Feasibility study of a unilateral RF array coil for MR-scintimammography - PubMed (original) (raw)

Feasibility study of a unilateral RF array coil for MR-scintimammography

Seunghoon Ha et al. Phys Med Biol. 2011.

Abstract

Despite its high sensitivity, the variable specificity of magnetic resonance imaging (MRI) in breast cancer diagnosis can lead to unnecessary biopsies and over-treatment. Scintimammography (SMM) could potentially supplement MRI to improve the diagnostic specificity. The synergistic combination of MRI and SMM (MRSMM) could result in both high sensitivity from MRI and high specificity from SMM. Development of such a dual-modality system requires the integration of a radio frequency (RF) coil and radiation detector in a strong magnetic field without significant mutual interference. In this study, we developed and tested a unilateral breast array coil specialized for MRSMM imaging. The electromagnetic field, specific absorption ratio and RF coil parameters with cadmium-zinc-telluride detectors encapsulated in specialized RF and gamma-ray shielding mounted within the RF coil were investigated through simulation and experimental measurements. Simultaneous MR and SMM images of a breast phantom were also acquired using the integrated MRSMM system. This work, we feel, represents an important step toward the fabrication of a working MRSMM system.

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Figures

Figure 1

(a) Illustration of the MRSMM assembly. Each CZT detector is enclosed in RF and gamma-ray shielding. (b) Modeling of the RF coil and RF shielded blocks in the simulation program. The blocks are each located 10mm from a brick-shaped phantom. (c) Experimental setup for testing RF and gamma-ray shielding in the RF coil. (d) Gamma-ray shielding box (left) and additional RF shielding (right).

Figure 2

Illustration of breast compression at various angles. The two lesions (red circles) will be distinguishable in the SMM images acquired at 0° compression, but indistinguishable at 90° compression.

Figure 3

The simulated RMS magnitude B1 field distribution (left column) and RMS magnitude E1 electric field distribution (right column) generated by the RF array coil tunned to 127 MHz without the conductive copper blocks (top row), the coil shifted to 138 MHz with the introduction of the conductive blocks (middle row), and coil with the conductive blocks re-tuned to 127 MHz. A shift in the electric field intensity around discrete components such as capacitors accounts for the assymetry in (b). The B1 field maps (unit=dB) were normalized to one input power for 2.37e-010 A/m2 source power in A and the electric field maps (unit=dB) were normalized to one input power for 2.59e-008 V/m2 source power in V.

Figure 4

The simulated B1 field distribution (top row), E1 electric field distribution (middle row) and SAR distribution (bottom row) generated by the RF array coil tuned to 127 MHz without the conductive copper blocks (left column) and with the copper blocks (right column). The B1 maps (unit=dB) were normalized to one input power for 2.37e-010 A/m2 source power in A, the electric field maps (unit=dB) were normalized to one input power for 2.59e-008 V/m2 source power in V and the SAR maps (unit=dB) were normalized to one input power 5.48e-020 mW/g. source power in mW.

Figure 5

The frequency spectra (impedance in Ω versus frequency in Hz) of the RF array coil with the RF shielding (top row), gamma-ray shielding (middle row) and both shielding (bottom row). It was measured following location at 125 mm (black solid line), 85 mm (black dotted line), 52 mm (black dashed line), 42 mm (gray dashed line), 36 mm (gray dotted line), and 26 mm (gray solid line) from the isocenter of RF coil. The red line was RF spectrum re-tuned at 26mm away location from the isocenter of RF coil.

Figure 6

MR images of the brick phantom with no shielding (top row), RF shielding (2nd row), gamma-ray shielding (3rd row) and both shielding (bottom row) placed 10 mm from the phantom within the RF coil. All magnitude and phase images were each scaled to identical contrast levels.

Figure 7

MR and SMM images from the top detector (left images of each column) and bottom detector (right images of each column) of the breast phantom with three different simulated compression angles for three different background configurations. Each SMM image was normalized to the maximum value of all the images. The yellow box denotes the ROI used to measure the radioactive counts.

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Feasibility study of a unilateral RF array coil for MR-scintimammography - PubMed (original) (raw)