Effect of Delayed Acquisition Times on Gadolinium‐enhanced Magnetic Resonance Imaging of the Presumably Normal Canine Brain

Abstract

Effect of delayed acquisition times on Gadolinium-enhanced MRI of the presumably normal canine brain. A delay in imaging following intravenous contrast medium administration has been recommended to reduce misdiagnoses. However, the normal variation of contrast enhancement in dogs following a delay has not been characterized. Contrast enhanced MR imaging of 22 dogs was assessed, in terms of identification of normal anatomic structures, to investigate the variation associated with 10 minute delay between contrast medium administration and imaging. All dogs had a normal brain MR imaging study and unremarkable CSF. Specific ROIs were assessed both objectively, using computer software, and subjectively using three observers. Mean contrast enhancement greater than 10% was seen in the pituitary gland, choroid plexus, meninges, temporal muscle, trigeminal nerve and the trigeminal nerve root. Structures with an active blood-brain-barrier had minimal contrast enhancement (<6%). Enhancing structures had significantly more contrast enhancement at t=1min versus t=10min, except in temporal muscle, the trigeminal nerve and the trigeminal nerve root.Inter-observer agreement was moderate to good in favor of the initial post contrast T1w sequence.The observers found either no difference or poor agreement in identification of the non-vascular structures. Intra-observer agreement was very good with all vascular structures and most nonvascular structures. A degree of meningeal enhancement was a consistent finding. The initial acquisition had higher enhancement characteristics and observer agreement for some structures; however, contrast-to-noise was comparable in the delayed phase or not significantly different. We provide baseline references and suggest that the initial T1w post contrast sequence is preferable but not essential should a delayed post contrast T1w sequence be performed.

Generalized myoclonic epilepsy with photosensitivity in juvenile dogs caused by a defective DIRAS family GTPase 1

“…Ventricle asymmetry is also frequently present in dogs without epileptic seizures, and thus may be clinically not relevant (12). Similarly, a small amount of meningeal enhancement is consistently demonstrated in normal dogs (36). However, we cannot exclude that some of the structural abnormalities interacted with the phenotype: for example, lowered seizure threshold on both hemispheres.…”

Exclusion of a Brain Lesion: Is Intravenous Contrast Administration Required after Normal Precontrast Magnetic Resonance Imaging?

“…Results may be dependent on magnetic field strength and sequence parameters 42, 43. The use of contrast‐enhanced FLAIR images,44 digital subtraction images, delayed image acquisition,14, 45, 46, 47 different doses47, 48 or other types of gadolinium‐based contrast media49 also may influence lesion detection. In this study, there was no suggestion that the utility of postcontrast sequences for lesion detection is dependent on low field magnet strength (0.2 T versus 0.23 T) or the use of different contrast agents (gadobenate dimeglumine versus gadobutrol).…”

“…Contrast enhancement of the pituitary gland, choroid plexus or trigeminal nerves could be rated as nonpathologic if deemed within normal limits 13, 14. Reviewers were asked to indicate if any abnormal contrast enhancement was visible on postcontrast sequences and to classify the entire study, with access to all sequences, as either normal or abnormal based on the presence of a clinically relevant brain lesion.…”

Appearance of the Canine Meninges in Subtraction Magnetic Resonance Images

“…T he meninges (dura mater, arachnoid, and pia mater) are affected by a variety of inflammatory and neoplastic conditions in dogs and, therefore, are tissues of importance for radiologists interpreting magnetic resonance (MR) images of the canine head. The lack of a blood–brain barrier in the meninges facilitates accumulation of gadolinium‐chelates, hence use of postgadolinium MR images has been emphasized for clinical examination of the meninges . Numerous clinical reports include descriptions of meningeal lesions in postgadolinium T1‐weighted MR images of dogs …”

“…In contrast, descriptions of the appearance of normal canine meninges in MR images are relatively sparse. Based primarily on descriptions of humans, the meninges are not considered to be visible as discrete structures in noncontrast MR images, but appear as short, thin curvilinear segments with minimal enhancement in T1‐weighted postgadolinium images . Meningeal enhancement may be divided into pachymeningeal (affecting the dura and periosteum on the inner aspect of the skull) and leptomeningeal (affecting the pia and arachnoid) .…”