MRI or CT?
Often a patient is sent for cross-sectional imaging for evaluation of a particular body part. This usually facilitates the choice of CT or MRI, as there are some clearly defined differences between the modalities when considering specific anatomic regions.
|Abdomen||CT is the current modality of choice providing good quality images and being much easier to perform.||MRI can be used, but requires special sequences and expertise. In the future MR may be used more for the characterization of abdominal masses and nodules in veterinary patients|
|Elbow and Hock||MRI may also be used and could provide additional information concerning bone oedema and Cartilage pathology.||CT usually recommended. Complimentary to arthroscopy in elbow disease|
|Shoulder and Stifle||MRI preferred—great potential for assessment of muscular, Tendinous, ligamentous and meniscal injury.||CT reserved for osseous disease|
|General skeleton||MRI advantageous in neoplastic disease (such as mandibular or maxillary tumours).||CT useful for angular limb deformities, fracture repair planning|
|Patients with metallic implants||In MRI non-ferrous implants may be placed into the magnet, but can create serious artefacts and hence non-diagnostic studies. The magni-tude of these artefacts differs de-pending on the MR sequence used.||The artefacts identified on CT examinations in patients with metallic implants can also prevent interpretation, but on occasion the gantry can be angled to avoid the metallic region and certain slices and reconstructions can limit their effect on the final image.|
|CT and MR angiography||Current applications include evaluation of portosystemic shunts, assessment for pulmonary thromboembolic disease, planning of vascular mass resection and many others.||Current applications include evaluation of portosystemic shunts, assessment for pulmonary thromboembolic disease, planning of vascular mass resection and many others.|
|Central nervous system (CNS)||Imaging modality of choice for CNS. Specific additional MRI sequences can be very useful – these include radient echo sequences(haemorrhage), diffusion weighted imaging (ischaemic disease), FLAIR sequences (perilesional oedema and identification of pure fluid), and STIR sequences (to evaluate muscle, bone and nerve root changes).||
CT myelography is necessary to identify significant sites of spinal cord compression. Intramedullary lesions are better recognized on MRI without the inherent risks of myelography. Use CT alone to diagnose brain dis-ease ONLY if MRI is not available. Not generally suitable for assessment of
foramen magnum herniation.
|Nasal cavities and sinuses||Both CT and MRI are extremely useful in assessment of the nasal cavities and frontal sinuses. Effective in the assessment of turbinate, maxillary and palatine destruction, mass lesions, presence of fluid, osteomyelitis, and contrast enhancing lesions.||Both CT and MRI are extremely useful in assessment of the nasal cavities and frontal sinuses. Effective in the assessment of turbinate, maxillary and palatine destruction, mass lesions, presence of fluid, osteomyelitis, and contrast enhancing lesions. CT can be used for guided FNA’s or biopsies and for thoracic metastatic screening.|
|External, middle and inner ears||CT and MRI both able to detect the fluid or mass lesions within the tympanic bulla and external ear canal, sclerosis or erosion of the bulla wall, associated retropharyngeal or para-aural lesions and regional lymphadenopathy. MRI allows assessment of cranial nerves VII and VIII, the cochlea and semicircular canals and the adjacent brainstem.||CT and MRI both able to detect the fluid or mass lesions within the tympanic bulla and external ear canal, sclerosis or erosion of the bulla wall, associated retropharyngeal or para-aural lesions and regional lymphadenopathy. CT can be used for thoracic metastatic screening if aural/para- aural neoplasia is suspected.|
|Thorax||MRI can be used for thoracic imaging in some situations. Useful for medi-astinal masses, thoracic wall masses and the pleural space disease. Respiratory and cardiac gating tech-niques are usually required.||CT definitely the modality of choice. Superior metastatic screening when compared to radiographs.|
|Pelvic region||Both CT and MRI suited to evaluation of the pelvic region.||Both CT and MRI suited to evaluation of the pelvic region.|
*In general contrast is advised for most CT examinations with the exception of cases where its administration could compromise the health of the patient, or in cases where bone imaging alone is required.
If you would like to discuss any case before imaging for advice on modality selection, please do not hesitate to contact BURGESS DIAGNOSTICS. Email Mike Hadfield at firstname.lastname@example.org giving full contact details and brief details of the case, and we will endeavour to answer your queries.