**5. Applications to veterinary medicine**

#### **5.1 Patient monitoring of bone density and body composition**

As a non-invasive methodology, DXA is effective for longitudinal quantification of bone health and nutritional status of patients. Thus, DXA has potential to be a powerful tool for

In mammals, DXA has been used most extensively with rodents. Due to the extent of published studies covering the use of DXA with rodents we elected to avoid their inclusion in this chapter except in a few instances for comparison. DXA has been used with species of agricultural concern including sheep (Mercier et al., 2006; Ponnampalam et al., 2007; Pouilles et al., 2000; Turner et al., 1995a), pigs (Clarys et al., 2010; Elowsson et al., 1998; Lee et al., 2011; Losel et al., 2010; Lukaski et al., 1999; Mitchell et al., 1998; Nielson et al., 2004), horses (McClure et al., 2001; Secombe et al., 2002), goats (Corten et al., 1997), and cattle (Zotti et al., 2010). Additionally, DXA has been applied to wildlife such as the grizzly bear (Felicetti, 2003 as cited in Stevenson & van Tets, 2008). DXA has been used to analyze excised bones of several species of marine mammals including Blainville's beaked whale (Zotti et al., 2009), Mediterranean monk seals (Mo et al., 2009), and bottlenose dolphins (Lucic et al., 2010). Finally, DXA has been applied to domestic pets including cats (Buelund et al., 2011; Turner et al., 1995b), rabbits (Castaneda et al., 2006; Hanafusa et al., 1995), guinea pigs (Fink et al., 2002), and dogs (Lorinson, 2009; Markel & Bogdanske, 1994a, 1994b; Mawby et al., 2004; Schneider et al., 2004; Toll et al., 1994; Zotti et al., 2004a). The use of DXA with ferrets has

been noted (Grier et al., 1996); however few published studies have been cited.

passerines (Korine et al., 2004).

(Jebb, 1997).

**5. Applications to veterinary medicine** 

**5.1 Patient monitoring of bone density and body composition** 

In birds, DXA has been used primarily with species in the food science industry such as domestic poultry, including the red junglefowl (Jensen et al., 2005), white leghorns (Kim et al., 2006; Jensen et al., 2005), and turkey (Zotti et al., 2003). It has also been applied to wildlife including wild turkey, ruffed grouse, bobwhite quail (Dirrigl et al., 2004) and small

In reptiles, fewer species have been used with DXA, but most major taxonomic groups are represented, including snakes (Secor & Nagy, 2003); turtles (Fledelius et al., 2005; Stone et al., 2010), and lizards (Zotti et al., 2004b). The focus of these studies was validating the use of DXA with these species; however, Zotti et al., (2004b) used DXA to study metabolic bone disease in the green iguana (*Iguana iguana*) and Fledelius et al, (2005) used DXA to

DXA has been used successfully and/or validated in a diverse number of animal species; however, there are a number of common household pets and research model species to which DXA has never been applied. This is especially true for exotic animals. Further research is needed to validate the use of DXA with these species before DXA can be put into practical use in animal research or medicine. To our knowledge, DXA has not been used or validated with amphibians or fish, despite the importance of these groups to animal research. In addition to filling in these "species gaps," further research is needed with species to which DXA has already been applied. Establishing a series of reference intervals for body composition in these species will provide important baseline data for future studies and will provide a frame of reference from which clinicians can use to diagnose pathology

As a non-invasive methodology, DXA is effective for longitudinal quantification of bone health and nutritional status of patients. Thus, DXA has potential to be a powerful tool for

investigate how supplementing calcium in the diet of tortoises impacts bone density.

preventative and post-operative health care because it allows veterinary practitioners to quantify and systematically monitor patients' body condition and bone health over time.

DXA has been previously used to monitor bone density changes during fracture healing in rodents (Millett et al., 1998). Significant increases in femur bone density were measured during fracture healing of Sprague-Dawley rats. The region of the bone closest to the callus showed the largest difference in bone mineral density between the experimental and control groups (non-fractured). A similar study was conducted in dogs, where DXA was used to quantify changes in bone mineral density at the site of fracture following ostectomies of various widths (Markel & Bogdanske, 1994b). The results of these and other studies suggest that DXA can be used to effectively monitor changes in bone density after fracture. The ability to conduct analyses at particular regions of interest (ROIs), in addition to whole body analyses, makes this an extremely effective tool for post-operative monitoring.

In addition to post-operative monitoring of bone healing, DXA shows great promise in preventative medicine, such as early identification/diagnosis of metabolic bone diseases. This would serve an important service to exotic animal practice, because metabolic bone disease is the most common disease of some captive reptiles (Raiti & Haramati, 1997). Furthermore, DXA has the potential for diagnosing increases in bone density found in third carpal bone disease of horses; however, its utility was not deemed practical due to the logistical issues of scanning time with large animals (Secombe et al., 2002).

Monitoring of changes in fat mass in patients is another effective use of DXA. In the domestic dog and cat, obesity is the most common nutritional disorder (Mawby et al., 2004; German, 2006). Therefore, DXA is potentially a useful tool to monitor the efficacy of therapies, nutrition, and weight reduction regimes for obese or overweight pets. Effective monitoring programs have been shown to be critical for successful weight loss (Yaissle et al., 2004 as cited in German, 2006) and long-term maintenance of a healthy body mass (Laflamme & Kuhlman, 1995 as cited in German, 2006).

### **5.2 Visual diagnosis of gravidity & foreign objects**

Because DXA scanners provide a digital image of the patient, DXA can be used for basic radiographic applications. The resolution of images produced by DXA is relatively poor compared to traditional X-ray radiography; therefore, DXA scanning is unlikely to replace traditional radiography for most applications requiring high resolution imaging (e.g. diagnosing of minor stress fractures). The poor resolution of images produced by DXA is a software issue, rather than a technological limitation of the technique per se. For instance, certain DXA imaging procedures provide sufficient resolution for visual diagnosis for minute quantities of calcification such as with aortic atherosclerosis (Wilson, 2006). Despite the limitations in resolution of routinely produced DXA images, image quality is sufficient to diagnose a variety of conditions. For example, in our research we have used DXA to determine if female turtles are gravid (Figure 4).

Additionally, we have used DXA to visually detect the presence of foreign objects in wildlife. Specifically, we have identified the ingestion of fish hooks in turtles (Figure 5). Fishhook injuries are common in aquatic wildlife such as turtles. Swallowing of fishhooks in household pets is also relatively common (Michels et al., 1995).

Use of Dual-Energy X-Ray Absorptiomtetry (DXA) with Non-Human Vertebrates:

healed from the gunshot wound.

0.22 caliber bullet (yellow arrow).

away from the source, where scatter radiation is minimal.

**6. DXA precision in non-human vertebrates** 

Application, Challenges, and Practical Considerations for Research and Clinical Practice 105

trauma and the external wound had completely healed. Upon our initial external inspection of the subject we failed to recognize the injury. It wasn't until we performed a DXA scan that we discovered a bullet located in the forelimb. After the diagnosis from the X-ray image, we visually identified the object as a hard palpable mass. The 0.22 caliber bullet was encysted in connective tissue surrounding the humerus, which was fractured and had not

Fig. 6. X-ray image of a red-eared slider turtle (*Trachemys scripta*) that had been shot by a

Even though DXA scans typically result in lower image quality, there are benefits to using it over traditional X-ray radiography. For instance, DXA offers important health benefits over traditional radiography for both the radiographer and the patient. X-ray exposure using DXA is a fraction of that produced by other means. Patient X-ray exposure during a typical whole-body DXA scan is a fraction of that during a typical chest X-ray. Furthermore, the technician's exposure to X-rays is generally negligible if the unit is operated several meters

Critical to the successful use of DXA in clinical and research settings is its ability to make accurate and, more importantly, precise estimates of body composition. Accuracy is of lesser importance because estimates can be corrected when systematic biases exist with a particular technique (Stone et al, 2010). On the other hand, precise estimates of body composition are critical to be able to detect longitudinal changes. We reviewed the precision of DXA in estimating body composition among a variety of taxa (Table 1). The precision among taxa was relatively low in most cases. Fat mass tended to be the least precisely estimated parameter of body composition; however, in most cases was within ranges seen in humans. A notable

Fig. 4. X-ray image of a gravid female Eastern Box Turtle (*Terrapene carolina*). Arrow identifies a single egg.

Fig. 5. X-ray image produced from a DXA scan of a wild-caught red-eared slider turtle (*Trachemys scripta*). Arrow indicates the presence of a fish hook lodged in the gastrointestinal tract.

Finally, we have used DXA to diagnose a gunshot wound in an adult wild-caught red-eared slider turtle (*Trachemys scripta;* Figure 6). In this case the subject showed no obvious signs of

Fig. 4. X-ray image of a gravid female Eastern Box Turtle (*Terrapene carolina*). Arrow identifies a

Fig. 5. X-ray image produced from a DXA scan of a wild-caught red-eared slider turtle (*Trachemys scripta*). Arrow indicates the presence of a fish hook lodged in the gastrointestinal

Finally, we have used DXA to diagnose a gunshot wound in an adult wild-caught red-eared slider turtle (*Trachemys scripta;* Figure 6). In this case the subject showed no obvious signs of

single egg.

tract.

trauma and the external wound had completely healed. Upon our initial external inspection of the subject we failed to recognize the injury. It wasn't until we performed a DXA scan that we discovered a bullet located in the forelimb. After the diagnosis from the X-ray image, we visually identified the object as a hard palpable mass. The 0.22 caliber bullet was encysted in connective tissue surrounding the humerus, which was fractured and had not healed from the gunshot wound.

Fig. 6. X-ray image of a red-eared slider turtle (*Trachemys scripta*) that had been shot by a 0.22 caliber bullet (yellow arrow).

Even though DXA scans typically result in lower image quality, there are benefits to using it over traditional X-ray radiography. For instance, DXA offers important health benefits over traditional radiography for both the radiographer and the patient. X-ray exposure using DXA is a fraction of that produced by other means. Patient X-ray exposure during a typical whole-body DXA scan is a fraction of that during a typical chest X-ray. Furthermore, the technician's exposure to X-rays is generally negligible if the unit is operated several meters away from the source, where scatter radiation is minimal.
