Real‐time MRI at a resolution of 20 ms

Abstract

The desire to visualize noninvasively physiological processes at high temporal resolution has been a driving force for the development of MRI since its inception in 1973. In this article, we describe a unique method for real-time MRI that reduces image acquisition times to only 20 ms. Although approaching the ultimate limit of MRI technology, the method yields high image quality in terms of spatial resolution, signal-to-noise ratio and the absence of artifacts. As proposed previously, a fast low-angle shot (FLASH) gradient-echo MRI technique (which allows for rapid and continuous image acquisitions) is combined with a radial encoding scheme (which offers motion robustness and moderate tolerance to data undersampling) and, most importantly, an iterative image reconstruction by regularized nonlinear inversion (which exploits the advantages of parallel imaging with multiple receiver coils). In this article, the extension of regularization and filtering to the temporal domain exploits consistencies in successive data acquisitions and thereby enhances the degree of radial undersampling in a hitherto unexpected manner by one order of magnitude. The results obtained for turbulent flow, human speech production and human heart function demonstrate considerable potential for real-time MRI studies of dynamic processes in a wide range of scientific and clinical settings.

Robot-Guided Open-Loop Insertion of Skew-Line Needle Arrangements for High Dose Rate Brachytherapy

“…Some studies like [47], [48] have explored use of MRI for real-time scanning. Tovar-Arriaga et al [49] and Ji [50] proposed workflows for needle insertion using CT and MRI feedback respectively.…”

Assessment of disintegrant efficacy with fractal dimensions from real-time MRI

“…Mildly T1-weighted real-time MRI at 13.3 frames per second was accomplished with use of an undersampled radial FLASH sequence and regularized nonlinear inversion (NLINV) for image reconstruction (Uecker et al, 2010;Zhang et al, 2010). To reduce image artifacts that may be caused by an inaccurate technical switching of the radial encoding gradients, linear and B 0 eddy-current effects were corrected by methods described by Block and Uecker (2011) and Moussavi et al (2014).…”

Towards MRI temperature mapping in real time—the proton resonance frequency method with undersampled radial MRI and nonlinear inverse reconstruction

“…Respective applications range from cardiac MRI without ECG synchronization and during free breathing (2) to real-time studies of blood flow (3), swallowing (4), dysphagia (5), esophageal functions (6), dynamics of the temporomandibular joint (7), respiration-induced flow of the cerebrospinal fluid (8,9) as well as movements of the articulators during normal speech (10) or brass playing of patients with embouchure dystonia (11). In a technical sense, the method is based on highly undersampled radial gradient-echo sequences in combination with iterative image reconstruction by nonlinear inversion (NLINV) and temporal regularization (1). These new possibilities are expected to vastly broaden the range of clinical MRI and, in particular, to stimulate renewed interest in "interventional MRI", i.e., the use of real-time MRI for monitoring and guiding minimally invasive procedures.…”