Fast three-dimensional contrast-enhanced magnetic resonance angiography of the canine lumbar spinal cord vascular supply: A feasibility study.

Magnetic resonance angiography (MRA) is the noninvasive spinal cord vascular imaging modality of choice in human medicine. The aim of this exploratory, prospective, descriptive study was to assess the feasibility of fast three-dimensional (3D) contrast-enhanced (CE) MRA for visualization of spinal vascular structures in the canine lumbar region. Fourteen canine patients weighing > 5 kg were included. The lumbar arteries were consistently visualized (14/14;100%). Spinal arteries, radicular branches, great radicular artery (of Adamkiewicz), ventral spinal artery, and dorsal spinal arteries were not visualized (0/14;0%). The internal vertebral venous plexus was visualized in 11 of 14 (79%) dogs. Overall, the results of this study show that fast 3D CE-MRA of the lumbar region in dogs is feasible. However, the smaller arteries responsible for the spinal cord vascular supply were not visualized in this study.

Ferumoxytol-enhanced magnetic resonance angiography provides comparable vascular conspicuity to CT angiography in dogs with intrahepatic portosystemic shunts.

Computed tomography angiography (CTA) is currently the gold standard imaging modality for anatomically characterizing canine hepatic vascular anomalies; with conventional, gadolinium-enhanced MR angiography being less frequently utilized. However, both imaging modalities are limited by a brief, first pass peak of contrast medium in the vasculature that necessitates precisely timed image acquisition. A long-acting purely intravascular magnetic resonance imaging (MRI) contrast agent, ferumoxytol, offers the potential to reduce complexity of magnetic resonance angiography (MRA) protocol planning by ensuring diagnostic contrast medium concentration in all the vessels that are targeted for imaging. Aims of this prospective, pilot, methods comparison study were to develop an optimized MRA protocol using ferumoxytol in dogs with hepatic vascular anomalies, perform a dose escalation trial to compare image quality with four-dose regimens of ferumoxytol, and compare accuracy of vascular anatomic depiction based on the gold standard of CTA. Six dogs (10.7-36.1 kg) with portosystemic shunts (four intrahepatic left divisional shunts and two intrahepatic right divisional shunts) were recruited for inclusion in the study. A dose-escalation trial was performed to compare image quality at four incremental dose levels of ferumoxytol (1, 2, 3, and 4 mg/kg) and to compare the accuracy of vascular anatomic detection to CTA. Ferumoxytol contrast-enhanced MRA (CE-MRA) at 4 mg/kg provided similar conspicuity of normal and abnormal vasculature compared to CTA with a minimal decrease in spatial resolution. Findings indicated that ferumoxytol holds promise for comprehensive, single breath hold CE-MRA of all abdominal vessels in dogs with portosystemic shunts. Background information provided in this study can be used to support development of other future applications such as intracranial and cardiac MRA, real-time imaging, flow quantification, and potentially sedated MRI imaging.

Diffusion-weighted and perfusion-weighted magnetic resonance imaging of the prostate gland of healthy adult dogs.

OBJECTIVE: To describe diffusion and perfusion characteristics of the prostate gland of healthy sexually intact adult dogs as determined by use of diffusion-weighted and perfusion-weighted MRI. ANIMALS: 12 healthy sexually intact adult Beagles. PROCEDURES: Ultrasonography of the prostate gland was performed. Subsequently, each dog was anesthetized, and morphological, diffusion-weighted, and perfusion-weighted MRI of the caudal aspect of the abdomen was performed. The apparent diffusion coefficient was calculated for the prostate gland parenchyma in diffusion-weighted MRI images in the central ventral and peripheral dorsal areas. Perfusion variables were examined in multiple regions of interest (ROIs) in the ventral and dorsal areas of the prostate gland and in the gluteal musculature. Signal intensity was determined, and a time-intensity curve was generated for each ROI. RESULTS: Results of ultrasonographic examination of the prostate gland revealed no abnormalities for any dog. Median apparent diffusion coefficient of the prostate gland was 1.51 × 10-3 mm2/s (range, 1.04 × 10-3 mm2/s to 1.86 × 10-3 mm2/s). Perfusion-weighted MRI variables for the ROIs differed between the prostate gland parenchyma and gluteal musculature. CONCLUSIONS AND CLINICAL RELEVANCE: Results provided baseline information about diffusion and perfusion characteristics of the prostate gland in healthy sexually intact adult dogs. Additional studies with dogs of various ages and breeds, with and without abnormalities of the prostate gland, will be necessary to validate these findings and investigate clinical applications.

Cardiovascular effects of two adenosine constant rate infusions in anaesthetized dogs.

OBJECTIVE: Adenosine induces vasodilatation. The aim of this study was to investigate cardiovascular effects of two adenosine constant rate infusion (CRI) doses in dogs. STUDY DESIGN: Experimental, longitudinal repeated measure design. ANIMALS: Ten healthy purpose-bred Beagle dogs. METHODS: Each dog was sedated with butorphanol. Anaesthesia was induced with propofol intravenously and maintained with sevoflurane (inspired oxygen fraction = 47-55%). Controlled mechanical ventilation was used to maintain normocapnia. Two doses of adenosine were administered as CRIs to each dog: 140 µg kg-1 minute-1 (A140) followed by 280 µg kg-1 minute-1 (A280). Pulse rate, invasive arterial pressure and stroke volume (by magnetic resonance phase contrast angiography) were measured at baseline, 3 minutes after starting adenosine and 3 and 10 minutes after discontinuing adenosine. Cardiac output, cardiac index and approximated systemic vascular resistances (approximate SVR) were calculated. Additionally, arterial blood gases, co-oximetry, electrolytes, glucose and lactate were measured and oxygen content and delivery calculated. One-way repeated measures analysis of variance (p < 0.05) was used for data analysis. RESULTS: A140 and A280 resulted in a significant decrease in arterial blood pressure [systolic (p = 0.008), mean (p = 0.003), and diastolic arterial pressure (p = 0.004)] and approximate SVR (p = 0.008) compared with baseline. No significant changes were detected for the other variables. All values returned to baseline within 3 minutes after adenosine discontinuation. CONCLUSIONS AND CLINICAL RELEVANCE: Adenosine CRI decreases arterial pressure by vasodilatation in healthy dogs. No additional effects were observed with the higher dose. The effects in compromised dogs remain to be investigated.

Use of three-dimensional time-of-flight magnetic resonance angiography at 1.5 Tesla to evaluate the intracranial arteries of 39 dogs with idiopathic epilepsy.

OBJECTIVE: To assess visualization of the intracranial arteries and internal carotid artery (ICA) on 3-D time-of-flight (TOF) magnetic resonance angiography (MRA) images obtained at 1.5 T and to investigate factors that affect the image quality of those arteries in dogs. ANIMALS: 39 dogs with idiopathic epilepsy. PROCEDURES: Each dog underwent 3-D TOF MRA, and 5 pairs of intracranial arteries, the basilar artery, and both ICAs were evaluated. Each artery was assigned an image-quality score on a scale of 0 to 3, where 0 = poor and 3 = excellent. Multivariable regression analysis was used to assess whether age, body weight (BW), serum total cholesterol concentration, intracranial volume (ICV), and mean arterial pressure were significantly associated with the image quality of each vessel. RESULTS: In all dogs, the image-quality score was 2 or 3 for the proximal middle cerebral arteries, basilar artery, and caudal aspect of the caudal communicating arteries. In some dogs, the rostral cerebellar arteries, rostral aspect of the caudal communicating arteries, and middle and rostral aspects of the ICA were poorly visualized. For various arteries, image quality was negatively associated with age and positively associated with BW and ICV. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that 3-D TOF MRA images obtained at 1.5 T did not consistently and clearly delineate the ICA and narrow or peripheral intracranial arteries of dogs; therefore, careful attention is required when such images are assessed. Patient age, BW, and ICV can also affect the image quality of some intracranial arteries on 3-D TOF MRA images. (Am J Vet Res 2019;80:480-489).

Perfusion-weighted and diffusion-weighted magnetic resonance imaging of the liver, spleen, and kidneys of healthy adult male cats.

OBJECTIVE To describe perfusion and diffusion characteristics of the liver, spleen, and kidneys of healthy adult male cats as determined by morphological, perfusion-weighted, and diffusion-weighted MRI. ANIMALS 12 healthy adult male cats. PROCEDURES Each cat was anesthetized. Morphological, perfusion-weighted, and diffusion-weighted MRI of the cranial aspect of the abdomen was performed. A region of interest (ROI) was established on MRI images for each of the following structures: liver, spleen, cortex and medulla of both kidneys, and skeletal muscle. Signal intensity was determined, and a time-intensity curve was generated for each ROI. The apparent diffusion coefficient (ADC) was calculated for the hepatic and splenic parenchyma and kidneys on diffusion-weighted MRI images. The normalized ADC for the liver was calculated as the ratio of the ADC for the hepatic parenchyma to the ADC for the splenic parenchyma. RESULTS Perfusion-weighted MRI variables differed among the 5 ROIs. Median ADC of the hepatic parenchyma was 1.38 × 10-3 mm2/s, and mean ± SD normalized ADC for the liver was 1.86 ± 0.18. Median ADC of the renal cortex and renal medulla was 1.65 × 10-3 mm2/s and 1.93 × 10-3 mm2/s, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Results provided preliminary baseline information about the diffusion and perfusion characteristics of structures in the cranial aspect of the abdomen of healthy adult male cats. Additional studies of cats of different sex and age groups as well as with and without cranial abdominal pathological conditions are necessary to validate and refine these findings.

Myoclonus and hypercalcemia in a dog with poorly differentiated lymphoproliferative neoplasia.

A 1-year, 8-month-old Rhodesian Ridgeback was presented with obtundation, ambulatory tetraparesis, and myoclonus. Initial clinical findings included ionized hypercalcemia with an apparent marked increase in parathyroid hormone, thrombocytopenia, and nonregenerative anemia. Low numbers of circulating atypical cells were noted on blood film evaluation. Brain magnetic resonance imaging identified an extra-axial contrast enhancing subtentorial lesion, and cerebrospinal fluid (CSF) analysis documented a marked atypical lymphocytic pleocytosis. Flow cytometry performed on the CSF demonstrated expression of only CD45, CD90, and MHC class II, with Pax5 positivity on subsequent immunohistochemistry. The final diagnosis was of B-cell lymphoblastic lymphoma or acute leukemia, given the distribution of disease and the presence of significant bone marrow infiltration alongside an aggressive clinical course. The unusual immunophenotype of the neoplastic cells and hypercalcemia presented antemortem diagnostic challenges, highlighting the need for a multidisciplinary approach and caution in the interpretation of clinical abnormalities in cases with multiple comorbidities.

Anatomical variations in the circle of Willis in canines.

The circle of Willis (CW) supplies blood to the brain. In humans, anatomical variations in the CW are an important risk factor for transient ischaemic attack and stroke. In canines, anatomical variations in the CW have not been reported. The aim of this study was to determine anatomical variations in the CW in dogs by magnetic resonance angiography. Normal configuration of the CW was observed in 82%, aplasia of the precommunicating segment of the rostral cerebral artery was observed in 14%, and aplasia of the rostral communicating artery was observed in 4% of dogs included in the study.

Cardiac-gated, phase contrast magnetic resonance angiography is a reliable and reproducible technique for quantifying blood flow in canine major cranial abdominal vessels.

Blood flow changes in cranial abdominal vessels are important contributing factors for canine hepatic disease. This prospective, experimental, pilot study aimed to evaluate cardiac-gated, phase contrast magnetic resonance angiography (PCMRA) as a method for characterizing blood flow in canine major cranial abdominal vessels. Eleven, healthy, adult beagle dogs were sampled. Cardiac-gated, phase contrast magnetic resonance angiography of the cranial abdomen was performed in each dog and blood flow was independently measured in each of the major cranial abdominal vessels by three observers, with two observers recording blood flow values once and one observer recording blood flow values three times. Each dog then underwent ultrasonographic examination of the liver with fine needle aspirations and biopsies submitted to cytologic and histologic examination. The mean absolute stroke volume and velocity were respectively 9.6 ± 1.9 ml and -11.1 ± 1.1 cm/s for the cranial abdominal aorta, 2.1 ± 0.6 ml and -6.6 ± 1.9 cm/s for the celiac artery, and 2.3 ± 1.0 ml and -7.9 ± 3.1 cm/s for the cranial mesenteric artery. The mean absolute stroke volume and velocity were respectively 6.7 ± 1.3 ml and 3.9 ± 0.9 cm/s for the caudal vena cava and 2.6 ± 0.9 ml and 3.2 ± 1.2 cm/s for the portal vein. Intraobserver reliability was excellent (intraclass correlation coefficient > 0.9). Interobserver reproducibility was also excellent (intraclass correlation coefficient 0.89-0.99). Results of liver ultrasonography, cytology, and histopathology were unremarkable. Findings indicated that cardiac-gated, phase contrast magnetic resonance angiography is a feasible technique for quantifying blood blow in canine major cranial abdominal vessels. Blood flow values from this sample of healthy beagles can be used as background for future studies on canine hepatic disease.

Comparison of left and right ventricular stroke volume of dogs calculated on the basis of morphology and blood flow determined by use of cardiac magnetic resonance imaging.

OBJECTIVE To compare stroke volume (SV) calculated on the basis of cardiac morphology determined by MRI and results of phase-contrast angiography (PCA) of ventricular inflow and outflow in dogs. ANIMALS 10 healthy Beagles. PROCEDURES Cardiac MRI was performed twice on each Beagle. Cine gradient echo sequences of both ventricles in short-axis planes were used for morphological quantification of SVs by assessment of myocardial contours. From the long-axis plane, SVs in 4-chamber and left ventricular 2-chamber views were acquired at end diastole and end systole. For calculation of SV on the basis of blood flow, PCA was performed for cardiac valves. RESULTS Mean ± SD values for SV quantified on the basis of blood flow were similar in all valves (aortic, 17.8 ± 4.1 mL; pulmonary, 17.2 ± 5.4 mL; mitral, 17.2 ± 3.9 mL; and tricuspid, 16.9 ± 5.1 mL). Morphological quantification of SV in the short-axis plane yielded significant differences between left (13.4 ± 2.7 mL) and right (8.6 ± 2.4 mL) sides. Morphological quantification of left ventricular SV in the long-axis plane (15.2 ± 3.3 mL and 20.7 ± 3.8 mL in the 4- and 2-chamber views) yielded variable results, which differed significantly from values for flow-based quantification, except for values for the morphological 4-chamber view and PCA for the atrioventricular valves, for which no significant differences were identified. CONCLUSIONS AND CLINICAL RELEVANCE In contrast to quantification based on blood flow, calculation on the basis of morphology for the short-axis plane significantly underestimated SV, probably because of through-plane motion and complex right ventricular anatomy.

Evidence for Concerted and Mosaic Brain Evolution in Dragon Lizards.

The brain plays a critical role in a wide variety of functions including behaviour, perception, motor control, and homeostatic maintenance. Each function can undergo different selective pressures over the course of evolution, and as selection acts on the outputs of brain function, it necessarily alters the structure of the brain. Two models have been proposed to explain the evolutionary patterns observed in brain morphology. The concerted brain evolution model posits that the brain evolves as a single unit and the evolution of different brain regions are coordinated. The mosaic brain evolution model posits that brain regions evolve independently of each other. It is now understood that both models are responsible for driving changes in brain morphology; however, which factors favour concerted or mosaic brain evolution is unclear. Here, we examined the volumes of the 6 major neural subdivisions across 14 species of the agamid lizard genus Ctenophorus (dragons). These species have diverged multiple times in behaviour, ecology, and body morphology, affording a unique opportunity to test neuroevolutionary models across species. We assigned each species to an ecomorph based on habitat use and refuge type, then used MRI to measure total and regional brain volume. We found evidence for both mosaic and concerted brain evolution in dragons: concerted brain evolution with respect to body size, and mosaic brain evolution with respect to ecomorph. Specifically, all brain subdivisions increase in volume relative to body size, yet the tectum and rhombencephalon also show opposite patterns of evolution with respect to ecomorph. Therefore, we find that both models of evolution are occurring simultaneously in the same structures in dragons, but are only detectable when examining particular drivers of selection. We show that the answer to the question of whether concerted or mosaic brain evolution is detected in a system can depend more on the type of selection measured than on the clade of animals studied.

Interictal diffusion and perfusion magnetic resonance imaging features of cats with familial spontaneous epilepsy.

OBJECTIVE To evaluate the usefulness of diffusion and perfusion MRI of the cerebrum in cats with familial spontaneous epilepsy (FSECs) and identify microstructural and functional deficit zones in affected cats. ANIMALS 19 FSECs and 12 healthy cats. PROCEDURES Diffusion-weighted, diffusion tensor, and perfusion-weighted MRI of the cerebrum were performed during interictal periods in FSECs. Imaging findings were compared between FSECs and control cats. Diffusion (apparent diffusion coefficient and fractional anisotropy) and perfusion (relative cerebral blood volume [rCBV], relative cerebral blood flow [rCBF], and mean transit time) variables were measured bilaterally in the hippocampus, amygdala, thalamus, parietal cortex gray matter, and subcortical white matter. Asymmetry of these variables in each region was also evaluated and compared between FSECs and control cats. RESULTS The apparent diffusion coefficient of the total amygdala of FSECs was significantly higher, compared with that of control cats. The fractional anisotropy of the right side and total hippocampus of FSECs was significantly lower, compared with that of control cats. The left and right sides and total hippocampal rCBV and rCBF were significantly lower in FSECs than in control cats. The rCBV and rCBF of the parietal cortex gray matter in FSECs were significantly lower than in control cats. CONCLUSIONS AND CLINICAL RELEVANCE In FSECs, diffusion and perfusion MRI detected microstructural changes and hypoperfusion (lowered function) in the cerebrum during interictal periods from that of healthy cats. These findings indicated that diffusion and perfusion MRI may be useful for noninvasive evaluation of epileptogenic foci in cats.

Pituitary Macrotumor Causing Narcolepsy-Cataplexy in a Dachshund.

Familial narcolepsy secondary to breed-specific mutations in the hypocretin receptor 2 gene and sporadic narcolepsy associated with hypocretin ligand deficiencies occur in dogs. In this report, a pituitary mass is described as a unique cause of narcolepsy-cataplexy in a dog. A 6-year-old male neutered Dachshund had presented for acute onset of feeding-induced cataplexy and was found to have a pituitary macrotumor on magnetic resonance imaging (MRI). Cerebral spinal fluid hypocretin-1 levels were normal, indicating that tumor effect on the ventral lateral nucleus of the hypothalamus was not the cause of the dog's narcolepsy-cataplexy. The dog was also negative for the hypocretin receptor 2 gene mutation associated with narcolepsy in Dachshunds, ruling out familial narcolepsy. The Dachshund underwent stereotactic radiotherapy (SRT), which resulted in reduction in the mass and coincident resolution of the cataplectic attacks. Nine months after SRT, the dog developed clinical hyperadrenocorticism, which was successfully managed with trilostane. These findings suggest that disruptions in downstream signaling of hypocretin secondary to an intracranial mass effect might result in narcolepsy-cataplexy in dogs and that brain MRI should be strongly considered in sporadic cases of narcolepsy-cataplexy.

Pulmonary perfusion quantification with flow-sensitive inversion recovery (FAIR) UTE MRI in small animal imaging.

Blood perfusion in lung parenchyma is an important property for assessing lung function. In small animals, its quantitation is limited even with radioactive isotopes or dynamic contrast-enhanced MRI techniques. In this study, the feasibility flow-sensitive alternating inversion recovery (FAIR) for the quantification of blood flow in lung parenchyma in free breathing rats at 7 T has been investigated. In order to obtain sufficient signal from the short T2 * lung parenchyma, a 2D ultra-short echo time (UTE) Look-Locker read-out has been implemented. Acquisitions were segmented to maintain acquisition time within an acceptable range. A method to perform retrospective respiratory gating (DC-SG) has been applied to investigate the impact of respiratory movement. Reproducibilities within and between sessions were estimated, and the ability of FAIR-UTE to identify the decrease of lung perfusion under hyperoxic conditions was tested. The implemented technique allowed for the visualization of lung parenchyma with excellent SNR and no respiratory artifact even in ungated acquisitions. Lung parenchyma perfusion was obtained as 32.54 ± 2.26 mL/g/min in the left lung, and 34.09 ± 2.75 mL/g/min in the right lung. Application of retrospective gating significantly but minimally changes the perfusion values, implying that respiratory gating may not be necessary with this center-our acquisition method. A decrease of 10% in lung perfusion was found between normoxic and hyperoxic conditions, proving the feasibility of the FAIR-UTE approach to quantify lung perfusion changes.

Three-dimensional time of flight magnetic resonance angiography of the heart and associated vessels in a cat.

The aim of this study was to describe the normal magnetic resonance angiography (MRA) of the heart and associated vessels in a mature female cat using a 1.5-Tesla magnet. Non-contrast enhanced MRA was performed using a three-dimensional time of flight (TOF) sequence in parasagittal and dorsal aspects. Relevant cardiac and vascular structures were labelled on three-dimensional Time of flight images. Time of flight imaging showed details of the heart cavities and vessels lumen due to the high signal intensity of fast-flowing blood compared with bones, muscles, and lungs, which appeared with low signal intensity. Three-dimensional TOF sequences provided adequate anatomical details of the heart and good differentiation of the vascular structures that could be used for interpretation of cardiac images and to assist in future MRA studies.

Maximal and submaximal mouth opening with mouth gags in cats: implications for maxillary artery blood flow.

The use of spring-loaded mouth gags in cats can be associated with the development of central neurological deficits, including blindness. In this species, the maxillary arteries are the main source of blood supply to the retinae and brain. Spring-loaded gags generate constant force after placement that could contribute to bulging of the soft tissues between the mandible and the tympanic bulla. Under these circumstances, the maxillary arteries can become compressed as they course between these osseous structures. Smaller gags that might apply less force to the mouth were investigated to determine if they preserved maxillary artery blood flow. Six healthy adult cats were anesthetized. Electroretinography (ERG) and magnetic resonance angiography (MRA) were performed without the use of a mouth gag and during submaximal (plastic mouth gags of 20, 30 and 42 mm in length between canine teeth) and maximal mouth opening. Maximal mouth opening produced alterations in ERG waveforms consistent with circulatory compromise in 1/6 cats and reductions in signal intensity during MRA in 4/6 cats. Placement of a 42 mm plastic gag produced a reduction in MRA signal in 1/6 cats. No changes were observed with smaller gags. The force applied against the mouth was significantly higher with the spring-loaded gag than with any other gags. The use of a smaller mouth gags was associated with fewer alterations of indicators of maxillary artery blood flow. Nevertheless, a 42 mm plastic gag, equivalent to the size of a needle cap, resulted in an abnormal MRA in one cat.

Variations in magnetic resonance venographic anatomy of the dorsal dural venous sinus system in 51 dogs.

Variations in intracranial dural venous sinus anatomy have been widely reported in humans, but there have been no studies reporting this in dogs. The purpose of this retrospective study was to describe variations in magnetic resonance (MR) venographic anatomy of the dorsal dural venous sinus system in a sample population of dogs with structurally normal brains. Medical records were searched for dogs with complete phase contrast, intracranial MR venograms and a diagnosis of idiopathic epilepsy. Magnetic resonance venograms were retrieved for each dog and characteristics of the dorsal dural sinuses, symmetry of the transverse sinuses and other anatomic variations were recorded. A total of 51 dogs were included. Transverse sinus asymmetry was present in 58.8% of the dogs, with transverse sinus hypoplasia seen in 39.2%, and aplasia in 23.5% of dogs. For 70.6% of dogs, at least one anatomic variation in the dorsal sagittal sinus was observed, including deviation from the midline (33.3%) and collateral branches from either the dorsal sagittal sinus or dorsal cerebral veins (54.9%). In 5 dogs (9.8%) a vessel was also identified running from the proximal transverse sinus to the distal sigmoid sinus, in a similar location to the occipital sinus previously reported in children. Findings from this study indicated that, as in humans, anatomic variations are common in the intracranial dural venous sinus system of dogs. These anatomic variations should be taken into consideration for surgical planning or diagnosis of cerebrovascular disease.

Evaluation of maxillary arterial blood flow in anesthetized cats with the mouth closed and open.

The mouth-gag is a common tool used in veterinary medicine during oral and transoral procedures in cats but its use has recently been associated with the development of blindness. The goal of this study was to investigate whether maximal opening of the mouth affects maxillary artery blood flow in six anesthetized cats. To assess blood flow, the electroretinogram (ERG), brainstem auditory evoked response (BAER) and magnetic resonance angiography (MRA) were evaluated qualitatively with the mouth closed and open. During dynamic computer tomography (CT) examinations, detection of contrast medium in the maxillary artery was quantified by measuring the Hounsfield units (HUs). The peak HU, time to peak and mean HU were determined. Changes ⩾10% of these parameters were considered indicative of altered blood flow. ERG and BAER were normal with the mouth closed in all cats, but was abnormal with the mouth opened maximally in two cats and one cat, respectively. During MRA, blood flow was undetected in either maxillary artery in one cat and reduced in the right maxillary artery in two cats, when the mouth was open. During CT, the peak HU decreased ⩾10% in three cats, the time to peak was ⩾10% longer in two cats, and the mean HU was ⩾10% lower in one cat when the mouth was open. No cat developed apparent blindness or deafness. Maximal opening of the mouth caused alterations in several indicators of blood flow in some individual cats.

Time-of-flight magnetic resonance angiography (TOF-MRA) of the normal equine head.

REASONS FOR PERFORMING STUDY: Noncontrast magnetic resonance angiography (MRA) is widely used in human and small animal medicine. However, this technique has not yet been described in the horse, and compared to other angiographic techniques MRA could be more cost efficient and potentially safer. OBJECTIVES: The aim of this study was to provide a comprehensive anatomical reference of the normal equine head vasculature using a noncontrast MRA technique, on both low- and high-field MRI. METHODS: Five healthy adult horses were examined, 4 with a low-field magnet (0.23T) and the remaining one with a high-field magnet (1.5T). The magnetic resonance angiography sequence used was TOF (time-of-flight) 2D-MRA and CT images of a vascular corrosion cast were subsequently used as anatomical references. RESULTS: The MRA imaging protocol provided good visualisation of all major intra- and extracranial vessels down to a size of approximately 2 mm in diameter on both low- and high-field systems. This resulted in identification of vessels to the order of 3rd-4th branches of ramification. The visibility of the arteries was higher than of the veins, which showed lower signal intensity. Overall, MRA obtained with the high-field protocol provided better visualisation of the arteries, showing all the small arterial branches with a superior resolution. CONCLUSIONS: The use of a specific vascular sequence such as TOF 2D-MRA allows good visualisation of the equine head vasculature and eliminates the need for contrast media for MRA. POTENTIAL RELEVANCE: Magnetic resonance angiography allows for visualisation of the vasculature of the equine head. Vessel morphology, symmetry and size can be evaluated and this may possibly play a role in preoperative planning or characterisation of diseases of the head, such as neoplasia or guttural pouch mycosis.

Comparison of digital subtraction angiography, micro-computed tomography angiography and magnetic resonance angiography in the assessment of the cerebrovascular system in live mice.

PURPOSE: Mice are often used as small animal models of brain ischemia, venous thrombosis, or vasospasm. This article aimed at providing an overview of the currently available methodologies for in vivo imaging of the murine cerebrovasculature and comparing the capabilities and limitations of the different methods. METHODS: Micro-computed tomography angiography (CTA) was performed during intra-arterial and intravenous administration of a contrast agent bolus. Digital subtraction angiography (DSA) was performed during intra-arterial administration of contrast agent using the micro-CT scanner. Time-of-flight (ToF) magnetic resonance (MR) angiography was performed using a small animal scanner (9.4 T) equipped with a cryogenic transceive quadrature coil. Datasets were compared for scan time, contrast-to-noise ratio (CNR), temporal and spatial resolution, radiation dose, contrast agent dose and detailed recognition of cerebrovascular structures. RESULTS: Highest spatial resolution was achieved using micro-CTA (16 x 16 x 16 µm) and DSA (14 x 14 µm). Compared to micro-CTA (20-40 s) and ToF-MRA (57 min), DSA provided highest temporal resolutions (30 fps) allowing analyses of the cerebrovascular blood flow. Highest mean CNR was reached using ToF-MRA (50.7 ± 15.0), while CNR of micro-CTA depended on the intra-arterial (19.0 ± 1.0) and intravenous (1.3 ± 0.4) use of agents. The CNR of DSA was 10.0 ± 1.8. CONCLUSIONS: The use of dedicated small animal scanners allows cerebrovascular imaging in live animals as small as mice. As each of the methods analyzed has its advantages and limitations, choosing the best suited imaging modality for a defined question is of great importance. By this means the aforementioned methods offer a great potential for future projects in preclinical cerebrovascular research including ischemic stroke or vasospasm.