ISSN 2398-2942      

Computed tomography


Synonym(s): CT


  • Computed tomography (CT) is a non-invasive imaging modality that utilizes X-rays to generate cross-sectional images of an anatomical area.
  • Typical CT scanner composed of a gantry (ring-shaped), which houses the X-ray tube and detectors, a table for patient positioning, a generator, which produces high voltage and transmits it to the X-ray tube and a control desk for the operator.
  • X-ray tube moves in a circular path within the gantry and around patient.
  • Patient positioned on the table is advanced into the gantry either continuously or at fixed time intervals.
  • X-rays emitted by the tubes reach the patient and pass through it and are partially absorbed or scattered.
  • X-ray attenuation is measured by detectors which are aligned behind patient, opposite to x-ray source.
  • Most images are acquired in a transverse plane.
  • Multiplanar images, such as parasagittal and dorsal, and 3D renderings can be mathematically reconstructed.
  • CT image is generated by computer after collecting x-ray attenuation data and creating a matrix of values, called Hounsfield units (HU) or CT numbers, depicted in various shades of gray.
  • There are 4096 gray tones which represent different density levels in HUs.
  • Monitor can display a maximum of 256 gray tones though the human eye is able to only discriminate about 20.
  • Water is equal to 0 and dry air is equal to -1000 HU.
  • Density levels of almost all soft-tissue organs lie between 10 and 90 HUs.
  • Density level of bone is around 300 HUs.
  • Density level of lung is around -600 HUs.
  • Manipulation of the gray scale can be performed to enhance appearance of different tissues.
  • When image is displayed, grey scale is adjusted by setting window level and window width.
  • Window width (WW) determines the range of HUs represented on the image and influences the contrast of the image.
  • The narrower the window, the greater the contrast since the 20 observable gray tones cover a smaller range of densities.
  • Window level (WL) selects the center HU of the window width and should be set as close to the mean density level of the tissue to be examined as possible, eg a WW=300 and WL=0 indicates that HU values range from -150 to +150 on the image. If the WL is changed to 200, then HU values range from +50 to +350.


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Further Reading


Refereed papers


  • Henninger W & Pavlicek M (2001) State-of-the art incremental CT scan protocols in the dog for the optimal use of contrast media. Kleintierpraxis 46 (12), 761-772 VetMedResource.
  • Jones J C (2000) Three-dimensional computed tomography: user-friendly images. Compend Contin Educ Pract Vet 22 (6), 562-566 VetMedResource.
  • Ottesen N & Moe L (1998) An introduction to computed tomography (CT) in the dog. Eur J Comp Anim Pract (1), 29-36 VetMedResource.
  • Tidwell A S & Johnson K L (1994) Computed tomography-guided percutaneous biopsies in the dog and cat: description of the technique and preliminary evaluation in 14 patients. Vet Radiol Ultras 35 (6), 445-456 VetMedResource.


  • Crawford J T, Manley P A & Adams W M (2003) Comparison of computed tomography, tangential view radiography, and conventional radiography evaluation of canine pelvic trauma. Vet Radiol Ultras 44 (6), 619-628 PubMed.
  • Davis G J, Kapatkin A S, Craig L E et al (2002) Comparison of radiography, computed tomography, and magnetic resonance imaging for evaluation of appendicular osteosarcoma in dogs. J Am Vet Med Ass 220 (8), 1171-1176 PubMed.
  • De Rycke L M, Gielen I M, van Bree H et al (2002) Computed tomography of the elbow joint in clinically normal dogs. Am J Vet Res 63 (10), 1400-1407 PubMed.
  • Gielen I M, van Bree H J, Van Ryssen B et al (2002) Radiographic, computed tomographic and arthroscopic findings in 23 dogs with osteochondrosis of the tarsocrural joint. Vet Rec 150 (14), 442-447 PubMed.
  • Meyer-Lindenberg A, Heinen V, Fehr M et al (2002) Incomplete ossification of the humeral condyle as the cause of lameness in dogs. Vet Comp Orth Traumatol 15 (3), 187-194 VetMedResource.
  • Rovesti G L, Biasibetti M, Schumacher A et al (2002) The use of computed tomography in the diagnostic protocol of the elbow in the dog: 24 joints. Vet Comp Orth Traumatol 15 (1), 35-43 VetMedResource.
  • Samii V F, Les Clifford M, Schulz K S et al (2002) Computed tomographic osteoabsorptiometry of the elbow joint in clinically normal dogs. Am J Vet Res 63 (8), 1159-1166 PubMed.
  • Gielen I M, de Rycke L M, van Bree H J et al (2001) Computed tomography of the tarsal joints in clinically normal dogs. Am J Vet Res 62 (12), 1911-1915 PubMed.
  • McEntee M C & Thrall D E (2001) Computed tomographic imaging of infiltrative lipoma in 22 dogs. Vet Radiol Ultras 42 (3), 221-225 PubMed.
  • Niles J D, Dyce J & Mattoon J S (2001) Computed tomography for the diagnosis of a lumbosacral nerve sheath tumor and management by hemipelvectomy. J Sm Anim Pract 42 (5), 248-252 PubMed.
  • Radlinsky M A (2001) Ancillary diagnostic techniques for the lame patient. Vet Clin N Amer Sm Anim Pract 31 (1), 181-192, vii PubMed.
  • Reichle J K, Park R D & Bahr A M (2000) Computed tomographic findings of dogs with cubital joint lameness. Vet Radiol Ultras 41 (2), 125-130 PubMed.
  • Fitch R B, Wilson E R, Hathcock J T et al (1997) Radiographic, computed tomographic and magnetic resonance imaging evaluation of a chronic long digital extensor tendon avulsion in the dog. Vet Radiol Ultras 38 (3), 177-181 PubMed.
  • Braden T D, Stickle R L, Dejardin L M et al (1994) The use of computed tomography in fragmented coronoid disease: a case report. Vet Comp Ortho Traumatol (1), 40-44 VetMedResource.
  • Marcellin-Little D J, DeYoung D J, Ferris K K et al (1994) Incomplete ossification of the humeral condyle in spaniels. Vet Surg 23 (6), 475-487 PubMed.
  • McCarthy R J, Feeney D A & Lipowitz A J (1993) Preoperative diagnosis of tumors of the brachial plexus by use of computed tomography in three dogs. J Am Vet Med Assoc 202 (2), 291-294 PubMed.


  • Lefebvre J, Kuehn N F & Wortinger A (2005) Computed tomography as an aid in the diagnosis of chronic nasal disease in dogs. JSAP 46 (6), 280-285 PubMed.
  • De Rycke L M, Saunders J H, Gielen I M et al (2003) Magnetic resonance imaging, computed tomography and cross-sectional views of the anatomy of normal nasal cavities and paranasal sinuses in mesaticephalic dogs. Am J Vet Res 64 (9), 1093-1098 PubMed.
  • Saunders J H, Duchateau L, Störk C et al (2003) Use of computed tomography to predict the outcome of a non-invasive intranasal infusion in dogs with nasal aspergillosis. Canadian Vet J 44 (4), 305-311 PubMed.
  • Saunders J H & van Bree H J (2003) Comparison of radiography and computed tomography for the diagnosis of canine nasal aspergillosis. Vet Radiol Ultras 44 (4), 414-419 PubMed.
  • Saunders J H, van Bree H J, Gielen I et al (2003) Diagnostic value of computed tomography in dogs with chronic nasal disease. Vet Radiol Ultras 44 (4), 409-413 PubMed.
  • Saunders J H, Zonderland J L, Clercx C et al (2002) Computed tomographic findings in 35 dogs with nasal aspergillosis. Vet Radiol Ultras 43 (1), 5-9 PubMed.
  • Van Camp S, Fisher P & Thrall D E (2000) Dynamic CT measurements of contrast medium washin kinetics in canine nasal tumors. Vet Radiol Ultras 41 (5), 403-408 PubMed.
  • Park R D, Beck E R & LeCouteur R A (1992) Comparison of computed tomography and radiography for detecting changes induced by malignant nasal neoplasia in dogs. J Am Vet Med Assoc 201 (11), 1720-1724 PubMed.

Ear and TMJ

  • Dickie A M, Doust R, Cromarty L et al (2003) Comparison of ultrasonography, radiography and a single computed tomographic slice for the identification of fluid within the canine tympanic bulla. Res Vet Sci 75 (3), 209-216 PubMed.
  • Garosi L S, Dennis R & Schwarz T (2003) Review of diagnostic imaging of ear diseases in the dog and cat. Vet Radiol Ultras 44 (2), 137-146 PubMed.
  • Ziemer L S, Schwarz T & Sullivan M (2003) Otolithiasis in three dogs. Vet Radiol Ultras 44 (1), 28-31 PubMed.
  • Schwarz T, Weller R, Dickie A M et al (2002) Imaging of the canine and feline temporomandibular joint: a review. Vet Radiol Ultras 43 (2), 85-97 PubMed.
  • Lone N E, Kramer R W, Spodnick G J et al (1995) Radiographic and computed tomographic evaluation of otitis media in the dog. Vet Radiol Ultras 36 (5), 375-379 VetMedResource.


  • Gandini G, Gentilini F, Cimatti L et al (2003) Evaluation of the clinical signs and computed tomographic findings in 27 dogs with intracranial space-occupying lesions (1999-2000). Vet Res Commun 27 (Suppl 1), 399-401 PubMed.
  • Nykamp S G, Steffey M A, Scrivani P V et al (2003) Computed tomographic appearance of epidural empyema in a dog. Canadian Vet J 44 (9), 729-731 PubMed.
  • Giroux A, Jones J C, Bøhn J H et al (2002) A new device for stereotactic CT-guided biopsy of the canine brain: design, construction, and needle placement accuracy. Vet Radiol Ultras 43 (3), 229-236 PubMed.
  • Moissonnier P, Blot S, Devauchelle P et al (2002) Stereotactic CT-guided brain biopsy in the dog. J Sm Anim Pract 43 (3), 115-123 PubMed.
  • Nykamp S G, Scrivani P, de Lahunta A et al (2002) Chronic subdural hematoma and hydrocephalus in a dog. Vet Radiol Ultras 42 (6), 511-514 VetMedResource.
  • Van der Vlught-Meijer R H, Voorhout G & Meij B P (2002) Imaging of the pituitary gland in dogs with pituitary-dependent hyperadrenocorticism. Molec Cell Endocrinol 197 (1-2), 81-87 PubMed.
  • Bergman R, Jones J, Lanz O et al (2000) Post-operative computed tomography in two dogs with cerebral meningioma. Vet Radiol Ultras 41 (5), 425-432 PubMed.
  • Love N E, Fisher P & Hudson L (2000) The computed tomographic enhancement pattern of the normal canine pituitary gland. Vet Radiol Ultras 41 (6), 507-510 PubMed.
  • Ducoté J M, Johnson K E, Dewey C W et al (1999) Computed tomography of necrotizing meningoencephalitis in 3 Yorkshire Terriers. Vet Radiol Ultras 40 (6), 617-621 PubMed.
  • Cauzinille L (1997) Cerebrovascular accident in a two-year-old dog. A clinical case and review of non-traumatic vascular disorders of the brain in veterinary medicine. Prat Med Chirurg l'Anim Comp 32 (2), 143-150 VetMedResource.
  • Tidwell A S, Ross L A & Kleine L J (1997) Computed tomography and magnetic resonance imaging of cavernous sinus enlargement in a dog with unilateral exophthalmos. Vet Radiol Ultras 38 (5), 363-370 PubMed.
  • Drost W T, Berry C R & Fisher P E (1996) Computed tomographic appearance of a normal variant of the canine tentorium cerebelli osseum. Vet Radiol Ultras 37 (5), 351-353 VetMedResource.
  • Dzyban L A & Tidwell A S (1996) Imaging diagnosis: granulomatous meningoencephalitis in a dog. Vet Radiol Ultras 37 (6), 428-430 VetMedResource.
  • Wolf M, Pedroia V, Higgins R J et al (1995) Intracranial ring-enhancing lesions in dogs: a correlative CT scanning and neuropathologic study. Vet Radiol Ultras 36 (1), 16-20 VetMedResource.
  • Tidwell A S, Mahony O M, Moore R P et al (1994) Computed tomography on an acute hemorrhagic cerebral infarct in a dog. Vet Radiol Ultras 35 (4), 290-296 VetMedResource.
  • Norton F (1992) Cerebral infarction in a dog. Progr Vet Neurol (4), 120-125 VetMedResource.


  • Platt S R, Radaelli S T & McDonnell J J (2002) Computed tomography after mild head trauma in dogs. Vet Rec 151 (8), 243 PubMed.
  • Attali-Soussay K, Jegou J P & Clerc B (2001) Retrobulbar tumors in dogs and cats: 25 cases. Vet Ophthalmol (1), 19-27 PubMed.
  • Hathcock J T & Newton J C (2000) Computed tomographic characteristics of multilobular tumor of bone involving the cranium in 7 dogs and zygomatic arch in 2 dogs. Vet Radiol Ultras 41 (3), 214-217 PubMed.
  • Boroffka S A & Voorhout G (1999) Direct and reconstructed multiplanar computed tomography of the orbits of healthy dogs. Am J Vet Res 60 (12), 1500-1507 PubMed.
  • Calia C M, Kirschner S E, Baer K E et al (1994) The use of computed tomography scan for the evaluation of orbital disease in cats and dogs. Vet Comp Ophthalmol (1), 24-30 VetMedResource.
  • Hudson J A, Montgomery R D, Hathcock J T et al (1994) Computed tomography of craniomandibular osteopathy in a dog. Vet Radiol Ultras 35 (2), 94-99 VetMedResource.
  • George T F II & Smallwood J E (1992) Anatomic atlas for computed tomography of the mesaticephalic dog: head and neck. Vet Radiol Ultras 33 (4), 217-240 VetMedResource.


  • Gnirs K, Ruel Y, Blot S et al (2003) Spinal subarachnoid cysts in 13 dogs. Vet Radiol Ultras 44 (4), 402-408 PubMed.
  • Kinzel S, Hein S, Buecker A et al (2003) Diagnosis and treatment of arthrosis of cervical articular facet joints in Scottish Deerhounds: 9 cases (1998-2000). J Am Vet Med Assoc 223 (9), 1311-1315 PubMed.
  • Leskovar A, Coates J R, Russell K E et al (2003) Surgical removal of an intramedullary spinal cord foreign body granuloma in a dog. J Am Vet Med Assoc 39 (3), 306-310 PubMed.
  • Steffen F, Flueckiger M & Montavon P M (2003) Traumatic atlanto-occipital luxation in a dog; associated hypoglossal nerve deficit and use of 3-dimensional computed tomography. Vet Surg 32 (5), 411-415 PubMed.
  • Pease A P, Berry C R, Mott J P et al (2002) Radiographic, computed tomographic and histopathologic appearance of a presumed spinal chordoma in a dog. Vet Radiol Ultras 43 (4), 338-342 PubMed.
  • Rylander H, Lipsitz D, Berry W L et al (2002) Retrospective analysis of spinal arachnoid cysts in 14 dogs. J Vet Int Med 16 (6), 690-696 PubMed.
  • Gonzalo-Orden J M, Altónaga J R, Orden M A et al (2000) Magnetic resonance, computed tomographic and radiologic findings in a dog with discospondylitis. Vet Radiol Ultras 41 (2), 142-144 PubMed.
  • Jones J C, Banfield C M & Ward D L (2000) Association between postoperative outcome and results of magnetic resonance and computed tomography in working dogs with degenerative lumbosacral stenosis. J Am Vet Med Assoc 216 (11), 1769-1774 PubMed.
  • Olby N J, Muñana K R, Sharp N J et al (2000) The computed tomographic appearance of acute thoracolumbar intervertebral disc herniations in dogs. Vet Radiol Ultras 41 (5), 396-402 PubMed.
  • Schwarz T, Owen M R, Long S et al (2000) Vacuum disk and facet phenomenon in a dog with cauda equina syndrome. J Am Vet Med Assoc 217 (6), 862-864, 844 PubMed.
  • Tassani-Prell M & Kosfeld H U (1998) Computed tomographic diagnosis and surgical therapy of an atlas fracture in a dog. Kleintierpraxis 43 (9), 693-696, 699 VetMedResource.
  • Jones J C, Sorjonen D C, Simpson S T et al (1996) Comparison between computed tomographic and surgical findings in nine large-breed dogs with lumbosacral stenosis. Vet Radiol Ultras 37 (4), 247-256 VetMedResource.
  • Jones J C, Wright J C & Bartels J E (1995) Computed tomographic morphometry of the lumbosacral spine of dogs. Am J Vet Res 56 (9), 1125-1132 PubMed.
  • Jones J C, Cartee R E & Bartels J E (1995) Computed tomographic anatomy of the canine lumbosacral spine. Vet Radiol Ultras 36 (2), 91-99 VetMedResource.
  • Chambers J N, Selcer B A, Butler T W et al (1994) A comparison of computed tomography to epidurography for the diagnosis of suspected compressive lesions at the lumbosacral junction in dogs. Progr Vet Neurol (1), 30-34 VetMedResource.
  • Hathcock J T (1994) Vacuum phenomenon of the canine spine: CT findings in 3 patients. Vet Radiol Ultras 35 (4), 285-289 VetMedResource.
  • Hara Y, Tagawa M, Ejima H et al (1994) Usefulness of computed tomography after myelography for surgery on dogs with cervical intervertebral disc protrusion. J Vet Med Sci 56 (4), 791-794 PubMed.
  • Jones J C, Wilson M E & Bartels J E (1994) A review of high resolution computed tomography and a proposed technique for regional examination of the canine lumbosacral spine. Vet Radiol Ultras 35 (5), 339-346 VetMedResource.


  • Cipone M, Diana A, Gandini G et al (2003) Use of computed tomography in thoracic diseases of small animals. Vet Res Commun 27 (Suppl 1), 381-384 PubMed.
  • Morandi F, Mattoon J S, Lakritz J et al (2003) Correlation of helical and incremental high-resolution thin-section computed tomographic imaging with histomorphometric quantitative evaluation of lungs in dogs. Am J Vet Res 64 (7), 935-944 PubMed.
  • Watine S, Hamaide A, Peeters D et al (2003) Resolution of chilothorax after resection of a rib chondroma in a dog. J Sm Anim Pract 44 (12), 546-549 PubMed.
  • Essman S C, Hoover J P, Bahr R J et al (2002) An intrathoracic malignant peripheral nerve sheath tumor in a dog. Vet Radiol Ultras 43 (3), 255-259 PubMed.
  • Dvir E, Kirberger R M & Mallekzek D (2001) Radiographic and computed tomographic changes and clinical presentation of spirocercosis in the dog. Vet Radiol Ultras 42 (2), 119-129 PubMed.
  • Resoagli E H, Bode F F, Llano E G et al (1999) Comparison of thoracic transversal sections with axial computed tomography in the dog. Revista de Medicina Veterinaria - Buenos Aires 80 (6), 465-469 VetMedResource.
  • Schwarz L A & Tidwell A S (1999) Alternative imaging of the lung. Clin Tech Small Anim Pract 14 (4), 187-206 PubMed.
  • Smallwood J E & George T F (1993) Anatomic atlas for computed tomography in the mesaticephalic dog: thorax and cranial abdomen. Vet Radiol Ultras 34 (2), 65-83 VetMedResource.


  • Frank P, Mahaffey M, Egger C et al (2003) Helical computed tomography portography in ten normal dogs and ten dogs with a portosystemic shunt. Vet Radiol Ultras 44 (4), 392-400 PubMed.
  • Head L L, Daniel G B, Tobias K et al (2003) Evaluation of feline pancreas using computed tomography and radiolabeled leukocytes. Vet Radiol Ultras 44 (4), 420-428 PubMed.
  • Jaeger J Q, Mattoon J S, Bateman S W et al (2003) Combined use of ultrasonography and contrast enhanced computed tomography to evaluate acute necrotizing pancreatitis in two dogs. Vet Radiol Ultras 44 (1), 72-79 PubMed.
  • Katamoto H, Kumagai D, Kouzai N et al (2003) Space-occupying leiomyoma in the pelvic canal of a dog. J Sm Anim Pract 44 (6), 277-279 PubMed.
  • Rozear L & Tidwell A S (2003) Evaluation of the ureter and ureterovesicular junction using helical computed tomographic excretory urography in healthy dogs. Vet Radiol Ultras 44 (2), 155-164 PubMed.
  • Thompson M S, Graham J P & Mariani C L (2003) Diagnosis of a porto-azygous shunt using helical computed tomography angiography. Vet Radiol Ultras 44 (3), 287-291 PubMed.
  • Patsikas M N, Rallis T, Kladakis S E et al (2001) Computed tomographic diagnosis of isolated splenic torsion in a dog. Vet Radiol Ultras 42 (3), 235-237 PubMed.
  • Probst A & Kneissl S (2001) Computed tomographic anatomy of the canine pancreas. Vet Radiol Ultras 42 (3), 226-230 PubMed.
  • Rosenstein D S (2000) Diagnostic imaging in canine pheocromocytoma. Vet Radiol Ultras 41 (6), 499-506 PubMed.
  • Kneissl S, Probst A, Henninger W et al (1997) Computed tomographic differentiation of the canine liver lobes. Wiener Tierärztliche Monatsschrift 84 (6), 162-170 VetMedResource.
  • Yamazoe K, Ohashi F, Kadosawa T et al (1994) Computed tomography on renal masses in dogs and cats. J Vet Med Sci 56 (4), 813-816 PubMed.
  • Smallwood J E & George T F II (1993) Anatomic atlas for computed tomography in the mesaticephalic dog: caudal abdomen and pelvis. Vet Radiol Ultras 34 (3), 143-167 VetMedResource.

Other sources of information

  • Assheuer J & Sager M (1997) MRI and CT atlas of the dog. Blackwell Science, Berlin, Wien, Oxford.
  • Romans L E (1995) Introduction to Computed Tomography. Williams and Wilkins, Media PA.

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