Search

Segmentation is the process of partitioning an image into subdivisions and can be applied to medical images to isolate anatomical or pathological areas for further analysis. This process can be done manually or automated by the use of image processing computer packages. Atlas-based segmentation automates this process by the use of a pre-labelled template and a registration algorithm. We developed an ovine brain atlas that can be used as a model for neurological conditions such as Parkinson's disease and focal epilepsy. 17 female Corriedale ovine brains were imaged in-vivo in a 1.5T (low-resolution) MRI scanner. 13 of the low-resolution images were combined using a template construction algorithm to form a low-resolution template. The template was labelled to form an atlas and tested by comparing manual with atlas-based segmentations against the remaining four low-resolution images. The comparisons were in the form of similarity metrics used in previous segmentation research. Dice Similarity Coefficients were utilised to determine the degree of overlap between eight independent, manual and atlas-based segmentations, with values ranging from 0 (no overlap) to 1 (complete overlap). For 7 of these 8 segmented areas, we achieved a Dice Similarity Coefficient of 0.5-0.8. The amygdala was difficult to segment due to its variable location and similar intensity to surrounding tissues resulting in Dice Coefficients of 0.0-0.2. We developed a low resolution ovine brain atlas with eight clinically relevant areas labelled. This brain atlas performed comparably to prior human atlases described in the literature and to intra-observer error providing an atlas that can be used to guide further research using ovine brains as a model and is hosted online for public access.

Objective: To develop representative MRI atlases of the canine brain and to evaluate 3 methods of atlas-based segmentation (ABS)., Animals: 62 dogs without clinical signs of epilepsy and without MRI evidence of structural brain disease., Procedures: The MRI scans from 44 dogs were used to develop 4 templates on the basis of brain shape (brachycephalic, mesaticephalic, dolichocephalic, and combined mesaticephalic and dolichocephalic). Atlas labels were generated by segmenting the brain, ventricular system, hippocampal formation, and caudate nuclei. The MRI scans from the remaining 18 dogs were used to evaluate 3 methods of ABS (manual brain extraction and application of a brain shape-specific template [A], automatic brain extraction and application of a brain shape-specific template [B], and manual brain extraction and application of a combined template [C]). The performance of each ABS method was compared by calculation of the Dice and Jaccard coefficients, with manual segmentation used as the gold standard., Results: Method A had the highest mean Jaccard coefficient and was the most accurate ABS method assessed. Measures of overlap for ABS methods that used manual brain extraction (A and C) ranged from 0.75 to 0.95 and compared favorably with repeated measures of overlap for manual extraction, which ranged from 0.88 to 0.97., Conclusions and Clinical Relevance: Atlas-based segmentation was an accurate and repeatable method for segmentation of canine brain structures. It could be performed more rapidly than manual segmentation, which should allow the application of computer-assisted volumetry to large data sets and clinical cases and facilitate neuroimaging research and disease diagnosis.

Objective: To evaluate the use of high-resolution MRI for hippocampal volumetry in dogs and to define a lower reference limit for hippocampal formation (HF) volume., Animals: 20 dogs (with no history of seizures and no underlying structural brain disease) that underwent MRI of the brain., Procedures: The MRI protocol included a high-resolution T1-weighted 3-D ultrafast gradient-echo sequence aligned in a dorsal plane perpendicular to the long axis of the HF. Images obtained with MRI were retrospectively analyzed by 2 observers (A and B). Intraobserver and interobserver agreement were calculated with the Lin concordance correlation coefficient. Volume measurements of the HF were adjusted for intracranial volume, and a lower 95% reference limit for adjusted HF volume was calculated., Results: There was substantial intraobserver agreement (Lin concordance correlation coefficient, 0.97 [95% confidence interval {CI}, 0.94 to 0.99]) but poor interobserver agreement (Lin concordance correlation coefficient, 0.63 [95% CI, 0.37 to 0.79]). The lower 95% reference limit for adjusted HF volume was 0.56 cm(3) (90% CI, 0.52 to 0.60 cm(3)) for the right HF and 0.55 cm(3) (90% CI, 0.52 to 0.58 cm(3)) for the left HF., Conclusions and Clinical Relevance: HF volumes should be adjusted for intracranial volume to account for the large variation in canine skull size. The amount of time required to perform HF volumetry and low interobserver agreement may restrict this technique to research applications, such as the investigation of epileptic patients for hippocampal sclerosis or other cognitive disorders.

A 6-year-old male neutered cat presented with blindness, lethargy, polydipsia, hyposthenuria and severe hypernatraemia. Central diabetes insipidus was demonstrated by means of a low measured anti-diuretic hormone (ADH) concentration in the face of hypernatraemia, and clinical response to supplementation with desmopressin. Magnetic resonance imaging of the brain showed a discrete mass in the region of the hypothalamus. The cat was euthanased and post-mortem histological examination demonstrated B cell lymphoma involving the brain, optic nerves, urinary bladder wall and diaphragm. To the authors' knowledge, this case report is the first to describe central diabetes insipidus caused by central nervous system lymphoma in the cat., (Copyright © 2011 ISFM and AAFP. All rights reserved.)

The use of advanced clinical nurses (ACNs) has enabled expansion of the Hypertension Clinic at the Johannesburg Hospital. The ACNs care for elderly patients whose hypertension is stable and who require a minimum of drugs. Blood pressure control in this group of patients is satisfactory and the default rate is low. The ACN therefore appears acceptable, at least to the patient. However, problems of continuing education, evaluation and official recognition remain. The case for allowing the ACN to prescribe from a limited pharmacopoeia is presented.