Principles and concepts of computed tomography

An application of the density standard and scaled-pixel-counting protocol to assess the radiodensity of equine incisor teeth affected by resorption and hypercementosis: preliminary advancement in dental radiography

BACKGROUND

Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) syndrome is a dental disease where the radiographic signs may be quantified using radiographic texture features. This study aimed to implement the scaled-pixel-counting protocol to quantify and compare the image structure of teeth and the density standard in order to improve the identification of the radiographic signs of tooth resorption and hypercementosis using the EOTRH syndrome model.

METHODS AND RESULTS

A detailed examination of the oral cavity was performed in 80 horses and maxillary incisor teeth were evaluated radiographically, including an assessment of the density standard. On each of the radiographs, pixel brightness (PB) was extracted for each of the ten steps of the density standard (S1-S10). Then, each evaluated incisor tooth was assigned to one of 0-3 EOTRH grade-related groups and annotated using region of interest (ROI). For each ROI, the number of pixels (NP) from each range was calculated. The linear relation between an original X-ray beam attenuation and PB was confirmed for the density standard. The NP values increased with the number of steps of the density standard as well as with EOTRH degrees. Similar accuracy of the EOTRH grade differentiation was noted for data pairs EOTRH 0-3 and EOTRH 0-1, allowing for the differentiation of both late and early radiographic signs of EOTRH.

CONCLUSION

The scaled-pixel-counting protocol based on the use of density standard has been successfully implemented for the differentiation of radiographic signs of EOTRH degrees.

A phantom study on usefulness of modifying image parameters to reduce radiation exposure and maintain image quality in chest HRCT

PURPOSE

To investigate the feasibility of reducing radiation dose by modifying tube voltage, window settings, and algorithm while maintaining image quality, based on the qualitative evaluation of its quality and the radiation dose, using raw data acquired in chest high-resolution computed tomography (HRCT).

METHODS

Radiation exposure was measured using a Fluke dosimeter while modifying the tube voltage to 80 and 100 from 120 kVp in a 64-slice multi-detector computed tomography for comparison and analysis. Changes in image quality as a result of the different tube voltage settings, 3 different window settings (-550, -600, and -700), and 2 algorithms (standard and edge) were analyzed using ImageJ.

RESULTS

Relative to 120kVp, the dose decreased by approximately 67.8% and 36.9% at 80 and 100 kVp, respectively. Image quality assessment showed that changing the window setting to -700 (window level) after scanning with the tube voltage set at 100 kVp and applying the edge algorithm reduced the radiation dose while maintaining the image quality.

CONCLUSIONS

The findings are significant with respect to the reduction of scan dose in that they demonstrate how radiation exposure can be reduced in a clinical scenario by altering the settings on an existing HRCT apparatus. Additional clinical trials and image assessments should be conducted on human participants to confirm the feasibility of altering HRCT settings for reducing scan doses.

Image Quality and Dose Comparison of Single-Energy CT (SECT) and Dual-Energy CT (DECT)

CT and its comprehensive usage have become one of the most indispensable components in medical field especially in the diagnosis of several diseases. SECT and DECT have developed CT diagnostic potentials in several means. In this review article we have discussed the basic principles of single-energy and dual-energy computed tomography and their important physical differences which can cause better diagnostic evaluation. Moreover, different organs diagnostic evaluations through single-energy and dual-energy computed tomography have been discussed. Conventional or single-energy CT (SECT) uses a single polychromatic X-ray beam (ranging from 70 to 140 kVp with a standard of 120 kVp) emitted from a single source and received by a single detector. The concept of dual-energy computed tomography (DECT) is almost as old as the CT technology itself; DECT initially required substantially higher radiation doses (nearly two times higher than those employed in single-energy CT) and presented problems associated with spatial misregistration of the two different kV image datasets between the two separate acquisitions. The basic principles of single-energy and dual-energy computed tomography and their important physical differences can cause better diagnostic evaluation. Moreover, different organs diagnostic evaluations through single-energy and dual-energy computed tomography have been discussed. According to diverse data and statistics it is controversial to definitely indicate the accurate comparison of image quality and dose amount.

CT and gross pathology are comparable methods for detecting some degenerative sacroiliac joint lesions in dogs

Degenerative sacroiliac joint disease is a cause of lumbosacral pain in dogs; however, published information on cross-sectional imaging characteristics is limited. Objectives of this retrospective, secondary analysis, methods-comparison study were to test hypotheses that CT lesions reported in humans with degenerative sacroiliac joint disease are also present in dogs, and that CT is comparable to gross pathology for detecting these lesions. Matched CT and gross pathology slice images of 30 sacroiliac joints were retrieved from a previous prospective, canine cadaver study. A veterinary radiologist interpreted randomized CT images for each joint based on previously published CT characteristics of lesions in humans with degenerative sacroiliac joint disease. A veterinary pathologist independently interpreted randomized gross pathology images using the same criteria. All joints had at least one CT lesion consistent with degenerative sacroiliac joint disease. A new CT lesion was also identified and termed "subarticular cleft." The CT and gross pathology methods agreed for detecting joints with subchondral sclerosis, subchondral erosion, and intra-articular ankylosis lesions (P > .05, McNemar's test), but disagreed for detection of joints with subchondral cyst, para-articular ankylosis, and subarticular cleft lesions (P ≤ .05). Using gross pathology as the reference standard, CT had 100% sensitivity for detection of subarticular cleft and subchondral cyst lesions, with 56% and 22% specificity, respectively. Para-articular ankylosis lesions were detected by CT but not by gross pathology. Findings supported the hypothesis that CT lesions reported in humans with degenerative sacroiliac joint disease are also present in dogs, and partially supported the hypothesis that CT is comparable to gross pathology for detecting joints with these lesions.

Aparência tomográfica dos discos intervertebrais mineralizados em cães da raça Dachshund Miniatura

RESUMO Objetivou-se com este trabalho descrever os aspectos de tomografia computadorizada de discos intervertebrais de cães da raça Dachshund com um ano de idade, assim como quantificar, qualificar e localizar a mineralização nos componentes do DIV e no espaço intervertebral da coluna vertebral. Dez cães dessa raça, com um ano de idade, foram submetidos à tomografia computadorizada (TC). Nas imagens de reconstrução sagital dos animais, procedeu-se à identificação de sete DIV em cada animal, entre as vértebras T9 e L3, totalizando a análise de 70 DIV. Entre os DIV mineralizados, a presença da alteração foi determinada quanto à localização no núcleo pulposo (NP), no anel fibroso (AF) e em AF/NP. Dos 70 DIV avaliados, 45 foram considerados como mineralizados. Entre os classificados como mineralizados, 20% (9/45), 17,8% (8/45) e 62,2% (28/45) estavam localizados nas regiões do NP, AF e AF/NP, respectivamente. A mineralização encontrada neste estudo esteve caracterizada por aumento de atenuação radiográfica com densidade mineral na topografia do DIV, havendo variações da localização e da radiodensidade de área calcificada entre animais e DIV no mesmo indivíduo. As alterações relativas à mineralização dos DIV podem ser classificadas tomograficamente quanto à localização da alteração no disco em AF, NP e AF/NP.

Phenotyping of lumbosacral stenosis in Labrador retrievers using computed tomography

Deep phenotyping tools for characterizing preclinical morphological conditions are important for supporting genetic research studies. Objectives of this retrospective, cross-sectional, methods comparison study were to describe and compare qualitative and quantitative deep phenotypic characteristics of lumbosacral stenosis in Labrador retrievers using computed tomography (CT). Lumbosacral CT scans and medical records were retrieved from data archives at three veterinary hospitals. Using previously published qualitative CT diagnostic criteria, a board-certified veterinary radiologist assigned dogs as either lumbosacral stenosis positive or lumbosacral stenosis negative at six vertebral locations. A second observer independently measured vertebral canal area, vertebral fat area, and vertebral body area; and calculated ratios of vertebral canal area/vertebral body area and vertebral fat area/vertebral body area (fat area ratio) at all six locations. Twenty-five dogs were sampled (lumbosacral stenosis negative, 11 dogs; lumbosacral stenosis positive, 14 dogs). Of the six locations, cranial L6 was the most affected by lumbosacral stenosis (33%). Five of six dogs (83%) with clinical signs of lumbosacral pain were lumbosacral stenosis positive at two or more levels. All four quantitative variables were significantly smaller at the cranial aspects of the L6 and L7 vertebral foramina than at the caudal aspects (P < 0.0001). Fat area ratio was a significant predictor of lumbosacral stenosis positive status at all six locations with cranial L6 having the greatest predictive value (R² = 0.43) and range of predictive probability (25-90%). Findings from the current study supported the use of CT as a deep phenotyping tool for future research studies of lumbosacral stenosis in Labrador retrievers.

Computed tomographic measurements with and without myelography to characterise thoracolumbar extruded disc herniation

OBJECTIVE

To determine association between computed tomography measurements of spinal cord compression and postoperative outcome.

METHODS

A retrospective review of medical records of dogs presenting with intervertebral disease. Data were collected with a minimum of 2 years follow-up period. Computed tomography morphometric indices, particularly the ratio of spinal cord or herniated disc to vertebral canal dimensions, were obtained from survey and myelogram computed tomographic images. The pattern of disc disease was scored as single or continuous (multiple herniated discs), and was compared to postoperative outcome.

RESULTS

Fifty-two dogs were included. There was no significant correlation between the degree of spinal cord compression and postoperative outcome. However, postoperative outcome differed significantly between dogs with single or continuous patterns of disc disease (P=0·001). Of those with single patterns, 75% had a postoperative outcome score greater than 75% while 75% of continuous pattern cases had scores lower than 83%.

CLINICAL SIGNIFICANCE

Simple observation of the pattern of disc disease as revealed by computed tomography could be used as a prognostic indicator. The outcome tends to be better for single patterns of disc disease, whereas the outcome was poor for most cases with continuous patterns.

Tomografia computadorizada do encéfalo do cão: aspectos da normalidade e correlação anatômica

Obtiveram-se imagens tomográficas sem alterações da cabeça de cães, visando à familiarização com os aspectos normais do encéfalo e correlacionaram-se os achados com a respectiva anatomia da região estudada. Várias estruturas anatômicas foram identificadas, tais como o parênquima dos lobos frontal, parietal, temporal e occipital, a fissura longitudinal, o sistema ventricular, o cerebelo, o bulbo olfatório, o corpo caloso, o diencéfalo, a ponte, a medula oblonga e o sulco quiasmático, de forma direta ou relacionando-as com estruturas vizinhas que auxiliaram na sua identificação.

Feline Cerebrovascular Disease: Clinical and Histopathologic Findings in 16 Cats

Sixteen cats with cerebrovascular disease confirmed via histology to be of nontraumatic and nonneoplastic origins are described. In addition, the anatomy of the arterial supply of the cat's brain is reviewed. It is suggested that this unique arterial design may influence the incidence of cerebrovascular accidents in this species. Of the 16 cats reviewed, seven cats had ischemic infarctions, five had hemorrhagic infarctions, and four were diagnosed with intracranial hemorrhage. The median age was 8 yr and 9.5 yr in cats with infarctions and intracranial hemorrhages, respectively. Clinical signs were severe, acute, consistent with the localization of the cerebrovascular lesion, and influenced by underlying pathology. Four cats with infarction showed lateralized neurologic signs. Four cats with infarctions were diagnosed with pulmonary disease antemortem and three cats had hyperthyroidism. Cerebrospinal fluid analysis and computed tomography scans were available in two cats. None of the infarctions were grossly visible. All cats with hemorrhagic infarcts had severe liver pathology and nephritis was identified in four cats. Hypoxia was a feature in four cats and one cat suffered cardiac failure. In conclusion, the clinical picture is influenced by the type of cerebrovascular disease, the localization of the intracranial lesions, and any underlying pathology.

Pathophysiology and diagnosis of third carpal bone disease in horses: A review

Third carpal bone (C3) disease is a significant cause of lameness in Standardbred and Thoroughbred horses. The bone density of C3 increases as a result of exercise, reducing the compliance of the bone and predisposing it to injury. Currently, the most widely used method of diagnosis is subjective radiography using the tangential view. Radiographically, increases in bone mineral density (BMD) appear as sclerosis but it is not known at what point increases in sclerosis indicate the onset of disease or increased risk of C3 fracture. A quantitative assessment of the BMD of C3 in horses would improve understanding of the changes that occur within this bone and guide athletic management, as it is thought that BMD changes precede articular cartilage damage. Methods of non-invasive bone-mineral analysis used for the detection of osteoporosis in humans include single photon absorptiometry (SPA), dual x-ray absorptiometry (DXA), computed tomography (CT), radioabsorptiometry (RA), quantitative ultrasonography (QU) and magnetic resonance imaging (MRI). To date, DXA and RA are the most commonly used methods of quantitative non-invasive bone-mineral analysis in horses. The cost of equipment and difficulties in performing DXA in live animals preclude the routine use of this technique for diagnostic purposes. RA may become clinically applicable to C3 analysis in horses, but small variations in x-ray beam angle when taking the tangential view significantly affect results, making this technique clinically inapplicable at this time. Currently, methods of quantitative non-invasive bone-mineral analysis of C3 in horses are not suited to clinical application.

Cerebellar leptomeningeal carcinomatosis in a dog

Diffuse cerebellar meningeal carcinomatosis secondary to haematogenous dissemination from an anaplastic solid mammary carcinoma was diagnosed in an old German shepherd dog suffering from seizures and rapidly progressing to stupor. A single computed tomography cerebellar scan identified an unusual homogeneous density area that was considered to be associated with a vascular disorder, in the absence of space-occupying lesions. At necropsy, nodular masses were observed in the mammary gland, lungs, tracheobronchial lymph nodes and adrenals. Cerebellar leptomeninges were affected by diffuse blood effusion. Histology showed a solid mammary tumour, characterised by anaplastic cells with a cytoplasmic keratin-positive and vimentin-negative immunoreaction. The tumour had spread to the lungs, tracheobronchial lymph nodes and adrenals. Cerebellar leptomeninges were diffusely infiltrated by the cytokeratin-positive neoplastic cells. Even though computed tomography scan gave no evidence of meningeal carcinomatosis, it was considered that a cerebellar vascular disorder might be present. This was subsequently confirmed by neuropathological investigation and seen to be associated with a cerebellar leptomeningeal carcinomatosis.

Fragmented coronoid process in the dog: is there a role for incongruency?

Fragmented coronoid process in the dog is a common yet frustrating and poorly understood condition. Elbow joint incongruency, which refers to malalignment of the joint surfaces of the elbow, has been proposed as a key factor in the pathogenesis of fragmented coronoid process, and various surgical procedures have been devised to treat the proposed incongruency. However, precise characterisation of incongruency present in cases of fragmented coronoid process has not been reported consistently. In this article, the literature relating to the pathogenesis of fragmented coronoid process, the role of incongruency and its implications are reviewed.

Normal morphometry of the thoracic aorta in the german shepherd dog: a computed tomographic study

Computed tomographic images of the thoracic aorta of 14 German shepherd dogs were examined in order to determine the morphometry of the thoracic aorta. Examinations were carried out in the transverse plane at both intervertebral and mid-vertebral levels of each thoracic vertebra between T(5) and T(13). The dorsoventral and transversal diameters as well as cross-section area of the thoracic aorta were measured. The widest transversal diameter was observed at T(4-5), whereas the largest dorsoventral diameter was detected at T(5). The maximum cross-section area was detected at T(4-5). When dorsoventral and transversal diameters were compared between males and females, the aortic diameter was found to be smaller in males than in females. Although the shape of the thoracic aorta was transversal oval in the majority of the examined females, the shape of the thoracic aorta was dorsoventral oval in the majority of the males. There were significant differences between all levels measured for transversal (P < 0.001), dorsoventral (P < 0.001) diameters and cross-section area (P < 0.001) of the thoracic aorta. And there was a significant correlation between the three parameters examined. However, the correlation coefficient was highest in females.

Revisão anatômica do seio venoso sagital dorsal no crânio de cães braquicéfalos

Os seios venosos do crânio realizam a drenagem do cérebro e da medula espinhal, a fim de manter a homeostasia e o perfeito funcionamento do sistema nervoso central. Lesões na rede venosa cerebral podem causar déficits severos tais como hemiplegia, hemorragia, coma e morte. Os seios venosos são importantes pontos de referência para a realização de técnicas cirúrgicas de acesso ao cérebro. Este estudo visou analisar o trajeto do seio venoso sagital dorsal no crânio de cães braquicéfalos. Os animais braquicéfalos possuem crânios curtos e com características biométricas específicas. Foram utilizados 8 crânios de cães da raça Boxer, que foram submetidos à injeção de látex com pigmento corado e sulfato de bário. Após a perfusão, foram feitas radiografias contrastadas e imagens de tomografia computadorizada para relacionar o seio venoso com a estrutura óssea e dimensões relativas da calota craniana. Os crânios apresentaram índice cefálico (IC) médio de 91,24±8,34mm e índice crânio-facial (ICF) médio de 2,89±0,23mm. As mensurações do seio venoso sagital dorsal, relativas à calota craniana, apresentaram os seguintes valores médios: Área = 10,18±4,69mm²; D1 = 11,84±2,35mm; D2 = 19,57±2,61mm; D3 = 17,88±2,31mm; D4 = 25,32±5,68mm; e D5= 24,84±4,40mm.

Computed tomography in small animals – Basic principles and state of the art applications

Since its clinical introduction, computed tomography (CT) has revolutionized veterinary medicine and is considered to be one of the most valuable tools for the imaging work-up of neurological, oncological and orthopaedic canine and feline patients. In small animals with acute trauma, particularly those involving complex anatomic areas such as the head, spine or pelvis, CT has been established as a standard imaging method. With the increasing availability of radiation therapy in veterinary medicine, CT has also become the principal tool to stage a tumour, assess response, and guide radiation therapy. The increasing availability of helical CT in veterinary medicine has allowed novel techniques such as spiral CT angiography and high-resolution CT. This review provides a brief overview of the historical and technical development of CT and literature reviews of the major clinical CT applications in small animals such as intracranial and extracranial lesions, the spine, the appendicular skeleton, and abdominal and thoracic diseases.

Intraobserver and interobserver agreement, reproducibility, and accuracy of computed tomographic measurements of pituitary gland dimensions in healthy dogs

OBJECTIVE

To determine the reproducibility and accuracy of computed tomographic (CT) measurements of pituitary gland dimensions in healthy dogs.

ANIMALS

35 healthy sexually intact adult dogs.

PROCEDURES

2 observers independently viewed CT images of the skull in 35 dogs twice. Pituitary gland height, width, length, and volume and pituitary gland height-to-brain area ratio (P:B ratio) were measured or calculated. Intraobserver and interobserver agreement indexes (AIs) were calculated for pituitary gland dimensions. Computed tomography was performed also on 5 phantoms, and both observers measured phantom dimensions twice. True-value AIs were calculated for the phantom study.

RESULTS

The mean +/- SD interobserver AI between observer 1 and 2 for pituitary gland height and the P:B ratio was 0.90 +/- 0.07. The intraobserver AI for pituitary gland height and the P:B ratio was 0.97 +/- 0.04 for observer 1 and 0.94 +/- 0.04 for observer 2. The intra and interobserver AIs for the other dimensions were lower than those for pituitary gland height and the P:B ratio. All phantom dimensions on CT images were underestimated significantly, compared with their true values.

CONCLUSIONS AND CLINICAL RELEVANCE

The intra- and interobserver AIs for pituitary gland dimension measurements on CT images were high. However, the same observer preferably should perform serial measurements. Window settings influence pituitary gland dimension measurements, and predetermined window settings are recommended to make comparisons among dogs. Pituitary gland dimension measurements made from CT images in our study underestimated the true values.

Nasal computed tomography

Chronic nasal disease is often a challenge to diagnose. Computed tomography greatly enhances the ability to diagnose chronic nasal disease in dogs and cats. Nasal computed tomography provides detailed information regarding the extent of disease, accurate discrimination of neoplastic versus nonneoplastic diseases, and identification of areas of the nose to examine rhinoscopically and suspicious regions to target for biopsy.

Evaluation of elbow incongruency using reconstructed CT in dogs suffering fragmented coronoid process

OBJECTIVES

A retrospective study was undertaken to evaluate elbow joint congruency in dogs suffering fragmented coronoid process (FCP).

METHODS

Based on clinical, radiographic and computed tomographic (CT) examinations, elbows were divided into control and FCP groups. Standardised CT reconstructions were formatted in the frontal and sagittal planes. Humeroradial and humeroulnar joint space measurements were obtained from the Images and incongruencies were calculated by comparing the two measurements.

RESULTS

Forty-two FCP and 29 control elbows were identified. No incongruencies were noted at the coronoid base. At the level of the coronoid apex, FCP elbows exhibited a significant radioulnar incongruency compared with controls (P < 0.0001), though incongruency was not identified in all cases. Comparing FCP and control elbows at the level of the apex, the humeroradial joint space was increased in FCP elbows (P = 0.0006) whereas no difference was noted in the humeroulnar space.

CLINICAL SIGNIFICANCE

This study supports the hypothesis that joint incongruency is associated with FCP in dogs, though is not present in every case at the time of diagnosis. The precise mechanism of development of this incongruency cannot be determined from these data.

Histomorphometric and Densitometric Evaluation of the Effects of Platelet-Rich Plasma on the Remodeling of β-Tricalcium Phosphate in Beagle Dogs

Countless possibilities are available in maxillofacial surgery for the filling of bone defects. The best bone substitute known at present is osteogenic autogenous bone, but its use is accompanied by numerous disadvantages. The question has arisen of whether results attained with osteoconductive bone substitutes approach those achieved by the transplantation of autogenous bone. The aims of the investigation were to measure the effects in animal experiments of the growth factors to be found in the platelets on the rate of remodeling of beta-tricalcium phosphate, and on the quality of the new bone formed. Defects formed in the mandibles of 10 Beagle dogs were filled with beta-tricalcium phosphate or with a mixture of beta-tricalcium phosphate and platelet-rich plasma obtained from autogenous blood. The quality of the hard tissue formed and the effect of the platelet-rich plasma were examined by statistical analysis of the densitometric results obtained after 6 weeks and the histological and histomorphometric results obtained after 12 weeks. The densitometric study revealed that the bone formation was significantly more effective when platelet-rich plasma was used; at this stage, histomorphometric evaluation did not indicate a significant difference. After 12 weeks, however, the histomorphometric study demonstrated a significant difference in favor of the bone substitute used together with platelet-rich plasma. The results strongly suggest that use of the platelet-rich plasma suspension accelerates the remodeling of beta-tricalcium phosphate and leads to the formation of hard tissue with a quality similar to that of the autogenous bone.

Ophthalmic imaging

The availability of advanced imaging modalities in veterinary medicine has greatly widened the diagnostic imaging capabilities possible. Ultrasonography provides a rapid noninvasive modality that provides detailed examination and resolution of the intraocular structures and soft tissues surrounding the orbit of opaque eyes. Ultrasonography is cost-effective and widely available to practitioners,referral centers, and academic institutions. In many areas,mobile specialist ultrasonographers are available to supplement the equipment and skills of the practitioner. The added strengths of CT and MRI lie in their cross-sectional capability and better image quality. Unfortunately, the cost of CT and MRI currently limits their availability to referral centers and academic institutions. Primarily because of financial considerations, CT is currently more widely available for evaluation of equine disorders than MRI. A thorough evaluation of the multiple images and an understanding of normal anatomy and abnormal tissue patterns are indicated to maximize the use of each modality. Unlike ultrasonography, which can be performed in awake horses, the costs and contraindications of general anesthesia in some critical patients should also be considered when using CT and MRI. Finally, imaging artifacts are frequently encountered with each of these modalities. Thus, a thorough understanding of the various types of artifacts that occur is important so as to avoid interpretation pitfalls.

Morphometry of the thoracic spine in German shepherd dog: a computed tomographic study

Computed tomographic images of the thoracic spine of 13 German shepherd dogs were examined in order to determine the thoracic spine morphometry. Examinations were carried out in the transverse plane both intervertebral and mid-vertebral levels of the each thoracic vertebrae. The dorsoventral and interpedicular diameters of the spinal canal, the dorsoventral and transverse diameters of the vertebral body, the dorsoventral and transverse diameters of the spinal cord and also the cross-section area of the spinal canal were measured. The maximum values were found to be at the level of C7-T1. The shapes of the spinal canal and cord were circular in middle part, the shape became transverse oval in the cranial and caudal parts of the thoracic spine. The most significant correlation between the diameters was found to be in male dogs, except between dorsoventral diameters of the spinal canal and that of the vertebral body and between dorsoventral diameters of the spinal canal and transverse diameters of the vertebral body.

Thick-section reformatting of thinly collimated computed tomography for reduction of skull-base-related artifacts in dogs and horses

Computed tomography (CT) of the caudal fossa of 10 canine and nine equine cadaver heads was performed with conventional slice widths of 5 and 10 mm, respectively, and with thin collimations of 1 and 2 mm, respectively. Reformatting of thinly collimated slices was done by addition of thinly collimated slices to section thicknesses of 5 and 10 mm, respectively. Seventy-six pairs of conventional and reformatted images of identical anatomic locations were evaluated for magnitude of skull-base-related artifacts and image noise. A film-based subjective evaluation of artifact and noise was performed by four radiologists on a five-point score system. There was a statistically significant reduction of artifacts of canine and equine heads by 33% and 50%, respectively, on reformatted images compared with conventional ones but no difference in image noise. On objective artifact assessment based on the magnitude of standard deviation of attenuation values in the interpetrosal region, there was a statistically significant reduction of artifacts of canine and equine heads by 23% and 39%, respectively, on reformatted images. Thick-section reformatting significantly improves image quality of CT scans of the caudal fossa in dogs and horses.

Assessment of the accuracy of computed tomography for measurement of normal equine pituitary glands

OBJECTIVE

To describe the anatomic features of the pituitary gland region in horses via computed tomography (CT) and determine the accuracy of CT for estimating normal equine pituitary gland dimensions.

ANIMALS

25 adult horses with no clinical signs of pituitary disease.

PROCEDURE

Transverse CT images and gross transverse tissue sections were compared in 2 horses. Contrast-enhanced CT of the pituitary gland region was performed postmortem in 23 horses with 4 slice thickness and interval settings (10-mm contiguous or overlapping slices and 4-mm contiguous or overlapping slices). Gross and CT estimates of pituitary gland dimensions were compared via ANOVA. Accuracy of CT estimates was calculated with gross pituitary gland measurements as the known value.

RESULTS

Pituitary glands were located between the temporomandibular joints and had contrast enhancement. Mean gross dimensions were length, 2.11 cm; width, 2.16 cm; height, 0.98 cm; and volume, 2.66 cm3. Gross measurements and CT estimates of pituitary gland length from 10-mm contiguous and overlapping slices did not differ. Gross measurements and CT estimates of pituitary gland width from 4-mm contiguous and overlapping slices did not differ. Estimates of height and volume from all CT techniques differed from gross measurements. Accuracies for CT estimates were length, 88 to 99%; width, 81 to 92%; height, 58 to 71%; and volume, 43 to 55%.

CONCLUSIONS AND CLINICAL RELEVANCE

Accuracy of estimates of pituitary gland dimension in horses varied with CT scanning technique; via CT estimates of length and width of glands were more accurate than estimates of height or volume.

Brain abscesses as a metastatic manifestation of strangles: symptomatology and the use of magnetic resonance imaging as a diagnostic aid

REASONS FOR PERFORMING STUDY

The occurrence of unexpectedly high numbers of horses with neurological signs during two outbreaks of strangles required prompt in-depth researching of these cases, including the exploration of magnetic resonance imaging (MRI) as a possible diagnostic technique.

OBJECTIVES

To describe the case series and assess the usefulness of MRI as an imaging modality for cases suspected of space-occupying lesions in the cerebral cavity.

METHODS

Four cases suspected of suffering from cerebral damage due to Streptococcus equi subsp. equi infection were examined clinically, pathologically, bacteriologically, by clinical chemistry (3 cases) and MRI (2 cases). In one case, MRI findings were compared to images acquired using computer tomography (CT).

RESULTS

In all cases, cerebral abscesses positive for Streptococcus equi subsp. equi were found, which explained the clinical signs. Although the lesions could be visualised with CT, MRI images were superior in representing the exact anatomic reality of the soft tissue lesions.

CONCLUSIONS

The diagnosis of bastard strangles characterised by metastatic brain abscesses was confirmed. MRI appeared to be an excellent tool for the imaging of cerebral lesions in the horse.

POTENTIAL CLINICAL RELEVANCE

The high incidence of neurological complications could not be explained but possibly indicated a change in virulence of certain strains of Streptococcus equi subsp. equi. MRI images were very detailed, permitting visualisation of much smaller lesions than demonstrated in this study and this could allow prompt clinical intervention in less advanced cases with a better prognosis. Further, MRI could assist in the surgical treatment of brain abscesses, as has been described earlier for CT.

Use of computed tomography in the diseased feline thorax

Computed tomography (CT) scanning of the thorax is gaining more attention in veterinary medicine as therapeutic possibilities increase. Plain and contrast-enhanced CT images of the thorax of five referred cats with signs of respiratory disease were evaluated using soft tissue (pleural) and lung windows. The common CT pattern in all cats was involvement of the lung lobes, either as a homogeneous or heterogeneous single lobe hyperdensity. It involved the main bronchus, invaded the cranial or caudal mediastinum, and crossed the border to the opposite lung. Right lung atelectasis and mediastinal shift caused left lung overinflation. Bronchial lymph node enlargement was found unilaterally or bilaterally. CT-guided percutaneous fine needle aspiration biopsy of the lobar lung lesion was performed in four cats; in three cases it revealed carcinoma and in one inflammation, although the cat with suspected inflammation was subsequently found to have a carcinoma on lung lobectomy. Histopathology confirmed lung metastasis in one case and bronchial adenocarcinoma in four cases. A protocol for systematic examination of thoracic CT images is proposed.

Use of computed tomographic densitometry to quantify contrast enhancement of compressive soft tissues in the canine lumbosacral vertebral canal

OBJECTIVES

To evaluate computed tomography (CT) densitometry as a technique for quantifying contrast enhancement of compressive soft tissues in the canine lumbosacral vertebral canal and to determine whether the degree of contrast enhancement can be used to help predict tissue type or histopathologic characteristics.

ANIMALS

29 large breed dogs with lumbosacral stenosis.

PROCEDURE

Contrast-enhanced CT of L5-S3 was performed by use of a previously described protocol. At each disk level, CT densities of a water-filled syringe, epaxial muscles, and 4 vertebral canal locations were measured. Mean tissue enhancement was calculated by vertebral canal location, using water-filled syringe enhancement as a correction factor. Corrected CT enhancement was compared with tissue type, degree of tissue inflammation, and degree of tissue activity.

RESULTS

Intravenous contrast administration of contrast medium significantly increased CT densities of water-filled syringes and epaxial muscles. Corrected CT enhancement of vertebral canal soft tissues at stenotic sites was greater than at nonstenotic sites. There was no association between enhancement and tissue type for any vertebral canal location. There was no correlation between enhancement and degree of tissue inflammation. There was a correlation between enhancement and tissue activity in the dorsal vertebral canal only.

CONCLUSIONS AND CLINICAL RELEVANCE

A water-filled syringe is a useful calibration tool for CT density measurements. The degree of tissue contrast enhancement, measured by CT densitometry, can be helpful for predicting the location of compressive soft tissues in dogs with lumbosacral stenosis. However, it is of limited value for predicting compressive soft-tissue types or histopathologic characteristics.

Physical principles and technical considerations for equine computed tomography and magnetic resonance imaging

This article discusses how cross-sectional imaging methods such as computed tomography and magnetic resonance imaging can provide unique and diagnostically important information in situations where radiography or diagnostic ultrasound have been unrewarding.

Magnetic resonance imaging of otitis media in a dog

Otitis media/interna was diagnosed in a 20-month-old German shepherd with the assistance of magnetic resonance (MR) imaging. The MR images were acquired primarily to exclude a brain lesion responsible for vestibular signs. No brain lesion was detected, but obvious signs of chronic changes in the left bulla and external ear canal were confirmed. Thickening of the epithelium and soft tissue surrounding the external ear canal and a laminated appearance of high and low T2 intensities in the tympanic bulla's mucosa were present. The hypointense lines were suspected to be fibrous tissue, indicating chronic changes. This report suggests that MR imaging may serve as a useful imaging tool for otitis media and that it supplies information not obtained with radiography or computed tomography.

Identification of an ossicle associated with the palmar aspect of the carpus in the horse

An ossicle associated with the palmar aspect of the carpus is described in five horses. The size of the ossicle varied from 3 x 4 mm to approximately 12 x 10 mm. The ossicles were located at the junction of the proximal and distal rows of carpal bones, between the palmaromedial aspect of the fourth carpal bone and the ulnar carpal bone. In 3 horses they were bilateral, in one horse unilateral, and only one limb was examined in the remaining horse. In all horses it was an incidental finding and not regarded to be a pathologic entity.

Detection of a radiographically occult fracture of the lateral palmar process of the distal phalanx in a horse using computed tomography

A horse with a suspected injury of the distal phalanx was examined using radiography at day two and 19 after the onset of the lameness, with no definite diagnosis. Using computed tomography an incomplete fracture of the lateral wing of the distal phalanx was diagnosed at day 25. Based on computed tomography it was determined that the fracture probably did not enter the joint or involve the palmar cortex throughout its length which were of prognostic importance. The day following the CT examination a new oblique radiographic projection was made. In this radiography which was based on, and never would have been attempted without, the information about the geometric pattern of the fracture achieved by CT examination, a radiolucent area indicative of a wing fracture was seen. This report emphasizes the value of computed tomography in diagnosing a geometric complicated nonarticular oblique fracture of the palmar process of the pedal bone in a horse.

A review of imaging techniques for canine cauda equina syndrome

There are many imaging modalities available for evaluating the canine lumbosacral region. These include conventional radiography, stress radiography, myelography, epidurography, transosseous and intravenous venography, discography, linear tomography, computed tomography, and magnetic resonance imaging. Myelography, epidurography and discography are commonly used, but often lack sensitivity. Myelography is of little value when evaluating the cauda equina because the dural sac is elevated from the vertebral canal floor and frequently ends before the lumbosacral junction. Epidurography will identify a ventrally located compressive lesion and discography can delineate the dorsal extent of the diseased disc; however, both are sometimes difficult to interpret. Therefore, more than one of these imaging techniques must be used in order to make a diagnosis. Computed tomography and magnetic resonance imaging have become valuable in evaluating the lumbosacral region in dogs. These modalities have proven to be both sensitive and specific for determining cauda equina compression in both humans and in dogs.

Computed tomography and magnetic resonance findings in two dogs and a cat with intracranial lesions

Two dogs and a cat with intracranial lesions were evaluated by both computed tomography (CT) and magnetic resonance (MR) imaging. In a dog with vestibular syndrome, better quality images of the medulla oblongata surrounded by thick bones were obtained by MR than by CT, on which the appearance of artifacts impeded the clear image of the area. In a dog with multiple brain metastases of lymphoma, contrast CT delineated lesions more clearly than MR, which was performed one week after CT. During that week dexamethasone which might affect the clarity of MR images of the lesion was administered to reduce brain edema. In a cat with meningeal syndrome of lymphocytic leukemia, only contrast MR imaging identified the width and site of the lesion. These results indicate that it is necessary to select either one of these imaging methods according to the type and site of lesions that are suspected in a particular case.

Artifacts and technical errors presented as part of the 1996 ACVR oral certification examination

Cases used for the examination consisted of various imaging artifacts and technical errors. The candidate was expected to name or identify the problem and discuss its cause and prevention. For the purpose of completeness, the scope and detail given here is in excess of that needed to pass the examination. Unless the problem was obvious, the examiner pointed out the problem to be discussed.

Skeletal origins of exercise intolerance in horses

Skeletal origins of exercise intolerance and performance failure can reside in multiple tissues. Diagnosis of injury that results in an ability to continue to exercise, yet inefficiently do so, requires familiarity with evaluation of subtle lameness and often with the specific demands of the different equine sports. Imaging is usually vital to diagnosis development and understanding of lesion influences on locomotion. Therapy is lesion dependent. Return to competitive exercise and performance is dictated by an understanding of skeletal tissue response to injury, rational progressive treatment, and a controlled reintroduction of exercise demands.