CSF flow studies

CSF flow studies are performed using a variety of MRI techniques and are able to qualitatively assess and quantify pulsatile CSF flow. The most common technique used is time-resolved 2D phase contrast MRI with velocity encoding. 

MRI pulse sequence abbreviations

This article contains a list of commonly and less commonly used MRI pulse sequence abbreviations and their meaning. If available, an explanation is included in a separate article.

MRI sequence

An MRI sequence is a number of radiofrequency pulses and gradients that result in a set of images with a particular appearance. This article presents a simplified approach to recognizing common MRI sequences, but does not concern itself with the particulars of each sequence.

For a more complete and accurate discussion please refer to MRI pulse sequences.

MRI safety

MRI scanners, although free from potentially cancer-inducing ionising radiation found in plain radiography and CT, have a host of safety issues which must be taken very seriously. MRI safety can be divided into:

1. main magnetic field
2. varying magnetic (gradient) fields
3. radiofrequency

Spiral pulse sequences

Spiral scanning in MRI is unlike spiral scanning in CT where the x-ray tube is continuously rotating and data is continuously being acquired. In MRI the word "spiral" refers to the pattern of sampling k-space. In conventional imaging sequences including spin echo and gradient echo and in fast imaging sequences, a line or multiple lines of k-space in the frequency direction are acquired consecutively. In spiral scanning, k-space is acquired in a spiral trajectory. The entire k-space can be acquired during a single acquisition, or interleaved using more than one acquisition. This sequence allows faster image acquisition than the fast echo sequences but is slower than echo-planar imaging. Spiral scanning tends to have fewer artifacts than echo-planar imaging since adjacent points in k-space are acquired in close temporal proximity. The figures to the right show how the acquisition of data in k-space is done with conventional sequences and with spiral scanning.

PD weighted spin-echo images

Proton-density weight images are related to the number of nuclei in the area being imaged (number of hydrogen protons), as opposed to the magnetic characteristics of the hydrogen nuclei. They are produced from the first echo. PD weight images result when the contribution of both T1 and T2 contrast is minimized.  They have a long TR (2000+ms) to minimize T1 differences because all tissues exhibit full longitudinal relaxation prior to the next 90 degrees RF pulse. They have a short TE (TE1, 20ms) to minimize T2 differences. High PD tissues appear bright.

Fast spin echo

Fast or turbo spin echo (FSE/TSE) is an adaptation of conventional spin-echo (SE) acquisition technique designed to reduce imaging time. It has largely supplanted the original spin-echo technique due to vastly improved imaging speed.