Comparison of a 28‐channel receive array coil and quadrature volume coil for morphologic imaging and T2 mapping of knee cartilage at 7T

Abstract

Purpose To compare a new birdcage-transmit, 28 channel-receive array (28 Ch) coil and a quadrature volume coil for 7 Tesla morphologic MRI and T2 mapping of knee cartilage. Methods The right knees of ten healthy subjects were imaged on a 7 Tesla whole body MR scanner using both coils. 3-dimensional fast low-angle shot (3D-FLASH) and multi-echo spin-echo (MESE) sequences were implemented. Cartilage signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), thickness, and T2 values were assessed. Results SNR/CNR was 17–400% greater for the 28 Ch compared to the quadrature coil (p≤0.005). Bland-Altman plots show mean differences between measurements of tibial/femoral cartilage thickness and T2 values obtained with each coil to be small (−0.002±0.009 cm/0.003±0.011 cm) and large (−6.8±6.7 ms/−8.2±9.7 ms), respectively. For the 28 Ch coil, when parallel imaging with acceleration factors (AF) 2, 3, and 4 was performed, SNR retained was: 62–69%, 51–55%, and 39–45%. Conclusion A 28 Ch knee coil provides increased SNR/CNR for 7T cartilage morphologic imaging and T2 mapping. Coils should be switched with caution during clinical studies because T2 values may differ. The greater SNR of the 28 Ch coil could be used to perform parallel imaging with AF2 and obtain similar SNR as the quadrature coil.

Probing articular cartilage damage and disease by quantitative magnetic resonance imaging

“…As mentioned previously, T 2 and T 1r cannot be attributed to single biochemical factors [107]. Values for T 2 , T 1,Gd and T 1r , even in normal cartilage, differ in the literature and can be dependent on pulse sequence [92], the strength of the static magnetic field [32,119] and the radiofrequency coil [91]. A number of studies have shown that loading history [93,120 -122] and joint alignment [93,123] can also affect some of these qMRI measures.…”

7 Tesla MRI of bone microarchitecture discriminates between women without and with fragility fractures who do not differ by bone mineral density

“…In addition, the higher SNR provided by 7 T facilitates imaging of deeper anatomy such as the femur, since coil sensitivity for detection of the MR signal decreases exponentially as the distance from the coil to the object of interest increases [42]. Finally, the use of a 28-channel coil also facilitates high-resolution imaging, as the 28-channel coil at 7 T provides approximately 17–400 % higher image SNR compared to the use of a conventional 2-channel quadrature coil [43]. We leveraged the higher SNR provided by the 7 T MRI scanner and the 28-channel receive coil to decrease imaging time to 7 min and 9 s via parallel imaging, while still being able to acquire 80 axial images at 1 mm slice thickness.…”

High resolution morphologic imaging and T2 mapping of cartilage at 7 Tesla: comparison of cartilage repair patients and healthy controls

“…The greater SNR of 7 T can be converted into increases in image spatial resolution, since image voxel size is directly proportional to SNR [12]. Alternatively, the greater SNR of 7 T can be used to decrease image acquisition times while maintaining the same image quality compared to 1.5 or 3 T either by decreasing the number of signal averages or by employing parallel imaging if a multichannel coil is used [9, 32, 33]. Although decreasing the number of signal averages or using parallel imaging incurs SNR losses, 7 T allows the use of these techniques because of the greater baseline intrinsic SNR available.…”

“…The higher SNR of 7 T allowed us to obtain these higher resolution images with a shorter scan time compared to 1.5 or 3 T. Because parallel imaging does incur an SNR penalty, which can render images lower in quality, we did not use a higher parallel acceleration factor greater than 2. It has been shown that at a parallel acceleration factor of 2 with a 28 channel knee coil at 7 T, the SNR is approximately equivalent to that obtained with a quadrature knee coil at 7 T [33]. …”