Technique for ghost artifact suppression in MRI imaging
Magnetic Resonance Imaging (MRI) is a safe, non-invasive test that creates detailed images of organs and tissues. In MRI, data is acquired by a scanner running software that sends a sequence of radio frequency (RF) pulses into the tissue placed in a strong magnetic field. The magnetic field causes the spins of protons in the tissue to align. Each RF pulse disrupts this alignment. When the pulse ends, the magnetization of the sample returns (or relaxes) to its resting state, thereby producing another RF signal that is detected and used to create the images. The time course of this relaxation depends on the tissue composition. Some tissue species (such as pericardial effusion, pleural effusion, cerebro-spinal fluid, stomach fluid, saline in breast implants) have relaxation times much longer than those of tissues of interest (such as body organs). These species are prone to create artifact “ghost” images in pulse sequence scans since their magnetization doesn’t stabilize between the pulses. “Ghost images” can hamper clinical image evaluation and sometimes prevent MRI-based clinical diagnosis. Existing methods of ghost artifact suppression include introducing “dummy acquisition time” into the imaging sequence or placing a saturation slab on top of the problematic region. Although yielding some image improvement, these methods have a variety of problems: they either do not completely remove ghost artifacts, or are not feasible for every organ, or result in a prolonged scan duration that becomes unfeasible as the patient is not able to hold their breath for that long. Therefore, there is a need for an improved, robust method of ghost image suppression.
Researchers at Duke Cardiovascular MR Center invented a technique that suppresses the signal from long-relaxation time species without reducing image quality. Their method relies on introducing a “suppression module” to the RF imaging sequence before the conventional imaging sequence begins. This module consists of saturation recovery pre-pulse and a time delay during which magnetization of species with long relaxation time stabilizes. The invention has been successfully tested on a commercial Siemens scanner. Since this technique achieves ghost image suppression by a simple software change, no additional hardware modifications are necessary and it can be implemented on any commercial MRI scanner. It suppresses artifacts in various regions of the human body with no disadvantage for the patient.
- Allows reliable complete artifact suppression without an increase in patient breath hold time and without any operator input.
- Works for all body regions (cardiac, head/neuro, pleural, orthopedic MR, etc)
- No signal-to-noise reduction