Application of Basic Principles of Physics to Head and Neck MR Angiography: Troubleshooting for Artifacts

Abstract

Neurovascular imaging studies are routinely used for the assessment of headaches and changes in mental status, stroke workup, and evaluation of the arteriovenous structures of the head and neck. These imaging studies are being performed with greater frequency as the aging population continues to increase. Magnetic resonance (MR) angiographic imaging techniques are helpful in this setting. However, mastering these techniques requires an in-depth understanding of the basic principles of physics, complex flow patterns, and the correlation of MR angiographic findings with conventional MR imaging findings. More than one imaging technique may be used to solve difficult cases, with each technique contributing unique information. Unfortunately, incorporating findings obtained with multiple imaging modalities may add to the diagnostic challenge. To ensure diagnostic accuracy, it is essential that the radiologist carefully evaluate the details provided by these modalities in light of basic physics principles, the fundamentals of various imaging techniques, and common neurovascular imaging pitfalls.

Hyperintense Thyroid Incidentaloma on Time of Flight Magnetic Resonance Angiography

“…When rapidly applied radiofrequency pulses are repeated at a region, stationary spins in that region cannot relax between pulses, and any background signal arising from these stationary spins degrades TOF data, eventually resulting in effective suppression of background signals except moving spins newly entering the section, such as blood. In spite of background suppression, lesions or materials with extremely short T1 relaxation time (i.e., thrombus, subacute hemorrhage, and melanin) can unintentionally be showed on TOF images ( 11 ). Therefore, thyroid nodules with such internal contents can be visualized on TOF-MR angiography.…”

Serial testing of the ICHD-3 beta diagnostic criteria for probable reversible cerebral vasoconstriction syndrome: A prospective validation study

“…Second, TOF MRA is a non-invasive and safe method (6), while DSA carries a substantial risk of deterioration in patients with RCVS (11). Although both MRA and CTA have limitations for the detection of distal vasoconstrictions (12), limitations of TOF MRA, flow-related artifact and in-plane saturation artifact can be overcome by follow-up imaging, which helped to differentiate true reversible vasoconstrictions versus artifact in distal intracranial arteries (14).…”

A vascular cause of neck pain

“…Patent blood vessels with fast flowing blood create ''flow voids'' on MRI that appear a black signal along the vessel course [3]. This artifact is related to protons in the blood moving out of the region imaged in between the radiofrequency excitation pulse and the time that the excited protons relax, and release the radiofrequency that is measured to produce an image.…”