Pulmonary 4D-flow MRI imaging in landrace pigs under rest and stress.

4D-flow MRI is a promising technique for assessing vessel hemodynamics. However, its utilization is currently limited by the lack of reference values, particularly for pulmonary vessels. In this work, we have analysed flow and velocity in the pulmonary trunk (PT), left and right pulmonary arteries (LPA and RPA, respectively) in Landrace pigs at both rest and stress through the software MEVISFlow. Nine healthy Landrace pigs were acutely instrumented closed-chest and transported to the CMR facility for evaluation. After rest measurements, dobutamine was administered to achieve a 25% increase in heart rate compared to rest. 4D-flow MRI images have been analysed through MEVISFlow by two independent observers. Inter- and intra-observer reproducibility was quantified using intraclass correlation coefficient. A significant difference between rest and stress regarding flow and velocity in all the pulmonary vessels was observed. Mean flow increased 55% in PT, 75% in LPA and 40% in RPA. Mean peak velocity increased 55% in PT, 75% in LPA and 66% in RPA. A good-to-excellent reproducibility was observed in rest and stress for flow measurements in all three arteries. An excellent reproducibility for velocity was found in PT at rest and stress, a good one for LPA and RPA at rest, while poor reproducibility was found at stress. The current study showed that pulmonary flow and velocity assessed through 4D-flow MRI follow the physiological alterations during cardiac cycle and after stress induced by dobutamine. A clinical translation to assess pulmonary diseases with 4D-flow MRI under stress conditions needs investigation.

Cardiovascular magnetic resonance-derived left ventricular mechanics-strain, cardiac power and end-systolic elastance under various inotropic states in swine.

BACKGROUND: Cardiovascular magnetic resonance (CMR) strain imaging is an established technique to quantify myocardial deformation. However, to what extent left ventricular (LV) systolic strain, and therefore LV mechanics, reflects classical hemodynamic parameters under various inotropic states is still not completely clear. Therefore, the aim of this study was to investigate the correlation of LV global strain parameters measured via CMR feature tracking (CMR-FT, based on conventional cine balanced steady state free precession (bSSFP) images) with hemodynamic parameters such as cardiac index (CI), cardiac power output (CPO) and end-systolic elastance (Ees) under various inotropic states. METHODS: Ten anaesthetized, healthy Landrace swine were acutely instrumented closed-chest and transported to the CMR facility for measurements. After baseline measurements, two steps were performed: (1) dobutamine-stress (Dobutamine) and (2) verapamil-induced cardiovascular depression (Verapamil). During each protocol, CMR images were acquired in the short axisand apical 2Ch, 3Ch and 4Ch views. MEDIS software was utilized to analyze global longitudinal (GLS), global circumferential (GCS), and global radial strain (GRS). RESULTS: Dobutamine significantly increased heart rate, CI, CPO and Ees, while Verapamil decreased them. Absolute values of GLS, GCS and GRS accordingly increased during Dobutamine infusion, while GLS and GCS decreased during Verapamil. Linear regression analysis showed a moderate correlation between GLS, GCS and LV hemodynamic parameters, while GRS correlated poorly. Indexing global strain parameters for indirect measures of afterload, such as mean aortic pressure or wall stress, significantly improved these correlations, with GLS indexed for wall stress reflecting LV contractility as the clinically widespread LV ejection fraction. CONCLUSION: GLS and GCS correlate accordingly with LV hemodynamics under various inotropic states in swine. Indexing strain parameters for indirect measures of afterload substantially improves this correlation, with GLS being as good as LV ejection fraction in reflecting LV contractility. CMR-FT-strain imaging may be a quick and promising tool to characterize LV hemodynamics in patients with varying degrees of LV dysfunction.

Estimation of total collagen volume: a T1 mapping versus histological comparison study in healthy Landrace pigs.

Right ventricular biopsy represents the gold standard for the assessment of myocardial fibrosis and collagen content. This invasive technique, however, is accompanied by perioperative complications and poor reproducibility. Extracellular volume (ECV) measured through cardiovascular magnetic resonance (CMR) has emerged as a valid surrogate method to assess fibrosis non-invasively. Nonetheless, ECV provides an overestimation of collagen concentration since it also considers interstitial space. Our study aims to investigate the feasibility of estimating total collagen volume (TCV) through CMR by comparing it with the TCV measured at histology. Seven healthy Landrace pigs were acutely instrumented closed-chest and transported to the MRI facility for measurements. For each protocol, CMR imaging at 3T was acquired. MEDIS software was used to analyze T1 mapping and ECV for both the left ventricular myocardium (LVmyo) and left ventricular septum (LVseptum). ECV was then used to estimate TCVCMR at LVmyo and LVseptum following previously published formulas. Tissues were prepared following an established protocol and stained with picrosirius red to analyze the TCVhisto in LVmyo and LVseptum. TCV measured at LVmyo and LVseptum with both histology (8 ± 5 ml and 7 ± 3 ml, respectively) and T1-Mapping (9 ± 5 ml and 8 ± 6 ml, respectively) did not show any regional differences. TCVhisto and TCVCMR showed a good level of data agreement by Bland-Altman analysis. Estimation of TCV through CMR may be a promising way to non-invasively assess myocardial collagen content and may be useful to track disease progression or treatment response.

Cardiovascular magnetic resonance feature tracking in pigs: a reproducibility and sample size calculation study.

Cardiovascular magnetic resonance feature tracking (CMR-FT) is a novel technique for non-invasive assessment of myocardial motion and deformation. Although CMR-FT is standardized in humans, literature on comparative analysis from animal models is scarce. In this study, we measured the reproducibility of global strain under various inotropic states and the sample size needed to test its relative changes in pigs. Ten anesthetized healthy Landrace pigs were investigated. After baseline (BL), two further steps were performed: (I) dobutamine-induced hyper-contractility (Dob) and (II) verapamil-induced hypocontractility (Ver). Global longitudinal (GLS), circumferential (GCS) and radial strain (GRS) were assessed. This study shows a good to excellent inter- and intra-observer reproducibility of CMR-FT in pigs under various inotropic states. The highest inter-observer reproducibility was observed for GLS at both BL (ICC 0.88) and Ver (ICC 0.79). According to the sample size calculation for GLS, a small number of animals could be used for future trials.

CMR-guidance of passively tracked endomyocardial biopsy in an in vivo porcine model.

Endomyocardial biopsy (EMB) is considered to be the diagnostic gold-standard in detection of myocardial-inflammation. EMB is usually conducted under fluoroscopy without any specific target information. Specific target-information provided by cardiovascular magnetic resonance (CMR) may improve specificity of EMB. The aim was to investigate feasibility and safety of CMR-guided and targeted EMB in a preclinical-model using passively-tracked devices. Procedures were performed on a MRI-System equipped with an Interventional Software-Platform for real-time imaging. Ex vivo experiments were conducted to optimize visibility of the guide-sheath. In vivo experiments were conducted in 2 pigs for technical feasibility assessment and in 4 pigs after acute myocardial infarction to test feasibility of guided and lesion targeted EMB. For anatomical real-time imaging a single-shot-balanced-SSFP-sequence was applied. Myocardial targets were identified under real-time imaging (single-shot-T2 (sshT2) and single-shot Late-Gadolinium-Enhancement (sshLGE) sequences). Ex vivo experiments demonstrated best visibility of continuously labelled guide-sheath. CMR-guided EMB was feasible in all cases without major complications. Likewise, lesion-targeting endomyocardial biopsy was feasible in two cases. Biopsies exhibited appropriate sizes and qualities. Real-time lesion sequences revealed comparable CNR values to clinical-protocols. Real-time imaging of lesions showed following signal- and contrast-to-noise ratios (SNR/CNR): SNR of sshT2- and sshLGE was 124 ± 35 and 67 ± 51 respectively, whereas CNR was 81 ± 30 and 57 ± 44. This study demonstrates feasibility and safety of CMR-guided and basically targeted EMB with passively-tracked devices. Signal-to-noise ratios of real-time sequences is non-inferior to standard sequences for lesion detection. CMR-guidance may improve diagnostic accuracy of EMB since CMR can detect myocardial-targets under real-time-imaging.

Role of T2 mapping in left ventricular reverse remodeling after TAVR.

BACKGROUND: Patients with severe aortic stenosis (AS) are subjected to left ventricular hypertrophy (LVH) with increasing morbidity and mortality. Transcatheter aortic valve replacement (TAVR) induces reverse left ventricular remodeling which can be monitored by cardiovascular magnetic resonance (CMR). CMR is able to analyze myocardial tissue properties by magnetic relaxation times (parametric CMR). The objective of this study was to study myocardial T2 relaxation in reverse ventricular remodeling after TAVR. METHODS: Forty-three patients with severe AS (19 males, 81.9 ±â€¯4.9 years) underwent CMR with T2 mapping before and 6 months after TAVR. A cohort of age- and gender-matched volunteers served as controls. Analyzed parameters included left ventricular ejection fraction (LV-EF), mass indexed to body surface area (LVMi), interventricular septum thickness (IVS), end-diastolic volume (LVEDV), global longitudinal strain (GLS), peak diastolic strain rate (SRe) and myocardial T2 values. RESULTS: CMR characteristics for patients with AS displayed LVH concomitant to elevated myocardial T2 values, reduced GLS and SRe. Patients with T2 values above 70.2 ms at baseline were characterized by eccentric hypertrophy with reduced LV-EF. T2 values decreased after TAVR (67.4 ±â€¯3.4 to 63.3 ±â€¯4.2 ms, p < 0.01) during left ventricular remodeling. Patients with T2 values above 70.2 ms at baseline exhibited pronounced reverse remodeling which proved to be a significant predictor of LV-EF improvement and LVEDV reduction in uni- and multivariate analyses. CONCLUSIONS: Multiparametric CMR can be used to characterize myocardial hypertrophy due to severe AS and to monitor myocardial adaptations after TAVR. It may provide additional information in the prediction of left ventricular remodeling after TAVR.

T2 mapping cardiovascular magnetic resonance identifies the presence of myocardial inflammation in patients with dilated cardiomyopathy as compared to endomyocardial biopsy.

Aims: The aim of this study was to determine the value of T2 mapping for the non-invasive assessment of myocardial inflammation in different stages of systolic left ventricular dysfunction in dilated cardiomyopathy (DCM) in comparison with endomyocardial biopsy (EMB). Methods and results: A total of 132 subjects were enrolled between 2013 and 2016 (62 controls and 70 patients with DCM). All patients underwent CMR at 1.5 T and received coronary angiogram and EMB. CMR applied standard protocols including T2 mapping with Gradient And SpinEcho sequence (GRASE). Global T2 relaxation time was significantly increased in patients with DCM compared to the healthy controls (T2 time DCM vs. controls: 65.9 ± 6.2 vs. 60.0 ± 4.2 ms; P < 0.001). Of note, patients with the presence of inflammatory cells in EMB exhibited further elevation of T2 values (T2 time in patients with the presence of inflammatory cells vs. T2 time in patients without: 68.8 ± 5.8 vs. 64.7 ± 5.9 ms; P = 0.02). Receiver operating characteristic analysis of our data deciphered a global myocardial T2 time >65.3 ms as the best cut-off for distinction between the healthy controls and patients with myocardial inflammation [sensitivity 93%, specificity 90%, P < 0.01, area under the curve (AUC) 0.95]. In patients with DCM, this threshold identified patients with biopsy-proven inflammation with a sensitivity of 79% and specificity 58% (AUC 0.72). Conclusion: In patients with DCM and presence of inflammatory cells in the myocardium, myocardial T2 relaxation times may help to non-invasively detect myocardial inflammation. Although there is an overlap of T2 values between patients and healthy controls, T2 mapping may facilitate the identification of patients who may benefit from EMB for therapeutic decision-making.

Magnetic resonance guided renal denervation using active tracking: first in vivo experience in Swine.

Interventional cardiovascular magnetic resonance (iCMR) might evolve as a technique to improve procedural success rates in cardiovascular interventions by combining intraprocedural guidance and simultaneous lesion imaging. The objective of the present study was to prove feasibility and estimate safety of renal sympathetic denervation guided by real-time iCMR using active tracking. Six pigs were examined in a 1.5 T MRI-System (Achieva, Philips Healthcare, Best, Netherlands) equipped with non-invasive hemodynamic control and in-room monitors displaying an interventional software platform [Interventional MRI Suite (iSuite), Philips Research, Hamburg, Germany]. MR-guided renal denervation was performed using a MR conditional non-irrigated ablation catheter with active tracking (Imricor, Burnsville, MN, USA). Real-time imaging for device guidance was performed with a TFE sequence, vessel patency was assessed with a 3D non-contrast angiography and velocity encoded imaging. Oedema of the renal artery was visualized by a high-resolution T2 SPIR sequence. Renal sympathetic denervation was feasible in all cases with survival of all animals. Non-contrast angiography displayed renal artery patency accompanied by equal flow conditions before and after the ablation in all cases as measured by velocity encoded imaging. Oedema imaging displayed a significant increase in relative signal intensity at renal artery ablations sites pre and post intervention (p < 0.05). The histologic examination revealed no signs of perforation or bleeding, while sufficient ablation lesions could be depicted. MR-guided renal sympathetic denervation using active tracking is feasible and the initial data suggest safety of this procedure. MR-guided renal sympathetic denervation offers the inherent strength of high soft tissue contrast thereby providing target information without the use of iodinated contrast agents or radiation.

Tissue characterization by T1 and T2 mapping cardiovascular magnetic resonance imaging to monitor myocardial inflammation in healing myocarditis.

AIMS: Monitoring disease activity in myocarditis is important for tailored therapeutic strategies. This study evaluated the ability of T1 and T2 mapping cardiovascular magnetic resonance (CMR) to monitor the course of myocardial inflammation in healing myocarditis. METHODS AND RESULTS: Forty-eight patients with strictly defined acute myocarditis underwent CMR at 1.5 T in the acute stage, at 3-months (n = 39), and at 12-months follow-up (FU) (n = 21). Normal values were obtained in a control group of 27 healthy subjects. The CMR protocol included standard ('Lake-Louise') sequences as well as T1 (modified Look-Locker inversion recovery sequence, MOLLI) and T2 (gradient- and spin-echo sequence, GraSE) mapping. T1, T2, and extracellular volume (ECV) maps were generated using an OsiriX plug-in. Native myocardial T1, T2, and ECV values were increased in the acute stage, but declined with healing of myocarditis. The performances of global native T1 and T2 to differentiate acute from healed myocarditis stages were significantly better compared with all other global CMR parameters with AUCs of 0.85 (95% CI, 0.76-0.94) and 0.83 (95% CI, 0.73-0.93). Furthermore, regional native T1 and T2 in myocarditis lesions provided AUCs of 0.97 (95% CI, 0.93-1.02) and 0.93 (95% CI, 0.85-1.01), which were significantly superior to any other global or regional CMR parameter. CONCLUSION: Healing of myocarditis can be monitored by native myocardial T1 and T2 measurements without the need for contrast media. Both native myocardial T1 and T2 provide an excellent performance for assessing the stage of myocarditis by CMR.

Comparison of acquisition time and dose for late gadolinium enhancement imaging at 3.0 T in patients with chronic myocardial infarction using Gd-BOPTA.

OBJECTIVES: To compare contrast doses and acquisition times for late gadolinium enhancement (LGE) imaging at 3.0 T using gadobenate dimeglumine (Gd-BOPTA) in patients with chronic myocardial infarction. METHODS: Thirty-four patients with chronic myocardial infarction were randomised to 0.10, 0.15 and 0.20 mmol/kg of Gd-BOPTA. T1-weighted inversion recovery gradient echo sequences were performed at 5, 10, 15 and 20 min post-administration of contrast in a 3.0-T scanner. Scar-to-myocardium contrast-to-noise ratio (CNR), scar-to-blood CNR, scar size and image quality were assessed. RESULTS: Imaging at 5 min was associated with a lower scar-to-blood CNR in comparison to 10, 15 and 20 min at 0.10 mmol/kg, and in comparison to 15 and 20 min at 0.20 mmol/kg. At 0.10-mmol/kg, imaging at 5 min yielded smaller infarct sizes in comparison to 15 and 20 min. Finally, at 0.20-mmol/kg, imaging at 5 min was associated with poorer image quality in comparison to later times. CONCLUSIONS: In LGE imaging at 3.0 T, low doses of Gd-BOPTA perform equally well as higher doses. Early acquisition (5 min) is associated with lower infarct sizes and image quality. Studies with sufficient diagnostic quality can be obtained after 10 min using 0.10 mmol/kg Gd-BOPTA. KEY POINTS: Good performance of low Gd-BOPTA doses for LGE imaging at 3.0 T. Imaging at 5 min yields lower contrast, infarct sizes and image quality. Diagnostic quality can be obtained after 10 min using 0.10-mmol/kg Gd-BOPTA.

Magnetic resonance imaging of the active second stage of labour: proof of principle.

OBJECTIVE: To prove that magnetic resonance imaging of foetal anatomy during the active second stage of vaginal delivery is feasible. MATERIALS AND METHODS: Initially, five pregnant volunteers around the 30th week of gestation were examined in an open MRI. Based on the findings, one vaginal delivery was acquired under real-time imaging. To monitor the birth status during image acquisition, an MR-compatible wireless cardiotocography (CTG) system was built. Single-shot sequence parameters were optimised to compensate motion artefacts during labour. RESULTS: Safety requirements to monitor the birth process under real-time MR imaging were met. High-resolution MR images were acquired immediately before and after delivery. In one patient, TSE single-shot cinematic sequences of the active second stage of labour were obtained. All sequences were adapted to tolerate movement of the mother and infant, as well as residual noise from the CTG. Furthermore, the MR imaging during labour showed only minor image artefacts. CONCLUSION: CTG-monitored acquisition of MRI series during the active second stage of delivery is feasible. Image quality should allow various further studies to improve models for birth simulation as well as potential investigation of obstructed labour and obstetric complications.

High spatial resolution myocardial perfusion imaging during high dose dobutamine/atropine stress magnetic resonance using k-t SENSE.

PURPOSE: To prospectively evaluate the feasibility and diagnostic accuracy of high spatial resolution myocardial perfusion imaging during high dose dobutamine/atropine stress magnetic resonance (DSMR) for the detection of coronary artery disease (CAD). METHODS AND RESULTS: DSMR-wall motion was combined with perfusion imaging (DSMR-perfusion) in 78 patients prior to clinically indicated invasive coronary angiography. For DSMR-perfusion an in-plane spatial resolution of 1.5 × 1.5mm(2) was attained by using 8 × k-space and time sensitivity encoding (k-t SENSE). Image quality and extent of artifacts during perfusion imaging were evaluated. Wall motion and perfusion data were interpreted sequentially. Significant CAD (stenosis ≥ 70%) was present in 52 patients and involved 86 coronary territories. One patient did not reach target heart rate despite maximum infusion of dobutamine/atropine. Two studies (3%) were non-diagnostic due k-t SENSE related artifacts resulting from insufficient breathhold capability. Overall image quality was good. Dark-rim artifacts were limited to the endocardial border at a mean width of 1.8mm. The addition of DSMR-perfusion to DSMR-wall motion data improved sensitivity for the detection of CAD (92% vs. 81%, P=0.03) and accurate determination of disease extent (85% vs. 66% of territories, P<0.001). There were no significant differences between DSMR-perfusion and DSRM-wall motion regarding overall specificity (83% vs. 87%, P=1) and accuracy (89% vs. 83%, P=0.13). CONCLUSION: High spatial resolution DSMR-perfusion imaging at maximum stress level was feasible, improved sensitivity over DSMR-wall motion for the detection of CAD and allowed an accurate determination of disease extent. Specificity of DSMR-perfusion with k-t SENSE improved compared to prior studies using lower spatial resolution.

Value of additional myocardial perfusion imaging during dobutamine stress magnetic resonance for the assessment of intermediate coronary artery disease.

This study was performed to assess the role of additional myocardial perfusion imaging during high dose dobutamine/atropine stress magnetic resonance (DSMR-wall motion) for the evaluation of patients with intermediate (50-70%) coronary artery stenosis. Routine DSMR-wall motion was combined with perfusion imaging (DSMR-perfusion) in 174 consecutive patients with chest pain syndromes who were scheduled for a clinically indicated coronary angiography. When defining CAD as the presence of a ≥ 50% stenosis, the addition of perfusion imaging improved sensitivity (90 vs. 79%, P < 0.001) with a non-significant reduction in specificity (85 vs. 90%, P = 0.13) and an improvement in overall diagnostic accuracy (88 vs. 84%, P = 0.008). Adding perfusion imaging improved sensitivity in patients with intermediate stenosis (87 vs. 72%, P = 0.03), but not in patients with severe (≥70%) stenosis (93 vs. 84%, P = 0.06). In patients with severe stenosis specificity of DSMR-perfusion versus DSMR-wall motion decreased (61 vs 70%, P = 0.001) resulting in a lower overall accuracy (71 vs 74%, P = 0.03). Using a cutoff of ≥50% for the definition of CAD, sensitivity of DSMR-perfusion compared to DSMR-wall motion was significantly higher in patients with single vessel (88 vs. 77%, P = 0.03) and multi vessel disease (93 vs. 79%, P = 0.03), whereas no significant differences were found using a cutoff of ≥70% stenosis for the definition of CAD. The addition of perfusion imaging during DSMR-wall motion improved the sensitivity in patients with intermediate coronary artery stenosis. Overall diagnostic accuracy increased only when defining CAD as ≥50% stenosis. In patients with ≥70% stenosis DSMR-wall motion alone had higher accuracy due to more false-positive cases with DSMR-perfusion.

MR-guided discography using an open 1 Tesla MRI system.

OBJECTIVE: To evaluate the feasibility of MR-guided discography using an open 1 Tesla MRI system. METHODS: 48 disc segments of 41 patients scheduled for intradiscal thermal treatment, total disc replacement or spondylodesis were examined. A 1.0-T open MRI was used for instrument guidance and imaging. After primary disc puncture under guidance of interactive PDw TSE imaging, 1-2 ml of gadolinium contrast saline mixture was injected into the disc. The occurrence of memory pain during injection was recorded. Axial and sagittal T1w TSE images with and without fat saturation were obtained. All MRI discograms were analysed by two readers, who were blinded to the clinical findings. RESULTS: Overall, the placement of the puncture needle in the targeted disc was accurate under real-time MR guidance. Injections were technically successful in all cases. No major complications occurred. The mean procedure time was 17 min (range 13-34 min). Image quality of contrast-enhanced MR discograms was excellent when using an optimized gadolinium contrast saline mixture of 1:600. Memory pain was detected in 16 out of 48 affected segments. CONCLUSION: MR-guided discography is accurate and safe. Multiplanar dynamic imaging facilitates the puncture of discs and provides high-quality MR discograms.

Screening for atherosclerotic plaques in the abdominal aorta in high-risk patients with multicontrast-weighted MRI: a prospective study at 3.0 and 1.5 tesla.

OBJECTIVE: This prospective study compares MRI of atherosclerotic plaque in the abdominal aorta at 3 T with that at 1.5 T in patients suffering from hereditary hyperlipidaemia, a major risk factor for atherosclerosis. METHODS: MRI of the abdominal aorta at 1.5 and 3 T was performed in 21 patients (mean age 58 years). The study protocol consisted of proton density (PD), T(1), T(2) and fat-saturated T(2) weighted black blood images of the abdominal aorta in corresponding orientation. Two independent radiologists performed image rating. First, image quality was rated on a five-point scale. Second, atherosclerotic plaques were scored according to the modified American Heart Association (AHA) classification and analysed for field strength-related differences. Weighted κ statistics were calculated to assess interobserver agreement. RESULTS: Interobserver agreement was substantial for nearly all categories. MRI at 3 T offered superior image quality in all contrast weightings, most significantly in T(1) and T(2) weighted techniques. Plaque burden in the study collective was unexpectedly moderate. The majority of plaques were classified as AHA III lesions; no lesions were classified above AHA V. There was no significant influence of the field strength regarding the AHA classification. CONCLUSION: Abdominal aortal plaque screening is basically feasible at both field strengths, whereas the image quality is rated superior at 3 T. However, the role of the method in clinical practice remains uncertain, since substantial findings in the high-risk collective were scarce.

Dobutamine stress magnetic resonance imaging for the detection of coronary artery disease in women.

BACKGROUND: Dobutamine stress magnetic resonance (DSMR) imaging represents an excellent imaging approach for the detection of coronary artery disease (CAD). However, most studies have predominantly reported the utility of DSMR in men. OBJECTIVE: To evaluate the diagnostic value of DSMR in men and women. METHODS AND RESULTS: High-dose dobutamine/atropine stress magnetic resonance imaging was performed and new or worsening wall motion abnormalities evaluated in 745 consecutive patients (204 women, 541 men). Invasive coronary angiography was performed within 30 days and served as the reference standard (> or =70% stenosis). DSMR was technically successful and had diagnostic image quality in all patients except one woman and three men (p=NS). In the absence of ischaemia, target heart rate was not reached in 9.3% of women and 8.5% of men (P=NS) despite maximum pharmacological infusion (1% and 2.2%, respectively, p=NS) or owing to limiting side effects (8.3% and 6.3%, respectively, p=NS). Diagnostic values (sensitivity/specificity/accuracy) for the detection of significant coronary stenoses were similar for men (86%/83%/85%) and women (85%/86%/85%). There was no gender-based difference in regional diagnostic accuracy of DSMR for all three coronary vascular territories in patients with single-vessel CAD (81% vs 81%, p=NS, respectively). CONCLUSION: The diagnostic capability of DSMR for the detection of haemodynamically relevant, obstructive CAD is independent of gender.

Dobutamine stress cardiovascular magnetic resonance at 3 Tesla.

PURPOSE: The assessment of inducible wall motion abnormalities during high-dose dobutamine-stress cardiovascular magnetic resonance (DCMR) is well established for the identification of myocardial ischemia at 1.5 Tesla. Its feasibility at higher field strengths has not been reported. The present study was performed to prospectively determine the feasibility and diagnostic accuracy of DCMR at 3 Tesla for depicting hemodynamically significant coronary artery stenosis (> or = 50% diameter stenosis) in patients with suspected or known coronary artery disease (CAD). MATERIALS AND METHODS: Thirty consecutive patients (6 women) (66 +/- 9.3 years) were scheduled for DCMR between January and May 2007 for detection of coronary artery disease. Patients were examined with a Philips Achieva 3 Tesla system (Philips Healthcare, Best, The Netherlands), using a spoiled gradient echo cine sequence. Technical parameters were: spatial resolution 2 x 2 x 8 mm3, 30 heart phases, spoiled gradient echo TR/TE: 4.5/2.6 msec, flip angle 15 degrees . Images were acquired at rest and stress in accordance with a standardized high-dose dobutamine-atropine protocol during short breath-holds in three short and three long-axis views. Dobutamine was administered using a standard protocol (10 microg increments every 3 minutes up to 40 microg dobutamine/kg body weight/minute plus atropine if required to reach target heart rate). The study protocol included administration of 0.1 mmol/kg/body weight Gd-DTPA before the cine images at rest were acquired to improve the image quality. The examination was terminated if new or worsening wall-motion abnormalities or chest pain occurred or when > 85% of age-predicted maximum heart rate was reached. Myocardial ischemia was defined as new onset of wall-motion abnormality in at least one segment. In addition, late gadolinium enhancement (LGE) was performed. Images were evaluated by two blinded readers. Diagnostic accuracy was determined with coronary angiography as the reference standard. Image quality and wall-motion at rest and maximum stress level were evaluated using a four-point scale. RESULTS: In 27 patients DCMR was performed successfully, no patient had to be excluded due to insufficient image quality. Twenty-two patients were examined by coronary angiography, which depicted significant stenosis in 68.2% of the patients. Patient-based sensitivity and specificity were 80.0% and 85.7% respectively and accuracy was 81.8%. Interobserver variability for assessment of wall motion abnormalities was 88% (kappa = 0.760; p < 0.0001). Negative and positive predictive values were 66.7% and 92.3%, respectively. No significant differences in average image quality at rest versus stress for short or long-axis cine images were found. CONCLUSION: High-dose DCMR at 3T is feasible and an accurate method to depict significant coronary artery stenosis in patients with suspected or known CAD.

MR coronary artery imaging with 3D motion adapted gating (MAG) in comparison to a standard prospective navigator technique.

Magnetic resonance coronary angiography (MRCA) has been proven to be feasible for imaging of the proximal and medial portions of the three main coronary arteries. Free breathing techniques allow for high resolution imaging but prolong scan time. This could potentially be shortened by improving the efficiency, robustness and accuracy of the navigator gating algorithm. Aim of this study was to determine the feasibility, efficiency, and image quality of a new motion compensation algorithm (3D-MAG) for coronary artery imaging with navigator techniques. In 21 patients the coronaries were imaged in plane with a 3D k-space segmented gradient echo sequence. A T2 preparation prepulse was used for suppression of myocardial signal, during free breathing and a navigator technique with using real time slice following and a gating window of 5 mm was applied to suppress breathing motion artefacts. Imaging was performed with standard gating and compared to 3D-MAG. Image quality was visually compared, contrast-to-noise and signal-to-noise ratio were calculated, the length of visualized coronary arteries was measured and scan duration and scan efficiency were calculated. Standard navigator imaging was feasible in 19 of 21 (90.5%) patients 3D-MAG in 21/21 (100%). Scan efficiency and duration was significantly improved with 3D-MAG (p < .05) without change in image quality. 3D-MAG is superior to conventional navigator correction algorithms. It improves feasibility and scan efficiency without reduction of image quality. This approach should be routinely used for MR coronary artery imaging with navigator techniques.

Cardiac magnetic resonance imaging: long term reproducibility of the late enhancement signal in patients with chronic coronary artery disease.

OBJECTIVE: To determine long term reproducibility of the late enhancement (LE) signal in contrast enhanced magnetic resonance imaging (MRI) and potential changes of the signal after revascularisation. METHODS: 33 patients (29 men, mean (SD) 61 (11) years) with coronary artery disease (CAD) and left ventricular dysfunction (ejection fraction 30 (7)%) underwent two contrast enhanced MRI procedures within 9 (3) months. Fifteen patients (group A: 14 men, 59 (12) years) had no interventions between the two studies. Eighteen patients underwent revascularisation after MRI 1 (group B: 15 men, 62 (9) years). Changes in the LE signal between the first and second MRIs were investigated in both groups as well as intraobserver and interobserver variabilities for delineation of the signal. RESULTS: The LE signal was highly reproducible in groups A and B for segmental analysis (concordance 86% v 82%, respectively; kappa = 0.70 v 0.67) and summed scores (group A: r = 0.97, p < 0.001; group B: r = 0.93, p < 0.001). The LE signal was quantified as 27 (27) cm3 in group A versus 30 (16) cm3 in group B in the first MRI and 26 (25) cm3 versus 30 (15) cm3, respectively, for the second MRI (both not significant). Moreover, low intraobserver and interobserver variabilities were observed in segmental analysis (kappa = 0.86 and 0.74, respectively, for group A, and kappa = 0.87 and 0.82, respectively, for group B). CONCLUSION: In patients with chronic CAD, the LE signal in contrast enhanced MRI is very stable over an extended time period. These results further characterise contrast enhanced MRI as a useful tool for myocardial viability assessment. Low intraobserver and interobserver variabilities promise robustness of the method for clinical application.

Determinants of myocardial response in CMR perfusion imaging using Gd-BOPTA (Multihance).

PURPOSE: Different centers and vendors use different sequences and contrast agent application schemes for MR myocardial perfusion imaging. The purpose of this study was to evaluate the role of different sequences, dosages, and injection speeds of contrast media for semiquantitative MR-perfusion assessment. METHODS: In a pilot study with 58 consecutive patients three of the most commonly used sequences for MR myocardial perfusion imaging (T1-GrE, GrE-EPI or SSFP) were compared to each other in terms of peak myocardial enhancement and image quality. For the main part of the study dynamic first pass MR perfusion imaging (Philips Intera CV, Best, Tthe Netherlands) was performed in 24 patients using the most favorable sequence from the pilot study (SSFP) after peripheral i.v. administration of Gd-BOPTA during adenosine stress. Two doses (0.05 mmol/kg bw and 0.025 mmol/kg bw) and four different injection speeds (8, 4, 3, 2 ml/s) were used. Signal intensity time curves were determined in the LV and myocardial segments supplied by normal coronary arteries and correlation between LV and myocardial upslope as well as peak enhancement were noted. RESULTS: The SSFP-sequence showed a higher peak enhancement when using 0.05 mmol/kg bw of Gd-BOPTA and a superior image quality for both dosage regimen compared with the other sequences and was consequently applied for the main study. A significant correlation was found between the upslopes in the LV and the myocardium (r square = 0.85, p < 0.001). However, LV and myocardial upslopes were largely independent of the dosage. Myocardial upslope was significantly slower at an injection rate of 2 ml/s compared to 3 and 4 ml/s. Higher Gd-doses led to significantly higher enhancement (p < 0.001). CONCLUSION: In healthy myocardial segments, the myocardial upslope is mainly determined from the LV upslope. Both myocardial enhancement and upslope are largely independent from the injection rate of a contrast agent bolus as long as the injection speed is not below 3 ml/s. Myocardial enhancement, however, is dose dependent. Thus, a simple correction for LV upslope allows to normalize a wide variety of input parameters. Differences of myocardial upslope or peak signal intensity after correction should be mainly dependent on blood flow.