Susceptibility weighted imaging at 1.5 Tesla magnetic resonance imaging in dogs: Comparison with T2*‐weighted gradient echo sequence and its clinical indications

Abstract

Susceptibility weighted imaging (SWI) is a high resolution, fully velocity‐compensated, three‐dimensional gradient echo (GE) MRI technique. In humans, SWI has been reported to be more sensitive than T2*‐weighted GE sequences in the identification of both intracranial hemorrhage and intra‐vascular deoxyhemoglobin. However, published clinical studies comparing SWI to T2*‐weighted GE sequences in dogs are currently lacking. The aim of this retrospective, observational study was to compare SWI and T2*‐weighted GE sequences in a group of dogs with intracranial disease. Medical records were searched for dogs that underwent a brain MRI examination that included T2*‐weighted GE and SWI sequences. The presence and appearance of non‐vascular and vascular signal voids observed on T2*‐weighted GE and SWI were compared. Thirty‐two dogs were included with the following diagnoses: presumed and confirmed intracranial neoplasia (27), cerebrovascular accidents (3), and trauma (2). Hemorrhagic lesions were significantly more conspicuous on SWI than T2*‐weighted GE sequences (P < .0001). Venous structures were well defined in all SWI sequences, and poorly defined in all dogs on T2*‐weighted GE. Susceptibility weighted imaging enabled identification of vascular abnormalities in 30 of 32 (93.8%) dogs, including: neovascularization in 19 of 32 (59.4%) dogs, displacement of perilesional veins in five of 32 (15.6%) dogs, and apparent dilation of perilesional veins in 10 of 32 (31.3%) dogs. Presence of neovascularization was significantly associated with T1‐weighted post‐contrast enhancement (P = .0184). Hemorrhagic lesions and venous structures were more conspicuous on SWI compared to T2*‐weighted GE sequences. Authors recommend adding SWI to standard brain protocols in dogs for detecting hemorrhage and identifying venous abnormalities for lesion characterization.

Intracranial Lesion Detection and Artifact Characterization: Comparative Study of Susceptibility and T2*-Weighted Imaging in Dogs and Cats

“…This phenomenon is proportional to the field strength ( 18 ). Although the feasibility of the sequence has been reported in veterinary medicine ( 1 , 3 ), evaluation of SWI phase images and artifact characterization are currently lacking.…”

“…One of the advantages of SWI in comparison with T2 * WI in humans is increased sensitivity for the detection of small brain parenchymal hemorrhages ( 11 , 12 ). In dogs, increased conspicuity of hemorrhagic lesions and venous structures has been described ( 3 ). While cerebral microbleeds have been defined as ASV under 4 mm in T2 * WI in dogs ( 25 ), this measurement does not represent the true size of the lesion but the size of the blooming artifact produced by the magnetic field distortion.…”

“…Absent or minuscule air-filled frontal sinuses are known in some small-breed dogs, including many brachycephalic breeds ( 22 ). The current literature describing the use of SWI in veterinary medicine reports field strength of 1.5 Tesla (T) ( 1 , 3 ). In human medicine, lesion contrast and venous vessel contrast are increased in 3 compared with 1.5 T; however, susceptibility artifacts caused by anatomical structures are also more prominent ( 17 ).…”

“…In human neuroimaging, SWI is used predominantly for the evaluation of intracranial hemorrhage, vascular malformations, traumatic brain injury, brain tumors, congenital, infections, and neurodegenerative disorders ( 6 , 7 , 15 ). In veterinary medicine, the utility of SWI sequence has been proven in dogs affected by traumatic brain injury and for detecting hemorrhage and identifying intracranial venous abnormalities ( 1 , 3 ). A recently published study demonstrated that venous structures and hemorrhagic lesions are more conspicuous in SWI than in T2 * WI in dogs ( 3 ), but studies in cats as well as the influence of unwanted artifacts on the image evaluation are currently lacking.…”

“…In veterinary medicine, the utility of SWI sequence has been proven in dogs affected by traumatic brain injury and for detecting hemorrhage and identifying intracranial venous abnormalities ( 1 , 3 ). A recently published study demonstrated that venous structures and hemorrhagic lesions are more conspicuous in SWI than in T2 * WI in dogs ( 3 ), but studies in cats as well as the influence of unwanted artifacts on the image evaluation are currently lacking.…”