Comparison of two fat-suppressed magnetic resonance imaging pulse sequences to standard t2-weighted images for brain parenchymal contrast and lesion detection in dogs with inflammatory intracranial disease

Gadolinium contrast medium administration does not adversely affect T2*-weighted gradient recalled echo magnetic resonance imaging of the canine brain at 1.5 Tesla

As gadolinium-based contrast agents are paramagnetic and have T2 shortening effects, they have the potential to adversely affect gradient recalled echo sequences. The aim of this prospective, cross-sectional study was to evaluate the effects of gadolinium administration on T2*-weighted sequence diagnostic quality and signal intensity when imaging the canine brain. A total of 100 dogs underwent brain magnetic resonance imaging (MRI) including pre- and postcontrast T2*-weighted sequences acquired with a delay (Group A) or immediately (Group B) following gadolinium administration. Pre- and postcontrast images were subjectively compared. In dogs with intracranial enhancing masses, regions of interest were drawn on corresponding images and signal intensity ratios were calculated. The effect of degree and pattern of contrast enhancement, susceptibility artifacts, and time between contrast injection and T2*-weighted sequence acquisition on signal intensity ratio was evaluated. Overall 31 dogs had contrast enhancing intracranial masses. Subjectively, there was no difference in image quality of T2*-weighted sequences obtained before and after contrast medium administration. No significant signal intensity differences of intracranial contrast enhancing masses were found (Group A P = 0.9999; Group B P = 0.9992). Susceptibility artifacts did not differ in appearance, and there was no effect on calculated signal intensity ratio (P = 0.8142). Similarly, there was no effect of degree of enhancement or contrast heterogeneity on signal intensity ratio (P = 0.4413). No correlation was found between signal intensity ratio and the time to acquisition (P = 0.199). Administration of gadolinium-based MRI contrast agents does not adversely affect T2*-weighted imaging of the brain in dogs at 1.5 T even in the presence of contrast enhancing lesions.

Consensus recommendations on standardized magnetic resonance imaging protocols for multicenter canine brain tumor clinical trials

The National Cancer Institute Comparative Brain Tumor Consortium, Patient Outcomes Working Group, propose a consensus document in support of standardized magnetic resonance imaging protocols for canine brain tumor clinical trials. The intent of this manuscript is to address the widely acknowledged need to ensure canine brain tumor imaging protocols are relevant and have sufficient equivalency to translate to human studies such that: (1) multi-institutional studies can be performed with minimal inter-institutional variation, and (2) imaging protocols are consistent with human consensus recommendations to permit reliable translation of imaging data to human clinical trials. Consensus recommendations include pre- and postcontrast three-dimensional T1-weighted images, T2-weighted turbo spin echo in all three planes, T2*-weighted gradient recalled echo, T2-weighted fluid attenuated inversion recovery, and diffusion weighted imaging/diffusion tensor imaging in transverse plane; field of view of ≤150 mm; slice thickness of ≤2 mm, matrix ≥ 256 for two-dimensional images, and 150 or 256 for three-dimensional images.

Hyperintensity of Cerebrospinal Fluid on T2-Weighted Fluid-Attenuated Inversion Recovery Magnetic Resonance Imaging Caused by High Inspired Oxygen Fraction

In veterinary medicine, patients undergo magnetic resonance imaging (MRI) under general anesthesia to enable acquisition of artifact-free images. The fraction of inspired oxygen (FiO₂) ranges between 30 and 95%. In humans, a high FiO₂ is associated with incomplete signal suppression of peripheral cerebrospinal fluid (CSF) spaces on T2-weighted fluid-attenuated inversion recovery (T2w-FLAIR) sequences. The influence of FiO₂ on T2w-FLAIR images remains unreported in small animals. The aim of this prospective study was to investigate whether a high FiO₂ is associated with hyperintensity in peripheral CSF spaces on T2w-FLAIR images in dogs and cats. Client-owned patients undergoing brain MRI were prospectively enrolled. Animals with brain parenchymal abnormalities and/or meningeal contrast enhancement on MRI images and/or abnormal CSF analysis were excluded. Consequently, twelve patients were enrolled. Anesthesia was maintained by isoflurane 0.5-1 minimal alveolar concentration in 30% oxygen. After acquisition of transverse and dorsal T2w-FLAIR images, the FiO₂ was increased to 95%. The T2w-FLAIR sequences were then repeated after 40 min. Arterial blood gas analysis was performed in six patients at the same time as T2w-FLAIR sequence acquisition. Plot profiles of the signal intensity (SI) from CSF spaces of three cerebral sulci and adjacent gray and white matter were generated. SI ratios of CSF space and white matter were compared between the T2w-FLAIR images with 30 and 95% FiO₂. An observer blinded to the FiO₂, subjectively evaluated the SI of peripheral CSF spaces on T2w-FLAIR images as high or low. There was significant difference in the partial pressure of oxygen between the two arterial samples (P < 0.001). The SI ratios obtained from the T2w-FLAIR images with 95% FiO₂ were significantly higher compared with those obtained from the T2w-FLAIR images with 30% FiO₂ (P < 0.05). The peripheral CSF spaces were subjectively considered hyperintense in 11 of 12 cases on T2w-FLAIR images with 95% FiO₂ (P < 0.005). A clear difference in SI, dependent on the FiO₂ was seen in the peripheral CSF spaces on T2w-FLAIR images. In conclusion, the influence of FiO₂ must be considered when differentiating pathological and normal CSF spaces on T2w-FLAIR images in dogs and cats.