Magnetic resonance imaging features of presumed intracerebral hemorrhages in dogs show a significant association between apparent diffusion coefficient peripheral layer and estimated bleeding age and commonly exhibit a T2 blackout effect.

In humans, intracranial hematomas commonly exhibit a T2 blackout effect (BOE) with diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps. Published descriptions of comparable findings in dogs with intracerebral hemorrhages are lacking. Aims of this retrospective observational study were to describe the appearance of presumed intracerebral hemorrhages (PICHs) in DWI regardless of the underlying etiology and presence of T2 blackout effect (T2 BOE) in dogs and to test potential associations with DWI and ADC findings versus the estimated age of the hemorrhage. Magnetic resonance imaging studies of dogs with presumed PICHs based on the combined evaluation of T2*W gradient echo and/or susceptibility-weighted imaging, T1W and T2W images were enrolled. The age of the hemorrhage was estimated according to published criteria based on T1W and T2W sequences. The association between the age of the hemorrhage and the appearance of each finding (stratified or mixed), their signal intensities in DWI/ADC and the presence of the T2 BOE, was evaluated. A total of 35 PICHs were included: 13 of them were stratified and 22 had a mixed aspect. Only the ADC appearance of the peripheral layer in stratified PICHs was significantly associated with estimated age of the hemorrhage (p = .033), being hypointense in all hyperacute cases and hypo-/isointense in acute cases. The T2 BOE was present in 29/35 PICHs. The DWI sequences showed limited utility to date PICHs in this study population. As in humans, the T2 BOE was commonly seen in DWI and ADC maps of dogs with PICHs.

Investigated regional apparent diffusion coefficient values of the morphologically normal feline brain.

OBJECTIVES: Diffusion-weighted imaging (DWI) MRI is increasingly available in veterinary medicine for investigation of the brain. However, apparent diffusion coefficient (ADC) values have only been reported in a small number of cats or in research settings. The aim of this study was to investigate the ADC values of different anatomical regions of the morphologically normal brain in a feline patient population. Additionally, we aimed to assess the possible influence on the ADC values of different patient-related factors, such as sex, body weight, age, imaging of the left and right side of the cerebral hemispheres and white vs grey matter regions. METHODS: This retrospective study included cats undergoing an MRI (3T) examination with DWI sequences of the head at the Vetsuisse Faculty of the University Zurich between 2015 and 2021. Only cats with morphologically normal brains were included. On the ADC maps, 10 regions of interest (ROIs) were manually drawn on the following anatomical regions: caudate nucleus; internal capsule (two locations); piriform lobe; thalamus; hippocampus; cortex cerebri (two locations); cerebellar hemisphere; and one ROI in the centre of the cerebellar vermis. Except for the ROI at the cerebellar vermis, each ROI was drawn in the left and right hemisphere. The ADC values were calculated by the software and recorded. RESULTS: A total of 129 cats were included in this study. The ADC varied in the different ROIs, with the highest mean ADC value in the hippocampus and the lowest in the cerebellar hemisphere. ADC was significantly lower in the white cerebral matter compared with the grey matter. ADC values were not influenced by age, with the exception of the hippocampus and the cingulate gyrus. CONCLUSION AND RELEVANCE: ADC values of different anatomical regions of the morphologically normal feline brain in a patient population of 129 cats in a clinical setting are reported for the first time.

Dogs and cats with presumed or confirmed intracranial abscessation have low apparent diffusion coefficient values.

Intracranial abscessation is a life-threatening condition in dogs and cats, and rapid diagnosis is important for prognosis and treatment planning. The aims of this retrospective, single-center, case series study were to describe clinical and MRI diffusion-weighted imaging characteristics in three dogs and three cats with presumed or confirmed intracranial abscessation. All lesions appeared hyperintense on b1000 trace diffusion-weighted images, hypointense on apparent diffusion coefficient (ADC) map, with mean ADC values ranging from 0.37 to 1.24 × 10-3  mm2 /s. The majority (5/6) of the obtained mean ADC values were low (<1.10 × 10-3  mm2 /s), as previously reported in the human literature.

Characterizing the canine and feline optic pathways in vivo with diffusion MRI.

The visual system is known to be vital for cognition and perception in the feline and canine and much behavioral research for these species has used visual stimuli and focused on visual perception. There has been extensive investigations into the visual pathway in cats and dogs via histological and neurobiological methods, however to date, only one study has mapped the canine optic pathway in vivo. Advanced imaging methods such as diffusion MRI (DTI) have been routinely used in human research to study the visual system in vivo. This study applied DTI imaging methods to assess and characterize the optic pathway of feline and canine subjects in vivo. The optic nerve (ON), optic tract (OT), and optic radiation (OR) were successfully delineated for each species and the average volume and FA for each tract is reported. The application of DTI to map the optic pathway for canine and feline subjects provides a healthy baseline for comparison in future studies.

Reduced field-of-view diffusion-weighted MRI can identify restricted diffusion in the spinal cord of dogs and cats with presumptive clinical and high-field MRI diagnosis of acute ischemic myelopathy.

Diffusion-weighted imaging MRI is the gold standard imaging technique for diagnosis of suspected acute brain ischemia in dogs and cats; however, it is technically challenging to apply to spinal cord imaging, due to its very small size, the inherent low spatial resolution of diffusion-weighted imaging, and the marked distortion resulting from magnetic field inhomogeneities caused by the osseous components of the vertebral column surrounding the spinal cord. Ischemic myelopathy is a common cause of acute non-compressive myelopathy in dogs and cats. Technological improvement in diffusion-weighted imaging pulse sequences allow imaging at smaller field of view with better spatial resolution and less image distortion. We sought to evaluate reduced field-of-view diffusion-weighted imaging MRI using a dedicated proprietary pulse sequence (FOCUS, General Electric) in a small sample of dogs and cats with a presumptive clinical and MRI diagnosis of acute ischemic myelopathy that were imaged with this pulse sequence. Five dogs and two cats fitted these inclusion criteria. In all of them, hyperintense spinal cord parenchyma signal was seen on diffusion-weighted imaging images corresponding to decreased signal on apparent diffusion coefficient map indicative of restricted diffusion, consistent with ischemia and cytotoxic edema. These areas matched the areas of abnormal T2-weighted signal and cord swelling observed on conventional spinal MRI. This small exploratory descriptive study indicates feasibility and possible usefulness of reduced field-of-view diffusion-weighted imaging MRI in dogs and cats with suspected acute ischemic myelopathy and that it may be added to the imaging protocol of the spine in such patients in an appropriate clinical setting.

Less enhancement and low apparent diffusion coefficient value on magnetic resonance imaging may be helpful to detect canine prostate adenocarcinoma in case series.

In dogs, diagnosis of prostate cancer is often delayed because clinical signs are not pathognomonic. Although ultrasonography is mainly performed to detect prostate cancer, the ultrasonographic appearance is not specific. In humans, magnetic resonance imaging (MRI), including diffusion-weighted imaging (DWI) is used to localize the prostate tumour. To our knowledge, there are no studies of MRI findings for detecting or localizing prostate cancer. The purpose of this study was to assess MRI findings of prostate cancer. As a control, three prostate hyperplasia cases were included. MRI data were analysed, and the following parameters were noted: signal intensity (SI) of prostate lesion on T2-weighted imaging, T1-weighted imaging and DWI, enhancement pattern of prostate lesion, and relative contrast enhancement indices (RCEI) and apparent diffusion coefficient (ADC) value of prostate lesion. For MRI examination, the mean RCEI of the adenocarcinoma was significantly lower than that of hyperplasia (P = .01, r = .8). The SI of the DWI of adenocarcinoma was significantly higher compared to hyperplasia (P = .03, φ = 1). The mean ADC values of the adenocarcinoma were significantly lower than that of hyperplasia (P = .03, r = .82). Thus, less enhancement on MRI, and low ADC value on MRI may help to detect prostate adenocarcinoma.

Atypical and malignant canine intracranial meningiomas may have lower apparent diffusion coefficient values than benign tumors.

Canine intracranial meningiomas can be graded based on histological classification as benign (grade I), atypical (grade II), and anaplastic or malignant (grade III). In people, grade II/III meningiomas behave more aggressively, have a higher potential for recurrence after surgical resection, and have lower apparent diffusion coefficient (ADC) values with diffusion weighted imaging (DWI). In this retrospective analytical cross-sectional study, 42 dogs had ADC values quantified in an attempt to differentiate tumor histologic grade. Our hypothesis was that ADC values would be significantly lower in grade II and III versus grade I meningiomas in dogs. On each ADC image, a polygonal region of interest (ROI) was hand-drawn along the lesion's periphery, excluding fluid-filled and hemorrhagic regions. Mean ADC value (ADCmean ) and minimum ADC value (ADCmin ) were calculated. Additionally, two smaller, ovoid ROI were drawn within the lesion with mean ADC calculated (ADCmean sR and ADCmin sR ). Normalized ADC values using white matter were also calculated (ADCn and ADCn sR ). Grades of each tumor were assigned based on histopathology review. Association between ADC parameters and histological grade was tested by means of two-sample t-tests. There were 14 grade I (33.3%), 25 grade II (59.5%), and three grade III (7.2%) meningiomas. ADCmean sR and ADCmin sR were significantly lower when comparing grade II/III to grade I (P < .05). Grade II tumors had significantly lower ADCmean , ADCmean sR , ADCmin sR , ADCn , and ADCn sR than grade I meningiomas. This preliminary study supports the potential of ADC values to help predict the histological grade of intracranial meningiomas in dogs.

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.

Evaluation of diffusion-weighted magnetic resonance imaging at 3.0 Tesla for differentiation between intracranial neoplastic and noninfectious inflammatory lesions in dogs.

OBJECTIVE: To evaluate the utility of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values obtained by diffusion-weighted MRI (DWI) at 3.0 T for differentiating intracranial neoplastic lesions from noninfectious inflammatory lesions (NIILs) in dogs. ANIMALS: 54 dogs that met inclusion criteria (ie, had a histologically confirmed intracranial lesion and DWI of the brain performed) with 5 lesion types: meningioma [n = 18], glioma [14], metastatic hemangiosarcoma [3], other metastatic neoplasms [5], and NIIL [14]). PROCEDURES: Two observers, who were blinded to the histologic diagnoses, independently determined the mean ADC and FA values for each evaluated intracranial lesion on the basis of 3 circular regions of interest on DWI images. Findings were compared among the 5 lesion types, between all neoplasms combined and NIILs, and between the 5 legion types and previously determined values for corresponding locations for neurologically normal dogs. RESULTS: The mean ADC and FA values did not differ significantly among the 5 lesion types or between all neoplasms combined and NIILs. However, 35% (14/40) of the neoplastic lesions had an ADC value ≥ 1.443 × 10-3 mm2/s, whereas all NIILs had ADC values < 1.443 × 10-3 mm2/s. Meningiomas and NIILs had FA values that were significantly lower than those for neurologically normal dogs. CONCLUSIONS AND CLINICAL RELEVANCE: In this population of dogs, the FA values for meningiomas and NIILs differed significantly from those previously reported for neurologically normal dogs. In addition, an ADC cutoff value of 1.443 × 10-3 mm2/s appeared to be highly specific for diagnosing neoplastic lesions (vs NIILs), although the sensitivity and accuracy were low.

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.

Ultrahigh-Field Quantitative MR Microscopy of the Chicken Eye In Vivo Throughout the In Ovo Period.

PURPOSE: Ultrahigh-field MRI (UHF-MRI) with an in-plane spatial resolution of less than 100 µm is known as MR microscopy (MRM). MRM provides highly resolved anatomical images and allows quantitative assessment of different tissue types using diffusion-weighted imaging (DWI). The aim of the present study was to evaluate the feasibility of combined in vivo anatomical and quantitative assessment of the developing chicken eye in ovo. PROCEDURES: Thirty-eight fertilized chicken eggs were examined at 7.1 T (ClinScan, Bruker Biospin, Germany) acquiring a dataset comprising T2-weighted anatomical images, DWI, and diffusion tensor imaging. To reduce motion artifacts, the eggs were moderately cooled before and during MR imaging. Two eggs were imaged daily for the entire developmental period, and 36 eggs were examined pairwise at only one time point of the embryonic period. Development of the eye was anatomically and quantitatively assessed. RESULTS: From the D5 embryonic stage (116-124 h), MRM allowed differentiation between lens and vitreous body. The lens core and periphery were first identified at D9. DWI allowed quantification of lens maturation based on a significant decrease in apparent diffusion coefficient values and course of fractional anisotropy. Repeated moderate cooling had no influence on the development of the chicken embryo. CONCLUSIONS: MRM allows in vivo assessment of embryonic development of the chicken eye in ovo without affecting normal development. The method provides anatomical information supplemented by quantitative evaluation of lens development using DWI. With increasing availability of ultrahigh-field MR systems, this technique may provide a noninvasive complementary tool in the field of experimental ophthalmology.

Diffusion weighted magnetic resonance imaging is a feasible method for characterizing regional lymph nodes in canine patients with head and neck disease.

In dogs diagnosed with solid tumors, regional lymph node involvement or evidence of distant metastasis can predict worse prognoses and significantly decreased survival. Lymph node size alone has been shown to be insufficient as a predictor for the accurate clinical staging of some canine neoplasia. However, certain regional lymph nodes (including those of the oral cavity) are difficult to access for routine tissue sampling. Diffusion weighted magnetic resonance imaging (MRI) has demonstrated the ability to differentiate metastatic from inflammatory/benign lymph nodes in clinical studies with human cancer patients through the calculation of quantitative values of diffusion termed apparent diffusion coefficients (ADC). The objective of this prospective, exploratory study was to evaluate diffusion-weighted MRI and ADC as potential methods for detecting metastatic lymph nodes in dogs with naturally occurring disease. We hypothesized that diffusion-weighted MRI would identify significantly different ADC values between benign and metastatic lymph nodes in a group of canine patients with head or neck disease. Our study population consisted of eight client-owned canine patients, with a total of 20 lymph nodes evaluated (six metastatic, 14 benign). Our results demonstrated that two of four observers identified a significant difference between the mean ADC values of the benign and metastatic lymph nodes. When data from all four observers were pooled, the difference between the mean apparent diffusion coefficients values of the benign and metastatic lymph nodes did not reach significance (P-value = 0.0566). Findings indicated that diffusion-weighted MRI is a feasible method for further characterizing enlarged lymph nodes in dogs with head and neck disease, however measured ADC values did not differ for benign vs. metastatic lymph nodes in this small sample of dogs.

Advances in High-Field MRI.

MRI techniques and systems have evolved dramatically over recent years. These advances include higher field strengths, new techniques, faster gradients, improved coil technology, and more robust sequence protocols. This article reviews the most commonly used advanced MRI techniques, including diffusion-weighted imaging, magnetic resonance spectrography, diffusion tensor imaging, and cerebrospinal fluid flow tracking.

Diffusion-weighted imaging of the brains of dogs with idiopathic epilepsy.

BACKGROUND: Idiopathic epilepsy is one of the most common neurological disorders in dogs. Unfortunately, up to 30% of dogs with idiopathic epilepsy show no improvement under antiepileptic drug treatment. Diffusion-weighted imaging is used in human medicine to identify epileptogenic foci in the brain to allow for more invasive treatments such as deep brain stimulation or surgical removal. The aim of this study was to ass the feasibility of interictal diffusion-weighted MRI in dogs and to evaluate the distribution of diffusion in the brains of dogs with idiopathic epilepsy (IE) and to compare these values to previously published values from healthy beagle dogs. Client-owned dogs with the final diagnosis of IE were included in this study. MRI examination was carried out using a 1.0Tesla superconductive magnet. Diffusion-weighted images using a single shot echo planar imaging sequence (SSh-EPI) with a b value of b = 0 s/mm2 and b = 800 s/mm2 were acquired in a dorsal and transverse plane with diffusion gradients in all three planes (x-, y- and z-plane). An ADC (apparent diffusion coefficient) map of the isometric image of each acquired slice was generated. Regions of interest (ROIs) were manually drawn around the caudate nucleus, the thalamus, the piriform lobe including the amygdala, the hippocampus, the semioval center and the temporal cerebral cortex by one of the authors. ROI drawings were repeated 5 times at different time points to assess intra-obersver variability. A multi-way mixed-model analysis of variance (ANOVA) and two-way ANOVA were used during statistical analysis. A p value of p < 0.05 was considered significant. RESULTS: Dogs with IE showed a significantly increased ADC in the amygdala within the piriform lobe and in the semioval center (p < 0.05) compared with the healthy control group. CONCLUSION: Changes in the piriform lobe in cases of epilepsy are reported infrequently in human and veterinary medicine. Similar to our results, ADC changes in the interictal phase usually include an increase in ADC due to cell loss and increased intercellular spaces. Diffusion MRI might be a promising technique for the examination of canine epileptic patients lacking other gross neuromorphological abnormalities.

Diffusion tensor MR imaging characteristics of cerebral white matter development in fetal pigs.

BACKGROUND: The purpose of this study was to investigate the anisotropic features of fetal pig cerebral white matter (WM) development by magnetic resonance diffusion tensor imaging, and to evaluate the developmental status of cerebral WM in different anatomical sites at different times. METHODS: Fetal pigs were divided into three groups according to gestational age: E69 (n = 8), E85 (n = 11), and E114 (n = 6). All pigs were subjected to conventional magnetic resonance imaging (MRI) and diffusion tensor imaging using a GE Signa 3.0 T MRI system (GE Healthcare, Sunnyvale, CA, USA). Fractional anisotropy (FA) was measured in deep WM structures and peripheral WM regions. After the MRI scans,the animals were sacrificed and pathology sections were prepared for hematoxylin & eosin (HE) staining and luxol fast blue (LFB) staining. Data were statistically analyzed with SPSS version 16.0 (SPSS, Chicago, IL, USA). A P-value < 0.05 was considered statistically significant. Mean FA values for each subject region of interest (ROI), and deep and peripheral WM at different gestational ages were calculated, respectively, and were plotted against gestational age with linear correlation statistical analyses. The differences of data were analyzed with univariate ANOVA analyses. RESULTS: There were no significant differences in FAs between the right and left hemispheres. Differences were observed between peripheral WM and deep WM in fetal brains. A significant FA growth with increased gestational age was found when comparing E85 group and E114 group. There was no difference in the FA value of deep WM between the E69 group and E85 group. The HE staining and LFB staining of fetal cerebral WM showed that the development from the E69 group to the E85 group, and the E85 group to the E114 group corresponded with myelin gliosis and myelination, respectively. CONCLUSIONS: FA values can be used to quantify anisotropy of the different cerebral WM areas. FA values did not change significantly between 1/2 way and 3/4 of the way through gestation but was then increased dramatically at term, which could be explained by myelin gliosis and myelination ,respectively.

Diffusion-weighted magnetic resonance imaging of the brain of neurologically normal dogs.

OBJECTIVE To acquire MRI diffusion data (apparent diffusion coefficient [ADC] and fractional anisotropy [FA] values, including separate measures for gray and white matter) at 3.0 T for multiple locations of the brain of neurologically normal dogs. ANIMALS: 13 neurologically normal dogs recruited from a group of patients undergoing tibial plateau leveling osteotomy. PROCEDURES: MRI duration ranged from 20 to 30 minutes, including obtaining preliminary images to exclude pathological changes (T2-weighted fluid-attenuated inversion recovery transverse and dorsal images) and diffusion-weighted images. , RESULTS: Globally, there were significant differences between mean values for gray and white matter in the cerebral lobes and cerebellum for ADC (range of means for gray matter, 0.8349 × 10-3 s/mm2 to 0.9273 × 10-3 s/mm2; range of means for white matter, 0.6897 × 10-3 s/mm2 to 0.7332 × 10-3 s/mm2) and FA (range of means for gray matter, 0.1978 to 0.2364; range of means for white matter, 0.5136 to 0.6144). These values also differed among cerebral lobes. In most areas, a positive correlation was detected between ADC values and patient age but not between FA values and patient age. CONCLUSIONS AND CLINICAL RELEVANCE: Cerebral interlobar and cerebellar diffusion values differed significantly, especially in the gray matter. Information about diffusion values in neurologically normal dogs may be used to diagnose and monitor abnormalities and was the first step in determining the clinical use of diffusion imaging. This information provided an important starting point for the clinical application of diffusion imaging of the canine brain.

Comparisons among MRI signs, apparent diffusion coefficient, and fractional anisotropy in dogs with a solitary intracranial meningioma or histiocytic sarcoma.

Although MRI has become widely used in small animal practice, little is known about the validity of advanced MRI techniques such as diffusion-weighted imaging and diffusion tensor imaging. The aim of this retrospective analytical observational study was to investigate the characteristics of diffusion parameters, that is the apparent diffusion coefficient and fractional anisotropy, in dogs with a solitary intracranial meningioma or histiocytic sarcoma. Dogs were included based on the performance of diffusion MRI and histological confirmation. Statistical analyses were performed to compare apparent diffusion coefficient and fractional anisotropy for the two types of tumor in the intra- and peritumoral regions. Eleven cases with meningioma and six with histiocytic sarcoma satisfied the inclusion criteria. Significant differences in apparent diffusion coefficient value (× 10-3 mm2 /s) between meningioma vs. histiocytic sarcoma were recognized in intratumoral small (1.07 vs. 0.76) and large (1.04 vs. 0.77) regions of interest, in the peritumoral margin (0.93 vs. 1.08), and in the T2 high region (1.21 vs. 1.41). Significant differences in fractional anisotropy values were found in the peritumoral margin (0.29 vs. 0.24) and the T2 high region (0.24 vs. 0.17). The current study identified differences in measurements of apparent diffusion coefficient and fractional anisotropy for meningioma and histiocytic sarcoma in a small sample of dogs. In addition, we observed that all cases of intracranial histiocytic sarcoma showed leptomeningeal enhancement and/or mass formation invading into the sulci in the contrast study. Future studies are needed to determine the sensitivity of these imaging characteristics for differentiating between these tumor types.

Perfusion- and diffusion-weighted magnetic resonance imaging of the liver of healthy dogs.

OBJECTIVE To describe the perfusion and diffusion characteristics of the liver in healthy dogs as determined by morphological, perfusion-weighted, and diffusion-weighted MRI. ANIMALS 11 healthy adult Beagles. PROCEDURES Each dog was anesthetized and underwent morphological, perfusion-weighted, and diffusion-weighted MRI of the cranial aspect of the abdomen. On the MRI images, a region of interest (ROI) was established for each of 6 structures (aorta, caudal vena cava, portal vein, hepatic parenchyma, splenic parenchyma, and skeletal [epaxial] muscle). The 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 in diffusion-weighted MRI images, and 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. Dogs also underwent abdominal ultrasonography, and ultrasound-guided fine-needle aspirate samples and biopsy specimens were obtained from the liver for cytologic and histologic examination. RESULTS Cytologic and histologic results suggested that the liver was clinically normal in all dogs. Perfusion-weighted MRI parameters varied among the 6 ROIs. The mean ± SD ADC of the hepatic parenchyma was 0.84 × 10(-3) mm(2)/s ± 0.17 × 10(-3) mm(2)/s, and the mean normalized ADC for the liver was 1.8 ± 0.4. CONCLUSIONS AND CLINICAL RELEVANCE Results provided preliminary baseline information about the diffusion and perfusion characteristics of the liver in healthy dogs. Additional studies on dogs of various breeds with and without hepatopathies are necessary to validate and refine these findings.

Artifact correction in diffusion MRI of non-human primate brains on a clinical 3T scanner.

BACKGROUND: Smearing artifacts were observed and investigated in diffusion tensor imaging (DTI) studies of macaque monkeys on a clinical whole-body 3T scanner. METHODS: Four adult macaques were utilized to evaluate DTI artifacts. DTI images were acquired with a single-shot echo-planar imaging (EPI) sequence using a parallel imaging technique. RESULTS: The smearing artifacts observed on the diffusion-weighted images and fractional anisotropy maps were caused by the incomplete fat suppression due to the irregular macaque frontal skull geometry and anatomy. The artifact can be reduced substantially using a novel three-dimensional (3D) shimming procedure. CONCLUSION: The smearing artifacts observed on diffusion weighted images and fractional anisotropy (FA) maps of macaque brains can be reduced substantially using a robust 3D shimming approach. The DTI protocol combined with the shimming procedure could be a robust approach to examine brain connectivity and white matter integrity of non-human primates using a conventional clinical setting.

Apparent diffusion coefficient is highly reproducible on preclinical imaging systems: Evidence from a seven-center multivendor study.

PURPOSE: To evaluate between-site agreement of apparent diffusion coefficient (ADC) measurements in preclinical magnetic resonance imaging (MRI) systems. MATERIALS AND METHODS: A miniaturized thermally stable ice-water phantom was devised. ADC (mean and interquartile range) was measured over several days, on 4.7T, 7T, and 9.4T Bruker, Agilent, and Magnex small-animal MRI systems using a common protocol across seven sites. Day-to-day repeatability was expressed as percent variation of mean ADC between acquisitions. Cross-site reproducibility was expressed as 1.96 × standard deviation of percent deviation of ADC values. RESULTS: ADC measurements were equivalent across all seven sites with a cross-site ADC reproducibility of 6.3%. Mean day-to-day repeatability of ADC measurements was 2.3%, and no site was identified as presenting different measurements than others (analysis of variance [ANOVA] P = 0.02, post-hoc test n.s.). Between-slice ADC variability was negligible and similar between sites (P = 0.15). Mean within-region-of-interest ADC variability was 5.5%, with one site presenting a significantly greater variation than the others (P = 0.0013). CONCLUSION: Absolute ADC values in preclinical studies are comparable between sites and equipment, provided standardized protocols are employed.