Figure 8. Contrast imaging at 3T vs. 7T. When TR=5ms, the signal intensity differences for different gadolinium concentrations are shown at 3T (A) and 7T (B). The relative signal changes for simulated benign (1.25uM/mL) and malignant (2.5uM/mL) tumors at 3T and 7T are demonstrated in (C).
When our multiple-port head coil is used in its CP mode (two-port transmit/receive), its SNR is 1.9 times the SNR of the 3T eightelement phased array coil in the central brain area, and 1.4 times the SNR of the 3T coil in the peripheral region, as shown in FIGURE 11. When our multiple-port volume strip array (VSA) is used as a 16ch transmit coil, it can achieve focused excitation. The advantage of focused excitation at 7T is that it can maximize the SNR and minimize the specific absorption rate (SAR) in the presence of dielectric resonance. Such regional excitation (as opposed to global excitation) allows a radiologist to specify a small area of the body to be scanned, and then only excite that particular region, using different modes to perform feedback processing and hence, customized regional scanning.
In addition to these exciting developments, we are in the process of completing several other landmark MRI coils, including a 32ch 3T body array, 7T pancreas coil, 7T prostate coil, and 7T spine array. We hope that the completion of this series of MRI coils will set the stage for our radiologists to take the lead in high field clinical MRI diagnosis and research.
Figure 9. Dynamic contrast enhanced breast imaging at 3T vs. 7T MRI in a cancer patient. The ratio of tumor to glandular tissue enhancement is 1.9 at 3T (A) and 4.1 at 7T (B).
Figure 10. 7T Multiple-Port Volume Strip Array (VSA). The VSA (A) and its setup for 16-port transmission (B).
Figure 11. 3T phased array images as compared to 7T
multiple-port volume strip array images. When SNRs from the 3T
eight-element phased array (A) is compared to the 7T multiple-port VSA in CP
mode (B), the SNR in the central area is 56 for 3T (A), and 108 for 7T (B).
The SNR in the peripheral area is 34 for 3T (A), and 46 for 7T (B).
RAY F. LEE, Ph.D., is Assistant Professor of Radiology and a member of the Research Division.
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