Diagnostic imaging modalities in veterinary medi-cine are becoming increasingly sophisticated, and the use of computed tomography (CT) and magnetic resonance imaging (MRI) has increased over the last decade. In the early years, limiting factors for implementation of CT and MRI in rabbit medicine were the long duration of the imaging procedures, length of anaesthesia, the small size of the animal and limited resolution of the images. In recent years, the modalities have evolved, resulting in decreased procedure times and high resolution images, and CT and MRI scanning in rabbit medicine have become routine imaging techniques in some clinics.
However, equipment for CT and MRI is expensive, in terms of both acquisition and maintenance, and an extensive knowledge of the technique and the acquired images is a necessity. These requirements can be difficult to accomplish in small veterinary practices. Fortunately, CT and MRI are becoming increasingly available in diagnostic imaging depart-ments at veterinary universities and referral clinics, so patients that are in need of CT or MRI can be referred to these centres.
Principles and equipment
CT and MRI are both tomographic techniques, tomos eanin slice’ in ree n t tec ni es the object is displayed as multiple images or pic-tures, with every image representing one slice of the object. Every picture consists of pixels (picture elements) that have a thickness equal to the slice t ic ness ese t ree di ensi nal 3 pi els’ are called voxels (volume elements) (Bushburg et al., 2002a). Creating CT and MR images is a complex process and therefore only some of the technical aspects will be highlighted in this section.
Computed tomography
Computed tomography (CT), or computed axial tomography (CAT) as it was previously named, was introduced in 1972. In the early period it took about 5 minutes to create one slice that was 13 mm thick and had pixels of 3 mm × 3 mm. The images were of low resolution with many artefacts (Bushburg et al., 2002a). Many developments, such as helical scan-ning and multi-slice techniques, have improved the imaging process such that, within milliseconds, high-resolution images can be created that have a
slice thickness of <1 mm. Helical scanning, consist-ing of continuous movement of the X-ray tube around the patient and simultaneous table move-ment, was introduced in 1989 and has improved scanning speed. The multi-slice technique, in which multiple slices are created in one rotation of the X-ray tube, was introduced in 1992 (Bushburg et al., 2002a). The development and availability of advanced software programs has made image reconstruction and rendering possible and, as slice thickness decreases, high-resolution 3D image reconstruction or multi-planar reconstruction (MPR) become available. The 3D image reconstruction enables evaluation of the shape of anatomical struc-tures such as the skull or blood vessels (CT angio-gram). In MPR images, all views in the x-, y- and z-axes are available for reviewing, and all the struc-tures in the reconstructed slice can be evaluated without superposition of other structures. The equip-ment available in veterinary medicine currently con-sists mostly of 1 to 64 multi-slice, helical scanners.
CT images are created by rotating an X-ray tube around the patient and computing the data (amount of X-rays) collected by a ring of X-ray detectors that is positioned around the gantry (the central opening in which the patient is located). The different anatom-ical tissues and fluids are projected in the image in varying grey values, which are named Hounsfield units (HU), according to the amount of X-ray attenua-tion by the tissues. Pure water has an HU value of zero, and therefore darker (hypoattenuating) areas in the image (e.g. air and fat) will have a negative HU value and lighter (hyperattenuating) areas (e.g. soft tissues, mineralized structures, contrast medium or metal) will have a positive HU value.
Intravenously injected contrast medium can be applied during CT imaging in rabbits using the same agents that are used in radiographic procedures (i.e.
ionic or non-ionic iodinated). The contrast medium will cause hyperattenuation where it is present in the image (Dennis and Herrtage, 1989).
There are up to 4200 grey values in every image, but the human eye can only detect up to 256. To maximize the visibility of these varying grey values, images are displayed in certain ranges. The centre of the range is called the level (L), and the width of grey values above and below this centre is called the window (W). To optimize evaluation of, for example, soft tissues or bones, these parameters
will be changed to HU values of, respectively, 350 (W) and 50 (L) or 3500 (W) and 500 (L). This is called windowing and levelling and allows the creation of soft tissue and bone settings. These images can be further improved by using filters that enhance various characteristics of the tissues, for example a soft tissue filter will smooth the image but a bone filter will enhance the bone borders by edge enhancement. All these improvements of the image quality for varying tissues are performed after image acquisition (Bushburg et al., 2002a).
Magnetic resonance imaging
Magnetic resonance imaging (MRI) was introduced in the mid-1980s as a sequel to spectroscopic studies in chemical and biochemical research (Bushberg et al., 2002b). MRI scanners have evolved during recent decades and are now available in veterinary medicine mostly as low-field 0.2–0.3 Tesla (open) systems or high-field 1–3 Tesla superconducting systems. The main difference between the low- and high-field sys-tems is the fact that low-field syssys-tems are generally magnetized only temporarily. These systems only cre-ate a magnetic field as electric power is turned on and they can be switched off in an emergency (Bushberg et al., 2002c). The high-field systems use a supercon-ducting wire kept in a cryogenic liquid such as liquid helium. A permanent current runs through the wire, creating a permanent magnetic field that can only be switched off by removing the cryogenic liquid (Bushberg et al., 2002c). As this is a very costly oper-ation, pre cautions must be taken to minimize the risk of an emergency requiring the shutdown of the sys-tem. All MRI systems are placed in a shielded room (Faraday cage) to protect the environment from the extensive magnetic field but more importantly to pro-tect the MRI system from environmental radio fre-quency (RF) pulses. RF pulses (e.g. FM broadcasts) interfere with the creation of the MR image because they are in the same range as the frequencies that the body emits during an imaging procedure (Bushberg et al., 2002c). All equipment and material inside the shielded room has to be MR-compatible, because all non-compatible objects can become lethal weapons when attracted by the magnet (e.g.
pairs of scissors, needles, chairs, oxygen tanks, anaesthesia monitors and machines). Even very small magnetic objects in the patient, such as identification chips or staples, can create large susceptibility arte-facts in the MR images and removal is advised when they would be in the scanning field of view.
Image acquisition for MRI is very different from CT image acquisition because there is only one method of creating an image in CT but several in MRI. The magnetic field created by the MRI system causes protons in the tissues to align accordingly, as if they were small magnets in a low-energy state.
Images are created by stimulating these protons using RF pulses. Some of the protons take up energy from these RF pulses and will eventually return to their low-energy state, emitting some of the energy absorbed previously by sending a weak RF signal.
This signal will be captured, processed and the MR image created, and every type of tissue or fluid will
emit the RF pulses in a different time span. By differ-entiating the times of RF pulse stimulation (TR, time of repetition; TI, time of inversion) and readout (TE, time of echo), the MR characteristics of these tissues, namely the T1, T2 and proton density, will become visible. In this way, several MRI sequences can be created with different grey scales for the different tissues. For example, cerebrospinal fluid (CSF) will be dark (hypointense) on T1-weighted images and bright (hyperintense) on T2-weighted images.
The intravenous contrast medium used in MR image acquisition is in most cases a derivative of gadolinium and affects the relaxation times (time to reach the low-energy state) of the protons. This is best appreciated on T1-weighted images. The T1 characteristics of the tissues in which the contrast medium is present will be brighter in the image (hyperintense) because protons in the tissues retain the energy of the RF pulse for a shorter duration (Kuriashkin and Losonsky, 2000). Lesions are more evident if there is increased vascularization or stasis of blood within these lesions.
There are at least three ways of creating an MRI sequence; the most frequently used in veterinary medicine are called spin echo, gradient echo and inversion recovery. All these sequences have T1, T2 and proton density imaging characteristics but are created in different ways. The major advancement for gradient echo sequences is the fact that images with very thin slices can be created, and therefore 3D reconstruction and MPR of the scanned area can be made. The inversion recovery sequences used in veterinary MRI consist of the fluid-attenuated inver-sion recovery (FLAIR) sequence, in which the signal of aqueous liquids (such as CSF) will be dark, and the short tau inversion recovery (STIR) sequence, in which the signal of fat will be dark (fat suppression).
The MRI sequences can be made in all desired planes (dorsal, transverse, sagittal), unlike CT where only the transverse plane is available (when the rab-bit is positioned longitudinally on the table). All these sequences, or a combination of these sequences, will be acquired after each other and therefore an MRI study can be lengthy (Bushberg et al., 2002b).
Resolution and scanning times are improving in MRI scanning as more and more high-field systems are introduced in veterinary medicine and imaging protocols with specific high-resolution sequences are developed (e.g. gradient echo). Because MR imaging with low-field systems is still inferior in image acquisition times to the relatively fast CT image acquisition, its use has been lagging behind.
The fragility and sensitivity to complications of rabbits during and after general anaesthesia requires use of the shortest scanning time possible.
The increasing availability of high-field MRI systems in veterinary medicine is offering new possibilities for rabbit imaging, as it has done in research facili-ties. In these facilities, high-field MRI systems have been available for many years and rabbits have been used frequently as MRI or CT models.
Therefore an extensive databank on MR and CT imaging in rabbits is available, and can be used as a guide and reference for imaging in veterinary
medicine (Mavinkurve et al., 2005; Yuan et al., 2005; Casteleyn et al., 2010; Qiuhang et al., 2010;
Van Caelenberg et al., 2010, 2011; Zhao et al., 2010; Zhang et al., 2011; Wei et al., 2012).
Indications for CT and MRI
Radiography and ultrasonography are the primary imaging techniques used in veterinary medicine;
they are affordable and available for many veter-inary practices and often provide sufficient inform-ation to enable diagnosis. However, given that medical CT and MRI systems offer high-resolution images in conjunction with excellent 3D and MPR possibilities, these techniques can be used as a clinical aid in diagnostics, to help in surgical plan-ning and even in planplan-ning radiotherapy protocols (Mavinkurve et al., 2005; Zotti et al., 2009; Figure 9.1). Most rabbits require CT or MRI scanning because of the need to specify the differential diag-nosis and treatment options. CT and MRI are indicated in areas where radiography and/or ultra-sonography offer insufficient information owing to technical limitations or tissue characterization. This can be a result of the super imposition of multiple anatomical structures (e.g. in the head), the lack of soft tissue differentiation in radio graphs, the lack of overview in ultrasound images or the limited acous-tic penetration of ultrasound waves where bone or air (e.g. in the lungs) is present.
Currently, CT examination of the head is per-formed most frequently for clinical signs related to dental problems such as anorexia, soft tissue swell-ings, epiphora or exophthalmos. The lack of super-imposition of multiple anatomical structures in the CT and MR images is a major benefit. Smaller struc-tures can be identified and evaluated for their pos-ition, shape, structure and size related to the adjacent anatomical structures. The images acquired allow moderate to good soft tissue differentiation, overview and penetration into all anatomical struc-tures. The use of intravenously applied contrast medium in both MRI and CT enhances tissue differ-entiation because of the differences in tissue vascu-larization. Necrotic areas will not be vascularized and will therefore lack contrast enhancement, but surrounding areas are often hypervascularized as a result of inflammation and will be enhanced strongly (ring enhancement). In the rabbit, this is most often seen in abscesses, where the centre will not be enhanced but the capsule surrounding the abscess will. The visibility of all these structures will assist in the diagnostic process and narrow the differential diagnosis list to the most plausible option. The images created can be used in planning of surgery (e.g. abscess drainage) or radiotherapy. The trans-verse images and possible 3D and MPR options are of great value at this stage (Figure 9.2). Note: All transverse CT and MR images in this chapter are displayed with the left lateral aspect of the rabbit on the right side of the image.
CT MRI
General concept
Mineralized structures (e.g. dental structures, bone); air-containing structures (e.g. ear canal and tympanic bulla); soft tissues; however, minimal
differentiation possible without intravenous contrast medium; intravenous contrast medium is used to evaluate vascularization of tissues
Soft tissues (e.g. brain, vertebral canal and spinal cord, abdominal organs, muscles, tendons, intervertebral discs); soft tissue changes in bone (e.g. bone marrow, osteomyelitis, neoplasia); intravenous contrast medium is used to evaluate vascularization of tissues Head
Dental problems (e.g. malocclusion, apical infection, fractures); abscess (e.g.
apical dental infection, foreign body); exophthalmos (e.g. dental problem, ne plasia epip ra e dental pr le in a at r pl ne plasia rhinitis (e.g. infection of nasal passages, apical dental infection, foreign body, neoplasia); ear problems (e.g. otitis externa, media and interna)
Epilepsy (primary or secondary); abnormal behaviour such as circlin and ne r l ical de cits s c as paral sis r ata ia e meningoencephalitis, hydrocephalus, infarct, neoplasia)
Spine
Paresis or paralysis (e.g. traumatic fracture, discospondylitis, neoplasia) Paresis or paralysis (e.g. traumatic myelopathy, intervertebral disc herniation, haemorrhage, neoplasia)
Thorax
Screening for metastases; dyspnoea (e.g. broncho pneumonia, neoplasia, foreign body); evaluation of size and position of mass lesions seen on radiographs (e.g. thymoma, pulmonary neoplasia)
(Functional imaging: cardiac)
Abdomen
Evaluation of size, position, structure of mass lesions (e.g. abscess, neoplasia); screening for metastases; vasculature; intestinal problems (e.g.
foreign body, neoplasia)
Evaluation of size, position and structure of mass lesions;
screening for metastases (more sensitive than CT in soft tissues such as liver and spleen); vasculature
All areas
Surgical planning; radiotherapy planning; screening for metastases Surgical planning; screening for metastases Comparison of indications for CT and MRI in the rabbit.
9.1
CT versus MRI
MR images are superior in soft tissue differentiation to CT images, but CT images are superior for bone imaging to MRI; therefore MRI is, for example, used most frequently for the brain or spinal cord and CT for the rest of the head or vertebrae. Soft tissues have a narrower range of attenuation (grey values) in CT images, making them harder to differentiate from each other, especially when positioned close together. Intravenous contrast can be of assistance in differentiating well vascularized and poorly vascu-larized tissues from each other, in both CT and MRI (MRI being more sensitive than CT for smaller changes). Cortical bone and mineralization is black on MRI and therefore small areas of mineralization are better visualized with CT. However, some bone pathologies (e.g. bone necrosis or oedema) can be appreciated with MRI at an early stage but not detected with CT at all.
Restraint and positioning
CT and MRI examinations in the rabbit are per-formed under general anaesthesia. Preparation and scanning time for a CT scan is short (usually less than 20 minutes). The patient is prepared for the anaesthesia in or near the scanning room to reduce the duration of anaesthesia. In most cases, pre-medication with an anxiolytic drug (e.g. midazolam) followed by an inhalant anaesthetic (e.g. isoflurane) is sufficient. An intravenous catheter is placed when a contrast study is deemed necessary and this is the most time-consuming procedure of the entire examination. MRI scanning takes considerably
(a) MPR enables the creation of CT images in all planes. The right-hand image (with the yellow box lining) corresponds to the yellow line in the left lower image. (b) 3D bone reconstruction, showing the head of a rabbit with bilateral apical infection of the mandibular cheek teeth at the level of the premolars. This is visible as a bony expansive lesion (
*
) ventral to the mandible.9.2
*
(a)
(b)
more time (up to an hour) than CT scanning. The anaesthetic equipment has to be MR-compatible, as do the monitors and positioning materials.
The rabbit is positioned in ventral recumbency and as symmetrically as possible, especially for the head, neck, thorax and pelvis. Although pos itioning the animal in dorsal recumbency creates a better spatial distribution of the abdominal organs, the pressure on the diaphragm, and therefore on the thorax, has to be kept in mind. Modern rendering and reconstruction software can recreate a symmet-rical image, but anatomical structures are very small and therefore positioning is important in creating the best images. After positioning the patient, straps are placed around the table and the rabbit to keep it in exactly the same position during movement of the table and, if the animal should wake up during scan-ning, to prevent it jumping off the table. Electro-cardiography cables, catheters, infusions and anaesthetic equipment should be kept out of the CT and MRI (even when MR-compatible) gantry as much as possible, because they may cause arte-facts which degrade the images.
Conditions in which CT or MRI scanning may be diagnostic
i en t at i a in tec ni es are a se el t clin ical examination, the clinical findings are an impor-tant part of image interpretation. A preliminary differential diagnosis guides the CT or MRI tech-nician and radiologist in creating the correct images (choosing the appropriate scanning proto-cols) and interpretation.
The head
CT examination of the dental structures with adja-cent bony structures, nasal passages, nasolacrimal canal, ear canal (external ear canal, tympanic bullae and inner ear) and calvarium is the most common CT procedure performed. MRI of soft tissue struc-tures and the brain can also be performed.
The teeth and nasal passages
The position, shape and attenuation (in HU) of the dental structures and the adjacent bony and soft tissue structures can be evaluated with CT (Van Caelenberg et al., 2008). When interpreting the CT images, the position of the crown and root is evaluated in all dental structures, starting with the incisors and continuing caudally to the maxil-lary and mandibular cheek teeth. The crown and occlusal surface of the incisors can easily be eval-uated clinically but, as the root is elongated and reaches to the nasal passages, this area is not vis-ualized clinically. CT of this area allows evaluation of the tooth roots as well as the surrounding alveo-lar bone and nasal passages. Some of the cheek teeth are poorly visualized during clinical examina-tion owing to their caudal posiexamina-tion. With CT, the entire row of cheek teeth can be visualized, because there is no superimposition of cheek teeth as would be present on a radiograph.
• Malocclusion of the dental structures and secondary changes such as hooks or
accumulation of cementum near the roots are all easily visualized with CT.
• The surrounding tissues such as the alveolar bone and nasal passages can be evaluated for possible secondary osteolysis or malformation due to periapical abnormalities (Figure 9.3a).
• Periapical abscesses that deform the alveolar bone are visible as widening of the alveolar space surrounding the roots. CT imaging is very sensitive for detection of minor changes in this area, and a hypoattenuating zone will be the first change visible.
• If inflammation has spread to the nasal passages to cause rhinitis or an abscess, the extent of deformation and destruction of the conchal structures, mucosal swelling and presence of purulent material can be evaluated with CT.
• The existence of an oronasal fistula due to destruction of the alveolar bone in an apical abscess is most often visible as osteolysis of the alveolar wall and concurrent changes (e.g. fluid accumulation) in the nasal passages.
• Abscess formation in conjunction with dental and bony abnormalities can be detected (Figure 9.3b) (Arzi and Sinclair, 2002; Van Caelenberg et al., 2008).
Contrast studies: Intravenous contrast medium can further specify the soft tissue attenuating structures in the images and more clearly demar-cate lesions on CT and MR images in fluid, necrotic areas or vascularized tissues. Contrast
* A * A
(a)
(a) Transverse CT image (bone setting) of the same rabbit as in Figure 9.2b. It shows bilateral severely deformed mandibles due to extensive apical abscessation (A) of the premolar cheek teeth (
*
). Theroots of the involved cheek teeth are deformed and hypoattenuating. (b) Transverse CT image (soft tissue setting) of a different rabbit, showing a large lobular abscess (A) lateral to the right maxilla. Ring enhancement is present. The adjacent maxillary bone is irregular (
*
),and apical infection with minimal nasal mucosal swelling and fluid is visible.
9.3 (b)
A *
enhancement patterns can differentiate abscesses and diffuse inflammation from neoplastic masses.
Diffuse inflammation will be vaguely defined and cause an increase in attenuation of the fascial fat lines as these are most often involved in the pro-cess. Neoplastic masses are more often well defined and, although necrosis or bleeding can be present in the mass, it will cause a diffuse patchy enhancement in both CT and MRI (Figure 9.4). CT and MRI can assist in evaluating the extent of the lesion, detection of the possible origin and treat-ment planning (Wagner et al., 2005; Ward, 2006).
Transverse CT image (soft tissue setting after intravenous contrast injection) of the head at the level of the cribriform plate. A well defined space
occupying neoplastic mass (M) is visible in the nasopharynx, extending intracranially and in the
retrobulbar area via osteolytic areas of the cribriform plate (<) and medial orbital wall (>). Minimal right-sided exophthalmos is present.
9.4
> M <
9.5 The nasolacrimal canal
Blockage of the nasolacrimal duct can be evaluated by performing a CT dacryocystography (Yoshikawa et al., 1998; Nykamp et al., 2004). The contrast medium is instilled directly into the nasolacrimal duct via the punctum lacrimale; if no abnormalities are present, the contrast medium will be visible in t e entire canal and nasal passa e i en t at offers a 3D and complete evaluation of the contrast material in the nasolacrimal canal, the exact loca-tion, extent, possible cause of the blockage and clinical or surg ical options can be evaluated (Figure 9.5). The advanced software available can create images in three-dimensional planes (MPR) with no superposition, which are superior to radiographs. A virtual endoscopy session can be created. The wall and the lumen of the naso lacrimal duct and the surrounding structures can all be evaluated with CT
scanning. Abnormalities in the lumen can be diff erentiated from external pressure caused by ab-normalities in the surroundings.
The ear canal
Head tilt, head shaking or other neurological defi-cits can indicate ear problems. Extensive evalua-tion of the ear is possible with CT scanning because the external ear canal, the tympanic bullae, the petrous bone and cochlea, and even the small ear ossicles may be seen (Stieve-Caldwell et al., 2009). With MRI, the emerging nerves and cochlear fluid can be evaluated.
The external ear canal is normally filled with air and has a certain diameter. In otitis externa, the air will be replaced partially or completely by a soft tissue structure and the lumen becomes narrowed or com-pletely obliterated. This may be due to seb aceous material or an increase in soft tissue, e.g. swelling or neoplasia of the wall of the external ear canal.
In the middle ear, the tympanic bulla is normally filled with air and delineated by a thin, smooth and well defined wall of bone (Figure 9.6a). Otitis media is visible as a partial or complete filling of the tym-panic bulla by a mucous to soft tissue material that is visible on both CT and MRI (Figure 9.6b).
Destruction of the tympanic bulla wall together with dystrophic mineralization can be present in chronic infections and the extent can be evaluated with CT (Figure 9.6c). Contrast CT and MRI offer further diagnostic possibilities when otitis interna is sus-pected but no bony abnormalities are visible.
Evaluation of adjacent structures, such as the fluid in the cochlea and the cranial nerves, is possible.
The brain and meninges
Meningitis or meningoencephalitis due to an intra-cranial extension of inner ear infection will cause enhancement of inflamed and hypervascularized tissues, and treatment can be changed accordingly.
Other intracranial conditions, such as pituitary ade-nomas, infarcts or haemorrhage, hydrocephalus or neoplastic lesions, can be detected with both CT and MRI (Figure 9.7) though they are not often encountered in the rabbit (Sikoski et al., 2008;
Qiuhang et al., 2010; Wei et al., 2012).
Dacryocystography.
(a) Transverse CT image (bone setting) of the head at the level of the premolars. Contrast medium is visible in the left nasolacrimal duct (
*
). Soft tissue attenuating material is present in the right nasolacrimal duct (>).(b) Dorsal MPR of the same rabbit.
Contrast medium is present in the left nasolacrimal canal (
*
). Only aminimal amount of contrast medium is visible, followed by air that is outlining a soft tissue attenuating structure blocking the right nasolacrimal canal (>). The large extent of the blockage is clearly visualized.
> *
(a)
> *
(b)
(a) Transverse CT image (bone setting) of the head at the level of the tympanic bullae (B) and axial external ear canal . oth are air filled and the wall of the tympanic bulla is smooth and thin. (b) Transverse CT image bone setting of the head at the level of the tympanic bullae the tympanic bullae are almost completely filled with a soft tissue attenuating material bilaterally. Note the minimal thickening of the tympanic bulla wall (>). (c) Transverse CT image (bone setting) of the head at the level of the tympanic bullae (B): note the bilateral extensive deformation and osteolysis of the tympanic bulla wall . The tympanic bullae are completely filled with a soft tissue attenuating material.
9.6
E
B B
>
(a) (b)
> B
(c)
(a) Transverse CT image (soft tissue setting after intravenous contrast medium) of the head at the level of the cranium. The slightly hyperattenuating structure in the central and ventral part of the cranium, together with the very small hyperattenuating rim adjacent to the cranial bones,
represents the brain tissue (B). The hypoattenuating area in between these two represents fluid in the lateral ventricles (
*
). The diagnosis was severe hydrocephalus. (b) Transverse T2-weighted MR image of the same rabbit.The fluid in the lateral ventricles is hyperintense (
*
) and the brain tissue (B) at the centre and near the cranial bones is slightly hypointense.9.7
B B * *
(b)
B *
(a)
The thorax and abdomen
CT of the thorax and abdomen in rabbits is mainly performed to evaluate the lungs, lymph nodes and other structures for metastasis (Figure 9.8). A major advantage of radiography and ultrasonography of the thorax and abdomen is that these modalities can be used in rabbits that are in poor body condi-tion where sedacondi-tion is not possible. However, CT has a much higher sensitivity for the detection of lung changes and therefore metastases will be detected at an earlier stage. Thoracic CT in com-panion animals such as dogs, cats and birds has become more popular in recent years and is used to evaluate and characterize lung lesions such as lower airway disease, spontaneous pneumothorax, neoplastic lesions or air sac disease in birds. CT of the abdomen is used for the evaluation of the vari-ous organs and vasculature. MRI is being used more frequently for abdominal scanning and it seems likely that the use of CT and MRI in evalua-tion of the thorax and abdomen in rabbits will increase in the future. CT has already been used in radiotherapy for thymoma in rabbits for planning of radiation dose and treatment area (Morrisey and McEntee, 2005).
(a)
*
(a) Transverse CT image (bone setting) of the thorax at the level of the caudal main bronchi: a soft tissue attenuating nodule is visible dorsal to the left caudal main bronchus (
*
). Multiple soft tissue nodules of varying size were present in the lungs and were considered to be metastases of a previously diagnosed uterine carcinoma. (continues)9.8
The vertebral column and extremities CT or MR imaging of the neck and trunk of the rabbit, as well as of intramedullary lesions, has been described mainly for research purposes (Mavinkurve et al., 2005; Zotti et al., 2009). In rabbit medicine, the use of these advanced techniques for diagnosis or treatment planning has been limited but they would be an excellent alternative to myelography and radio-graphic studies. MRI has almost completely replaced myelography in dogs and cats, and CT has proven to be much more accurate in the detection of bony abnormalities such as vertebral fractures or medial coronoid dysplasia in the elbow.
References and further reading
Arzi B and Sinclair KM (2002) Diagnostic imaging in veterinary dental practice. Journal of the American Veterinary Medical Association 236, 405–407
Bushburg JT, Seibert JA, Leidholdt EM Jr and Boone JM (2002a) Computed tomography. In: The Essential Physics of Medical Imaging, 2nd edn, pp. 327–372. Lippincott Williams & Wilkins, Philadelphia
Bushburg JT, Seibert JA, Leidholdt EM Jr and Boone JM (2002b) Nuclear magnetic resonance. In: The Essential Physics of Medical Imaging, 2nd edn, pp. 373–414. Lippincott Williams &
Wilkins, Philadelphia
Bushburg JT, Seibert JA, Leidholdt EM Jr and Boone JM (2002c) Magnetic resonance imaging. In: The Essential Physics of Medical Imaging, 2nd edn, pp. 415–468 Lippincott Williams &
Wilkins, Philadelphia (b)
* S
(continued) (b) Transverse CT image (soft tissue setting) of the abdomen at the level of the stomach (S) of the same rabbit. Irregular nodular changes (
*
) are seen in the abdominal fat, consistent withcarcinomatosis of the uterine carcinoma.
9.8
Casteleyn C, Cornillie P, Hermens A et al. (2010) Topography of the rabbit paranasal sinuses as a prerequisite to model human sinusitis. Rhinology 48, 300–304
Dennis R and Herrtage ME (1989) Low osmolar contrast media: a review. Veterinary Radiology 30, 2–12
Kuriashkin IV and Losonsky JM (2000) Contrast enhancement in magnetic resonance imaging using intravenous paramagnetic contrast media: a review. Veterinary Radiology and Ultrasound 41, 4–7
a in r e radilla e nani et al. (2005) A novel intramedullary spinal cord tumor model: functional, radiological, and histopathological characterization. Journal of Neurosurgery and Spine 3, 142–148
Morrisey JK and McEntee M (2005) Therapeutic options for thymoma in the rabbit. Seminars in Avian and Exotic Pet Medicine 14, 175–
a p 181 cri ani and ease 2 p ted tomography dacryocystography evaluation of the nasolacrimal apparatus. Veterinary Radiology and Ultrasound 45, 23–28 Qiuhang Z, Zhenlin W, Yan Q et al. (2010) Lymphatic drainage of the
skull base: comparative anatomic and advanced imaging studies in the rabbit and human with implications for spread of nasopharyngeal carcinoma. Lymphology 43, 98–109
Sikoski P, Trybus J, Cline JM et al. (2008) Cystic mammary adenocarcinoma associated with a prolactin-secreting pituitary adenoma in a New Zealand White rabbit (Oryctolagus cuniculus).
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