7T MULTIPLE PORT HEAD VOLUME STRIP ARRAY (VSA)
7T brain MRI has been in development for many years at a number of institutions. At high field strengths, however, certain physical phenomena arise, which cause sub-optimal imaging, and present technical hurdles for RF coil design. One problem, known as dielectric resonance, occurs when the wavelength of the electromagnetic field (EMF) is comparable to or less than the dimensions of the sample, such that the transmit magnetic field is no longer homogeneously distributed over the sample. This potentially causes severe flip angle variation, which could introduce artifacts. This effect is clearly visible in brain MRI at 7T and poses a significant challenge. We have developed a multiple-port 16ch transmit/receive head array, capable of working as a circular polarized (CP) transmit/receive, four-port transmit/receive, or 16ch transmit/receive coil, as a potential solution to the dielectric resonance dilemma. This coil also maximizes the SNR at 7T.
Figure 2. 2D gradient echo in vivo 3He lung MRI.
(A) conventional imaging without parallel data acquisition; (B) parallel imaging
with reduction factor two; (C) parallel imaging with reduction factor four.
(D), (E), and (F) are images of the left mainstem bronchus.
Figure 4. 3D gradient echo in vivo 3He lung parallel MRI. The entire lung can be scanned within a single breath hold (13s). These eight images are selected from 32 slices in the slab.
Figure 5. The first 7T MRI coil for the breast. (A) external and (B) internal views.
Figure 6. Comparison between 3T and 7T breast MRI in a normal breast. 3T (A) and 7T (B) breast MRIs at a resolution of 0.3 x 0.3 x 0.8mm in the same healthy volunteer are compared. At 7T (B) the morphology of ducts and glandular tissue is more clearly depicted.
Figure 7. Comparison between 3T and 7T breast MRI in a breast cancer. A high signal tumor nodule is demonstrated by both the 3T (A) and 7T (B) breast MRIs. However, the 7T image (B) better illustrates the spiculated margins and the size of the mass.
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