Optimizing contrast protocol for bone-subtraction CT angiography of intracranial arteries in normal dogs using 160-slice CT

BACKGROUND

Bone-subtraction computed tomography angiography (CTA) (BSCTA) is a new technique designed to overcome the limitation of three-dimensional CTA, where the vessels surrounded by bone and calcification can be obscured. An optimal contrast CT protocol for intracranial artery visualization with BSCTA has yet to be established in dogs.

OBJECTIVES

The purpose of this study was to determine the optimal contrast protocol of CTA for visualizing intracranial artery using an automatic bone-subtraction technique in dogs.

METHODS

Brain CTA was performed four times for each of nine healthy beagle dogs to cover all the contrast protocols: two different contrast iodine concentrations (300 and 370 mgI/mL) and two different contrast media injection rates (2 and 4 mL/s). Bone removal post-processing was performed automatically by subtracting the non-enhanced CT data from the contrast CT data using a dedicated workstation. The bone-subtracted intracranial vessels were analysed for quantitative and qualitative evaluation.

RESULTS

Quantitative evaluation showed significantly higher CT attenuation values for the group with a 370 mgI/mL iodine content at a rate of 4 mL/s than the two groups with a 300 mgI/mL iodine content at the rates of 2 and 4 mL/s (p < 0.001). Qualitative assessment revealed significantly higher mean scores for the 370 mgI/mL groups than the 300 mgI/mL groups and significantly higher mean scores for the 4 mL/s groups than the 2 mL/s groups (p < 0.05).

CONCLUSIONS

The optimal contrast protocol for BSCTA suggests that high iodine material concentration and high injection rate should be used for strong arterial attenuation and great visualization of the intracranial arterial structure in dogs.

Optimal placement of the region of interest for bolus tracking on brain computed tomography angiography in Beagle dogs

This study aimed to determine the optimal placement of the region of interest (ROI) among four anatomical sites-pulmonary artery (PA), pulmonary vein (PV), aortic arch (AA), and carotid artery (CA)-in computed tomography (CT) brain angiography with automatic bolus tracking in healthy beagle dogs. Six beagles were included, and CT brain angiography was performed four times for each dog, to cover each ROI. The scan parameters, amount, and injection rate of the contrast medium were the same. The major intracranial arteries were selected for quantitative and qualitative evaluation: caudal cerebellar artery (CcA), basilar artery (BA), rostral cerebellar artery (RcA), caudal cerebral artery (CCA), middle cerebral artery (MCA), and rostral cerebral artery (RCA). Quantitative evaluation showed significantly higher CT attenuation values for the RcA, CCA, and MCA in the PA group and RcA and MCA in the PV group than in the CA group. Qualitative analysis revealed significantly higher scores for the BA, CCA, and MCA in the PA and PV groups than in the CA group. Venous contamination did not differ significantly among the ROIs, but the mean scores of the AA and CA groups were higher than those of the PA and PV groups. CT brain angiography using bolus tracking in the beagle dogs showed that the ROI should be placed at the PA or PV rather than at the CA for optimal images with strong contrast enhancement of the BA, RcA, CCA, and MCA and minimal venous contamination.

Natural Cerebral Aneurysm and Spontaneous Subarachnoid Hemorrhage in Mammals Other Than Man: Is There a Scope for Comparative Medicine?

BACKGROUND

Concepts that showed substantial efficacy in animal models of subarachnoid hemorrhage (SAH) often failed to improve outcome in humans with aneurysmal SAH. The concept of "comparative medicine," an open-minded comparison across species, might offer an alternative to the "constructed" animal models' approach. Naturally occurring diseases in animals might bear more similarity to human diseases than models. In this context, the question arises whether spontaneous intracranial aneurysms exist in animals or not, and whether they cause SAH or not.

METHODS

A systematic literature search was performed. Only articles dealing with natural aneurysms and/or SAH of mammals other than man were included. All articles dealing with induced aneurysms and/or SAH were removed.

RESULTS

Of 2812 screened articles, 9 articles describing natural intracranial aneurysms and/or SAH were found. In total 1979 individual animals of 29 species were examined. Natural intracranial aneurysms were described in 7 individual animals of 6 species. Spontaneous SAH was described in 3 species. In 1 chimpanzee, a ruptured intracranial aneurysm caused an SAH. Histological descriptions of the aneurysms were strikingly similar to those of humans.

CONCLUSIONS

Although interesting and innovative, the concept of "comparative medicine" seems to be impracticable due to the seemingly ultralow incidence of natural aneurysmal SAH in mammals other than man. The answer to the question "why intracranial aneurysms are less common in animals despite the strong histological similarity of cerebral arteries" might be a key issue. Last but not least, primates likely matter in SAH-related research, as aneurysmal SAH occurs in primates.