High Spatial Resolution Cardiovascular Magnetic Resonance at 7.0 Tesla in Patients with Hypertrophic Cardiomyopathy - First Experiences: Lesson Learned from 7.0 Tesla.

BACKGROUND: Cardiovascular Magnetic Resonance (CMR) provides valuable information in patients with hypertrophic cardiomyopathy (HCM) based on myocardial tissue differentiation and the detection of small morphological details. CMR at 7.0T improves spatial resolution versus today's clinical protocols. This capability is as yet untapped in HCM patients. We aimed to examine the feasibility of CMR at 7.0T in HCM patients and to demonstrate its capability for the visualization of subtle morphological details. METHODS: We screened 131 patients with HCM. 13 patients (9 males, 56 ±31 years) and 13 healthy age- and gender-matched subjects (9 males, 55 ±31years) underwent CMR at 7.0T and 3.0T (Siemens, Erlangen, Germany). For the assessment of cardiac function and morphology, 2D CINE imaging was performed (voxel size at 7.0T: (1.4x1.4x2.5) mm3 and (1.4x1.4x4.0) mm3; at 3.0T: (1.8x1.8x6.0) mm3). Late gadolinium enhancement (LGE) was performed at 3.0T for detection of fibrosis. RESULTS: All scans were successful and evaluable. At 3.0T, quantification of the left ventricle (LV) showed similar results in short axis view vs. the biplane approach (LVEDV, LVESV, LVMASS, LVEF) (p = 0.286; p = 0.534; p = 0.155; p = 0.131). The LV-parameters obtained at 7.0T where in accordance with the 3.0T data (pLVEDV = 0.110; pLVESV = 0.091; pLVMASS = 0.131; pLVEF = 0.182). LGE was detectable in 12/13 (92%) of the HCM patients. High spatial resolution CINE imaging at 7.0T revealed hyperintense regions, identifying myocardial crypts in 7/13 (54%) of the HCM patients. All crypts were located in the LGE-positive regions. The crypts were not detectable at 3.0T using a clinical protocol. CONCLUSIONS: CMR at 7.0T is feasible in patients with HCM. High spatial resolution gradient echo 2D CINE imaging at 7.0T allowed the detection of subtle morphological details in regions of extended hypertrophy and LGE.

Diffusion-sensitized ophthalmic magnetic resonance imaging free of geometric distortion at 3.0 and 7.0 T: a feasibility study in healthy subjects and patients with intraocular masses.

OBJECTIVES: This study is designed to examine the feasibility of diffusion-sensitized multishot split-echo rapid acquisition with relaxation enhancement (RARE) for diffusion-weighted ophthalmic imaging free of geometric distortions at 3.0 and 7.0 T in healthy volunteers and patients with intraocular masses. MATERIALS AND METHODS: A diffusion-sensitized multishot split-echo RARE (ms-RARE) variant is proposed as an alternative imaging strategy for diffusion-weighted imaging. It is compared with standard single-shot echo planar imaging (EPI) and readout-segmented EPI in terms of geometric distortions in a structure phantom as well as in vivo at 3.0 and 7.0 T. To quantify geometric distortions, center of gravity analysis was carried out. Apparent diffusion coefficient (ADC) mapping in a diffusion phantom was performed to verify the diffusion sensitization within ms-RARE. An in vivo feasibility study in healthy volunteers (n = 10; mean age, 31 ± 7 years; mean body mass index, 22.6 ± 1.7 kg/m²) was conducted at 3.0 and 7.0 T to evaluate clinical feasibility of ms-RARE. As a precursor to a broader clinical study, patients (n = 6; mean age, 55 ± 12 years; mean body mass index, 27.5 ± 4.7 kg/m²) with an uveal melanoma and/or retinal detachment were examined at 3.0 and 7.0 T. In 1 case, the diseased eye was enucleated as part of the therapy and imaged afterward with magnetic resonance microscopy at 9.4 T. Macrophotography and histological investigation was carried out. For qualitative assessment of the image distortion, 3 independent readers reviewed and scored ms-RARE in vivo images for all subjects in a blinded reading session. Statistical significance in the difference of the scores (a) obtained for the pooled ms-RARE data with b = 0 and 300 s/mm² and (b) for the 3 readers was analyzed using the nonparametric Mann-Whitney test. RESULTS: The assessment of geometric integrity in phantom imaging revealed the ability of ms-RARE to produce distortion-free images. Unlike ms-RARE, modest displacements (2.3 ± 1.4 pixels) from the fast low angle shot imaging reference were observed for readout-segmented EPI, which were aggravated for single-shot EPI (8.3 ± 5.7 pixels). These observations were confirmed in the in vivo feasibility study including distortion-free diffusion-weighted ophthalmic images with a 0.5 × 0.5 × 5 mm³ spatial resolution at 3.0 T and as good as 0.2 × 0.2 × 2 mm³ at 7.0 T. The latter represents a factor of 40 enhancement in spatial resolution versus clinical protocols recently reported for diffusion-weighted imaging of the eye at 1.5 T. Mean ADC values within the vitreous body were (2.91 ± 0.14) × 10⁻³ mm²/s at 3.0 T and (2.93 ± 0.41) × 10⁻³ mm²/s at 7.0 T. Patient data showed severe retinal detachment in the anatomical images. Whereas the tumor remained undetected in T1-weighted and T2-weighted imaging at 3.0/7.0 T, in vivo ADC mapping using ms-RARE revealed the presence of a uveal melanoma with a significant contrast versus the surrounding subretinal hemorrhage. This observation was confirmed by high-resolution ex vivo magnetic resonance microscopy and histology. Qualitative analysis of image distortion in ms-RARE images obtained for all subjects yielded a mean ± SD image quality score of 1.06 ± 0.25 for b = 0 s/mm² and of 1.17 ± 0.49 for b = 300 s/mm². No significant interreader differences were observed for ms-RARE with a diffusion sensitization of b = 0 s/mm² and 300 s/mm². CONCLUSIONS: This work demonstrates the capability of diffusion-sensitized ms-RARE to acquire high-contrast, high-spatial resolution, distortion-free images of the eye and the orbit at 3.0 and 7.0 T. Geometric distortions that are observed for EPI-based imaging approaches even at lower field strengths are offset by fast spin-echo-based imaging techniques. The benefits of this improvement can be translated into the assessment of spatial arrangements of the eye segments and their masses with the ultimate goal to provide guidance during diagnostic treatment of ophthalmological diseases.

Ophthalmic magnetic resonance imaging at 7 T using a 6-channel transceiver radiofrequency coil array in healthy subjects and patients with intraocular masses.

OBJECTIVES: This study was designed to examine the feasibility of ophthalmic magnetic resonance imaging (MRI) at 7 T using a local 6-channel transmit/receive radiofrequency (RF) coil array in healthy volunteers and patients with intraocular masses. MATERIALS AND METHODS: A novel 6-element transceiver RF coil array that makes uses of loop elements and that is customized for eye imaging at 7 T is proposed. Considerations influencing the RF coil design and the characteristics of the proposed RF coil array are presented. Numerical electromagnetic field simulations were conducted to enhance the RF coil characteristics. Specific absorption rate simulations and a thorough assessment of RF power deposition were performed to meet the safety requirements. Phantom experiments were carried out to validate the electromagnetic field simulations and to assess the real performance of the proposed transceiver array. Certified approval for clinical studies was provided by a local notified body before the in vivo studies. The suitability of the RF coil to image the human eye, optical nerve, and orbit was examined in an in vivo feasibility study including (a) 3-dimensional (3D) gradient echo (GRE) imaging, (b) inversion recovery 3D GRE imaging, and (c) 2D T2-weighted fast spin-echo imaging. For this purpose, healthy adult volunteers (n = 17; mean age, 34 ± 11 years) and patients with intraocular masses (uveal melanoma, n = 5; mean age, 57 ± 6 years) were investigated. RESULTS: All subjects tolerated all examinations well with no relevant adverse events. The 6-channel coil array supports high-resolution 3D GRE imaging with a spatial resolution as good as 0.2 × 0.2 × 1.0 mm, which facilitates the depiction of anatomical details of the eye. Rather, uniform signal intensity across the eye was found. A mean signal-to-noise ratio of approximately 35 was found for the lens, whereas the vitreous humor showed a signal-to-noise ratio of approximately 30. The lens-vitreous humor contrast-to-noise ratio was 8, which allows good differentiation between the lens and the vitreous compartment. Inversion recovery prepared 3D GRE imaging using a spatial resolution of 0.4 × 0.4 × 1.0 mm was found to be feasible. T2-weighted 2D fast spin-echo imaging with the proposed RF coil afforded a spatial resolution of 0.25 × 0.25 × 0.7 mm. CONCLUSIONS: This work provides valuable information on the feasibility of ophthalmic MRI at 7 T using a dedicated 6-channel transceiver coil array that supports the acquisition of high-contrast, high-spatial resolution images in healthy volunteers and patients with intraocular masses. The results underscore the challenges of ocular imaging at 7 T and demonstrate that these issues can be offset by using tailored RF coil hardware. The benefits of such improvements would be in positive alignment with explorations that are designed to examine the potential of MRI for the assessment of spatial arrangements of the eye segments and their masses with the ultimate goal to provide imaging means for guiding treatment decisions in ophthalmological diseases.