台式低场MRI设备梯度场线性度间接测量和评价方法研究

Undirected Measurement and Evaluation Method Research on Gradient Field Linearity of Desktop MRI Devices with Lower Field

目的:为了在MRI使用前能够简单对其梯度场线性度状态进行度量和评价,以便在实际使用过程中保证可靠性或在维护时对其梯度场可靠性进行验证,本文对台式低场MRI设备梯度线圈系统线性度间接测量和评价方法进行了研究。方法:目前人们对磁共振成像设备梯度线圈梯度场线性度大小的间接度量一般基于不同梯度场条件下所获得的图像来实现。通常按照一定的梯度步长采用不同的梯度对已知大小的体模或物体目标进行一系列成像,再根据图像的某个方向的像素或尺度度量来计算出梯度场线性变化趋势,从而对梯度场线性度进行度量和评价。结果:采用间接评价方法,基于NMI20台式低场磁共振成像与分析仪作为实验仪器,本文对10 mm高大豆油试管样品进行了一系列成像实验,并通过基于Opencv机器视觉库编制的椭圆拟合及其横纵轴长度自动度量程序对样品的磁共振横断面图像进行了精确测量。在此基础上,对该仪器GZ和GX线性度进行测评,最后取得了预期的理想结果。结论:本文所给出的线性度测评方法对基于横断面为圆形或椭圆形的任一磁共振成像目标或样本对任何磁共振成像仪器的梯度场线性度实施间接测量具有普适性意义,因此具有相当的实用价值。

Objective： To measure and evaluate linearity status of the gradient field simply before MRI usage and assure the online reliability as well as its verification during maintenance, undirected measurement and evaluation method research on coil linearity of gradient system about lower field desktop MRI devices are performed in this paper. Methods： Presently, indirect linearity value measurement of MRI gradient field produced by its gradient coils is commonly achieved by images obtained under different conditions of gradient field. Usually, a series of imaging processes are firstly performed by different gradient field according to certain gradient step for a phantom or object with known size. Then variation tendency of the gradient field are figured out based on MR/image pixels or dimension measurement along certain direction and gradient field linearity can thus be measured and evaluated. Results： Adopting NMI20 lower field desktop magnetic resonance imaging and analyzing instrument as main experiment device, a series of imaging tests are performed on the soybean oil sample held in a 10-millimetre test tube and based on undirected method, the Gz and Gx linearity of the device are measured and evaluated. The expected ideal result is obtained finally. Conclusions： The linearity measurement and evaluation method presented in this paper is of universal sense for arbitrary MRI device while performing indirect linearity measurement of the gradient field based on any imaging objects or samples with circular or eclipse transverse section and therefore possesses considerable practical value.