Bart Steensma

Bart Steensma
University Medical Center Utrecht | UMC Utrecht · Department of Radiotherapy

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25
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143
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Publications

Publications (25)
Article
Full-text available
Patients with medical implants often are deprived of magnetic resonance imaging examination because of safety risks. One specific risk is the enhancement of the radiofrequency fields around the medical implant potentially resulting in significant tissue heating and damage. The assessment of this enhancement is a computationally demanding task, with...
Article
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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...
Article
Full-text available
Purpose The coax dipole antenna, a flexible antenna for body imaging at 7T is presented. Similar to the high impedance coil, this coaxial cable antenna is fed on the central conductor and through gaps in the shield, the current passes to the outside of the antenna to generate B1 field. This could achieve more favorable current distributions and bet...
Article
Full-text available
Purpose: To investigate inter-subject variability of B1+ , SAR and temperature rise in a database of human models using a local transmit array for 7 T cardiac imaging. Methods: Dixon images were acquired of 14 subjects and segmented in dielectric models with an eight-channel local transmit array positioned around the torso for cardiac imaging. E...
Article
Full-text available
Background and purpose The restricted bore diameter of current simultaneous positron emission tomography/magnetic resonance imaging (PET/MRI) systems can be an impediment to achieving similar patient positioning during PET/MRI planning and radiotherapy. Our goal was to evaluate the B1 transmit (B1⁺) uniformity, B1⁺ efficiency, and specific absorpti...
Article
Full-text available
Purpose The introduction of a linear safety factor to address peak local specific absorption rate (pSAR10g) uncertainties (eg, intersubject variation, modeling inaccuracies) bears one considerable drawback: It often results in over‐conservative scanning constraints. We present a more efficient approach to define a variable safety margin based on th...
Article
Full-text available
Purpose To improve imaging performance for body MRI with a local transmit array at 10.5T, the geometry of a dipole antenna was optimized to achieve lower peak specific absorption rate (SAR) levels and a more uniform transmit profile. Methods Electromagnetic simulations on a phantom were used to evaluate the SAR and ‐performance of different dipole...
Article
In this contribution we present numerical and experimental results of a parametric quantitative study of radiative dipole antennas in a phased array configuration for efficient body magnetic resonance imaging at 7 T via parallel transmission. For magnetic resonance imaging (MRI) at ultrahigh fields (7 T and higher) dipole antennas are commonly used...
Article
Full-text available
Purpose: Local specific absorption rate (SAR) cannot be measured and is usually evaluated by offline numerical simulations using generic body models that of course will differ from the patient's anatomy. An additional safety margin is needed to include this intersubject variability. In this work, we present a deep learning-based method for image-b...
Article
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Trifluridine/tipiracil (TAS-102) has shown a significant overall survival benefit in patients with heavily pre-treated metastatic colorectal cancer. However, predicting treatment response and toxicity in individual patients remains challenging. Fluorine (¹⁹F)-containing drugs can be detected with magnetic resonance spectroscopy (MRS) to determine t...
Article
Full-text available
To explore the use of five meandering dipole antennas in a multi‐transmit setup, combined with a high density receive array for breast imaging at 7 T for improved penetration depth and more homogeneous B1 field. Five meandering dipole antennas and 30 receiver loops were positioned on two cups around the breasts. Finite difference time domain simula...
Article
Full-text available
Background In MRI, the signal‐to‐noise ratio (SNR) theoretically increases with B0 field strength. However, because of attenuation of the radiofrequency (RF) fields at 7T, it is not certain if this SNR gain can be realized for prostate imaging. Purpose/Hypothesis To investigate the SNR gain in prostate imaging at 7T as compared with 3T. It is expe...
Article
The cover image, by Bart R. Steensma et al., is based on the Research Article Design of a forward view antenna for prostate imaging at 7 T, https://doi.org/10.1002/nbm.3993.
Data
Figure S1: transmit efficiency in the phantom, 6 cm away from the round tip of the forward view antenna, as a function of waveguide length. Figure S2: B1 +‐fields and SAR distributions for a setup of 8 fractionated dipole antennas with and without the forward view antenna present as a passive element. All slices cut through the center of the prost...
Article
Full-text available
Purpose To design a forward view antenna for prostate imaging at 7 T, which is placed between the legs of the subject in addition to a dipole array. Materials and methods The forward view antenna is realized by placing a cross‐dipole antenna at the end of a small rectangular waveguide. Quadrature drive of the cross‐dipole can excite a circularly p...
Article
Full-text available
Objective: To demonstrate imaging performance for cardiac MR imaging at 7 T using a coil array of 8 transmit/receive dipole antennas and 16 receive loops. Materials and methods: An 8-channel dipole array was extended by adding 16 receive-only loops. Average power constraints were determined by electromagnetic simulations. Cine imaging was perfor...
Article
Purpose: (13) C magnetic resonance spectroscopy (MRS) in combination with infusion of (13) C-labeled substrates has led to unique insights into human brain metabolism and neurotransmitter cycling. However, the low sensitivity of direct (13) C MRS and high radiofrequency power requirements has limited (13) C MRS studies to predominantly data acquis...
Article
Full-text available
In this contribution we present numerical and experimental results of a parametric quantitative study of radiative dipole antennas in a phased array configuration for efficient body magnetic resonance imaging at 7T via parallel transmission. For magnetic resonance imaging (MRI) at ultrahigh fields (7T and higher) dipole antennas are commonly used i...

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