A silent MRI apparatus with 3D radial acquisition
Publication Date: 2014-Aug-08
The IP.com Prior Art Database
Page 01 of 5
Title of the invention: A silent MRI apparatus with 3D radial acquisition
This invention is for silent MR. In this invention we proposed to acquire the data with non-Cartesian radial acquisition using modified ramp sampling by shaping the gradient to suppress the high frequency acoustic noise, the acoustic noise of this method will be equal or below the ambient noise. The advantages of this scheme are that it's a silent Zero TE method which could acquire with the k space center, higher SNR and more accurate T1 contrast. Moreover, the method is not limited ZTE for other weighted imaging.
Detailed description of the invention
Background of the invention
An unwanted side effect of MRI is the uncomfortable and sometimes harmful acoustic noise. Sound pressure level (SPL) of 70-120 dB is reported . Shaping and derating gradient waveform can be used to reduce the SPL by suppressing high harmonic frequency part [2, 3, 4, 5]. Gradient coil redesign was also to use mitigate the SPL, such as force balancing by Lorentz  or using a rotating DC gradient . Active shielding for MRI acoustic noise reduction can also be used . Conventional Zero TE (ZTE) method uses constant gradient as readout , and it has been used for imaging in humans, with dramatically reduced noise.
Problems or disadvantages overcome by the invention
Rotating the gradient coil or active shield will increase the cost. Conventional shaping gradient waveform methods will increase the TE and reduce image quality. All prior arts can only mitigate the acoustic, and can't reduce the SPL to ambient noise level.
Because constant gradient is used before excitation and dead time is generated by discrete filter and T/R switch, current ZTE method misses the centric k space, and changes the image contrast.
Abstract of the invention:
Page 02 of 5
Figure 1 Prior art ZTE sequence diagram, K space center is missed.
The essential feature(s) of the invention
The key idea of this invention is 3D radial acquisition with ramp-sampling by predetermined gradient ramping-up shapes for silent MRI.
Data acquisition is started from the k-space center to minimize gradient switch with shaped waveform;
The gradient waveform is shaped to minimize gradient spectrum frequency. the main part of gradient spectrum was limited to low frequency.
Time delay between excitation and ramp sampling is used to get other contrast.
Detailed description of how to build and use the invention
Using ZTE as a specific example, the detailed description of the invention is provided below.
This method is based on 3D radial acquisition with ramp-sampling, which acquires the data starting from the k-space center at gradient switch on, so k space center can be acquired for ZTE and the gradient spectrum frequency is minimized by reduced gradient switch. All k-space data was acquired by rotating the gradient waveform (Fig. 2). Because k-space center is reserved, its SNR is optimized a...