Spectral Adiabatic Inversion Recovery (SPAIR) MR imaging of the Abdomen

Magnetic resonance imaging (MRI) has become a major imaging tool for the depiction and characterization of abdominal disease. Standard abdominal MRI protocols encompass different forms of T1-weighted (T1w) and T2-weighted (T2w) data acquisition. These sequences can be collected in less than 20 seconds, which typically is within the patients’ ability to suspend respiration. Hence, artifacts due to physiological motion including respiration and bowel motion can be reduced, if not avoided. While most T1-weighted imaging techniques of the abdomen include gradient echo (GRE) sequences, T2-weighted imaging is based on the collection of single shot fast spin echo (SSFSE) data. The latter sequences in conjunction with fat saturation play a key role for the interpretation of different abdominal processes as liver lesions can be most accurately delineated and specified [1]. Furthermore, T2-weighted imaging with fat saturation is crucial for the depiction of edema and/or free fluid. This is particularly helpful for the depiction of inflammatory processes of the bowel, e.g. in patients with Crohn’s disease [2, 3], appendicitis [4, 5] or diverticulitis [6–8]. Finally, T2-weighted data may be particularly useful in the setting of pregnant patients*. As the intravenous administration of gadolinium based contrast agents is contraindicated in this patient group, T1-weighted imaging is restricted and only provides limited information. Hence, T2-weighted imaging with fat saturation has been found to be the key sequence in pregnant* women with suspected abdominal inflammation or tumor disease [9–12]. Different techniques for fat saturation in MRI can be used. The most common form in abdominal imaging is the use of a 180° excitation pre-pulse, which suppresses the signal specific tissue depending on the inversion time applied. The inversion time (TI) is set according to the T1 of fat in order to selectively null the fat signal (TI = 150-170 ms). In the most common implementation, the inversion pulse is applied with a wide frequency bandwidth to include both fat and water spins. A potential drawback to this approach is that the water signal will not be fully recovered during data acquisition, and the overall water signalto-noise ratio (SNR) will be diminished. This can negatively impact the contrastto-noise ratio (CNR) of lesions surrounded by tissue, such as tumors within the liver.