Susceptibility artifact

Fig. 5.4a,b. Susceptibility artifacts due to the vicinity of air in the sphenoid sinus the flow signal of ICA is lowered symmetrically on the TOF images (a), when a fat-signal suppressing water excitation pulse sequence was used. The conventional TOF/ TONE sequence shows no false vessel extinction, but a higher background signal from fat tissue (b)... 

Unlike TIA patients with infarction on DWI, it is not obvious that patients with normal DWI have suffered from ischemia as the cause of their transient symptoms. In these patients, TIA mimics should also be considered (see Chap. 19). However, an ischemic etiology for transient symptoms cannot be excluded by the lack of an associated hyperintense lesion on DWI. A short-lasting episode of ischemia without DWI changes, or with reversible DWI changes as demonstrated in animals (Minematsu et al. 1992 Mintorovitch et al. 1991), might have occurred at the time of symptoms. In addition, DWI may occasionally miss very small infarctions, especially in the brainstem location (Ay et al. 1999 Kuker et al. 2002 Lovblad et al. 1998). This is most likely due to susceptibility artifacts induced by surrounding bones at the skull base. New multi-array head coil systems and parallel imaging techniques promise to overcome this limitation and improve the detection rate of small infarctions in the brainstem. 

Gradient echo-based sequences, such as constructive interference in steady state sequences, also are used for the imaging of the inner ear region (Casselman et al. 1996 Held et al. 1997). However, the specific absorption rate of these sequences may be higher than that of 3D fast spin echo-based sequences, and susceptibility artifacts may be more pronounced, especially at 3 T scanners. 

Typically, 3D FT volume studies have been conducted with gradient echo sequences that could offer short acquisition time due to their short repetition time. Currently, 3D fast or turbo spin echo sequences can be applied clinically, and they offer pure T2-weighted volumetric images without susceptibility artifacts. Although fast or turbo spin echo sequences utilize... 

Due to significant susceptibility artifact created by surgical hardware, MRl is not the study of choice for postoperative evaluations, especially for the assessment of healing of treated fractures and complications such as osteomyelitis or recurrence of a skeletal tumor (Fayad et al. 2005). When hardware is present, postoperative review of patients can be effectively accomplished by 3D volume rendering... 

MRCP is helpful in the detection of biliary strictures, bile leaks, and biloma formation. Thick-slab MRCP images are particularly useful in the presence of biliary dilatation (Fig. 4.2.25). However, proximal biliary dilatation may be absent in the transplanted patient with stenosis at the anastomotic site (Laghi et al. 1999 Pandharipande et al. 2001). Careful analysis of thin-slice MR images can help to identify the stricture and/or leak (Fig. 4.2.26). False MR positive and negative results may occur in the presence of surgical clips due to susceptibility artifact obscuring the biliary ducts. 

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