Three-dimensional contrast-enhanced magnetic-resonance angiography of the renal arteries: interindividual comparison of 0.2 mmol/kg gadobutrol at 1.5 T and 0.1 mmol/kg gadobenate dimeglumine at 3.0 T

Diagnostic Performance of a Lower-dose Contrast-Enhanced 4D Dynamic MR Angiography of the Lower Extremities at 3 T Using Multisegmental Time-Resolved Maximum Intensity Projections

BACKGROUND

For peripheral artery disease (PAD), MR angiography (MRA) is a well-established diagnostic modality providing morphologic and dynamic information comparable to digital subtraction angiography (DSA). However, relatively large amounts of contrast agents are necessary to achieve this.

PURPOSE

To evaluate the diagnostic accuracy of time-resolved 4D MR-angiography with interleaved stochastic trajectories (TWIST-MRA) by using maximum intensity projections (MIPs) of dynamic images acquired with reduced doses of contrast agent.

STUDY TYPE

Retrospective.

POPULATION

Forty adult PAD patients yielding 1088 artery segments.

FIELD STRENGTH/SEQUENCE

A 3.0 T, time-resolved 4D MR-angiography with TWIST-MRA and MIP of dynamic images.

ASSESSMENT

DSA was available in 14 patients (256 artery segments) and used as reference standard. Three-segmental MIP reconstructions of TWIST-images after administration of 3 mL of gadolinium-based contrast agent (Gadoteridol/Prohance®, 0.5 M) per anatomical level (pelvis, thighs, and lower legs) yielded 256 artery segments for correlation between MRA and DSA. Three independent observers rated image quality (scale: 1 [nondiagnostic] to 4 [excellent]) and the degree of venous overlay (scale: 0 [none] to 2 [significant]) for all segments. Diagnostic accuracy for the detection of >50% stenosis and artery occlusion was calculated for all observers.

STATISTICAL TESTS

Binary classification test (sensitivity, specificity, positive/negative predictive values, diagnostic accuracy). Intraclass correlation coefficients (ICCs), logistic regression analysis with comparison of areas under the receiver-operating-characteristics (ROC) curves (AUCs) with the DeLong method. Bland-Altman-comparison.

RESULTS

High diagnostic performance was achieved for the detection of >50% stenosis (sensitivity 92.9% [84.3-99.9% (95%-CI)] and specificity 98.5% [95.7-99.8% (95%-CI)]) and artery occlusion (sensitivity 93.1% [77.2-99.2% (95%-CI)] and specificity 99.1% [96.9-99.9% (95%-CI)]). Inter-reader agreement was excellent with ICC values ranging from 0.95 to 1.0 for >50% artery stenosis and occlusion. Image quality was good to excellent for both readers (3.41 ± 0.72, 3.33 ± 0.65, and 3.38 ± 0.61 [mean ± SD]) with good correlation between observer ratings (ICC 0.71-0.81). No significant venous overlay was observed (0.06 ± 0.24, 0.23 ± 0.43 and 0.11 ± 0.45 [mean ± SD]).

DATA CONCLUSION

MIPs of dynamic TWIST-MRA offer a promising diagnostic alternative necessitating only reduced amounts (50%) of gadolinium-based contrast agents for the entire runoff vasculature.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 2.

Abdominal Magnetic Resonance Angiography

MR imaging hardware and software improvements have led to new applications for contrast-enhanced and noncontrast-enhanced magnetic resonance angiography in the abdomen and pelvis. Higher magnetic field strength MR imaging scanners have greater signal-to-noise ratio and contrast-to-noise ratio, which is used to improve spatial resolution or temporal resolution for these techniques. New noncontrast-enhanced sequences offer high-resolution magnetic resonance angiography without contrast and provide additional hemodynamic information. Magnetic resonance angiography is particularly well suited to imaging patients with chronic mesenteric ischemia, renal vascular disease, pelvic congestion syndrome, and vascular malformations.

Gadobutrol versus gadofosveset-trisodium in MR venography of the lower extremities

Objectives

MR venography (MRV) protocols have used bloodpool contrast agents and long scan sequences to identify patients suitable for treatment and preoperatively. However, variable availability of bloodpool contrast agents, high costs and a need to shorten acquisition times for routine MR protocols hamper everyday practice.

Materials

20 patients (11 men; mean age 54 ± 11.8 years; body mass index 23.6 ± 2.5) were enrolled in this prospective study. An intra-individual comparison of image quality, interpretation and findings for two different contrast agents (regular gadolinium contrast agent gadobutrol vs. bloodpool contrast agent gadofosveset-trisodium) and two different scan protocols (long acquisition time protocol using a high-resolution fast field echo (FFE) sequence vs. short acquisition time protocol using an ultra-fast gradient echo (GE) sequence) were performed.

Results

Image quality (average of 4.94 vs. 4.92 on a five-point scale), interpretation and contrast-to-noise ratio (44 vs. 45) were equal for both contrast agents. Image findings showed no statistical significant differences between the MR protocols or contrast agents (overall p = 0.328).

Conclusions

For high-resolution MRV, it is possible to replace gadofosveset-trisodium with gadobutrol. Furthermore, an ultra-fast GE sequence for MRV might considerably shorten acquisition time, without loss of image quality or diagnostic yield.

Key Points

• High-quality MRV can be performed with a regular gadolinium-based contrast agent.

• Ultra-fast GRE vs. HR-FFE MRV: equally suitable for evaluation of venous obstruction.

• Regular gadolinium-based contrast agent can supersede a bloodpool contrast agent for MRV.

• Equal confidence for gadobutrol vs gadofosveset-trisodium in MRV.

• MRV accessible for routine daily practice.

Lower-limb magnetic resonance angiography: performance of extracellular contrast agents versus blood pool contrast agent for both dynamic and high spatial resolution imaging in extended phase

AIM

To prospectively compare the performance of extracellular space contrast agents (ECSCAs) versus a blood-pool contrast agent (BPCA) for a comprehensive lower-limb magnetic resonance angiography (MRA) protocol in patients with either claudication or critical ischaemia.

MATERIALS AND METHODS

Thirty patients with claudication underwent lower-limb magnetic resonance angiography (MRA) (dynamic crural, three-station bolus chase, and infra-inguinal high resolution) using a triphasic injection method with both a ECSCA and BPCA to allow intra-individual comparison, and 30 patients with critical ischaemia were scanned with either a ECSCA or BPCA. The dynamic, bolus chase, and high-resolution images were scored for quality on a Likert scale (from 1-5). Signal- and contrast-to-noise ratios were analysed and statistical analysis performed.

RESULTS

Overall, there was no statistically significant difference between the ECSCAs and BPCA for arteriographic dynamic imaging, bolus chase MRA, or the high spatial resolution imaging. Venous image quality was rated higher quality for BPCA scans than for ECSCA images for calf veins (not significantly for thigh veins). Venous imaging signal intensity measures were higher for BPCA imaging.

CONCLUSION

Extended-phase imaging using an ECSCA with this protocol provides arteriographic image quality equal to imaging with a BPCA. Venous depiction is good using ECSCAs with this approach, although better with BPCA.

Prospective glioma grading using single-dose dynamic contrast-enhanced perfusion MRI

AIM

To evaluate the sensitivity and specificity of single-dose dynamic contrast-enhanced (DCE) perfusion magnetic resonance imaging (MRI) in prospective evaluation of glioma grading and to correlate the relative cerebral blood volume (rCBV) values with mitotic and ki-67 indexes obtained at histopathology.

MATERIALS AND METHODS

A total of 53 histologically proven patients with glioma were included in this study. DCE-MRI perfusion with a single dose of contrast medium was included in brain tumour protocol and prospective grading of glioma into low and high grade was done based on a previously reported rCBV cut-off value of 3. Tumours with rCBV ≥ 3 were considered to be high grade and rCBV < 3 were considered to be low grade. The sensitivity and specificity of the cut-off value were estimated. Ki-67 and mitotic indexes were also obtained on histopathological analysis along with histological grading.

RESULTS

Based on pre-defined rCBV cut-off values, prospective grading of low- and high-grade glioma was achieved with a sensitivity and specificity of 97.22% and 100%, respectively. Significant correlation was found between the mitotic/ki-67 indexes and rCBV values when data for high- and low-grade tumours was combined.

CONCLUSION

DCE-MRI performed with a single dose of contrast medium is as effective as a protocol with a double-dose of contrast medium for glioma grading using 3 T MRI and could be added to the routine evaluation protocol of brain tumours.

Magnetic resonance evaluation of renal artery stenosis in a swine model: performance of low-dose gadobutrol versus gadoterate meglumine in comparison with digital subtraction intra-arterial catheter angiography

PURPOSE

The aim of this study was to compare low-dose imaging with gadobutrol and gadoterate meglumine (Gd-DOTA) for evaluation of renal artery stenosis with 3-T magnetic resonance angiography (MRA) in a swine model.

METHOD AND MATERIALS

A total of 12 experimental animals were evaluated using equivalently dosed gadobutrol and Gd-DOTA for time-resolved and static imaging. For time-resolved imaging, the time-resolved imaging with stochastic trajectories (TWIST) technique (temporal footprint, 4.4 seconds) was used; a dose of 1 mL of gadobutrol was injected at 2 mL/s and a dose of 2 mL of Gd-DOTA was injected at both 2 and 4 mL/s. For a separate static acquisition, doses were doubled. The static scans were used for stenosis gradation and the time-resolved scans for comparison of enhancement dynamics, signal-to-noise ratio (SNR), and qualitative assessments.

RESULTS

The average magnitude of difference in the stenosis measurements with static gadobutrol scans relative to digital subtraction intra-arterial catheter angiography (mean [SD], 7.4% [5.6%]) was less than with both the 2 mL/s (10.6% [6.2%]) and 4 mL/s (11.5% [7.8%]) Gd-DOTA MRA protocols. On time-resolved scans, peak signal-to-noise ratio was greatest with the gadobutrol protocol (P < 0.05), and the gadobutrol TWIST scan was preferred to the TWIST Gd-DOTA scan in terms of image quality and stenosis visualization in every case for every reader.

CONCLUSION

Low-dose gadobutrol (~0.05 mmoL/kg) contrast-enhanced MRA results in improved accuracy of renal artery stenosis assessments relative to equivalently dosed Gd-DOTA at 3 T.

Time-resolved MR angiography of renal artery stenosis in a swine model at 3 Tesla using gadobutrol with digital subtraction angiography correlation

PURPOSE

To establish the minimum dose required for detection of renal artery stenosis using high temporal resolution, contrast enhanced MR angiography (MRA) in a porcine model.

MATERIALS AND METHODS

Surgically created renal artery stenoses were imaged with 3 Tesla MR and digital subtraction angiography (DSA) in 12 swine in this IACUC approved protocol. Gadobutrol was injected intravenously at doses of 0.5, 1, 2, and 4 mL for time-resolved MRA (1.5 × 1.5 mm(2) spatial resolution). Region of interest analysis was performed together with stenosis assessment and qualitative evaluation by two blinded readers.

RESULTS

Mean signal to noise ratio (SNR) and contrast to noise ratio (CNR) values were statistically significantly less with the 0.5-mL protocol (P < 0.001). There were no statistically significant differences among the other evaluated doses. Both readers found 10/12 cases with the 0.5-mL protocol to be of inadequate diagnostic quality (κ = 1.0). All other scans were found to be adequate for diagnosis. Accuracies in distinguishing between mild/insignificant (<50%) and higher grade stenoses (>50%) were comparable among the higher-dose protocols (sensitivities 73-93%, specificities 62-100%).

CONCLUSION

Renal artery stenosis can be assessed with very low doses (~0.025 mmol/kg bodyweight) of a high concentration, high relaxivity gadolinium chelate formulation in a swine model, results which are promising with respect to limiting exposure to gadolinium based contrast agents.

Assessment of the kidneys: magnetic resonance angiography, perfusion and diffusion

Renal magnetic resonance (MR) imaging has undergone major improvements in the past several years. This review focuses on the technical basics and clinical applications of MR angiography (MRA) with the goal of enabling readers to acquire high-resolution, high quality renal artery MRA. The current role of contrast agents and their safe use in patients with renal impairment is discussed. In addition, an overview of promising techniques on the horizon for renal MR is provided. The clinical value and specific applications of renal MR are critically discussed.

Magnetic resonance angiography: current status and future directions

With recent improvement in hardware and software techniques, magnetic resonance angiography (MRA) has undergone significant changes in technique and approach. The advent of 3.0 T magnets has allowed reduction in exogenous contrast dose without compromising overall image quality. The use of novel intravascular contrast agents substantially increases the image windows and decreases contrast dose. Additionally, the lower risk and cost in non-contrast enhanced (NCE) MRA has sparked renewed interest in these methods. This article discusses the current state of both contrast-enhanced (CE) and NCE-MRA. New CE-MRA methods take advantage of dose reduction at 3.0 T, novel contrast agents, and parallel imaging methods. The risks of gadolinium-based contrast media, and the NCE-MRA methods of time-of-flight, steady-state free precession, and phase contrast are discussed.

Prospective comparison of image quality and diagnostic accuracy of 0.5 molar gadobenate dimeglumine and 1.0 molar gadobutrol in contrast-enhanced run-off magnetic resonance angiography of the lower extremities

PURPOSE

To compare image quality and diagnostic accuracy of 0.5 molar gadobenate dimeglumine and 1.0 molar gadobutrol in contrast-enhanced (CE) magnetic resonance angiography (MRA) of the lower extremities interindividually.

MATERIALS AND METHODS

The study was approved by our Institutional Review Board. Written informed consent was obtained from all patients before enrollment in the study. We prospectively included 74 patients (21 women, 53 men; mean age ± SD: 67.9 ± 11.0 years) with suspected peripheral occlusive vascular disease. All patients underwent a contrast-enhanced MRA of both lower extremities with either 0.1 mL/kg body weight gadobutrol or gadobenate dimeglumine. Image quality, stenosis grade, and artifacts were assessed by two blinded, independent investigators. Signal intensity (SI), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured by a third investigator. Contrast agent groups were compared to each other using a two-sided Student's t-test.

RESULTS

The results did not show significant differences for SI, SNR, or CNR. Both investigators were in significant accordance (P < 0.05) with regard to stenosis detection.

CONCLUSION

We conclude that application of standard clinical doses (0.1 mL/kg body weight) of both contrast agents provides similar diagnostic results and gadolinium dose could be reduced by the application of a single dose of gadobenate dimeglumine for CE run-off MRA.

[MRI for therapy control in patients with aortic isthmus stenosis]

Aortic isthmus stenosis is the most common congenital aortic anomaly and is often a problem for therapy surveillance. In addition to possible comorbidities (e.g. bicuspid aortic valve) it is accompanied by various middle and long-term complications depending on the primary choice of the therapeutic procedure. Magnetic resonance imaging (MRI) plays an important role for the mostly young patients in the control of the aortic isthmus stenosis and therapy because it is non-invasive and there is no X-ray exposure. Radiologists should be well-informed on the principles of the therapeutic procedure in order to be competent in the interpretation of MRI findings. Due to the continuous development of MRI technology, techniques for functional evaluation (e.g. dynamic MRA, 4D PC flow measurement) are increasingly becoming available in addition to high-resolution MR angiography (MRA), which could predict the risk of possible complications, such as aneurysms. However, in this aspect further studies are necessary. Interventional therapy with stents and stent grafts is often employed for the therapy of possible complications following an operation (aneurysms, restenosis) but because of massive metal artefacts the use of MRI is often sometimes severely limited.

Evaluation of gadobutrol, a macrocyclic, nonionic gadolinium chelate in a brain glioma model: comparison with gadoterate meglumine and gadopentetate dimeglumine at 1.5 T, combined with an assessment of field strength dependence, specifically 1.5 versus 3 T

PURPOSE

To evaluate in a rat brain glioma model intraindividual tumor enhancement at 1.5 T using gadobutrol (Gadovist), a nonionic, macrocyclic chelate currently in clinical trials in the United States, in comparison with both an ionic macrocyclic chelate, gadoterate meglumine (Dotarem), and an ionic linear chelate, gadopentetate dimeglumine (Magnevist), and to compare the degree of tumor enhancement with gadobutrol at 1.5 and 3 T.

MATERIALS AND METHODS

A total of 24 rats, divided into three groups with n = 8 animals per group, were evaluated. Animals in group 1 received injections of gadobutrol and gadopentetate dimeglumine, whereas those in group 2 received gadobutrol and gadoterate meglumine. Injections were performed in random order and separated by 24 hours. Magnetic resonance imaging (MRI) examinations were performed immediately following each contrast injection with a 1.5 T MR system. Animals in group 3 received gadobutrol injections using the same protocol but with scans performed at 1.5 and 3 T. In all examinations, T1-weighted images were acquired precontrast, 1 minute postcontrast, and at 4 consecutive 2-minute intervals thereafter. A contrast dose of 0.1 mmol/kg was used in all instances.

RESULTS

In groups 1 and 2, tumor signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were higher for gadobutrol compared to both other agents at each timepoint postcontrast injection. The improvement in tumor CNR with gadobutrol, depending on time, was between 12% and 40% versus gadopentetate dimeglumine, with the difference achieving statistical significance at 7 minutes. The improvement in tumor CNR with gadobutrol, depending on time, was between 15% and 27% versus gadoterate meglumine, with the difference statistically significant at 5 and 9 minutes. In group 3 the improvement in tumor SNR and CNR seen with the increase in field strength from 1.5 to 3 T for gadobutrol was statistically significant at all acquired timepoints (P < 0.002). CNR mean values ranged from 10.4 +/- 2.9 to 24.6 +/- 5.0 at 1.5 T and from 20.5 +/- 5.9 to 47.8 +/- 15.7 at 3 T depending on the timepoint postcontrast.

CONCLUSION

Consistently greater tumor enhancement was noted at all measured timepoints following contrast injection with gadobutrol compared to both gadopentetate dimeglumine and gadoterate meglumine at 1.5 T. A substantial further improvement in tumor enhancement was noted using gadobutrol at 3 T.

Magnetic resonance angiography of abdominal vessels at 3 T

Magnetic resonance angiography (MRA) has evolved significantly since first described in the early 1990s. Unrivaled image quality and freedom from artifacts has made it a reliable and widely utilized technique. Imaging at 3 T offers the potential for higher resolutions images with better temporal resolution compared to 1.5 T. This article will review the technique and contrast agents required to perform MRA at 3 T and the relevant clinical applications. We also discuss non-contrast enhanced MRA in the era of nephrogenic systemic fibrosis and future prospect for MRA at 3 T.

64-Slice CT angiography of the abdominal aorta and abdominal arteries: comparison of the diagnostic efficacy of iobitridol 350 mgI/ml versus iomeprol 400 mgI/ml in a prospective, randomised, double-blind multi-centre trial

Purpose

The purpose of this study was to assess the influence of iodine concentration on diagnostic efficacy in multi-detector-row computed tomography (MDCT) angiography of the abdominal aorta and abdominal arteries.

Methods

IRB approval and informed consent were obtained. In this double-blind trial, patients were randomised to undergo MDCT angiography of the abdominal arteries during administration of iobitridol (350 mgI/ml) or iomeprol (400 mgI/ml). Each centre applied its own technique for delivery of contrast medium, regardless of iodine concentration. Diagnostic efficacy, image quality, visualisation of the arterial wall and arterial enhancement were evaluated. A total of 153 patients received iobitridol and 154 received iomeprol.

Results

The ability to reach a diagnosis was “satisfactory” to “totally satisfactory” in 152 (99.3%) and 153 (99.4%) patients respectively. Image quality was rated as being “good” to “excellent” in 94.7 and 94.8% segments respectively. Similar results were observed for image quality of arterial walls (84.3 vs. 83.2%). The mean relative changes in arterial enhancement between baseline and arterial phase images showed no statistically significant differences.

Conclusion

This study demonstrated the non-inferiority of the 350 versus 400 mgI/ml iodine concentration, in terms of diagnostic efficacy, in abdominal MDCT angiography. It also confirmed the high robustness and reliability of this technique across multi-national practices.

Imaging in endovascular therapy: our future

The endovascular therapist now has many modern imaging techniques available to plan and execute treatment, whereas in the past vascular surgeons relied mostly on clinical examination and arteriography. Advances in computer technology have enabled fast acquisition and processing of the large amounts of digital data essential to capture the dynamic information from fast-flowing blood at high resolution. Functional imaging has begun to play a role in predicting stability of progressive vascular disease and the need for and risks of intervention. Computing power now affords the interventionist the ability to handle imaging data in powerful 3-dimensional programs and electronically "in-lay" a variety of devices to plan complex endovascular procedures from the familiar platform of a laptop. In four major clinical areas, carotid intervention, peripheral intervention, endoluminal grafting, and cardiac imaging, we review the latest advances and changes with an eye toward how we should best be using imaging in our patients undergoing endovascular treatment...now and into the future.