How is image quality assessed in an MRI system?

Image quality in an MRI system is assessed through a combination of subjective and objective methods, focusing on factors such as spatial resolution, contrast, signal-to-noise ratio (SNR), and artifacts. Spatial resolution refers to the ability to distinguish between two closely spaced objects as separate entities in the image. It is often assessed using phantoms containing test patterns with varying line spacings. Contrast refers to the ability to differentiate between tissues with slightly different signal intensities. It depends on the MRI pulse sequence parameters and the inherent tissue properties. SNR, or signal-to-noise ratio, is a measure of the strength of the desired signal relative to the background noise. A higher SNR results in a clearer image with less graininess. SNR is typically measured by calculating the ratio of the average signal intensity in a region of interest to the standard deviation of the signal intensity in a background region. Artifacts are distortions or errors in the image that do not represent actual anatomical structures. Common MRI artifacts include motion artifacts, chemical shift artifacts, and susceptibility artifacts. The presence and severity of artifacts are visually assessed by experienced radiologists and MRI technologists. Quantitative measurements, such as geometric distortion measurements, may also be performed to assess the magnitude of certain artifacts. Regular quality control testing using standardized phantoms is essential for monitoring the stability and performance of the MRI system. These tests involve acquiring images of the phantoms and analyzing them to assess various image quality parameters. The results of these tests are compared to baseline values to detect any changes in system performance. In addition to phantom-based testing, clinical image quality is also assessed by radiologists as part of their routine image interpretation. They evaluate the overall clarity, sharpness, and diagnostic utility of the images.