The difference of contrast effects of myelography in normal dogs: comparison of iohexol (180 mgI/ml), iohexol (240 mgI/ml) and iotrolan (240 mgI/ml)

The contrast effects of three different contrast media preparations (iohexol 180 mgI/ml, iohexol 240 mgI/ml and iotrolan 240 mgI/ml) in conventional and CT myelography were compared. Three beagle dogs were used and the study employed a cross-over method (total of 9) for each contrast media. The result of CT myelography showed that the contrast effect of iohexol (180 mgI/ml), which had low viscosity, was highest in cranial sites, and the contrast effect of high-viscosity iotrolan (240 mgI/ml) was highest in caudal sites 5 min after injection of the contrast media preparations. This shows that the diffusion of contrast media preparations in the subarachnoid space is influenced by viscosity. The results of conventional myelography also showed that the diffusion of contrast media preparations is influenced by viscosity. Therefore, it is important to identify the location of spinal lesions in veterinary practice, and low viscosity contrast medium preparation with wide spread contrast effects is considered suitable for myelography.     

Comparison of excretory urographic contrast effects of dimeric and monomeric non-ionic iodinated contrast media in dogs

In excretory urography, the osmolarity of contrast media has rarely been treated as important in veterinary medicine. In this study, the contrast effect of two contrast media (monomeric iohexol and dimeric iodixanol) in the renal cortex and aorta were compared using computed tomography (CT). Five beagle dogs were used and the study employed a cross-over method for each contrast media. The results showed that there was no difference between the media in the aorta, but iodixanol showed higher CT value and a longer contrast effect than iohexol in the renal cortex, in spite of having the same iodine dosage. It is believed that iodixanol, with its low osmolarity, is diluted less by osmotic diuresis than monomeric iohexol. It is important to consider the osmolarity of the contrast media when evaluating the contrast effect, and it is essential to use the same contrast media for each examination, or the renal excretory speed will be under/overestimated.     

QUANTITATIVE METHODS FOR INDIRECT CT LYMPHOGRAPHY

In this investigation, we applied quantitative CT methods to characterize contrast enhanced lymph nodes opacified using iodinated contrast media for indirect CT lymphography. lodinated nanoparticles were injected into the buccal submucosa and SQ into the metatarsus and metacarpus of four normal swine (1.0–4.0 ml/site, 76 mg I/ml). Attenuation (HU), volume (cm³), iodine concentration (mg I/cm³), total iodine uptake (mg I), contrast-to-noise ratio (CNR), and percent injected dose (%ID) were estimated in opacified inguinal, cervical and parotid/mandibular lymph nodes using manual image segmentation techniques on 24 hour post-contrast CT images. Lymph node volumes estimated by multiple slice ROI analysis were compared with estimates obtained by post-excisional weight measurements. HU and iodine concentration increased 5–20 fold in opacified nodes (p < 0.01) and CNR increased more than four-fold (p < 0.001). %ID ranged between 3.5 and 11.9% and did not appear dose related. ROI estimated lymph node volumes approximated volumes calculated from weight measurements. (R²= 0.94, p < 0.0001). We conclude that interstitially injected iodinated nanoparticles increase attenuation and conspicuity of targeted nodes on CT images. Quantitative methods could play an important clinical role in more accurate metastasis detection.     

USE OF IOHEXOL AS A GASTROINTESTINAL CONTRAST MEDIUM IN THE DOG

Iohexol was administered orally in five dogs. The dose, gastrointestinal (GI) transit time, appearance of mucosal patterns and side effects were studied. Three different doses (525, 700, 875 mgI/kg) were used in each dog at 1-week intervals. GI transit time was rapid. In each dose, gastric emptying commenced immediately after administration of the contrast medium, and was completed within 30–60 min with doses of 525–700 mgI/kg and 90–120 min with 875 mgI/kg. Large intestinal filling was observed within 60-90 min. In the majority of studies, the mucosal border appeared as a thin homogeneous halo of lucency surrounding the more opaque bowel lumen contents. The contrast intensity was not adequate with the lowest dose. The image quality did not deteriorate along the GI tract. No adverse reactions were found. Iohexol is an alternative GI contrast medium in the dog when contrast media are contraindicated.     

A comparison between injection speed and iodine delivery rate in contrast-enhanced computed tomography (CT) for normal beagles

The purpose of this study was to compare between the injection speed and iodine delivery rate in order to establish a concept for reproducible contrast timing in contrast-enhanced computed tomography (CT) for small animals. Clinically healthy beagle dogs were administered a nonionic iodinate contrast medium at a dose of 800 mgI/kg; they were divided into 3 groups (n=5, crossover method): in one group, the injection speed was fixed at 1.0 ml/sec, and in the second and third groups, the iodine delivery rate was fixed (the injection durations were 30 and 60 sec, respectively). The variation in scatter of the time to aortic and hepatic peak enhancement in the fixed iodine delivery groups was lower than that in the fixed injection speed group. These results suggest that in contrast-enhanced CT for small animals, the contrast medium should be injected at a fixed iodine delivery rate in order to provide reproducible contrast timing.     

IOHEXOL AS A GASTROINTESTINAL CONTRAST MEDIUM IN THE CAT

Iohexol was evaluated as a radiologic contrast medium in the gastrointestinal (GI) tract in cats. Three different doses (525, 700, 875 mg iodine/kg with an iodine concentration of 300 mg iodine/mL) diluted with tap water until a total volume of 10 ml/kg, were administered via an orogastric tube, to 5 cats at weekly intervals. The GI transit time was rapid and variable. Gastric emptying commenced immediately after administration of the contrast medium and was complete within 10–30 min. In each dose, iohexol reached the large intestine within 10–20 min. In 73% (11/15) of studies, the mucosal border appeared as a thin homogeneous "halo" of lucency surrounding the more opaque contents of the small intestine. Radiographic image quality of the GI tract was inadequate with the lowest dose (525 mg iodine/kg). Image quality did not deteriorate along the GI tract. Absorption of iohexol from the GI tract was observed in 40% (6/15) of examinations, where opacification of the urinary bladder was seen. No side effects were observed. lohexol should be considered as an alternative GI contrast medium in the cat when the use of other radiologic contrast media is contraindicated.     

Comparison of varying injection rates of saline chasers on intravascular contrast enhancement for dynamic CT in cattle

Dynamic CT was performed in five normal Holstein calves to investigate the effect of saline chasers on intravascular contrast enhancement when administered at three different rates. The five calves were imaged using dynamic CT in a crossover study design. Group A was administered only contrast medium (600 mg iodine/kg, 4 ml/s), while groups B, C and D were administered contrast medium at 30 per cent reduction followed by saline chasers injected at 2, 4 and 8 ml/s, respectively. Attenuation values were obtained from the right and left maxillary arteries and dorsal sagittal sinus. Maximum enhancement value and mean value of the enhancement plateau obtained from the maxillary arteries were significantly lower in group B than in the other groups. The duration of the enhancement plateau was longer in group C than in groups B and D (P<0.05).     

Anatomical study of the gastrointestinal tract of a pudu (Pudu puda) using contrast-enhanced abdominal computed tomography

The pudu (Pudu puda), which is the smallest deer in the world and inhabits central and southern Chile and Argentina, is a ruminant and a browsing herbivore. The aim of this study was to provide a reference for interpretation of the normal anatomy of the pudu's gastrointestinal tract as imaged by abdominal computed tomography (CT). For the study, one adult female pudu was used. After a 24-h fast, the pudu was anaesthetized and positioned in sternal recumbency at the CT table. Image acquisition began immediately after intravenous injection of contrast media (MD-76(?); 370 mgI/ml) into the cephalic vein. Injection of contrast material was administered as a biphasic protocol. First, a manual bolus of contrast material was injected at a rate of 4 ml/s. Then, an additional continuous infusion injection (0.1 ml/min) was performed for adequate opacification of vascular structures. Transverse images of 5 mm thickness and 5 mm interval were obtained with a fourth-generation CT scanner, from the ninth thoracic vertebra (T9) until the first sacral (S1) vertebrae. CT images were labelled and compared with anatomical reference images for ruminants. Structures that were identified in the abdominal cavity included the stomach with its four compartments (rumen, reticulum, omasum and abomasum), the small and large intestines, liver, spleen, kidneys and some major blood vessels (aorta, caudal vena cava). The distal loop of the ascending colon, the transverse colon, the pancreas and lymph nodes could not be identified. The resulting CT images provide a reference for normal cross-sectional abdominal anatomy of the adult pudu.     

Effect of catheter size and injection rate of contrast agent on enhancement and image quality for triple‐phase helical computed tomography of the liver in small dogs

Rapid contrast injection is recommended for triple‐phase helical computed tomography (CT) of the liver. However, a large‐gauge catheter is needed for faster contrast injection and this is not practical for small breed dogs or cats. The purpose of this crossover group study was to evaluate applicability of a lower injection rate with a small‐gauge (G) catheter for triple‐phase hepatic CT in small dogs. Triple‐phase CT images were acquired for six beagle dogs using three protocols: an injection rate of 1.5 ml/s with a 24 G catheter, 3.0 ml/s with a 22 G catheter, and 4.5 ml/s with a 20 G catheter. Enhancement of the aorta, portal vein, and hepatic parenchyma was measured in each phase (arterial, portal, and delayed) and image quality was scored subjectively by two observers. Injection duration, time to scan delay, and time to peak enhancement were also recorded. Contrast injection duration decreased with a higher injection rate (n = 6, P ≤ 0.01), but time to peak enhancement and time to scan delay were not significantly affected by injection rates and catheter sizes. Contrast injection rate did not significantly affect aortic, portal, and hepatic enhancement. In addition, separation between each phase and quality of images was subjectively scored as good regardless of injection rate. Findings from the current study supported using an injection rate of 1.5 ml/s with a catheter size of 24 G for triple‐phase hepatic CT in small dogs (weight < 12 kg).     

Myelography in the dog with non-ionic contrast media at different iodine concentrations

image quality and side effects were evaluated retrospectively In a series of 183 myelographic studies performed with two non-ionic contrast media (iohexoi and iopamidoi) at different concentrations. Side effects during and following the procedure were recorded. image quallty was assessed uslng an arbitrary scoring system and statistical analysis was performed with the cross-tabulation test (4 times 2 table) by comparing two groups receiving contrast medium at higher and lower concentrations. No slgnlflcant differences On side effects were observed between the two groups but the ratings for image quality were significantly higher in the group receiving contrast medlum at the higher concentration than in the group recelvlng the lower concentration. The results suggest that a high concentration of non-ionic contrast media can safely be used In dogs and may improve image quality.     

Computed tomographic contrast tenography of the digital flexor tendon sheath of the equine hindlimb

Pre‐surgical investigation of digital flexor tendon sheath pathology remains challenging with current standard imaging techniques. The aim of this prospective, anatomical, pilot study was to describe the anatomy of the equine hind limb digital flexor tendon sheath using a combination of computed tomography (CT) and computed tomographic contrast tenography in clinically normal cadaver limbs. Ten pairs of hind limbs with no external abnormalities were examined from the level of the tarsometatarsal joint distally. Limbs initially underwent non‐contrast CT examination using 120 kVp, 300 mAs, and 1.5 mm slice thickness. Sixty millilitres of ioversol iodinated contrast media and saline (final concentration 100 mg/ml) were injected using a basilar sesamoidean approach. The computed tomographic contrast tenography examination was then repeated, before dissection of the specimens to compare gross and imaging findings. The combined CT and computed tomographic contrast tenography examinations provided excellent anatomical detail of intra‐thecal structures. The borders of the superficial and deep digital flexor tendons, and the manica flexoria were consistently identifiable in all limbs. Detailed anatomy including that of the mesotenons, two of which are previously undescribed, and the plantar annular ligament were also consistently identifiable. Dissection of all 10 pairs of limbs revealed there to be no pathology, in accordance with the imaging findings. In conclusion, the combination of CT and computed tomographic contrast tenography may be useful adjunctive diagnostic techniques to define digital flexor tendon sheath pathology prior to surgical exploration in horses.     

COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE NORMAL CANINE ELBOW

Comprehensive evaluation of canine elbow joint dysfunction includes assessment of articular cartilage, which can noninvasively be performed with contrast arthrography. Aims of this prospective study were to compare positive contrast computed tomographic (CT) arthrography and histomorphometry measures of cartilage thickness in normal canine elbows, and to determine the optimal contrast medium concentration. Thirty‐two canine cadaver elbows were examined using multidetector CT, before and after intra‐articular administration of iohexol at one of three different concentrations. Articular cartilage thickness was measured on both the CT arthrography images and corresponding histologic specimens. Mean difference (bias) between the CT arthrography and histomorphologic measurements was 0.18 and 0.19 mm in the sagittal and dorsal planes, respectively. Mean bias and precision of CT arthrography measurements made in the sagittal or dorsal reformations were not significantly different from one another. Computed tomographic arthrography measurements from elbows with 75 mg I/ml were significantly larger and had greater bias compared to other contrast medium groups (150 and 37.5 mg I/ml). There was no significant difference in CT arthrography measurement precision between different contrast medium concentrations. Histomorphologic thickness of the articular cartilage overlying the cranial aspect of the ulna (mean 0.32 mm) was significantly thinner than cartilage of the radius (0.36 mm) or humerus (0.36 mm). Findings from this cadaver study indicated that CT arthrography delineates articular cartilage of the normal canine elbow; yields cartilage thickness measures slightly greater than histomorphometry measures; and provides high measurement precision regardless of image plane, contrast medium concentration, or anatomic zone.     

Effects of hyperosmolar ionic and low osmolar non-ionic contrast media on acid base, blood gas and electrolyte status in dogs

The dogs in groups I, II and III in equal numbers received diatrizoate, iohexol and ioxilan at a dose of 700 mgI/kg intravenously (i.v.) as a bolus, respectively. Blood samples were collected prior to contrast media (CM) administration and thereafter at 3, 15, 30, 60, 90 and 180 min to evaluate acid-base, venous blood gas status (pH, PCO2, PO2, HCO, BE, O2) and electrolytes (Na+, Ca++, K+). Values of pH, PCO2, BE, HCO, Na+ and K+ remained unchanged or within non-significant fluctuations compared with the baseline values. PO2 was significantly different from the baseline values in group 1 up to 90 min after administration, significant alterations were found for O2 saturation in group 1 up to 90 min, and in group II at 3, 60 and 180 min; and for Ca++ in group 1 at all time points except at 90 min, and groups II and II at 3 and 15 min post administration. It was concluded that none of the CM are considered to cause long-lasting and major effects on acid-base, blood gas and electrolyte status.     

Cerebrospinal fluid changes after iopamidol and metrizamide myelography in clinically normal dogs.

Cerebrospinal fluid samples from 2 groups of clinically normal dogs were compared after iopamidol (n = 9) and metrizamide (n = 8) myelography. Iopamidol (200 mg of I/ml) and metrizamide (170 mg of I/ml) were administered by cerebellomedullary injection at dosage of 0.45 ml/kg of body weight. In dogs of both groups, postmyelographic CSF changes included high specific gravity, Pandy score, protein concentration, and WBC count. The high specific gravity and Pandy score were false-positive effects attributed to nonionic contrast media. Although postmyelographic protein concentration and total WBC count were greater in CSF samples from dogs given metrizamide than in those given iopamidol, differences were not statistically significant. The differential WBC counts were consistent with mild, acute leptomeningitis; these findings were supported by results of histologic examination. Iopamidol and metrizamide should be considered low-grade leptomeningeal irritants in dogs.     

Effects of hyperosmolar ionic and low osmolar non-ionic contrast media on coagulation times and some blood parameters in dogs: an in vivo study

The purpose of this study is to evaluate the effects of hyperosmolar ionic contrast media (CM) (diatrizoate) and low osmolar non-ionic CM (iohexol and ioxilan) on coagulation time and some blood parameters in dogs in vivo. The animals were divided into three groups in equal numbers. The dogs in groups I, II and III received diatrizoate, iohexol and ioxilan at the dose of 700 mgI/kg intravenously (IV) as a bolus, respectively. Administration of contrast media and blood samples were collected from vena cephalica antebrachii prior to CM administration and thereafter at 3, 15, 30, 60, 90 and 180 min and 24 h to measure the coagulation factors [activated partial thromboplastin time (APTT), prothorombin time (PT), fibrinogen and fibrinogen degradation products] and some other blood parameters [red blood cells, platelet, white blood cells, haematocrit (Ht) and haemoglobin (Hb)]. While a statistically significant decrease was observed on APTT at 15 min in group III, no significant differences were found in groups I and II. All the groups had insignificant alterations for PT, fibrinogen and fibrinogen degradation product, following CM administration. Significant decreases were observed for platelet at 3 min in all groups. This decrease was also significant at 15- and 30- min intervals in group I. There were significant decreases for erythrocytes, Ht and Hb measurements within 30 min, and no significant alterations were observed for leucocytes within 60 min in all groups compared with baseline values. No differences were observed with regard to coagulation times and some blood parameters as far as long-lasting and major effects of each CM are concerned.     

Three-dimensional CT angiography of the canine hepatic vasculature

Eight Beagle dogs were anesthetized and were imaged using a single channel helical CT scanner. The contrast medium used in this study was iohexol (300 mg I/ml) and doses were 0.5 ml/kg for a cine scan, 3 ml/kg for an enhanced scan. The flow rate for contrast material administration was 2 ml/sec for all scans. This study was divided into three steps, with unenhanced, cine and enhanced scans. The enhanced scan was subdivided into the arterial phase and the venous phase. All of the enhanced scans were reconstructed in 1 mm intervals and the scans were interpreted by the use of reformatted images, a cross sectional histogram, maximum intensity projection and shaded surface display. For the cine scans, optimal times were a 9-sec delay time post IV injection in the arterial phase, and an 18-sec delay time post IV injection in the venous phase. A nine-sec delay time was acceptable for the imaging of the canine hepatic arteries by CT angiography. After completion of arterial phase scanning, venous structures of the liver were well visualized as seen on the venous phase.     

EFFECT OF SODIUM DIATRIZOATE ON THE IN VITRO GROWTH OF THREE COMMON CANINE URINARY BACTERIAL SPECIES

The mean concentration of diatrizoate in urine specimens of eight dogs collected 20 minutes after intravenous injection of 2.2 ml/kg of sodium and meglumine diatrizoate (iodine concentration, 288 mg/ml) was 80 mg/ml (iodine concentration, 48 mg/ml). The mean concentration plus 1 SD was 111 mg/ml (iodine concentration, 66 mg/ml), and the mean concentration plus 2 SD was 142 mg/ml (iodine concentration, 85 mg/ml). The presence of diatrizoate at a concentration of 142 mg/ml did not inhibit in vitro bacterial growth of any of ten randomly selected canine urinary isolates of Escherichia coli or any of ten randomly selected urinary isolates of Staphylococcus aureus. In vitro bacterial growth of all ten randomly selected urinary bacterial isolates of Proteus mirabilis was significantly inhibited by a diatrizoate concentration of 80 mg/ml. Bacterial growth was progressively inhibited by increased diatrizoate concentrations.     

PULMONARY ANGIOGRAPHY USING 16 SLICE MULTIDETECTOR COMPUTED TOMOGRAPHY IN NORMAL DOGS

We report a canine computed tomography (CT) pulmonary angiography technique using multidetector CT (MDCT). CT pulmonary angiography using a 16 slice MDCT was performed on five healthy, anesthetized beagles. A helical acquisition with pitch of 1.4 was used. The time delay for the angiographic study was determined using a bolus‐tracking program. A dose of 400 mg I/kg of nonionic contrast medium (Iohexol 300 mg I/ml) was administered to each dog via a cephalic catheter using an angiographic power injector at a rate of 5 ml/s. In two dogs a second study, using a contrast medium dose of 200 and 600 mg I/kg was performed. Arterial enhancement of transverse and reformatted images was classified subjectively as excellent, good, or poor, and assessed objectively by measuring Hounsfield units at the right main pulmonary artery. Angiographic studies were evaluated by two radiologists to determine the number of subsegmental arterial branches visualized. The median number of subsegmental arterial branches identified was five (range: 2–7). Based on the time attenuation curve obtained by the bolus‐tracking program, there was consistent enhancement of the right main pulmonary artery beginning at 6 s and peaking at 8 s in 4/5 dogs. The contrast medium dose of 400 mg I/kg produced good to excellent vascular enhancement in the same 4/5 dogs. A dose of 200 mg I/kg resulted in poor enhancement. CT pulmonary angiography using MDCT and an automated bolus‐tracking program allows rapid, consistent evaluation of the pulmonary vasculature using a single dose of 400 mg I/kg of contrast medium.     

IOHEXOL AND IOPAMIDOL MYELOGRAPHY IN THE DOG: A CLINICAL TRIAL COMPARING ADVERSE EFFECTS AND MYELOGRAPHIC QUALITY

In a blind clinical trial, adverse effects after iohexol and iopamidol myelography were evaluated in 151 dogs. Eighty-one dogs were given iohexol (240 mgI/ml) and 70 dogs were given iopamidol (200 mgI/ml) by pre-determined assignment. Each dog was evaluated postmyelographically for seizures, hyperthermia, prolonged recovery from anesthesia and intensification of pre-existing neural signs. Myelographic quality was evaluated with a subjective scoring method. In comparing iohexol and iopamidol groups, there was not a statistically significant difference in the incidence of adverse effects or in myelographic quality. Iopamidol and iohexol appeared to be equally efficacious for routine canine myelography.