Coronary MR imaging: effect of timing and dose of isosorbide dinitrate administration

Coronary Magnetic Resonance Angiography: Technical Innovations Leading Us to the Promised Land?

Coronary artery disease remains the leading cause of cardiovascular morbidity and mortality. Invasive X-ray angiography and coronary computed tomography angiography are established gold standards for coronary luminography. However, they expose patients to invasive complications, ionizing radiation, and iodinated contrast agents. Among a number of imaging modalities, coronary cardiovascular magnetic resonance (CMR) angiography may be used in some cases as an alternative for the detection and monitoring of coronary arterial stenosis, with advantages including its versatility, excellent soft tissue characterization, and avoidance of ionizing radiation and iodinated contrast agents. In this review, we explore the recent advances in motion correction, image acceleration, and reconstruction technologies that are bringing coronary CMR angiography closer to widespread clinical implementation.

Non-contrast coronary magnetic resonance angiography: current frontiers and future horizons

Coronary magnetic resonance angiography (coronary MRA) is advantageous in its ability to assess coronary artery morphology and function without ionizing radiation or contrast media. However, technical limitations including reduced spatial resolution, long acquisition times, and low signal-to-noise ratios prevent it from clinical routine utilization. Nonetheless, each of these limitations can be specifically addressed by a combination of novel technologies including super-resolution imaging, compressed sensing, and deep-learning reconstruction. In this paper, we first review the current clinical use and motivations for non-contrast coronary MRA, discuss currently available coronary MRA techniques, and highlight current technical developments that hold unique potential to optimize coronary MRA image acquisition and post-processing. In the final section, we examine the various research-based coronary MRA methods and metrics that can be leveraged to assess coronary stenosis severity, physiological function, and atherosclerotic plaque characterization. We specifically discuss how such technologies may contribute to the clinical translation of coronary MRA into a robust modality for routine clinical use.

Coronary Computed Tomography Angiography in the Clinical Workflow of Athletes With Anomalous Origin of Coronary Arteries From the Contralateral Valsalva Sinus

PURPOSE

This study aimed to assess the role of coronary computed tomography-angiography (CCTA) in the workflow of competitive sports eligibility in a cohort of athletes with anomalous origin of the left-coronary artery (AOLCA)/anomalous origin of the right-coronary artery (AORCA) in an attempt to outline relevant computed tomography features likely to impact diagnostic assessment and clinic management.

MATERIALS AND METHODS

Patients with suspected AOLCA/AORCA at transthoracic echocardiography or with inconclusive transthoracic echocardiography underwent CCTA to rule out/confirm and characterize the anatomic findings: partially interarterial course or full-INT, high-take-off, acute-take-off-angle (ATO), slit-like origin, intramural course (IM), interarterial-course-length, and lumen-reduction/hypoplasia (HYPO).

RESULTS

CCTA identified 28 athletes: 6 AOLCA (3 males; 20.3±11.0 y) and 22 AORCA (18 males; 29.1±16.5 y). Symptoms were present only in 13 athletes (46.4%; 10 AORCA). Four patients (3 AORCA) had abnormal rest electrocardiogram, 11 (40.7%; 9 AORCA) had abnormal stress-electrocardiogram. The INT course was observed in 15 athletes (53.6%): 6/6 AOLCA and 9/22 AORCA (40.9%). Slit-like origin was present in 7/22 AORCA (31.8%) and never in AOLCA. Suspected IM resulted in 3 AOLCA (50%), always with HYPO/ATO, and in 6/22 AORCA (27.3%) with HYPO. No statistically significant differences were found between asymptomatic/symptomatic patients in the prevalence of partially INT/INT courses, high-take-off/ATO, and slit-like ostium. A slightly significant relationship between suspected proximal-IM (r=0.47, P<0.05) and proximal-HYPO of anomalous vessel (r=0.65, P<0.01) resulted in AORCA and was confirmed on AOLCA/AORCA pooled analysis (r=0.58, P<0.01 for HYPO). All AOLCA/AORCA athletes were disqualified from competitive sports and warned to avoid vigorous physical efforts. Surgery was recommended to all AOLCA athletes and to 13 AORCA (3 asymptomatic), but only 6 underwent surgery. No major cardiovascular event/ischemic symptoms/signs developed during a mean follow-up of 49.6±39.5 months.

CONCLUSION

CCTA provides essential information for safe/effective clinical management of athletes, with important prognostic/sport-activity implications.

Applying Nitroglycerin at Coronary MR Angiography at 1.5 T: Diagnostic Performance of Coronary Vasodilation in Patients with Coronary Artery Disease

Purpose

To evaluate the influence of applying nitroglycerin (NTG) on detecting significant coronary artery disease (CAD) and NTG-induced coronary vasodilation using coronary MR angiography in patients suspected of having CAD.

Materials and Methods

In this prospective study conducted from November 2017 to September 2018, 70 consecutive participants suspected of having CAD were recruited. Of those, 57 patients successfully underwent pre- and post-NTG coronary MR angiography, both of which were performed during the end-systolic phase of the cardiac cycle. Significant coronary stenosis was defined at x-ray coronary angiography as stenosis of 50% or more. Participants were divided into a significant CAD group (significant stenosis) and nonsignificant CAD group (no significant stenosis) based on x-ray coronary angiography. Paired and unpaired Student t, generalized linear mixed model, and McNemar tests were used.

Results

The diagnostic performance of coronary MR angiography was significantly improved after NTG (P < .001). Per-patient for coronary MR angiography, from before to after NTG, respectively, the sensitivity was 97.6% (95% confidence interval [CI]: 85.6%, 99.9%) to 97.6% (95% CI: 85.6%, 99.9%), specificity was 25.0% (95% CI: 8.3%, 52.5%) to 62.5% (95% CI: 35.9%, 83.7%), positive predictive value was 76.9% (95% CI: 62.8%, 87.0%) to 87.0% (95% CI: 73.0%, 94.6%), negative predictive value was 80.0% (95% CI: 29.9%, 98.9%) to 90.9% (95% CI: 57.1%, 99.5%), and accuracy was 77.2% (95% CI: 66.3%, 88.1%) to 87.7% (95% CI: 79.2%, 96.3%). The NTG-induced coronary vasodilation was significantly lower in the significant CAD group compared with the nonsignificant CAD group.

Conclusion

Administration of NTG significantly improved the diagnostic performance of coronary MR angiography for detecting significant CAD; however, NTG-induced coronary vasodilation was impaired in patients with significant CAD.© RSNA, 2020See also commentary by François in this issue.

A quantitative comparison between a navigated Cartesian and a self-navigated radial protocol from clinical studies for free-breathing 3D whole-heart bSSFP coronary MRA

PURPOSE

Navigator-gated 3D bSSFP whole-heart coronary MRA has been evaluated in several large studies including a multi-center trial. Patient studies have also been performed with more recent self-navigated techniques. In this study, these two approaches are compared side-by-side using a Cartesian navigator-gated and corrected (CNG) and a 3D radial self-navigated (RSN) protocol from published patient studies.

METHODS

Sixteen healthy subjects were examined with both sequences on a 1.5T scanner. Assessment of the visibility of coronary ostia and quantitative comparisons of acquisition times, blood pool homogeneity, and visible length and sharpness of the right coronary artery (RCA) and the combined left main (LM)+left anterior descending (LAD) coronary arteries were performed. Paired sample t-tests with P < .05 considered statistically significant were used for all comparisons.

RESULTS

The acquisition time was 5:40 ± 0:28 min (mean ± SD) for RSN, being significantly shorter than the 16:59 ± 5:05 min of CNG (P < .001). RSN images showed higher blood pool homogeneity (P < .001). All coronary ostia were visible with both techniques. CNG provided significantly higher vessel sharpness in the RCA (CNG: 50.0 ± 8.6%, RSN: 34.2 ± 6.9%, P < .001) and the LM+LAD (CNG: 48.7 ± 6.7%, RSN: 32.3 ± 7.1%, P < .001). The visible vessel length was significantly longer in the LM+LAD using CNG (CNG: 9.8 ± 2.7 cm, RSN: 8.5 ± 2.6 cm, P < .05) but not in the RCA (CNG: 9.7 ± 2.3 cm, RSN: 9.3 ± 2.9 cm, P = .29).

CONCLUSION

CNG provided superior vessel sharpness and might hence be the better option for examining coronary lumina. However, its blood pool inhomogeneity and prolonged and unpredictable acquisition times compared to RSN may make clinical adoption more challenging.

Effect of Nitroglycerin on the Performance of MR Coronary Angiography

PURPOSE

To systematically investigate the effect of sublingual glyceryl trinitrate (nitroglycerin=nitro=glyceryl trinitrate=GTN=C₃ H₅ N₃ O₉ [NTG]) on the diagnostic performance of MR coronary artery imaging (MRCA) to detect relevant coronary artery disease (CAD).

MATERIALS AND METHODS

Thirty-five healthy volunteers and 25 patients with suspected or proven CAD (all in sinus rhythm) underwent MRCA before and after NTG using a contrast-agent free, three-dimensional, navigator-based, steady state free precession acquisition (voxel size 1.0 × 0.7 × 0.7 mm³ ) at 1.5 Tesla. Target parameters were stenosis detection (>50%), visible vessel length (straightened planar reconstruction) and vessel diameter (curved planar reconstruction, measured proximal/medial/distal). In patients, invasive coronary angiography served as reference.

RESULTS

NTG led to increase of the coronary diameter both in healthy volunteers (right coronary artery [RCA]: 3.2 to 3.7 mm, P < 0.001; left anterior descending coronary artery [LAD]: 2.9 to 3.4 mm, P = 0.009; left circumflex coronary artery [LCx]: 2.8 to 3.3 mm, P < 0.001) and patients (RCA 3.5 to 4.0 mm, P = 0.01; LAD 3.3 to 3.7 mm, P = 0.008; LCx: 2.9 to 3.3 mm, P = 0.03). Visible vessel length increased after NTG for the LAD (volunteers: 72 to 84 mm, P = 0.03; patients: 56 to 78 mm, P = 0.01) and for LCx (volunteers: 48 to 60 mm, P = 0.02). Sensitivity to detect > 50% stenosis improved after NTG from 88.0 to 96%, specificity from 46.5 to 69.8%, diagnostic accuracy from 61.8 to 79.4% and positive/negative predictive value from 48.9 to 64.9% and 87.0 to 96.8%, respectively.

CONCLUSION

Sublingual administration of NTG significantly enhanced the visibility of the coronary arteries and improved the detection of coronary artery stenosis.

LEVEL OF EVIDENCE

2 J. MAGN. RESON. IMAGING 2017;45:1419-1428.

Accelerated isotropic sub-millimeter whole-heart coronary MRI: compressed sensing versus parallel imaging

PURPOSE

To enable accelerated isotropic sub-millimeter whole-heart coronary MRI within a 6-min acquisition and to compare this with a current state-of-the-art accelerated imaging technique at acceleration rates beyond what is used clinically.

METHODS

Coronary MRI still faces major challenges, including lengthy acquisition time, low signal-to-noise-ratio (SNR), and suboptimal spatial resolution. Higher spatial resolution in the sub-millimeter range is desirable, but this results in increased acquisition time and lower SNR, hindering its clinical implementation. In this study, we sought to use an advanced B1-weighted compressed sensing technique for highly accelerated sub-millimeter whole-heart coronary MRI, and to compare the results to parallel imaging, the current-state-of-the-art, where both techniques were used at acceleration rates beyond what is used clinically. Two whole-heart coronary MRI datasets were acquired in seven healthy adult subjects (30.3 ± 12.1 years; 3 men), using prospective 6-fold acceleration, with random undersampling for the proposed compressed sensing technique and with uniform undersampling for sensitivity encoding reconstruction. Reconstructed images were qualitatively compared in terms of image scores and perceived SNR on a four-point scale (1 = poor, 4 = excellent) by an experienced blinded reader.

RESULTS

The proposed technique resulted in images with clear visualization of all coronary branches. Overall image quality and perceived SNR of the compressed sensing images were significantly higher than those of parallel imaging (P = 0.03 for both), which suffered from noise amplification artifacts due to the reduced SNR.

CONCLUSION

The proposed compressed sensing-based reconstruction and acquisition technique for sub-millimeter whole-heart coronary MRI provides 6-fold acceleration, where it outperforms parallel imaging with uniform undersampling.

MDCT assessment of CAD in type-2 diabetic subjects with diabetic neuropathy: the role of Charcot neuro-arthropathy

OBJECTIVES

To compare the CACS and CAD severity assessed by MDCT in neuropathic type-2 diabetic patients with and without Charcot-neuroarthropathy (CN).

METHODS

Thirty-four CN asymptomatic-patients and 36 asymptomatic-patients with diabetic-neuropathy (DN) without CN underwent MDCT to assess CACS and severity of CAD. Patients were classified as positive for significant CAD in presence of at least one stenosis >50 % on MDCT-coronary-angiography (MDCT-CA). Groups were matched for age, sex and traditional CAD risk-factors. The coronary-angiography (CA) was performed in all patients with at least a significant stenosis detected by MDCT-CA, both as reference and eventually as treatment.

RESULTS

CN patients showed higher rates of significant CAD in comparison with DN subjects [p < 0.001], while non-significant differences were observed in CACS (p = 0.980). No significant differences were also observed in CACS distribution in all subjects for stenosis ≥/<50 % (p = 0.814), as well as in both groups (p = 0.661 and 0.559, respectively). The MDCT-CA showed an overall diagnostic-accuracy for significant CAD of 87%.

CONCLUSIONS

These preliminary data suggest that CN-patients have a higher prevalence of severe CAD in comparison with DN-patients, while coronary plaques do not exhibit an increased amount of calcium. MDCT may be helpful to assess the CV risk in such asymptomatic type-2-diabetic patients with autonomic-neuropathy.

KEY POINTS

Type 2-diabetic-patients with CN result having more severe coronary artery plaque-burden. MDCT-CA may stratify the CV risk in type 2-diabetic-patients with CN. Adequate diagnostic is mandatory for optimal management of type 2-diabetic-patients with CN.

Combined coronary lumen and vessel wall magnetic resonance imaging with i-T2prep: influence of nitroglycerin

It has been shown that sublingual nitroglycerin (NTG) improves image quality of coronary lumen magnetic resonance angiography. Our aim was to investigate the influence of NTG on coronary lumen and vessel wall image quality using a combined, single sequence approach (i-T2prep), which is able to image both within the known time frame of action of NTG. Ten healthy volunteers underwent right coronary artery lumen and vessel wall imaging using the i-T2prep sequence before and after administration of NTG. Image quality was assessed qualitatively and quantitatively. Diameter, length and wall thickness were also measured using dedicated semi-automatic software. NTG induced coronary vasodilatation (lumen diameter increased from 2.16 ± 0.32 to 2.52 ± 0.59 mm; p = 0.036). As a result, visualized lumen length (9.8 ± 2.6 to 11.4 ± 3.3 cm; p = 0.025) and qualitative lumen image quality (median 3 (interquartile range 2-3.25) vs. median 3 (interquartile range 3-4); p = 0.046) both improved. Vessel wall imaging also demonstrated a significant improvement in vessel wall sharpness after NTG (24.8 vs. 27.3 %; p = 0.036). This study demonstrates the benefits of NTG for coronary lumen and vessel wall imaging using a combined sequence, i-T2prep. The methodology described here has great potential for future pathophysiological studies.

Respiratory self-navigated postcontrast whole-heart coronary MR angiography: initial experience in patients

PURPOSE

To assess the diagnostic performance of respiratory self-navigation for whole-heart coronary magnetic resonance (MR) angiography in a patient cohort referred for diagnostic cardiac MR imaging.

MATERIALS AND METHODS

Written informed consent was obtained from all participants for this institutional review board-approved study. Self-navigated coronary MR angiography was performed after administration of a contrast agent in 78 patients (mean age, 48.5 years ± 20.7 [standard deviation]; 53 male patients) referred for cardiac MR imaging because of coronary artery disease (n = 40), cardiomyopathy (n = 14), congenital anomaly (n = 17), or "other" (n = 7). Examination duration was recorded, and the image quality for each coronary segment was assessed with consensus reading. Vessel sharpness, length, and diameter were measured. Quantitative values in proximal, middle, and distal segments were compared by using analysis of variance and t tests. A double-blinded comparison with the results of x-ray angiography was performed when such results were available.

RESULTS

When patients with different indications for cardiac MR imaging were examined with self-navigated postcontrast coronary MR angiography, whole-heart data sets with 1.15-mm isotropic spatial resolution were acquired in an average of 7.38 minutes ± 1.85. The main and proximal coronary segments could be visualized in 92.3% of cases, while the middle and distal segments could be visualized in 84.0% and 55.8% of cases, respectively. Subjective scores and vessel sharpness were significantly higher in the proximal segments than in the middle and distal segments (P < .05). Anomalies of the coronary arteries could be confirmed or excluded in all cases. Per-vessel sensitivity and specificity for stenosis detection were 64.7% and 85.0%, respectively, in the 31 patients for whom reference standard x-ray coronary angiography results were available.

CONCLUSION

The self-navigated coronary MR angiography sequence shows promise for coronary imaging. However, technical improvements are needed to improve image quality, especially in the more distal coronary segments.

Utility of respiratory-navigator-rejected k-space lines for improved signal-to-noise ratio in three-dimensional cardiac MR

PURPOSE

To develop and evaluate a technique that uses the k-space lines rejected by prospective respiratory navigator (NAV) to improve the signal-to-noise ratio (SNR) without increasing the scan time.

METHODS

In conventional image reconstruction, the motion-corrupted k-space lines rejected by the NAV are not used. In this study, a set of translational motion parameters for the NAV-rejected lines and a phase-corrected average for the k-space line are estimated jointly using a maximum-likelihood approach and the information from the corresponding accepted k-space lines. Left coronary artery images were acquired in 10 healthy adult subjects, and the proposed approach incorporating the NAV-rejected lines was compared with the conventional dataset with NAV-accepted lines only, as well as a simple average of all k-space lines, in terms of SNR, normalized vessel sharpness and qualitative image scores on a four-point scale (1 = poor, 4 = excellent). Late gadolinium enhancement images of the left atrium were also acquired in 21 patients with atrial fibrillation pre- or post-pulmonary vein isolation. Images reconstructed with the proposed, conventional, and simple averaging methods were compared in terms of SNR, and subjective image quality on a four-point scale.

RESULTS

For coronary MRI, there was a significant improvement in SNR with the proposed technique, but no significant difference in normalized vessel sharpness or qualitative image scores were observed with respect to the conventional method. Simple averaging resulted in an SNR gain, but significant loss in vessel sharpness and image quality. For late gadolinium enhancement, there was a significant increase in SNR, but no significant differences were observed in subjective image quality scores between the proposed and conventional methods. There was an SNR gain, but image quality loss for simple averaging, when compared with the conventional technique. In both coronary MRI and late gadolinium enhancement, the SNR gain of the proposed method was not significantly different than the maximum theoretical SNR gain.

CONCLUSION

The proposed technique improves SNR using the additional information from NAV-rejected k-space lines, while providing similar image quality to standard reconstruction using motion-free k-space data only, with no increase in scan time.

Accelerated contrast-enhanced whole-heart coronary MRI using low-dimensional-structure self-learning and thresholding

We sought to evaluate the efficacy of prospective random undersampling and low-dimensional-structure self-learning and thresholding reconstruction for highly accelerated contrast-enhanced whole-heart coronary MRI. A prospective random undersampling scheme was implemented using phase ordering to minimize artifacts due to gradient switching and was compared to a randomly undersampled acquisition with no profile ordering. This profile-ordering technique was then used to acquire contrast-enhanced whole-heart coronary MRI in 10 healthy subjects with 4-fold acceleration. Reconstructed images and the acquired zero-filled images were compared for depicted vessel length, vessel sharpness, and subjective image quality on a scale of 1 (poor) to 4 (excellent). In a pilot study, contrast-enhanced whole-heart coronary MRI was also acquired in four patients with suspected coronary artery disease with 3-fold acceleration. The undersampled images were reconstructed using low-dimensional-structure self-learning and thresholding, which showed significant improvement over the zero-filled images in both objective and subjective measures, with an overall score of 3.6 ± 0.5. Reconstructed images in patients were all diagnostic. Low-dimensional-structure self-learning and thresholding reconstruction allows contrast-enhanced whole-heart coronary MRI with acceleration as high as 4-fold using clinically available five-channel phased-array coil.

Contrast-enhanced whole-heart coronary MRI with bolus infusion of gadobenate dimeglumine at 1.5 T

We sought to investigate the T(1) kinetics of blood and myocardium after three infusion schemes of gadobenate dimeglumine (Gd-BOPTA) and subsequently compared contrast-enhanced whole-heart coronary MRI after a bolus Gd-BOPTA infusion with nonenhanced coronary MRI at 1.5 T. Blood and myocardium T(1) was measured in seven healthy adults, after each underwent three Gd-BOPTA infusion schemes (bolus: 0.2 mmol/kg at 2 mL/sec, hybrid: 0.1 mmol/kg at 2 mL/sec followed by 0.1 mmol/kg at 0.1 mL/sec, and slow: 0.2 mmol/kg at 0.3 mL/sec). Fourteen additional subjects underwent contrast-enhanced coronary MRI with an inversion-recovery steady-state free precession sequence after bolus Gd-BOPTA infusion. Images were compared with nonenhanced T(2) -prepared steady-state free precision whole-heart coronary MRI in signal-to-noise ratio, contrast-to-noise ratio, depicted vessel length, vessel sharpness, and subjective image quality. Bolus and slow infusion schemes resulted in similar T(1) during coronary MRI, whereas the hybrid infusion method yielded higher T(1) values. A bolus infusion of Gd-BOPTA significantly improved signal-to-noise ratio, contrast-to-noise ratio, depicted coronary artery length, and subjective image quality, when all segments were collectively compared but not when compared segment by segment. In conclusion, whole-heart steady-state free precision coronary MRI at 1.5 T can benefit from a bolus infusion of 0.2 mmol/kg Gd-BOPTA.