo experiments were performed in extremities and brain with SENSE acceleration factors of up to R = 8.

RESULTS

Single-echo Dixon reconstruction of highly undersampled data was successfully demonstrated. Dynamic contrast-enhanced water and fat images provided high spatial and temporal resolution dynamic images with image update times shorter than previous single-echo Dixon work.

CONCLUSION

Time-resolved contrast-enhanced MRI with single-echo Dixon fat suppression shows high image quality, improved vessel delineation, and reduced sensitivity to motion when compared to time-subtraction methods.

Inflammatory hepatic adenomas: Characterization with hepatobiliary MRI contrast agents

PURPOSE

To characterize the MRI appearance of inflammatory hepatic adenomas using hepatobiliary contrast agents.

MATERIALS AND METHODS

MRI was performed using hepatobiliary contrast agents (3 with gadobenate dimeglumine and 24 with gadoxetic acid) in 27 patients with immunohistochemistry-confirmed diagnosis of inflammatory hepatic adenoma. The appearance of the lesions on T2 and diffusion-weighted images, pre-gadolinium T1-weighted images, dynamic post-gadolinium images, and hepatobiliary phase images was assessed.

RESULTS

Seven lesions (26%) showed predominant hyperenhancement on hepatobiliary phase images in comparison with adjacent hepatic parenchyma: 1 lesion showed diffuse, mildly heterogeneous hyperenhancement, and the remaining 6 lesions showed peripheral hyperenhancement and central hypoenhancement. Twenty lesions (74%) were predominantly hypoenhancing compared to adjacent liver on hepatobiliary phase images. Nine lesions showed a pattern of peripheral hyperenhancement and central hypoenhancement on hepatobiliary phase images; in 6 of these lesions a majority of the mass appeared hyperenhancing, while the remaining 3 lesions showed predominant hypoenhancement.

CONCLUSIONS

This investigation shows that a significant percentage of inflammatory hepatic adenomas appear isointense or hyperintense in comparison to adjacent normal liver on hepatobiliary phase images, and therefore this feature should not be used to distinguish hepatic adenomas from focal nodular hyperplasia without additional supporting evidence.

Cardiac MR elastography using reduced-FOV, single-shot, spin-echo EPI

Purpose

To implement a reduced field of view (rFOV) technique for cardiac MR elastography (MRE) and to demonstrate the improvement in image quality of both magnitude images and post‐processed MRE stiffness maps compared to the conventional full field of view (full‐FOV) acquisition.

Methods

With Institutional Review Board approval, 17 healthy volunteers underwent both full‐FOV and rFOV cardiac MRE scans using 140‐Hz vibrations. Two cardiac radiologists blindly compared the magnitude images and stiffness maps and graded the images based on several image quality attributes using a 5‐point ordinal scale. Fisher's combined probability test was performed to assess the overall evaluation. The octahedral shear strain‐based signal‐to‐noise ratio (OSS‐SNR) and median stiffness over the left ventricular myocardium were also compared.

Results

One volunteer was excluded because of an inconsistent imaging resolution during the exam. In the remaining 16 volunteers (9 males, 7 females), the rFOV scans outperformed the full‐FOV scans in terms of subjective image quality and ghosting artifacts in the magnitude images and stiffness maps, as well as the overall preference. The quantitative measurements showed that rFOV had significantly higher OSS‐SNR (median: 1.4 [95% confidence interval (CI): 1.2–1.5] vs. 2.1 [95% CI: 1.8–2.4]), P < 0.05) compared to full‐FOV. Although no significant change was found in the median myocardial stiffness between the 2 scans, we observed a decrease in the stiffness variation within the myocardium from 2.1 kPa (95% CI: [1.9, 2.3]) to 1.9 kPa (95% CI: [1.7, 2.0]) for full‐FOV and rFOV, respectively (P < 0.05) in a subgroup of 7 subjects with ghosting present in the myocardium.

Conclusion

This pilot volunteer study demonstrated that rFOV cardiac MRE has the capability to reduce ghosting and to improve image quality in both MRE magnitude images and stiffness maps. Magn Reson Med 80:231–238, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Autologous Mesenchymal Stem Cells Increase Cortical Perfusion in Renovascular Disease

Atherosclerotic renovascular disease (RVD) reduces renal blood flow (RBF) and GFR and accelerates poststenotic kidney (STK) tissue injury. Preclinical studies indicate that mesenchymal stem cells (MSCs) can stimulate angiogenesis and modify immune function in experimental RVD. We assessed the safety and efficacy of adding intra-arterial autologous adipose-derived MSCs into STK to standardized medical treatment in human subjects without revascularization. The intervention group (n=14) received a single infusion of MSC (1.0 × 10⁵ or 2.5 × 10⁵ cells/kg; n=7 each) plus standardized medical treatment; the medical treatment only group (n=14) included subjects matched for age, kidney function, and stenosis severity. We measured cortical and medullary volumes, perfusion, and RBF using multidetector computed tomography. We assessed tissue oxygenation by blood oxygen level-dependent MRI and GFR by iothalamate clearance. MSC infusions were well tolerated. Three months after infusion, cortical perfusion and RBF rose in the STK (151.8-185.5 ml/min, P=0.01); contralateral kidney RBF increased (212.7-271.8 ml/min, P=0.01); and STK renal hypoxia (percentage of the whole kidney with R2*>30/s) decreased (12.1% [interquartile range, 3.3%-17.8%] to 6.8% [interquartile range, 1.8%-12.9%], P=0.04). No changes in RBF occurred in medical treatment only subjects. Single-kidney GFR remained stable after MSC but fell in the medical treatment only group (-3% versus -24%, P=0.04). This first-in-man dose-escalation study provides evidence of safety of intra-arterial infusion of autologous MSCs in patients with RVD. MSC infusion without main renal artery revascularization associated with increased renal tissue oxygenation and cortical blood flow.

Atherosclerotic renal artery stenosis is associated with elevated cell cycle arrest markers related to reduced renal blood flow and postcontrast hypoxia

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) reduces renal blood flow (RBF), ultimately leading to kidney hypoxia and inflammation. Insulin-like growth factor binding protein-7 (IGFBP-7) and tissue inhibitor of metalloproteinases-2 (TIMP-2) are biomarkers of cell cycle arrest, often increased in ischemic conditions and predictive of acute kidney injury (AKI). This study sought to examine the relationships between renal vein levels of IGFBP-7, TIMP-2, reductions in RBF and postcontrast hypoxia as measured by blood oxygen level-dependent (BOLD) magnetic resonance imaging.

METHODS

Renal vein levels of IGFBP-7 and TIMP-2 were obtained in an ARAS cohort (n= 29) scheduled for renal artery stenting and essential hypertensive (EH) healthy controls (n = 32). Cortical and medullary RBFs were measured by multidetector computed tomography (CT) immediately before renal artery stenting and 3 months later. BOLD imaging was performed before and 3 months after stenting in all patients, and a subgroup (N = 12) underwent repeat BOLD imaging 24 h after CT/stenting to examine postcontrast/procedure levels of hypoxia.

RESULTS

Preintervention IGFBP-7 and TIMP-2 levels were elevated in ARAS compared with EH (18.5 ± 2.0 versus 15.7 ± 1.5 and 97.4 ± 23.1 versus 62.7 ± 9.2 ng/mL, respectively; P< 0.0001); baseline IGFBP-7 correlated inversely with hypoxia developing 24 h after contrast injection (r = -0.73, P< 0.0001) and with prestent cortical blood flow (r = -0.59, P= 0.004).

CONCLUSION

These data demonstrate elevated IGFBP-7 and TIMP-2 levels in ARAS as a function of the degree of reduced RBF. Elevated baseline IGFBP-7 levels were associated with protection against postimaging hypoxia, consistent with 'ischemic preconditioning'. Despite contrast injection and stenting, AKI in these high-risk ARAS subjects with elevated IGFBP-7/TIMP-2 was rare and did not affect long-term kidney function.

Magnetic Resonance Imaging of Perirenal Pathology

The perirenal space can be involved by a variety of neoplastic, inflammatory, infectious, and proliferative disorders. Magnetic resonance imaging is often an ideal technique for identification and staging of lesions arising within the perirenal space, with its superior soft tissue characterization as well as its ability to visualize extension into blood vessels and adjacent organs. This pictorial essay describes the magnetic resonance imaging appearance of a variety of pathologies which can arise from or involve the perirenal space, and provides a framework for categorization and differential diagnosis of these lesions.

Differences in GFR and Tissue Oxygenation, and Interactions between Stenotic and Contralateral Kidneys in Unilateral Atherosclerotic Renovascular Disease

BACKGROUND AND OBJECTIVES

Atherosclerotic renal artery stenosis (ARAS) can reduce renal blood flow, tissue oxygenation, and GFR. In this study, we sought to examine associations between renal hemodynamics and tissue oxygenation with single-kidney function, pressor hormones, and inflammatory biomarkers in patients with unilateral ARAS undergoing medical therapy alone or stent revascularization.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Nonrandomized inpatient studies were performed in patients with unilateral ARAS (>60% occlusion) before and 3 months after revascularization (n=10) or medical therapy (n=20) or patients with essential hypertension (n=32) under identical conditions. The primary study outcome was change in single-kidney GFR. Individual kidney hemodynamics and volume were measured using multidetector computed tomography. Tissue oxygenation (using R(2)* as a measure of deoxyhemoglobin) was determined by blood oxygen level-dependent magnetic resonance imaging at 3 T. Renal vein neutrophil gelatinase-associated lipocalin (NGAL), monocyte chemoattractant protein-1 (MCP-1), and plasma renin activity were measured.

RESULTS

Total GFR did not change over 3 months in either group, but the stenotic kidney (STK) GFR rose over time in the stent compared with the medical group (+2.2[-1.8 to 10.5] versus -5.3[-7.3 to -0.3] ml/min; P=0.03). Contralateral kidney (CLK) GFR declined in the stent group (43.6±19.7 to 36.6±19.5 ml/min; P=0.03). Fractional tissue hypoxia fell in the STK (fraction R(2)* >30/s: 22.1%±20% versus 14.9%±18.3%; P<0.01) after stenting. Renal vein biomarkers correlated with the degree of hypoxia in the STK: NGAL(r=0.3; P=0.01) and MCP-1(r=0.3; P=0.02; more so after stenting). Renal vein NGAL was inversely related to renal blood flow in the STK (r=-0.65; P<0.001). Biomarkers were highly correlated between STK and CLK, NGAL (r=0.94; P<0.001), and MCP-1 (r=0.96; P<0.001).

CONCLUSIONS

These results showed changes over time in single-kidney GFR that were not evident in parameters of total GFR. Furthermore, they delineate the relationship of measurable tissue hypoxia within the STK and markers of inflammation in human ARAS. Renal vein NGAL and MCP-1 indicated persistent interactions between the ischemic kidney and both CLK and systemic levels of inflammatory cytokines.

Evaluation of liver stiffness with magnetic resonance elastography in patients with constrictive pericarditis: Preliminary findings

PURPOSE

To evaluate with magnetic resonance elastography (MRE) whether patients with constrictive pericarditis (CP) have increased hepatic stiffness. CP results in reduced pericardial compliance, ventricular interdependence, and right heart failure. Patients with untreated CP may develop liver fibrosis and ultimately cirrhosis due to chronic venous congestion. Chronic venous congestion ± fibrosis may lead to increased liver stiffness.

MATERIALS AND METHODS

Prospectively, patients with suspected CP underwent 2D transthoracic echocardiography, cardiac MRI, and liver MRE. An automated method was used to draw regions of interest (ROIs) on the stiffness maps to calculate the mean liver stiffness in kilopascals (kPa). A t-test with α = 0.05 was performed between stiffness values of patients with positive and negative CP findings based on previously published echocardiography criteria.

RESULTS

Nineteen patients met inclusion criteria with a mean ± standard deviation (SD) age of 51 ± 16 years. Nine patients (47%) had CP. Mean liver stiffness trended higher in patients with CP compared to those without CP (4.04 kPa vs. 2.46; P = 0.045). Liver stiffness correlated with MRI septal bounce (P = 0.04), inferior vena cava size (P = 0.003), echo abnormal septal motion (P = 0.04), and echo mitral inflow variation >25% (P = 0.02). Only MRI septal bounce predicted CP by echocardiography (P < 0.001).

CONCLUSION

CP was associated with increased liver stiffness. The increased stiffness is most likely secondary to chronic hepatic venous congestion and/or fibrosis. MRE may be useful for noninvasive liver stiffness assessment in CP. J. Magn. Reson. Imaging 2016;44:81-88.

MRI of uncommon lesions of the large bowel: a pictorial essay

This pictorial essay briefly discusses methods for optimizing bowel imaging with magnetic resonance imaging (MRI) and illustrates the MRI appearance of a variety of unusual lesions involving or related specifically to the large bowel.

Evaluation of apical subtype of hypertrophic cardiomyopathy using cardiac magnetic resonance imaging with gadolinium enhancement

Apical hypertrophic cardiomyopathy (HC) is an uncommon variant of HC. We sought to characterize cardiac magnetic resonance imaging (MRI) findings among apical HC patients. This was a retrospective review of consecutive patients with a diagnosis of apical HC who underwent cardiac MRI examinations at the Mayo Clinic (Rochester, MN) from August 1999 to October 2011. Clinical and demographic data at the time of cardiac MRI study were abstracted. Cardiac MRI study and 2-dimensional echocardiograms performed within 6 months of the cardiac MRI were reviewed; 96 patients with apical HC underwent cardiac MRI examinations. LV end-diastolic and end-systolic volumes were 130.7 ± 39.1 ml and 44.2 ± 20.9 ml, respectively. Maximum LV thickness was 19 ± 5 mm. Hypertrophy extended beyond the apex into other segments in 57 (59.4%) patients. Obstructive physiology was seen in 12 (12.5%) and was more common in the mixed apical phenotype than the pure apical (19.3 vs 2.6%, p = 0.02). Apical pouches were noted in 39 (40.6%) patients. Late gadolinium enhancement (LGE) was present in 70 (74.5%) patients. LGE was associated with severe symptoms and increased maximal LV wall thickness. In conclusion, cardiac MRI is well suited for studying the apical form of HC because of difficulty imaging the cardiac apex with standard echocardiography. Cardiac MRI is uniquely suited to delineate the presence or absence of an apical pouch and abnormal myocardial LGE that may have implications in the natural history of apical HM. In particular, the presence of abnormal LGE is associated with clinical symptoms and increased wall thickness.

Three-station three-dimensional bolus-chase MR angiography with real-time fluoroscopic tracking

PURPOSE

To determine the feasibility of using real-time fluoroscopic tracking for bolus-chase magnetic resonance (MR) angiography of peripheral vasculature to image three stations from the aortoiliac bifurcation to the pedal arteries.

MATERIALS AND METHODS

This prospective study was institutional review board approved and HIPAA compliant. Eight healthy volunteers (three men; mean age, 48 years; age range, 30-81 years) and 13 patients suspected of having peripheral arterial disease (five men; mean age, 67 years; age range, 47-81 years) were enrolled and provided informed consent. All subjects were imaged with the fluoroscopic tracking MR angiographic protocol. Ten patients also underwent a clinical computed tomographic (CT) angiographic runoff examination. Two readers scored the MR angiographic studies for vessel signal intensity and sharpness and presence of confounding artifacts and venous contamination at 35 arterial segments. Mean aggregate scores were assessed. The paired MR angiographic and CT angiographic studies also were scored for visualization of disease, reader confidence, and overall diagnostic quality and were compared by using a Wilcoxon signed rank test.

RESULTS

Real-time fluoroscopic tracking performed well technically in all studies. Vessel segments were scored good to excellent in all but the following categories: For vessel signal intensity and sharpness, the abdominal aorta, iliac arteries, distal plantar arteries, and plantar arch were scored as fair to good; and for presence of confounding artifacts, the abdominal aorta and iliac arteries were scored as fair. The MR angiograms and CT angiograms did not differ significantly in any scoring category (reader 1: P = .50, .39, and .39; reader 2: P = .41, .61, and .33, respectively). CT scores were substantially better in 20% (four of 20) and 25% (five of 20) of the pooled evaluations for the visualization of disease and overall image quality categories, respectively, versus 5% (one of 20) for MR scores in both categories.

CONCLUSION

Three-station bolus-chase MR angiography with real-time fluoroscopic tracking provided high-spatial-resolution arteriograms of the peripheral vasculature, enabled precise triggering of table motion, and compared well with CT angiograms.

A polymeric fastener can easily functionalize liposome surfaces with gadolinium for enhanced magnetic resonance imaging

Common methods of loading magnetic resonance imaging (MRI) contrast agents into nanoparticles often suffer from challenges related to particle formation, complex chemical modification/purification steps, and reduced contrast efficiency. This study presents a simple, yet advanced process to address these issues by loading gadolinium, an MRI contrast agent, exclusively on a liposome surface using a polymeric fastener. The fastener, so named for its ability to physically link the two functional components together, consisted of chitosan substituted with diethylenetriaminepentaacetic acid (DTPA) to chelate gadolinium, as well as octadecyl chains to stabilize the modified chitosan on the liposome surface. The assembly strategy, mimicking the mechanisms by which viruses and proteins naturally anchor to a cell, provided greater T1 relaxivity than liposomes loaded with gadolinium in both the interior and outer leaflet. Gadolinium-coated liposomes were ultimately evaluated in vivo using murine ischemia models to highlight the diagnostic capability of the system. Taken together, this process decouples particle assembly and functionalization and, therefore, has considerable potential to enhance imaging quality while alleviating many of the difficulties associated with multifunctional particle fabrication.

Prospective comparison of cartesian acquisition with projection-like reconstruction magnetic resonance angiography with computed tomography angiography for evaluation of below-the-knee runoff

PURPOSE

To compare prospectively the assessment of stenosis and radiologist confidence in the evaluation of below-the-knee lower extremity runoff vessels between computed tomography (CT) angiography and contrast-enhanced magnetic resonance (MR) angiography in a cohort of 19 clinical patients.

MATERIALS AND METHODS

The study was compliant with the Health Insurance Portability and Accountability Act of 1996 and approved by the institutional review board. Imaging was performed in 19 consecutive patients with known or suspected peripheral arterial disease; both CT angiography and a more recently developed MR angiography technique were performed within 24 hours of each other and before any therapeutic intervention. Resulting images were randomized and interpreted in blinded fashion by four board-certified radiologists with expertise in CT angiography and MR angiography. Vasculature of the lower leg was apportioned into 22 segments, 11 for each leg. For each segment, degree of stenosis and confidence of diagnosis were determined using a 3-point scale. Differences between CT angiography and MR angiography were assessed for significance using pooled histograms that were analyzed using the Wilcoxon signed rank test.

RESULTS

For assessment of stenosis, there was no difference in CT angiography compared with MR angiography for 20 of 22 segments. For confidence of diagnosis, assessment of popliteal arteries was superior on CT angiography compared with MR angiography (P<.05). Confidence in assessment of both tibioperoneal trunks and the left proximal anterior tibial artery was not significantly different between CT angiography and MR angiography. Confidence in assessment of all other 17 segments was superior with MR angiography compared with CT angiography (P<.02).

CONCLUSIONS

MR angiography using the method described here is a promising technique for evaluating lower extremity arterial runoff. MR angiography had an overall superior performance in radiologist confidence compared with CT angiography for imaging runoff vessels below the knee.

Stent revascularization restores cortical blood flow and reverses tissue hypoxia in atherosclerotic renal artery stenosis but fails to reverse inflammatory pathways or glomerular filtration rate

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) is known to reduce renal blood flow, glomerular filtration rate (GFR) and amplify kidney hypoxia, but the relationships between these factors and tubulointerstitial injury in the poststenotic kidney are poorly understood. The purpose of this study was to examine the effect of renal revascularization in ARAS on renal tissue hypoxia and renal injury.

METHODS AND RESULTS

Inpatient studies were performed in patients with ARAS (n=17; >60% occlusion) before and 3 months after stent revascularization, or in patients with essential hypertension (n=32), during fixed Na(+) intake and angiotensin converting enzyme/angiotensin receptors blockers Rx. Single kidney cortical, medullary perfusion, and renal blood flow were measured using multidetector computed tomography, and GFR by iothalamate clearance. Tissue deoxyhemoglobin levels (R(2)*) were measured by blood oxygen level-dependent MRI at 3T, as was fractional kidney hypoxia (percentage of axial area with R(2)*>30/s). In addition, we measured renal vein levels of neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α. Pre-stent single kidney renal blood flow, perfusion, and GFR were reduced in the poststenotic kidney. Renal vein neutrophil gelatinase-associated lipocalin, tumor necrosis factor-α, monocyte chemoattractant protein-1, and fractional hypoxia were higher in untreated ARAS than in essential hypertension. After stent revascularization, fractional hypoxia fell (P<0.002) with increased cortical perfusion and blood flow, whereas GFR and neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α remained unchanged.

CONCLUSIONS

These data demonstrate that despite reversal of renal hypoxia and partial restoration of renal blood flow after revascularization, inflammatory cytokines and injury biomarkers remained elevated and GFR failed to recover in ARAS. Restoration of vessel patency alone failed to reverse tubulointerstitial damage and partly explains the limited clinical benefit of renal stenting. These results identify potential therapeutic targets for recovery of kidney function in renovascular disease.

Breath-held MR cholangiopancreatography (MRCP) using a 3D Dixon fat-water separated balanced steady state free precession sequence

A novel 3D breath-held Dixon fat-water separated balanced steady state free precession (b-SSFP) sequence for MR cholangiopancreatography (MRCP) is described and its potential clinical utility assessed in a series of patients. The main motivation is to develop a robust breath-held alternative to the respiratory gated 3D Fast Spin Echo (FSE) sequence, the current clinical sequence of choice for MRCP. Respiratory gated acquisitions are susceptible to motion artifacts and blurring in patients with significant diaphragmatic drift, erratic respiratory rhythms or sleep apnea. A two point Dixon fat-water separation scheme was developed which eliminates signal loss arising from B0 inhomogeneity effects and minimizes artifacts from perturbation of the b-SSFP steady state. Preliminary results from qualitative analysis of 49 patients demonstrate robust performance of the 3D Dixon b-SSFP sequence with diagnostic image quality acquired in a 20-24s breath-hold.

Human renovascular disease: estimating fractional tissue hypoxia to analyze blood oxygen level-dependent MR

PURPOSE

To test the hypothesis that fractional kidney hypoxia, measured by using blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging, correlates with renal blood flow (RBF), tissue perfusion, and glomerular filtration rate (GFR) in patients with atherosclerotic renal artery stenosis (RAS) better than regionally selected region of interest-based methods.

MATERIALS AND METHODS

The study was approved by the institutional review board according to a HIPAA-compliant protocol, with written informed consent. BOLD MR imaging was performed in 40 patients with atherosclerotic RAS (age range, 51-83 years; 22 men, 18 women) and 32 patients with essential hypertension (EH) (age range, 26-85 years; 19 men, 13 women) during sodium intake and renin-angiotensin blockade. Fractional kidney hypoxia (percentage of entire axial image section with R2* above 30 sec(-1)) and conventional regional estimates of cortical and medullary R2* levels were measured. Stenotic and nonstenotic contralateral kidneys were compared for volume, tissue perfusion, and blood flow measured with multidetector computed tomography. Statistical analysis was performed (paired and nonpaired t tests, linear regression analysis).

RESULTS

Stenotic RBF was reduced compared with RBF of contralateral kidneys (225.2 mL/min vs 348 mL/min, P = .0003). Medullary perfusion in atherosclerotic RAS patients was lower than in EH patients (1.07 mL/min per milliliter of tissue vs 1.3 mL/min per milliliter of tissue, P = .009). While observer-selected cortical R2* (18.9 sec(-1) [stenosis] vs 18.5 sec(-1) [EH], P = .07) did not differ, fractional kidney hypoxia was higher in stenotic kidneys compared with kidneys with EH (17.4% vs 9.6%, P < .0001) and contralateral kidneys (7.2%, P < .0001). Fractional hypoxia correlated inversely with blood flow (r = -0.34), perfusion (r = -0.3), and GFR (r = -0.32).

CONCLUSION

Fractional tissue hypoxia rather than cortical or medullary R2* values used to assess renal BOLD MR imaging demonstrated a direct relationship to chronically reduced blood flow and GFR.

Micro-computed tomography and nuclear magnetic resonance imaging for noninvasive, live-mouse cholangiography

The cholangiopathies are a diverse group of biliary tract disorders, many of which lack effective treatment. Murine models are an important tool for studying their pathogenesis, but existing noninvasive methods for assessing biliary disease in vivo are not optimal. Here we report our experience with using micro-computed tomography (microCT) and nuclear magnetic resonance (MR) imaging to develop a technique for live-mouse cholangiography. Using mdr2 knockout (mdr2KO, a model for primary sclerosing cholangitis (PSC)), bile duct-ligated (BDL), and normal mice, we performed in vivo: (1) microCT on a Siemens Inveon PET/CT scanner and (2) MR on a Bruker Avance 16.4 T spectrometer, using Turbo Rapid Acquisition with Relaxation Enhancement, IntraGate Fast Low Angle Shot, and Half-Fourier Acquisition Single-shot Turbo Spin Echo methods. Anesthesia was with 1.5-2.5% isoflurane. Scans were performed with and without contrast agents (iodipamide meglumine (microCT), gadoxetate disodium (MR)). Dissection and liver histology were performed for validation. With microCT, only the gallbladder and extrahepatic bile ducts were visualized despite attempts to optimize timing, route, and dose of contrast. With MR, the gallbladder, extra-, and intrahepatic bile ducts were well-visualized in mdr2KO mice; the cholangiographic appearance was similar to that of PSC (eg, multifocal strictures) and could be improved with contrast administration. In BDL mice, MR revealed cholangiographically distinct progressive dilation of the biliary tree without ductal irregularity. In normal mice, MR allowed visualization of the gallbladder and extrahepatic ducts, but only marginal visualization of the diminutive intrahepatic ducts. One mouse died during microCT and MR imaging, respectively. Both microCT and MR scans could be obtained in ≤20 min. We, therefore, demonstrate that MR cholangiography can be a useful tool for longitudinal studies of the biliary tree in live mice, whereas microCT yields suboptimal duct visualization despite requiring contrast administration. These findings support further development and application of MR cholangiography to the study of mouse models of PSC and other cholangiopathies.

Novel protein therapeutics for systolic heart failure: chronic subcutaneous B-type natriuretic peptide

OBJECTIVES

The purpose of the present study was to translate our laboratory investigations to establish safety and efficacy of 8 weeks of chronic SC B-type natriuretic peptide (BNP) administration in human Stage C heart failure (HF).

BACKGROUND

B-Type natriuretic peptide is a cardiac hormone with vasodilating, natriuretic, renin-angiotensin inhibiting, and lusitropic properties. We have previously demonstrated that chronic cardiac hormone replacement with subcutaneous (SC) administration of BNP in experimental HF resulted in improved cardiovascular function.

METHODS

We performed a randomized double-blind placebo-controlled proof of concept study comparing 8 weeks of SC BNP (10 μg/kg bid) (n = 20) with placebo (n = 20) in patients with ejection fraction <35% and New York Heart Association functional class II to III HF. Primary outcomes were left ventricular (LV) volumes and LV mass determined by cardiac magnetic resonance imaging. Secondary outcomes include LV filling pressure by Doppler echo, humoral function, and renal function.

RESULTS

Eight weeks of chronic SC BNP resulted in a greater reduction of LV systolic and diastolic volume index and LV mass index as compared with placebo. There was a significantly greater improvement of Minnesota Living with Heart Failure score, LV filling pressure as demonstrated by the reductions of E/e' ratio, and decrease in left atrial volume index as compared with placebo. Glomerular filtration rate was preserved with SC BNP, as was the ability to activate plasma 3',5'-cyclic guanosine monophosphate (p < 0.05 vs. placebo).

CONCLUSIONS

In this pilot proof of concept study, chronic protein therapy with SC BNP improved LV remodeling, LV filling pressure, and Minnesota Living with Heart Failure score in patients with stable systolic HF on optimal therapy. Renin-angiotensin was suppressed, and glomerular filtration rate was preserved. Subcutaneous BNP represents a novel, safe, and efficacious protein therapeutic strategy in human HF. Further studies are warranted to determine whether these physiologic observations can be translated into improved clinical outcomes and ultimately delay the progression of HF. (Cardiac Hormone Replacement With BNP in Heart Failure: A Novel Therapeutic Strategy; NCT00252187).

Buildup of image quality in view-shared time-resolved 3D CE-MRA

Time-resolved three-dimensional contrast-enhanced MR angiography often relies on view sharing of peripheral k-space data to enable acquisition of angiograms with both high spatial resolution and a rapid frame rate. It is typically assumed that k-space will be fully sampled during passage of the contrast bolus arterial phase. However, this is not the case when view sharing is incomplete, for example, at the leading edge of an enhancing vessel or if acquisition time is limited as in fluoroscopic tracking for multistation bolus chase MR angiography. Incomplete view sharing will degrade image quality, for example, by reducing vessel signal and sharpness and increasing undersampling artifacts. In this work, the evolution of angiogram quality with view sharing is quantitatively assessed in phantom experiments and in vivo contrast-enhanced MR angiography calf studies. It is demonstrated that there are multiple sets of sequence parameters that can yield a target image update time, but the choice of parameters can profoundly affect how image quality evolves with view sharing. A fundamental tradeoff between vessel signal and sharpness and its relationship to the sequence temporal footprint is investigated and discussed.

Somatostatin analog therapy for severe polycystic liver disease: results after 2 years

BACKGROUND

We showed in a randomized double-blinded placebo-controlled clinical trial that octreotide long-acting repeatable depot.® (OctLAR(®)) for 12 months reduces kidney and liver growth in autosomal dominant polycystic kidney patients with severe polycystic liver disease (PLD) and liver growth in patients with severe isolated PLD. We have now completed an open-label extension for one additional year to assess safety and clinical benefits of continued use of OctLAR for 2 years (O → O) and examined drug effect in the placebo group who crossed over to OctLAR in Year 2 (P → O).

METHODS

The primary end point was change in total liver volume (TLV) measured by magnetic resonance imaging (MRI); secondary end points were changes in total kidney volume (TKV) measured by MRI, glomerular filtration rate (GFR), quality of life (QOL), safety, vital signs and laboratory parameters.

RESULTS

Forty-one of 42 patients received OctLAR (n = 28) or placebo (n = 14) in Year 1 and received OctLAR in Year 2 (maximum dose 40 mg). Patients originally randomized to placebo (P → O) showed substantial reduction in TLV after treatment with OctLAR in Year 2 (Δ% -7.66 ± 9.69%, P = 0.011). The initial reduction of TLV in the OctLAR group (O → O) was maintained for 2 years (Δ% -5.96 ± 8.90%), although did not change significantly during Year 2 (Δ% -0.77 ± 6.82%). OctLAR inhibited renal enlargement during Year 1 (Δ% +0.42 ± 7.61%) in the (O → O) group and during Year 2 (Δ% -0.41 ± 9.45%) in the (P → O) group, but not throughout Year 2 (Δ% +6.49 ± 7.08%) in the (O → O) group. Using pooled analyses of all individuals who received OctLAR for 12 months, i.e. in Year 1 for O → O patients and Year 2 for P → O patients, average reduction in TLV was -6.08 ± 7.58% (P = 0.001) compared to net growth of 0.9 ± 8.35% in the original placebo group. OctLAR-treated individuals continued to experience improvements in QOL in Year 2, although overall physical and mental improvements were not significant during Year 2 compared to Year 1. Changes in GFR were similar in both groups.

CONCLUSION

Over 2 years, OctLAR significantly reduced the rate of increase in TLV and possibly the rate of increase in TKV.

MR elastography in renal transplant patients and correlation with renal allograft biopsy: a feasibility study

RATIONALE AND OBJECTIVES

Magnetic resonance elastography (MRE) images the propagation of mechanical shear waves in tissue and uses that information to generate quantitative measures of tissue stiffness. Hepatic MRE has been successfully performed in thousands of patients, with good correlation between histologic grade of fibrosis and tissue stiffness. There has been no prior investigation of the utility of MRE for the assessment of kidney transplants. The aims of this study were to prospectively evaluate the feasibility of MRE in a small group of kidney transplant recipients and to correlate the measured magnetic resonance elastographic stiffness values with biopsy-proven histopathologic fibrosis.

MATERIALS AND METHODS

MRE of renal transplants was performed in 11 patients returning for protocol allograft biopsies. Calculated tissue stiffness values were compared to histologic degree of fibrosis in nine of the 11 patients.

RESULTS

The mean stiffness of two patients with moderate interstitial fibrosis was higher than the mean of six patients with mild interstitial fibrosis, but not significantly so (90 Hz, P = .12; 120 Hz, P = .17; 150 Hz, P = .26). The mean stiffness of the two patients with moderate interstitial fibrosis was slightly greater than the mean of one patient with no significant interstitial fibrosis at 90 Hz (P = .78) and slightly less at 120 and 150 Hz (P = .88 and P = .76). The mean stiffness of the six patients with mild interstitial fibrosis did not differ significantly from that of the one patient with no interstitial fibrosis (90 Hz, P = .35; 120 Hz, P = .22; 150 Hz, P = .16).

CONCLUSIONS

Preliminary results demonstrate feasibility and support known multifactorial influences on renal stiffness.

Time-resolved dual-station calf-foot three-dimensional bolus chase MR angiography with fluoroscopic tracking

PURPOSE

To refine, adapt, and evaluate the technical aspects of fluoroscopic tracking for generating dual-station high-spatial-resolution MR angiograms of the calves and feet using a single injection of contrast material.

MATERIALS AND METHODS

Nine subjects (seven healthy volunteers followed by two patients) were imaged using a two-station calf-foot three-dimensional time-resolved bolus chase MR angiography protocol which provided <1.0 mm(3) spatial resolution throughout and 2.5- and 6.6-s frame times at the calf and foot stations, respectively. Real-time reconstruction of calf station time frames allowed visually guided triggering of table advance to the foot station. The studies were independently read and scored by two radiologists in six image quality categories.

RESULTS

On average, overall diagnostic quality at the calf and foot stations was good-to-excellent, the calf arteries and all but the smallest foot arteries had good-to-excellent signal and sharpness, artifact and venous contamination were minor, and signal continuity across the inter-station interface was good.

CONCLUSION

The feasibility of fluoroscopic tracking has been demonstrated as an efficient approach for high spatiotemporal imaging of the arteries of the calves and feet with good-to-excellent diagnostic quality and low degrading venous contamination.

High temporal and spatial resolution 3D time-resolved contrast-enhanced magnetic resonance angiography of the hands and feet

Methods are described for generating 3D time-resolved contrast-enhanced magnetic resonance (MR) angiograms of the hands and feet. Given targeted spatial resolution and frame times, it is shown that acceleration of about one order of magnitude or more is necessary. This is obtained by a combination of 2D sensitivity encoding (SENSE) and homodyne (HD) acceleration methods. Image update times from 3.4-6.8 seconds are provided in conjunction with view sharing. Modular receiver coil arrays are described which can be designed to the targeted vascular region. Images representative of the technique are generated in the vasculature of the hands and feet in volunteers and in patient studies.

Blood oxygen level-dependent magnetic resonance imaging identifies cortical hypoxia in severe renovascular disease

Atherosclerotic renal artery stenosis has a range of manifestations depending on the severity of vascular occlusion. The aim of this study was to examine whether exceeding the limits of adaptation to reduced blood flow ultimately leads to tissue hypoxia, as determined by blood oxygen level dependent MRI. We compared 3 groups of hypertensive patients, 24 with essential hypertension, 13 with "moderate" (Doppler velocities 200-384 cm/s), and 17 with "severe" atherosclerotic renal artery stenosis (ARAS; velocities >384 cm/s and loss of functional renal tissue). Cortical and medullary blood flows and volumes were determined by multidetector computed tomography. Poststenotic kidney size and blood flow were reduced with ARAS, and tissue perfusion fell in the most severe lesions. Tissue medullary deoxyhemoglobin, as reflected by R2* values, was higher as compared with the cortex for all of the groups and did not differ between subjects with renal artery lesions and essential hypertension. By contrast, cortical R2* levels were elevated for severe ARAS (21.6±9.4 per second) as compared with either essential hypertension (17.8±2.3 per second; P<0.01) or moderate ARAS (15.7±2.1 per second; P<0.01). Changes in medullary R2* after furosemide administration tended to be blunted in severe ARAS as compared with unaffected (contralateral) kidneys. These results demonstrate that severe vascular occlusion overwhelms the capacity of the kidney to adapt to reduced blood flow, manifest as overt cortical hypoxia as measured by blood oxygen level-dependent MRI. The level of cortical hypoxia is out of proportion to the medulla and may provide a marker to identify irreversible parenchymal injury.

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.

Contrast-enhanced MR angiography of the abdomen with highly accelerated acquisition techniques

PURPOSE

To demonstrate that highly accelerated (net acceleration factor [R(net)] ≥ 10) acquisition techniques can be used to generate three-dimensional (3D) subsecond timing images, as well as diagnostic-quality high-spatial-resolution contrast material-enhanced (CE) renal magnetic resonance (MR) angiograms with a single split dose of contrast material.

MATERIALS AND METHODS

All studies were approved by the institutional review board and were HIPAA compliant; written consent was obtained from all participants. Twenty-two studies were performed in 10 female volunteers (average age, 47 years; range, 27-62 years) and six patients with renovascular disease (three women; average age, 48 years; range, 37-68 years; three men; average age, 60 years; range, 50-67 years; composite average age, 54 years; range, 38-68 years). The two-part protocol consisted of a low-dose (2 mL contrast material) 3D timing image with approximate 1-second frame time, followed by a high-spatial-resolution (1.0-1.6-mm isotropic voxels) breath-hold 3D renal MR angiogram (18 mL) over the full abdominal field of view. Both acquisitions used two-dimensional (2D) sensitivity encoding acceleration factor (R) of eight and 2D homodyne (HD) acceleration (R(HD)) of 1.4-1.8 for R(net) = R · R(HD) of 10 or higher. Statistical analysis included determination of mean values and standard deviations of image quality scores performed by two experienced reviewers with use of eight evaluation criteria.

RESULTS

The 2-mL 3D time-resolved image successfully portrayed progressive arterial filling in all 22 studies and provided an anatomic overview of the vasculature. Successful timing was also demonstrated in that the renal MR angiogram showed adequate or excellent portrayal of the main renal arteries in 21 of 22 studies.

CONCLUSION

Two-dimensional acceleration techniques with R(net) of 10 or higher can be used in CE MR angiography to acquire (a) a 3D image series with 1-second frame time, allowing accurate bolus timing, and (b) a high-spatial-resolution renal angiogram.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11110242/-/DC1.

Sparse-CAPR: highly accelerated 4D CE-MRA with parallel imaging and nonconvex compressive sensing

Cartesian Acquisition with Projection-Reconstruction-like sampling is a SENSE-type parallel 3DFT acquisition paradigm for 4D contrast-enhanced magnetic resonance angiography that has been demonstrated capable of providing high spatial and temporal resolution, diagnostic-quality images at very high acceleration rates. However, Cartesian Acquisition with Projection-Reconstruction-like sampling images are typically reconstructed online using Tikhonov regularization and partial Fourier methods, which are prone to exhibit noise amplification and undersampling artifacts when operating at very high acceleration rates. In this work, a sparsity-driven offline reconstruction framework for Cartesian Acquisition with Projection-Reconstruction-like sampling is developed and demonstrated to consistently provide improvements over the currently-employed reconstruction strategy against these ill-effects. Moreover, the proposed reconstruction strategy requires no changes to the existing Cartesian Acquisition with Projection-Reconstruction-like sampling acquisition protocol, and an efficient numerical optimization and hardware system are described that allow for a 256 × 160 × 80 volume contrast-enhanced magnetic resonance angiography volume to be reconstructed from an eight-channel data set in less than 2 min.

Aneurysms of the ascending aorta and arch: the role of imaging in diagnosis and surgical management

Thoracic aortic aneurysms tend to be asymptomatic and were previously often diagnosed only after a complication such as dissection or rupture occurred. Better imaging techniques and an increase in the use of cross-sectional imaging has led to an increase in the diagnosis of aortic aneurysms, which has allowed for elective treatment prior to the development of a complication. The location, size and etiology of an aneurysm all impact the clinical outcomes and these factors are used to determine the appropriate timing of surgical replacement. Surgeons often rely on the information obtained from preoperative imaging to determine when to intervene and what type of procedure will be necessary, making it important for the radiologist to understand these issues in order to provide the necessary information. Postoperative imaging after surgical replacement of the aorta is also important, as there are some common findings that occur in this patient population that can impact how they are treated. The purpose of this article is to review the etiology and associated findings of aneurysms of the ascending aorta and arch, with a focus on how computed tomography angiography and magnetic resonance angiography findings are used to determine the appropriate timing for elective replacement and the type of surgical procedure, as well as the role of follow-up imaging. This will include a review of the most commonly performed types of surgical procedures, to provide an understanding of how the findings of preoperative imaging studies impact what the surgeon does in the operating room, as well as the expected findings of postoperative imaging studies.

CT and MR imaging of the mitral valve: radiologic-pathologic correlation

Computed tomography (CT) and magnetic resonance (MR) imaging are increasingly important adjuncts to echocardiography for the evaluation of mitral valve disease. The mitral valve may be involved in various acquired or congenital conditions with resultant regurgitation or stenosis, and many of these conditions can be identified with CT or MR imaging. In addition, CT is useful for detecting and monitoring postoperative complications after mitral valve repair or replacement. As the use of CT and MR imaging increases, awareness of the CT and MR imaging appearances of the normal mitral valve and the various disease processes that affect it may foster recognition of unsuspected mitral disease in patients undergoing imaging for other purposes. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.306105518/-/DC1.

Max CAPR: high-resolution 3D contrast-enhanced MR angiography with acquisition times under 5 seconds

High temporal and spatial resolution is desired in imaging of vascular abnormalities having short arterial-to-venous transit times. Methods that exploit temporal correlation to reduce the observed frame time demonstrate temporal blurring, obfuscating bolus dynamics. Previously, a Cartesian acquisition with projection reconstruction-like (CAPR) sampling method has been demonstrated for three-dimensional contrast-enhanced angiographic imaging of the lower legs using two-dimensional sensitivity-encoding acceleration and partial Fourier acceleration, providing 1mm isotropic resolution of the calves, with 4.9-sec frame time and 17.6-sec temporal footprint. In this work, the CAPR acquisition is further undersampled to provide a net acceleration approaching 40 by eliminating all view sharing. The tradeoff of frame time and temporal footprint in view sharing is presented and characterized in phantom experiments. It is shown that the resultant 4.9-sec acquisition time, three-dimensional images sets have sufficient spatial and temporal resolution to clearly portray arterial and venous phases of contrast passage. It is further hypothesized that these short temporal footprint sequences provide diagnostic quality images. This is tested and shown in a series of nine contrast-enhanced MR angiography patient studies performed with the new method.

Time-resolved bolus-chase MR angiography with real-time triggering of table motion

Time-resolved bolus-chase contrast-enhanced MR angiography with real-time station switching is demonstrated. The Cartesian acquisition with projection reconstruction-like sampling (CAPR) technique and high 2D sensitivity encoding (SENSE) (6x or 8x) and 2D homodyne (1.8x) accelerations were used to acquire 3D volumes with 1.0-mm isotropic spatial resolution and frame times as low as 2.5 sec in two imaging stations covering the thighs and calves. A custom real-time system was developed to reconstruct and display CAPR frames for visually guided triggering of table motion upon passage of contrast through the proximal station. The method was evaluated in seven volunteers. High-spatial-resolution arteriograms with minimal venous contamination were consistently acquired in both stations. Real-time stepping table contrast-enhanced MR angiography is a method for providing time-resolved images with high spatial resolution over an extended field-of-view.

High spatial and temporal resolution imaging of the arterial vasculature of the lower extremity with contrast enhanced MR angiography

Vascular imaging can be essential in the diagnosis, monitoring, and planning and assessment of treatment of patients with peripheral vascular disease. The purpose of this work is to describe a recently developed three-dimensional (3D) time-resolved contrast-enhanced MR angiography (CE-MRA) technique, Cartesian Acquisition with Projection Reconstruction-like sampling (CAPR), and its application to imaging of the vasculature of the lower legs and feet. CAPR implements accelerated imaging techniques and uses specialized multielement imaging coil arrays to achieve high temporal and high spatial resolution imaging. Volunteer and patient studies of the vasculature of the lower legs and feet have been performed. Temporal resolution of 4.9-6.5 sec and spatial resolution less than or equal to 1 mm in all directions allow for the depiction of progressive arterial filling and complex flow patterns as well as sharp visualization of vascular structure as small as the fine muscular branches. High-quality diagnostic imaging is made possible with CAPR's advanced acquisition and reconstruction techniques and the use of specialized coil arrays.

A core-shell nanomaterial with endogenous therapeutic and diagnostic functions

In the present communication, we report the fabrication of a unique core-shell inorganic nanomaterial with potential therapeutic and diagnostic functions. It contains an iron–cobalt (FeCo) core that demonstrates magnetic resonance imaging (MRI) contrast property and a thin nanoshell of gold that inhibits the function of a pro-angiogenic growth factor, VEGF165. Au(FeCo) core-shell nanomaterials are fabricated in the gas phase and characterized using transmission electron microscopy, energy dispersive spectrum, inductively coupled plasma analysis, and MRI. Inhibition of VEGF165 function by Au(FeCo) is demonstrated against VEGF165/VPF-induced signaling cascades and proliferation of human umbilical vein endothelial cells (HUVECs). The self-contrast property of Au(FeCo) is determined in vitro by MRI after incubating HUVECs with Au(FeCo), demonstrating intrinsic contrast property of this potentially therapeutic nanomaterial. In brief, we report here the successful fabrication of an inorganic core-shell nanomaterial with potential therapeutic and diagnostic functions. It inhibits the function of VEGF165 and functions as a MRI contrast agent.

Preserved oxygenation despite reduced blood flow in poststenotic kidneys in human atherosclerotic renal artery stenosis

Atherosclerotic renal artery stenosis reduces blood flow and perfusion pressures to the poststenotic kidney producing renovascular hypertension and threatening glomerular filtration rate. Little is known regarding regional tissue oxygenation in human renovascular disease that develops slowly. We compared stenotic and contralateral kidneys regarding volume, tissue perfusion, blood flow measured by multidetector computed tomography, and blood oxygen level-dependent magnetic resonance values in the cortex and medulla in 14 patients with unilateral stenosis (mean: 71% by quantitative computed tomography) and in 14 essential hypertensive patients during 150 mEq/d of sodium intake and renin-angiotensin blockade. Stenotic kidney volume was reduced compared with the contralateral kidney (118.6+/-9.9 versus 155.4+/-13.7 mL; P<0.01), as was total blood flow (269.7+/-42.2 versus 383.7+/-49; P=0.02), mainly because of reduced cortical volume. Tissue perfusion was similar but lower than essential hypertension (1.5 versus 1.2 mL/min per milliliter; P<0.05). Blood oxygen level-dependent MR at 3 T confirmed elevated R2* values (a measure of deoxyhemoglobin) in deep medullary regions in all 3 sets of kidneys (38.9+/-0.7 versus cortex 17.8+/-0.36 s(-1); P<0.0001). Despite reduced blood flow, R2* values did not differ between atherosclerotic and essential hypertensive kidneys, although furosemide-suppressible fall in medullary R2* was reduced in stenotic kidneys (5.7+/-1.8 versus 9.4+/-1.9 s(-1); P<0.05). Renal venous oxygen levels from the stenotic kidney were higher than those from essential hypertensives (65.1+/-2.2 versus 58.1+/-1.2; P=0.006). These data indicate that, although stenosis reduced blood flow and volume, cortical and medullary oxygenation was preserved under these conditions.

Gadolinium enhanced magnetic resonance urography for upper urinary tract malignancy

PURPOSE

We retrospectively evaluated the accuracy of gadolinium enhanced magnetic resonance urography to detect upper urinary tract tumors.

MATERIALS AND METHODS

A total of 91 magnetic resonance urography studies for suspected upper tract malignancy were done in 70 males and 18 females with a mean age of 71.7 years. Breath hold coronal T2-weighted single shot fast spin-echo and breath-hold coronal 3-dimensional T1-weighted spoiled gradient-recalled echo images with fat suppression were obtained during the nephrographic and excretory phases after intravenous injection of gadolinium based contrast material. Two radiologists independently reviewed magnetic resonance images for a tumor by 4 regions (right/left and renal collecting system/ureter). Sensitivity, specificity and accuracy were calculated.

RESULTS

A total of 35 urinary tract regions in 18 males and 7 females with a mean age of 70.4 years were confirmed to have an upper tract malignant tumor and 219 urinary tract regions were confirmed to be tumor-free. Sensitivity, specificity and accuracy to detect upper urinary tract malignancy were 74.3%, 96.8% and 93.7% for reviewer 1, and 62.9%, 96.3% and 91.7% for reviewer 2, respectively. When patients with a ureteral stent or nephrostomy tube were excluded from analysis, sensitivity, specificity and accuracy were 86.2%, 99.5% and 97.7% for reviewer 1, and 72.4%, 97.9% and 94.6% for reviewer 2, respectively.

CONCLUSIONS

Gadolinium enhanced magnetic resonance urography is accurate to detect upper urinary tract malignant tumors.