Transplantation is used to treat fulminate organ failure, but severe shortages in the availability of suitable human donors have limited the application of organ transplants [4]. This donor shortage has stimulated interest in the possible use of animal organs for transplantation into humans. Animal-to-human transplantation (xenotransplantation) would offer an unlimited supply of organs and tissue for transplantation. Pigs are the most likely source animals for xenotransplantation due to their anatomical and physiological similarities with humans [1]. Additionally, the pig can be raised to obtain large numbers of specific-pathogen-free animals. The reproductive properties of pigs such as early sexual maturity, short gestation time, and generation of large litters can allow a large pool of animal donors for xenotransplantation [18]. The ability to genetically modify the pig also allows modification of the targets of the human immune response and amelioration of some aspects of the rejection process without directly affecting the recipient's immune system.

In order to transplant swine organs into humans, physiological or anatomical comparison and analyses are essential in the investigation of whether an individual donor organ is suitable to a prospective patient. However, an appropriate method for estimating micropig organs has not been established. This study examined the feasibility of evaluating the kidney and its related major vessels using multidetector row computed tomography (MDCT) in micropigs. In recent years, major technological improvements have been achieved in CT. The most significant development has been the introduction of MDCT, which has brought about substantial improvements in spatial and particularly temporal resolution [3,6]. The present study examined the feasibility of MDCT on evaluation of kidney and renal vascular system of micropig as a potential renal donor.

CT examinations were successfully performed in all animals. The mean body weight of the micropigs was 30.5 kg. There were 12 renal arteries in six micropigs. No accessory renal arteries or early branching arteries were detected. No arterial stenosis, aneurysm, or calcification was noted in any micropig (Fig. 1). The mean diameter of all 12 renal arteries was 0.45 ± 0.05 cm (min = 0.39, max = 0.56). The mean diameters of the renal artery were 0.44 ± 0.05 cm on the right side and 0.46 ± 0.06 cm on the left side. The mean lengths of the renal artery were 4.51 ± 0.55 cm on the right side and 3.36 ± 0.27 cm on the left side. The right renal artery was significantly longer than the left renal artery (p < 0.05).

There were 13 renal veins in the six animals. Two renal veins on the right side were observed in one micropig. No retroaortic or circumaortic renal vein was observed (Fig. 2). The mean diameter of the 13 renal veins was 1.41 ± 0.38 cm (min = 1.04, max = 2.51). The mean diameters of the renal vein were 1.44 ± 0.52 cm on the right side and 1.38 ± 0.17 cm on the left side. The mean lengths of the renal vein were 4.22 ± 1.29 cm on the right side and 5.15 ± 0.87 cm on the left side. The left renal vein was significantly longer than the right renal vein (p < 0.05).

The mean volume of all kidneys was 78.6 ± 13.6 mL (min = 61.6, max = 101.04). The mean volumes of the right kidney were 79.3 ± 14.5 mL and those of the left kidney were 78.0 ± 13.9 mL (Table 1). There was no significant difference in renal volume between the right and left kidneys. MDCT revealed no abnormalities in ureters and renal parenchyma in all micropigs. Furthermore, when compared with human data, considerable anatomic similarities were apparent between human and micropigs in renal vascular dimensions, although differences in renal volume were evident (Table 2).

Kidney transplants from living donors have become increasingly common during the past decade. Anatomical assessment of the donor kidneys is performed prior to transplantation to help select the kidney to be used and to plan the surgical approach [9]. An ideal imaging test should be free of morbidity, accurately estimate vascular and parenchymal structures, and recognize stone disease, renal parenchymal lesions, and other intra-abdominal pathologies. In human cases, preoperative knowledge of renal vascular, parenchymal, and urothelial anatomy based on imaging has always been important, not only to select suitable donor and kidney but also to avoid potential donor complications such as hemorrhage and potential recipient problems such as graft ischemia and urine leakage [14]. Although the micropig, a potential organ donor, should not be considered concerning postoperative complications, anatomical differences between donor and recipient should be determined. Indeed, congenital polycystic kidneys often occur in swine and can be inherited as an autosomal dominant trait [10]. Therefore, it is very important to establish the preoperative evaluation and selection system of the appropriate donor organ in micropigs.

In this study, we measured the vascular and volumetric parameters of right and left kidneys of micropigs using 64-channel MDCT. We reconfirmed that micropigs may be an appropriate renal donor because of the absence of arterial variations such as an accessory or early branching renal artery, and venous anomalies including retroaortic vein or circumaortic veins. In addition, comparison with human data revealed considerable anatomic similarities between human and micropigs in renal vascular dimensions, although differences in renal volume were found.

Since the introduction of MDCT in the early 1990s, the number of detectors has gradually increased [11], with 64-channel MDCT clinically used on humans at present. The advantages of MDCT include faster image acquisition, improved image resolution, and superior contrast reinforcement [2,19]. In addition, multiplanar reformation using MDCT is an optimal tool for imaging complicated anatomic and pathologic cases [7].

Conventional catheter digital subtraction angiography (DSA) has been performed on potential renal donors to show the number of renal arteries and the presence of early branching and vascular disease. However, it is invasive and sometimes traumatic, needs post-procedure observation, and has significant limitations in displaying renal veins and renal parenchyma. MDCT offers noninvasive imaging with minimal risk of morbidity. Over the past few years, MDCT has been used increasingly for noninvasive renal imaging [15,17]. MDCT angiography is highly accurate for detecting vascular anomalies and providing anatomic information of the kidney [8]. In addition, previous results showed that a more accurate evaluation of the renal arteries of potential donors can be achieved with MDCT angiography that with 3D magnetic resonance angiography. Furthermore, MDCT angiography can be used instead of digital subtraction angiography because the former can almost perfectly assess the number of renal arteries and the presence of proximal branches of the renal artery [9]. In addition to the vascularization of kidney, MDCT is usually used to detect various pathological conditions of the kidney including congenital anomalies, renal masses, cystic kidneys, or obstructive renal diseases [15]. Therefore, MDCT is an appropriate method is collecting data for the determination of normality and suitability of donor kidneys for transplantation.

In conclusion, 64-channel MDCT imaging allows the accurate determination of kidney morphological and spatial aspects, and understanding of renal vascular structures.