Cardiac magnetic resonance T2 mapping and feature tracking in athlete's heart and HCM.

OBJECTIVES: Distinguishing hypertrophic cardiomyopathy (HCM) from left ventricular hypertrophy (LVH) due to systematic training (athlete's heart, AH) from morphologic assessment remains challenging. The purpose of this study was to examine the role of T2 mapping and deformation imaging obtained by cardiovascular magnetic resonance (CMR) to discriminate AH from HCM with (HOCM) or without outflow tract obstruction (HNCM). METHODS: Thirty-three patients with HOCM, 9 with HNCM, 13 strength-trained athletes as well as individual age- and gender-matched controls received CMR. For T2 mapping, GRASE-derived multi-echo images were obtained and analyzed using dedicated software. Besides T2 mapping analyses, left ventricular (LV) dimensional and functional parameters were obtained including LV mass per body surface area (LVMi), interventricular septum thickness (IVS), and global longitudinal strain (GLS). RESULTS: While LVMi was not significantly different, IVS was thickened in HOCM patients compared to athlete's. Absolute values of GLS were significantly increased in patients with HOCM/HNCM compared to AH. Median T2 values were elevated compared to controls except in athlete's heart. ROC analysis revealed T2 values (AUC 0.78) and GLS (AUC 0.91) as good parameters to discriminate AH from overall HNCM/HOCM. CONCLUSION: Discrimination of pathologic from non-pathologic LVH has implications for risk assessment of competitive sports in athletes. Multiparametric CMR with parametric T2 mapping and deformation imaging may add information to distinguish AH from LVH due to HCM. KEY POINTS: • Structural analyses using T2 mapping cardiovascular magnetic resonance imaging (CMR) may help to further distinguish myocardial diseases. • To differentiate pathologic from non-pathologic left ventricular hypertrophy, CMR including T2 mapping was obtained in patients with hypertrophic obstructive/non-obstructive cardiomyopathy (HOCM/HNCM) as well as in strength-trained athletes. • Elevated median T2 values in HOCM/HNCM compared with athlete's may add information to distinguish athlete's heart from pathologic left ventricular hypertrophy.

Strain-encoded cardiac magnetic resonance imaging: a new approach for fast estimation of left ventricular function.

BACKGROUND: Recently introduced fast strain-encoded (SENC) cardiac magnetic resonance (CMR) imaging (fast-SENC) provides real-time acquisition of myocardial performance in a single heartbeat. We aimed to test the ability and accuracy of real-time strain-encoded CMR imaging to estimate left ventricular volumes, ejection fraction and mass. METHODS: Thirty-five subjects (12 healthy volunteers and 23 patients with known or suspected coronary artery disease) were investigated. All study participants were imaged at 1.5 Tesla MRI scanner (Achieva, Philips) using an advanced CMR study protocol which included conventional cine and fast-SENC imaging. A newly developed real-time free-breathing SENC imaging technique based on the acquisition of two images with different frequency modulation was employed. RESULTS: All parameters were successfully derived from fast-SENC images with total study time of 105 s (a 15 s scan time and a 90 s post-processing time). There was no significant difference between fast-SENC and cine imaging in the estimation of LV volumes and EF, whereas fast-SENC underestimated LV end-diastolic mass by 7%. CONCLUSION: The single heartbeat fast-SENC technique can be used as a good alternative to cine imaging for the precise calculation of LV volumes and ejection fraction while the technique significantly underestimates LV end-diastolic mass.

Feasibility study of MR-guided transgluteal targeted in-bore biopsy for suspicious lesions of the prostate at 3 Tesla using a freehand approach.

OBJECTIVE: The aim of our study was (1) to establish an in-bore targeted biopsy of suspicious prostate lesions, avoiding bowel penetration using a transgluteal approach and (2) to assess operator setup, patient comfort and safety aspects in the clinical setting for freehand real-time MR-guidance established for percutaneous procedures in an open MR-scanner. MATERIAL AND METHODS: 30 patients with suspect prostate lesions were biopsied in a cylindrical 3T-MRI system using a transgluteal approach in freehand technique. One to three biopsies were sampled using continuous dynamic imaging. Size, location and visibility of the lesion, intervention time, needle artefact size, interventional complications and histopathological diagnosis were recorded. RESULTS: All biopsies were technically successful. Nineteen patients showed evidence of prostate carcinoma. Cancer detection rate was 50 % in patients with previously negative TRUS-biopsy. The average intervention time was 26 min including a learning curve as the time was 13 min by the end of the study. No antibiotic prophylaxis was performed as none of the patients showed signs of infection. CONCLUSIONS: MR-guided targeted freehand biopsies of prostate lesions using a transgluteal approach are both technically feasible and time efficient in a standard closed-bore 3T-MR scanner as well as safe for the individual patient. KEY POINTS: • Open-bore freehand interventional principles were adapted to closed-bore systems. • Prostate MR-guided freehand biopsies were feasible in a clinical setting. • A transgluteal approach provides a short and simplified work flow. • An inoculation of the prostate with bowel flora is avoided. • The intervention time is comparable to the stereotactic approach.

Artefact-free late gadolinium enhancement imaging in patients with implanted cardiac devices using a modified broadband sequence: current strategies and results from a real-world patient cohort.

Aims: Cardiac magnetic resonance (CMR) imaging in patients with implanted cardiac devices is often limited by device-related imaging artefacts. Limitations can potentially be overcome by employing a broadband late gadolinium enhancement (LGE)-CMR imaging technique. The purpose of this study was to investigate the relationship between implanted cardiac devices and the optimal frequency offset on broadband LGE-CMR imaging to increase the artefact-free visibility of myocardial segments. Methods and results: A phantom study was performed to characterize magnetic field disturbances related to 15 different cardiac devices. This was complemented by B0 and B1+ imaging of three different device types in four healthy volunteers. Findings were validated in 28 patients with an indication for arrhythmogenic substrate characterization before catheter ablation. In the phantom study, the placement of a PM, implantable cardioverter-defibrillator (ICD) or CRT-D generator led to a significant impairment of the radiofrequency field. B0 mapping in phantom and volunteers showed the highest off-resonance maximum with CRT-D systems with the maximum off-resonance significantly decreasing for ICD or PM systems, respectively. In all patients, with conventional LGE imaging 73.1% (61.5-92.3%) of LV segments were free of device-related artefacts, while with the broadband LGE technique, a significant increase of artefact-free segments was achieved [96.4% (85.7-100%); P = 0.00008]. Conclusion: Using a modified broadband sequence for LGE imaging significantly increased the number of artefact-free myocardial segments thereby leading to improved diagnostic value of the CMR exam. Since the occurrence and extent of hyperintensity artefacts are closely related to the individual device, more studies are warranted to evaluate if the results can be extrapolated to other devices and manufacturers.

CMR stress testing in a patient with morbid obesity (BMI 58 kg/m2) and suspected coronary artery disease.

BACKGROUND: Severe obesity is asscociated with an increased risk of coronary artery disease (CAD) but non-invasive cardiac imaging modalities have important technical limits. CASE PRESENTATION: We report a case of a 58-year old patient with suspected CAD and severely elevated BMI of 58 kg/m2. CONCLUSIONS: Stress-CMR was able to non-invasively stratify risk with good imaging quality despite the body dimensions of the patient.

Fatty metaplasia quantification and impact on regional myocardial function as assessed by advanced cardiac MR imaging.

OBJECTIVE: This study aimed to investigate the advantages of recently developed cardiac imaging techniques of fat-water separation and feature tracking to characterize better individuals with chronic myocardial infarction (MI). MATERIALS AND METHODS: Twenty patients who had a previous MI underwent CMR imaging. The study protocol included routine cine and late gadolinium enhancement (LGE) technique. In addition, mDixon LGE imaging was performed in every patient. Left ventricular (LV) circumferential (EccLV) and radial (ErrLV) strain were calculated using dedicated software (CMR42, Circle, Calgary, Canada). The extent of global scar was measured in LGE and fat-water separated images to compare conventional and recent CMR imaging techniques. RESULTS: The infarct size derived from conventional LGE and fat-water separated images was similar. However, detection of lipomatous metaplasia was only possible with mDixon imaging. Subjects with fat deposition demonstrated a significantly smaller percentage of fibrosis than those without fat (10.68 ± 5.07% vs. 13.83 ± 6.30%; p = 0.005). There was no significant difference in EccLV or ErrLV between myocardial segments containing fibrosis only and fibrosis with fat. However, EccLV and ErrLV values were significantly higher in myocardial segments adjacent to fibrosis with fat deposition than in those adjacent to LGE only. CONCLUSIONS: Advanced CMR imaging ensures more detailed tissue characterization in patients with chronic MI without a relevant increase in imaging and post-processing time. Fatty metaplasia may influence regional myocardial deformation especially in the myocardial segments adjacent to scar tissue. A simplified and shortened myocardial viability CMR protocol might be useful to better characterize and stratify patients with chronic MI.

Acute versus Chronic Myocardial Infarction: Diagnostic Accuracy of Quantitative Native T1 and T2 Mapping versus Assessment of Edema on Standard T2-weighted Cardiovascular MR Images for Differentiation.

Purpose To analyze the diagnostic accuracy of native T1 and T2 mapping compared with visual and quantitative assessment of edema on T2-weighted cardiac magnetic resonance (MR) images to differentiate between acute and chronic myocardial infarction. Materials and Methods This study had institutional ethics committee approval. Written informed consent was obtained from 67 consecutive patients (57 years ± 12; 78% men) with a first acute myocardial infarction, who were prospectively enrolled between April 2011 and June 2015. Four serial 1.5-T MR imaging examinations were performed at 8 days ± 5, 7 weeks ± 2, 3 months ± 0.5, and 6 months ± 1.4 after infarction and included T2-weighted, native T1/T2 mapping, and late gadolinium enhancement MR imaging. Complete follow-up data were obtained in 42 patients. Regional native T1/T2 relaxation time, T2-weighted ratio, and extracellular volume were serially measured in infarcted and remote myocardium. Receiver operating characteristic (ROC) analysis was used to determine the diagnostic accuracy of the MR imaging parameters for discriminating between acute and chronic myocardial infarction. Results Native T1 of infarcted myocardium decreased from 1286 msec ± 99 at baseline to 1077 msec ± 50 at 6 months (P < .0001), whereas T2 decreased from 84 msec ± 10 to 58 msec ± 4 (P < .0001). The T2-weighted ratio decreased from 4.1 ± 1.0 to 2.4 ± 0.6 (P < .0001). Of all the MR imaging parameters obtained, native T1 and T2 yielded the best areas under the ROC curve (AUCs) of 0.975 and 0.979, respectively, for differentiating between acute and chronic myocardial infarction. Visual analysis of the presence of edema at standard T2-weighted cardiac MR imaging resulted in an inferior AUC of 0.863 (P < .01). Conclusion Native T1 and T2 of infarcted myocardium are excellent discriminators between acute and chronic myocardial infarction and are superior to all other MR imaging parameters. Online supplemental material is available for this article.

Re-evaluation of a novel approach for quantitative myocardial oedema detection by analysing tissue inhomogeneity in acute myocarditis using T2-mapping.

OBJECTIVES: To re-evaluate a recently suggested approach of quantifying myocardial oedema and increased tissue inhomogeneity in myocarditis by T2-mapping. METHODS: Cardiac magnetic resonance data of 99 patients with myocarditis were retrospectively analysed. Thirthy healthy volunteers served as controls. T2-mapping data were acquired at 1.5 T using a gradient-spin-echo T2-mapping sequence. T2-maps were segmented according to the 16-segments AHA-model. Segmental T2-values, segmental pixel-standard deviation (SD) and the derived parameters maxT2, maxSD and madSD were analysed and compared to the established Lake Louise criteria (LLC). RESULTS: A re-estimation of logistic regression models revealed that all models containing an SD-parameter were superior to any model containing global myocardial T2. Using a combined cut-off of 1.8 ms for madSD + 68 ms for maxT2 resulted in a diagnostic sensitivity of 75% and specificity of 80% and showed a similar diagnostic performance compared to LLC in receiver-operating-curve analyses. Combining madSD, maxT2 and late gadolinium enhancement (LGE) in a model resulted in a superior diagnostic performance compared to LLC (sensitivity 93%, specificity 83%). CONCLUSIONS: The results show that the novel T2-mapping-derived parameters exhibit an additional diagnostic value over LGE with the inherent potential to overcome the current limitations of T2-mapping. KEY POINTS: • A novel quantitative approach to myocardial oedema imaging in myocarditis was re-evaluated. • The T2-mapping-derived parameters maxT2 and madSD were compared to traditional Lake-Louise criteria. • Using maxT2 and madSD with dedicated cut-offs performs similarly to Lake-Louise criteria. • Adding maxT2 and madSD to LGE results in further increased diagnostic performance. • This novel approach has the potential to overcome the limitations of T2-mapping.

Magnetic resonance imaging guided transatrial electrophysiological studies in swine using active catheter tracking - experience with 14 cases.

OBJECTIVES: To evaluate the feasibility of performing comprehensive Cardiac Magnetic resonance (CMR) guided electrophysiological (EP) interventions in a porcine model encompassing left atrial access. METHODS: After introduction of two femoral sheaths 14 swine (41 ± 3.6 kg) were transferred to a 1.5 T MR scanner. A three-dimensional whole-heart sequence was acquired followed by segmentation and the visualization of all heart chambers using an image-guidance platform. Two MR conditional catheters were inserted. The interventional protocol consisted of intubation of the coronary sinus, activation mapping, transseptal left atrial access (n = 4), generation of ablation lesions and eventually ablation of the atrioventricular (AV) node. For visualization of the catheter tip active tracking was used. Catheter positions were confirmed by passive real-time imaging. RESULTS: Total procedure time was 169 ± 51 minutes. The protocol could be completed in 12 swine. Two swine died from AV-ablation induced ventricular fibrillation. Catheters could be visualized and navigated under active tracking almost exclusively. The position of the catheter tips as visualized by active tracking could reliably be confirmed with passive catheter imaging. CONCLUSIONS: Comprehensive CMR-guided EP interventions including left atrial access are feasible in swine using active catheter tracking. KEY POINTS: • Comprehensive CMR-guided electrophysiological interventions including LA access were conducted in swine. • Active catheter-tracking allows efficient catheter navigation also in a transseptal approach. • More MR-conditional tools are needed to facilitate left atrial interventions in humans.

A novel multiparametric imaging approach to acute myocarditis using T2-mapping and CMR feature tracking.

BACKGROUND: The aim of this study was to evaluate the diagnostic potential of a novel cardiovascular magnetic resonance (CMR) based multiparametric imaging approach in suspected myocarditis and to compare it to traditional Lake Louise criteria (LLC). METHODS: CMR data from 67 patients with suspected acute myocarditis were retrospectively analyzed. Seventeen age- and gender-matched healthy subjects served as control. T2-mapping data were acquired using a Gradient-Spin-Echo T2-mapping sequence in short-axis orientation. T2-maps were segmented according to the 16-segments AHA-model and segmental T2 values and pixel-standard deviation (SD) were recorded. Afterwards, the parameters maxT2 (the highest segmental T2 value) and madSD (the mean absolute deviation (MAD) of the pixel-SDs) were calculated for each subject. Cine sequences in three long axes and a stack of short-axis views covering the left and right ventricle were analyzed using a dedicated feature tracking algorithm. RESULTS: A multiparametric imaging model containing madSD and LV global circumferential strain (GCSLV) resulted in the highest diagnostic performance in receiver operating curve analyses (area under the curve [AUC] 0.84) when compared to any model containing a single imaging parameter or to LLC (AUC 0.79). Adding late gadolinium enhancement (LGE) to the model resulted in a further increased diagnostic performance (AUC 0.93) and yielded the highest diagnostic sensitivity of 97% and specificity of 77%. CONCLUSIONS: A multiparametric CMR imaging model including the novel T2-mapping derived parameter madSD, the feature tracking derived strain parameter GCSLV and LGE yields superior diagnostic sensitivity in suspected acute myocarditis when compared to any imaging parameter alone and to LLC.

Abnormal T2 mapping cardiovascular magnetic resonance correlates with adverse clinical outcome in patients with suspected acute myocarditis.

BACKGROUND: While most patients recover from suspected acute myocarditis (sAMC) some develop progressive disease with 5-year mortality up to 20%. Recently, parametric Cardiovascular Magnetic Resonance (CMR) approaches, quantifying native T1 and T2 relaxation time, have demonstrated the ability to increase diagnostic accuracy. However, prognostic implications of T2 values in this cohort are unknown. The purpose of the study was to investigate the prognostic relevance of elevated CMR T2 values in patients with sAMC. METHODS AND RESULTS: We carried out a prospective study in 46 patients with sAMC defined by current ESC recommendations. A combined endpoint was defined by the occurrence of at least one major adverse cardiac event (MACE) and hospitalisation for heart failure. Event rate was 24% (n = 11) for 1-year-MACE and hospitalisation. A follow-up after 11 ± 7 months was performed in 98% of the patients. Global T2 values were significantly increased at acute stage of disease compared to controls and decreased over time. During acute disease, elevated global T2 time (odds ratio 6.3, p < 0.02) as well as myocardial fraction with T2 time >80 ms (odds ratio 4.9, p < 0.04) predicted occurrence of the combined endpoint. Patients with clinical recovery revealed significantly decreased T2 relaxation times at follow-up examinations; however, T2 values were still elevated compared to healthy controls. CONCLUSION: Assessment of myocardial T2 relaxation times at initial presentation facilitates CMR-based risk stratification in patients with acute myocarditis. T2 Mapping may emerge as a new tool to monitor inflammatory myocardial injuries during the course of disease.

Cardiac Magnetic Resonance Imaging Using an Open 1.0T MR Platform: A Comparative Study with a 1.5T Tunnel System.

BACKGROUND: Cardiac magnetic resonance imaging (cMRI) has become the non-invasive reference standard for the evaluation of cardiac function and viability. The introduction of open, high-field, 1.0T (HFO) MR scanners offers advantages for examinations of obese, claustrophobic and paediatric patients.The aim of our study was to compare standard cMRI sequences from an HFO scanner and those from a cylindrical, 1.5T MR system. MATERIAL/METHOD: Fifteen volunteers underwent cMRI both in an open HFO and in a cylindrical MR system. The protocol consisted of cine and unenhanced tissue sequences. The signal-to-noise ratio (SNR) for each sequence and blood-myocardium contrast for the cine sequences were assessed. Image quality and artefacts were rated. The location and number of non-diagnostic segments was determined. Volunteers' tolerance to examinations in both scanners was investigated. RESULTS: SNR was significantly lower in the HFO scanner (all p<0.001). However, the contrast of the cine sequence was significantly higher in the HFO platform compared to the 1.5T MR scanner (0.685±0.41 vs. 0.611±0.54; p<0.001). Image quality was comparable for all sequences (all p>0.05). Overall, only few non-diagnostic myocardial segments were recorded: 6/960 (0.6%) by the HFO and 17/960 (1.8%) segments by the cylindrical system. The volunteers expressed a preference for the open MR system (p<0.01). CONCLUSIONS: Standard cardiac MRI sequences in an HFO platform offer a high image quality that is comparable to the quality of images acquired in a cylindrical 1.5T MR scanner. An open scanner design may potentially improve tolerance of cardiac MRI and therefore allow to examine an even broader patient spectrum.

Reproducibility of three different cardiac T2 -mapping sequences at 1.5T.

PURPOSE: To elucidate the impact of technical and intraindividual reproducibility on the overall variability of myocardial T2 relaxation times. MATERIALS AND METHODS: Thirty healthy volunteers were examined three times (day 1 morning/evening, evening after 2-3 weeks) at 1.5T. During each examination three different T2 -mapping sequences were acquired twice at three slices in short axis view: multi-echo-spin-echo (MESE), T2 -prepared balanced steady-state free precession (SSFP) (T2 prep), and gradient-spin-echo with and without fat saturation (GraSE/GraSEFS ). Repeated measurements were performed for T2 prep and GraSE. Segmented T2 -maps were generated for each slice according to the American Heart Association (AHA) 16-segment model. RESULTS: The coefficients of variation and intraclass correlation coefficients for intraobserver variability were: 1.3% and 0.89 for T2 prep, 1.5% and 0.93 for GraSE, 3.1% and 0.83 for MESE; and for interobserver variability: 3.3% and 0.66 for T2 prep, 2.0% and 0.83 for GraSE, 3.6% and 0.77 for MESE. No systematic difference of T2 times was observed due to diurnal effects and on long-term analysis using one-way analysis of variance (ANOVA) with Tukey-type multiple comparisons (morning vs. evening scan for T2 prep: 52.5 ± 2.4 vs. 51.7 ± 2.7 msec, P = 0.119; for GraSE: 58.6 ± 4.0 vs. 58.5 ± 3.8 msec, P = 0.984; for GraSEFS 57.1 ± 3.2 vs. 57.2 ± 3.9 msec, P = 0.998, and for MESE: 53.8 ± 2.7 vs. 53.3 ± 3.3 msec, P = 0.541; scans between weeks for T2 prep: 51.7 ± 2.7 vs. 51.4 ± 2.4 msec, P = 0.873; for GraSE: 58.5 ± 3.8 vs. 58.1 ± 3.4 msec, P = 0.736; for GraSEFS : 57.2 ± 3.9 vs. 57.0 ± 4.6 msec, P = 0.964, and for MESE: 53.3 ± 3.3 vs. 53.4 ± 2.4 msec, P = 0.970). ANOVA components, however, demonstrated a greater variance of T2 times over multiple timepoints than for repeated measurements within the same scan (variance components of the model fit for intraday variance vs. repeated measurements: T2 prep 2.22 vs. 1.36, GraSE 3.76 vs. 2.09, GraSEFS 3.96 vs. 1.58, MESE 1.86; and for interweeks variance vs. repeated measurements: T2 prep 2.21 vs. 0.80, GraSE 3.20 vs. 2.10, GraSEFS 8.82 vs. 1.18, and MESE 4.49). CONCLUSION: Technical reproducibility and intra- and interobserver agreement of myocardial T2 relaxation times are excellent and intraindividual variation over time is small. Therefore, we consider subject-related factors to explain most of the interindividual variability of myocardial T2 times reported in previous studies. The acknowledgment of this subject-related, biological variability may be important for the future diagnostic value of T2 -mapping. J. Magn. Reson. Imaging 2016;44:1168-1178.

Real-time magnetic resonance-guided ablation of typical right atrial flutter using a combination of active catheter tracking and passive catheter visualization in man: initial results from a consecutive patient series.

AIMS: Recently cardiac magnetic resonance (CMR) imaging has been found feasible for the visualization of the underlying substrate for cardiac arrhythmias as well as for the visualization of cardiac catheters for diagnostic and ablation procedures. Real-time CMR-guided cavotricuspid isthmus ablation was performed in a series of six patients using a combination of active catheter tracking and catheter visualization using real-time MR imaging. METHODS AND RESULTS: Cardiac magnetic resonance utilizing a 1.5 T system was performed in patients under deep propofol sedation. A three-dimensional-whole-heart sequence with navigator technique and a fast automated segmentation algorithm was used for online segmentation of all cardiac chambers, which were thereafter displayed on a dedicated image guidance platform. In three out of six patients complete isthmus block could be achieved in the MR scanner, two of these patients did not need any additional fluoroscopy. In the first patient technical issues called for a completion of the procedure in a conventional laboratory, in another two patients the isthmus was partially blocked by magnetic resonance imaging (MRI)-guided ablation. The mean procedural time for the MR procedure was 109 ± 58 min. The intubation of the CS was performed within a mean time of 2.75 ± 2.21 min. Total fluoroscopy time for completion of the isthmus block ranged from 0 to 7.5 min. CONCLUSION: The combination of active catheter tracking and passive real-time visualization in CMR-guided electrophysiologic (EP) studies using advanced interventional hardware and software was safe and enabled efficient navigation, mapping, and ablation. These cases demonstrate significant progress in the development of MR-guided EP procedures.

High-dose dobutamine stress steady-state free precession (SSFP) cine MRI at 3T with patient adaptive local radiofrequency (RF) shimming using dual-source RF transmission.

PURPOSE: To prospectively assess the feasibility, image quality, and diagnostic accuracy of high-dose dobutamine stress magnetic resonance imaging (DSMR) using steady-state free precession (SSFP) cine imaging at 3T applying a dual-source radiofrequency (RF) excitation magnetic resonance imaging (MRI) system with parallel transmission and patient adaptive local RF shimming. MATERIALS AND METHODS: DSMR using SSFP cine imaging was performed in 44 patients at 3T scheduled for a clinically indicated coronary angiography. The effect of conventional versus dual-source RF transmission was assessed regarding homogeneity of the B1 field, contrast-to-noise ratios (CNRs) at rest, image quality, and diagnostic accuracy of DSMR using long and short axis. RESULTS: The mean percentage of the intended flip angle within the heart increased from 88 ± 9.1% with single-source to 103 ± 5.6% (P < 0.001) dual-source RF transmission. CNR increased for dual-source particularly at the apex (63.4 ± 24.2 vs. 36.5 ± 16.5, P < 0.001) but also at the base of the left ventricle (LV) (50.1 ± 14.8 vs. 39.3 ± 15.8, P < 0.001). Image quality of dual-source was higher both at rest (2.8 ± 0.5 vs. 2.6 ± 0.7, P < 0.001) and stress (2.5 ± 0.7 vs. 2.0 ± 1.0, P < 0.001). The number of segments with severe artifacts or nondiagnostic image quality at stress was lower with dual-source RF transmission (8% vs. 27%, P < 0.001). The diagnostic accuracy of DSMR in coronary territories using dual-source RF transmission was significantly higher (77% vs. 65%, P = 0.04). CONCLUSION: Patient adaptive local RF shimming using dual-source RF transmission provided significantly improved image quality and higher diagnostic accuracy of SSFP during DSMR at 3T compared to conventional RF transmission.

Cardiac T2-mapping using a fast gradient echo spin echo sequence - first in vitro and in vivo experience.

BACKGROUND: The aim of this study was the evaluation of a fast Gradient Spin Echo Technique (GraSE) for cardiac T2-mapping, combining a robust estimation of T2 relaxation times with short acquisition times. The sequence was compared against two previously introduced T2-mapping techniques in a phantom and in vivo. METHODS: Phantom experiments were performed at 1.5 T using a commercially available cylindrical gel phantom. Three different T2-mapping techniques were compared: a Multi Echo Spin Echo (MESE; serving as a reference), a T2-prepared balanced Steady State Free Precession (T2prep) and a Gradient Spin Echo sequence. For the subsequent in vivo study, 12 healthy volunteers were examined on a clinical 1.5 T scanner. The three T2-mapping sequences were performed at three short-axis slices. Global myocardial T2 relaxation times were calculated and statistical analysis was performed. For assessment of pixel-by-pixel homogeneity, the number of segments showing an inhomogeneous T2 value distribution, as defined by a pixel SD exceeding 20 % of the corresponding observed T2 time, was counted. RESULTS: Phantom experiments showed a greater difference of measured T2 values between T2prep and MESE than between GraSE and MESE, especially for species with low T1 values. Both, GraSE and T2prep resulted in an overestimation of T2 times compared to MESE. In vivo, significant differences between mean T2 times were observed. In general, T2prep resulted in lowest (52.4 ± 2.8 ms) and GraSE in highest T2 estimates (59.3 ± 4.0 ms). Analysis of pixel-by-pixel homogeneity revealed the least number of segments with inhomogeneous T2 distribution for GraSE-derived T2 maps. CONCLUSIONS: The GraSE sequence is a fast and robust sequence, combining advantages of both MESE and T2prep techniques, which promises to enable improved clinical applicability of T2-mapping in the future. Our study revealed significant differences of derived mean T2 values when applying different sequence designs. Therefore, a systematic comparison of different cardiac T2-mapping sequences and the establishment of dedicated reference values should be the goal of future studies.

Mapping tissue inhomogeneity in acute myocarditis: a novel analytical approach to quantitative myocardial edema imaging by T2-mapping.

BACKGROUND: The purpose of the present study was to investigate the diagnostic value of T2-mapping in acute myocarditis (ACM) and to define cut-off values for edema detection. METHODS: Cardiovascular magnetic resonance (CMR) data of 31 patients with ACM were retrospectively analyzed. 30 healthy volunteers (HV) served as a control. Additionally to the routine CMR protocol, T2-mapping data were acquired at 1.5 T using a breathhold Gradient-Spin-Echo T2-mapping sequence in six short axis slices. T2-maps were segmented according to the 16-segments AHA-model and segmental T2 values as well as the segmental pixel-standard deviation (SD) were analyzed. RESULTS: Mean differences of global myocardial T2 or pixel-SD between HV and ACM patients were only small, lying in the normal range of HV. In contrast, variation of segmental T2 values and pixel-SD was much larger in ACM patients compared to HV. In random forests and multiple logistic regression analyses, the combination of the highest segmental T2 value within each patient (maxT2) and the mean absolute deviation (MAD) of log-transformed pixel-SD (madSD) over all 16 segments within each patient proved to be the best discriminators between HV and ACM patients with an AUC of 0.85 in ROC-analysis. In classification trees, a combined cut-off of 0.22 for madSD and of 68 ms for maxT2 resulted in 83% specificity and 81% sensitivity for detection of ACM. CONCLUSIONS: The proposed cut-off values for maxT2 and madSD in the setting of ACM allow edema detection with high sensitivity and specificity and therefore have the potential to overcome the hurdles of T2-mapping for its integration into clinical routine.

Myocardial T2 mapping reveals age- and sex-related differences in volunteers.

BACKGROUND: T2 mapping indicates to be a sensitive method for detection of tissue oedema hidden beyond the detection limits of T2-weighted Cardiovascular Magnetic Resonance (CMR). However, due to variability of baseline T2 values in volunteers, reference values need to be defined. Therefore, the aim of the study was to investigate the effects of age and sex on quantitative T2 mapping with a turbo gradient-spin-echo (GRASE) sequence at 1.5 T. For that reason, we studied sensitivity issues as well as technical and biological effects on GRASE-derived myocardial T2 maps. Furthermore, intra- and interobserver variability were calculated using data from a large volunteer group. METHODS: GRASE-derived multiecho images were analysed using dedicated software. After sequence optimization, validation and sensitivity measurements were performed in muscle phantoms ex vivo and in vivo. The optimized parameters were used to analyse CMR images of 74 volunteers of mixed sex and a wide range of age with typical prevalence of hypertension and diabetes. Myocardial T2 values were analysed globally and according to the 17 segment model. Strain-encoded (SENC) imaging was additionally performed to investigate possible effects of myocardial strain on global or segmental T2 values. RESULTS: Ex vivo studies in muscle phantoms showed, that GRASE-derived T2 values were comparable to those acquired by a standard multiecho spinecho sequence but faster by a factor of 6. Besides that, T2 values reflected tissue water content. The in vivo measurements in volunteers revealed intra- and interobserver correlations with R2=0.91 and R2=0.94 as well as a coefficients of variation of 2.4% and 2.2%, respectively. While global T2 time significantly decreased towards the heart basis, female volunteers had significant higher T2 time irrespective of myocardial region. We found no correlation of segmental T2 values with maximal systolic, diastolic strain or heart rate. Interestingly, volunteers´ age was significantly correlated to T2 time while that was not the case for other coincident cardiovascular risk factors. CONCLUSION: GRASE-derived T2 maps are highly reproducible. However, female sex and aging with typical prevalence of hypertension and diabetes were accompanied by increased myocardial T2 values. Thus, sex and age must be considered as influence factors when using GRASE in a diagnostic manner.

Gradient Spin Echo (GraSE) imaging for fast myocardial T2 mapping.

BACKGROUND: Quantitative Cardiovascular Magnetic Resonance (CMR) techniques have gained high interest in CMR research. Myocardial T2 mapping is thought to be helpful in diagnosis of acute myocardial conditions associated with myocardial edema. In this study we aimed to establish a technique for myocardial T2 mapping based on gradient-spin-echo (GraSE) imaging. METHODS: The local ethics committee approved this prospective study. Written informed consent was obtained from all subjects prior to CMR. A modified GraSE sequence allowing for myocardial T2 mapping in a single breath-hold per slice using ECG-triggered acquisition of a black blood multi-echo series was developed at 1.5 Tesla. Myocardial T2 relaxation time (T2-RT) was determined by maximum likelihood estimation from magnitude phased-array multi-echo data. Four GraSE sequence variants with varying number of acquired echoes and resolution were evaluated in-vitro and in 20 healthy volunteers. Inter-study reproducibility was assessed in a subset of five volunteers. The sequence with the best overall performance was further evaluated by assessment of intra- and inter-observer agreement in all volunteers, and then implemented into the clinical CMR protocol of five patients with acute myocardial injury (myocarditis, takotsubo cardiomyopathy and myocardial infarction). RESULTS: In-vitro studies revealed the need for well defined sequence settings to obtain accurate T2-RT measurements with GraSE. An optimized 6-echo GraSE sequence yielded an excellent agreement with the gold standard Carr-Purcell-Meiboom-Gill sequence. Global myocardial T2 relaxation times in healthy volunteers was 52.2 ± 2.0 ms (mean ± standard deviation). Mean difference between repeated examinations (n = 5) was -0.02 ms with 95% limits of agreement (LoA) of [-4.7; 4.7] ms. Intra-reader and inter-reader agreement was excellent with mean differences of -0.1 ms, 95% LoA = [-1.3; 1.2] ms and 0.1 ms, 95% LoA = [-1.5; 1.6] ms, respectively (n = 20). In patients with acute myocardial injury global myocardial T2-RTs were prolonged (mean: 61.3 ± 6.7 ms). CONCLUSION: Using an optimized GraSE sequence CMR allows for robust, reliable, fast myocardial T2 mapping and quantitative tissue characterization. Clinically, the GraSE-based T2-mapping has the potential to complement qualitative CMR in patients with acute myocardial injuries.

MR imaging-guided electrophysiological ablation studies in humans with passive catheter tracking: initial results.

PURPOSE: To assess if real-time magnetic resonance (MR) imaging-guided radiofrequency (RF) ablation for atrial flutter is feasible in patients. MATERIALS AND METHODS: The study complied with the Declaration of Helsinki and was approved by the local ethics committee. All patients were informed about the investigational nature of the procedures and provided written informed consent. Ten patients (six men; mean age ± standard deviation, 68 years ± 10) with symptomatic atrial flutter underwent isthmus ablation. In all patients, two MR imaging conditional steerable diagnostic and ablation catheters were inserted into the coronary sinus via femoral sheaths and into the right atrium with fluoroscopic guidance. The patients were then transferred to a 1.5-T whole-body MR imager for an ablation procedure, in which the catheters were manipulated by an electrophysiologist by using a commercially available interactive real-time steady-state free precession MR imaging sequence. RESULTS: All catheters were placed in standard positions successfully. Furthermore, simple programmed stimulation maneuvers were performed. In one of 10 patients, a complete conduction block was performed with MR imaging guidance. In nine of 10 patients, creating only a small number of additional touch-up lesions was necessary to complete the isthmus block with conventional fluoroscopy (median, three lesions; interquartile range, two to four lesions). CONCLUSION: Real-time MR imaging-guided placement of multiple catheters is feasible in patients, with subsequent performance of stimulation maneuvers and occasional complete isthmus ablation.