Experimental Validation of the MRcollar: An MR Compatible Applicator for Deep Heating in the Head and Neck Region

Clinical effectiveness of hyperthermia treatments, in which tumor tissue is artificially heated to 40–44 °C for 60–90 min, can be hampered by a lack of accurate temperature monitoring. The need for noninvasive temperature monitoring in the head and neck region (H&N) and the potential of MR thermometry prompt us to design an MR compatible hyperthermia applicator: the MRcollar. In this work, we validate the design, numerical model, and MR performance of the MRcollar. The MRcollar antennas have low reflection coefficients (<−15 dB) and the intended low interaction between the individual antenna modules (<−32 dB). A 10 °C increase in 3 min was reached in a muscle-equivalent phantom, such that the specifications from the European Society for Hyperthermic Oncology were easily reached. The MRcollar had a minimal effect on MR image quality and a five-fold improvement in SNR was achieved using the integrated coils of the MRcollar, compared to the body coil. The feasibility of using the MRcollar in an MR environment was shown by a synchronous heating experiment. The match between the predicted SAR and measured SAR using MR thermometry satisfied the gamma criteria [distance-to-agreement = 5 mm, dose-difference = 7%]. All experiments combined show that the MRcollar delivers on the needs for MR—hyperthermia in the H&N and is ready for in vivo investigation.

Comparison of different wireless coils for 1.5 T bilateral breast MRI

In this work, we compare three types of transceive wireless coils: Helmholtz-type coil, metamaterial-inspired coil and their combination. Each transceive coil is electromagnetically coupled to a body coil “birdcage” type of a 1.5 T MR scanner and improves bilateral breast imaging performance. While Helmholtz-type coil and metamaterial-inspired coil based on coupled split loop resonators are linearly polarized, their combination allows to couple with both linear components of the radiofrequency magnetic field, providing a more significant effect of a local boosting of the body coil’s transmit efficiency and radiofrequency safety in comparison with birdcage coil only.

Potential Reduction of Peripheral Local SAR for a Birdcage Body Coil at 3 Tesla Using a Magnetic Shield

The birdcage body coil, the standard transmit coil in clinical MRI systems, is typically a shielded coil. The shield avoids interaction with other system components, but Eddy Currents induced in the shield have an opposite direction with respect to the currents in the birdcage coil. Therefore, the fields are partly counteracted by the Eddy currents, and large coil currents are required to reach the desired B1+ level in the subject. These large currents can create SAR hotspots in body regions close to the coil. Complex periodic structures known as metamaterials enable the realization of a magnetic shield with magnetic rather than electric conductivity. A magnetic shield will have Eddy currents in the same direction as the coil currents. It will allow generating the same B1+ with lower current amplitude, which is expected to reduce SAR hotspots and improve homogeneity. This work explores the feasibility of a birdcage body coil at 3 T with a magnetic shield. Initially, we investigate the feasibility by designing a scale model of a birdcage coil with an anisotropic implementation of a magnetic shield at 7 T using flattened split ring resonators. It is shown that the magnetic shield destroys the desired resonance mode because of increased coil loading. To enforce the right mode, a design is investigated where each birdcage rung is driven individually. This design is implemented in a custom built birdcage at 7 T, successfully demonstrating the feasibility of the proposed concept. Finally, we investigate the potential improvements of a 3 T birdcage body coil through simulations using an idealized magnetic shield consisting of a perfect magnetic conductor (PMC). The PMC shield is shown to eliminate the peripheral regions of high local SAR, increasing the B1+ per unit maximum local SAR by 27% in a scenario where tissue is present close to the coil. However, the magnetic shield increases the longitudinal field of view, which reduces the transmit efficiency by 25%.

Differential Diagnosis of Benign and Malignant Level Tumors in Children by Quantitative MRI with Intracellular Contrast Agent

Purpose: Тo determine the possibilities of quantitative assessment of mpMRI with EOB-DTPA in the differential diagnosis of benign and malignant tumors in children.Material and methods: 30 patients (male — 17, female — 13) with 83 tumors underwent MRI. Age ranged from 5 months to 20 years. All children underwent MRI on 3T or 1.5T MR-scanners using body coil. Fat saturated T1WI were performed before and after hepatotropic MR-contrast agent (gadoxetic acid) injection in arterial, portal, venous and delayed phases (1, 5, 20, 40 min). Tumors were divided into 2 groups: benign (52) and malignant (31). In this work we use only pre- and postcontrast T1WI. Diagnosis was confirmed histologically (all malignant and a part of benign FLL) and long-term MRI follow-up studies (for benign). To eliminate influence of external factors we used coefficients for each MR-program, the signal was normalized to intact liver parenchyma, spleen, abdominal aorta and v. cava inferior, also normalization to native series has been performed. Coefficients were compared for malignant and benign tumors using Student’s t-test, significantly different parameters were further used to build mathematical model by constructing a logistic regression with step-by-step selection of the most informative values.Results: Regression model is presented by formula. The model is informative and statistically significant (p < 0.001). If A>0.5 tumors has a malignant nature if А ≤ 0.5–benign. Model sensitivity and specificity are 0.862 and 0.925, respectively.Conclusion: Our model could be an excellent assistance in differentiation of benign and malignant focal liver lesions and reduces diagnostic path, effects the proper patients management.

The Rule of Magnetic Resonance Angiography (MRA) in the Case of Angiofibroma in the Elbow Joint Region

Background: Using the MRI modality of 1.5 Tesla can alter vascular imaging (angiography) from invasive examination into a non-invasive examination. The Magnetic Resonance Angiography (MRA) can be performed on upper limb organs with and without contrast. One indication of the MRA examination is angiofibroma. Because of the pathology, clinicians want to see the flow of blood from the upper arm to the elbow so that body coil is used as an alternative to genu coil or ankle coil commonly used in this examination. Objective: The research intends to know how the technique of MRA elbow management using body coil in the angiofibroma case. Method: This research was conducted by observation. The researchers looked directly at the MRA elbow examination procedure using the body coil. Result: The result is the MRA elbow image using body coil from different sequences.