B0mapping

B0mapping refers to the process of associating the magnetic field strength of zero (B0) within a Magnetic Resonance Imaging (MRI) scanner. This is a crucial step in ensuring image quality and accuracy. In MRI, the main magnetic field, known as B0, is designed to be as uniform as possible across the entire imaging volume. However, imperfections in the scanner hardware, the presence of the patient within the bore, and even magnetic susceptibility differences in tissues can cause deviations from this ideal uniformity. B0mapping is the technique used to precisely measure and quantify these field variations.

The process typically involves acquiring specialized MRI sequences that are sensitive to local field inhomogeneities. These sequences generate data that can then be processed to create a map, or image, illustrating the deviation of the magnetic field from the nominal B0 value at each point in space. This map is often expressed in units of frequency, such as Hertz (Hz) or parts per million (ppm).

The primary applications of B0mapping are for correcting image distortions and signal losses that occur due to these field inhomogeneities. For example, in certain pulse sequences, particularly those with longer echo times or in regions with significant susceptibility gradients (like near air-tissue interfaces), B0 inhomogeneities can lead to spatial misregistration and blurring of anatomical structures. By knowing the B0 map, these distortions can be computationally corrected during image reconstruction or post-processing, leading to more accurate anatomical representation and improved diagnostic confidence. Furthermore, B0mapping is essential for techniques like magnetic resonance spectroscopy (MRS), where spectral resolution is highly dependent on field uniformity.