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Clinical Observations |
1 Department of Radiology, Erasmus Medical Center, P.O. Box 1738, 3000 DR,
Rotterdam, The Netherlands.
2 Department of Epidemiology and Biostatistics, Erasmus Medical Center,
Rotterdam, The Netherlands.
3 Department of Surgery, Erasmus Medical Center, Rotterdam, The
Netherlands.
4 Department of Internal Medicine, Erasmus Medical Center, Rotterdam, The
Netherlands.
Received May 28, 2004; accepted after revision October 2, 2004.
Address correspondence to M. G. M. Hunink
(m.hunink{at}erasmusmc.nl).
OBJECTIVE. The objective of our study was to evaluate the diagnostic agreement, the impact on decision making, and the costs of contrast-enhanced MR angiography and digital subtraction angiography in the workup of living renal donors.
CONCLUSION. Contrast-enhanced MR angiography for the preoperative evaluation of renal donors is superior to digital subtraction angiography in revealing vascular anomalies and depicting parenchymal abnormalities and is less costly; furthermore, it does not lead to preoperative decisions that differ from those based on digital subtraction angiography. If contrast-enhanced MR angiography does not provide sufficient information to make a confident decision, an additional digital subtraction angiography examination should be performed.
Kidney transplantation from living donors has become increasingly common during the past decade because of an increased shortage of postmortem organ donors and the superior outcomes of recipients of kidneys from living donors [1–4]. The annual number of living donor transplantations in The Netherlands has increased over the past decade, and this trend is consistent with the international trend [5, 6]. Currently, laparoscopic donor nephrectomy is the state of the art in our clinic and is preferred to open surgical resection because of its less invasive character and excellent outcomes [7–9]. For the preoperative diagnostic imaging in healthy—and often young—potential donors, minimally invasive techniques such as contrast-enhanced MR angiography are preferred.
Contrast-enhanced MR angiography has proven to be an accurate technique in depicting the kidney and its vascular structures and in revealing renal artery stenosis and vascular anomalies, both in patients with renovascular disease and in living renal donors [10–14]. In addition to imaging the renal arteries and the renal parenchyma, it also provides detailed information about the renal veins, the collecting system, and other abdominal organs [15]. Finding multiple renal arteries or veins may affect the decision about which kidney to resect and planning the nephrectomy [16]. This is especially important for laparoscopic nephrectomy because of technical difficulties that arise as a result of the limited amount of laparoscopic working space and anatomic characteristics that make the crucial relationships of arteries, veins, and other structures to one another difficult to see [17].
We use a comprehensive MRI protocol that is capable of revealing the anatomy of renal vessels and parenchyma and the relationship of the anatomic structures on high-quality images. We postulated that this MRI protocol may result in decisions with respect to which kidney to harvest that differ from those that are based on digital subtraction angiography. Contrast-enhanced MR angiography is a safe technique [18, 19] that is less invasive and probably less expensive than digital subtraction angiography [12, 20, 21]. Although most studies report contrast-enhanced MR angiography as highly accurate in the preoperative diagnostic workup of living renal donors [11–14, 22–25], the influence of contrast-enhanced MR angiography on decision making and the costs of contrast-enhanced MR angiography and of digital subtraction angiography from the hospital's perspective remain unknown.
The purpose of this study was to evaluate the diagnostic agreement, the impact on decision making, and the costs from the hospital's perspective of contrast-enhanced MR angiography and digital subtraction angiography in the preoperative diagnostic imaging of potential living renal donors.
Subjects and Methods
Potential Donors
All participants were consecutively enrolled at our institution, a tertiary
referral center, from May 2000 through September 2001. All potential living
renal donors within this period were informed about the study and asked to
participate. The study was approved by the institutional review board.
Inclusion criteria were renal donor candidates without contraindications found during the routinely performed extensive workup for kidney donation, consisting of an interview, physical examination, sonography, and laboratory tests, who were referred by the department of internal medicine to the department of radiology to undergo diagnostic imaging as part of the final workup. All participants had to give written informed consent and were scheduled to undergo both contrast-enhanced MR angiography and digital subtraction angiography on the same day. Donors were excluded if there were contraindications for undergoing MRI (e.g., pacemaker, recent surgery, ocular metallic foreign bodies, or cerebral clips), contraindications for undergoing angiography, or contraindications for receiving iodine contrast medium. Old age alone was not an absolute contraindication to donation.
Of the 52 potential living renal donors who were evaluated during the inclusion period, 42 were included in our study. Ten donors were excluded for the following reasons: One donor refused to undergo digital subtraction angiography; four donors refused to undergo contrast-enhanced MR angiography because of claustrophobic symptoms; three donors did not undergo either imaging examination because donation was cancelled for reasons unrelated to the anatomy (two cancellations due to death of the recipient and one donor continued the procedure in a neighboring country); one donor did not undergo MR angiography because the MR scanner was defective and rescheduling the examination was impractical for the donor; and one donor had ocular metallic foreign bodies. The mean age of the potential donors was 48 years (SE, 2 years; median, 47 years; range, 25–76 years). Of the 42 potential donors, four (10%) were older than 60 years and 18 (43%) were men.
Contrast-Enhanced MR Angiography Technique
MR images were obtained using a 1.5-T MR scanner (Signa CV/i, GE
Healthcare) with a torso phased-array coil. One coronal set of unenhanced
images was obtained with a heavily T2-weighted single-shot fast spin-echo or
half-Fourier single-shot turbo spin-echo sequence with the following
parameters: TR/TE, 
/120; flip angle, 90°; and acquisition time, 20
sec (breath-holding). Sagittal single-shot fast spin-echo or half-Fourier
single-shot turbo spin-echo imaging was performed with the following
parameters: /100; 90°; and 16–20 sec (breath-holding). Axial
T2-weighted fast spin-echo imaging with fat saturation was performed with the
following parameters: 2,000/100; 90°; and 2 min 36 sec (respiratory
triggering). A timing bolus sequence was performed with sagittal 3D fast
gradient-refocused echo imaging with the following parameters: 4.2/1.8;
70°; and an acquisition rate of once per second for 60 sec (free
breathing) during the injection of 2 mL of gadopentetate dimeglumine
(Magnevist, Schering) at a rate of 3 mL/sec with a power injector (Spectris,
Medrad), immediately followed by a 15-mL saline flush administered at the same
rate. The contrast material was injected in an antecubital vein using a
20-gauge IV catheter.
The arrival of contrast agent within the abdominal aorta was observed and used for calculating the imaging delay. Coronal 3D fast gradient-refocused echo MR angiography was performed with the following parameters: 4.7/1.4; flip angle, 30°; 0.6 signals acquired; 256 x 192 x 24 matrix with a section thickness of 2.4 mm, zero-filled to 48 sections with 50% overlapping reconstructed sections; and an acquisition time of 24 sec (breath-holding). The coronal 3D fast gradient-refocused echo MR venography examination was performed with the following parameters: 4.7/1.4; flip angle, 15°; 0.6 signals acquired; 256 x 192 x 24 matrix with a section thickness of 2.4 mm, zero-filled to 48 sections with overlapping reconstructed sections of 1.2-mm thickness; and an acquisition time of 24 sec (breath-holding). Axial delayed gadolinium-enhanced 3D fast gradient-refocused echo imaging with the following parameters was performed: 4.9/1.6; flip angle, 15°; a section thickness of 8 mm, zero-filled to 56 sections with 50% overlapping reconstructed sections; and an acquisition time of 21 sec (breath-holding) [15].
Intraarterial Digital Subtraction Angiography Technique
High-quality digital subtraction angiography images were acquired on the
same day as contrast-enhanced MR angiography images using a 38-cm field of
view and an image matrix of 1,024 x 1,024 pixels (Integris V3000,
Philips Medical Systems; or Angiostar Plus, Siemens Medical Solutions). A
4-French pigtail catheter was introduced transfemorally using the Seldinger
technique, and its tip was positioned in the abdominal aorta above the level
of the renal arteries between T12 and L1. An aortogram was obtained in the
anteroposterior projection by injecting 30 mL of nonionic 300 mg I/mL contrast
agent (Omnipaque [iohexol], Nycomed Amersham) at a rate of 15 mL/sec.
Subsequently, all renal arteries were projected after selective
catheterization with a 4-French Cobra 2 catheter and the amount of contrast
agent and the rate of administration were adjusted appropriately for the size
of the vessel. After 7 min, a urogram was obtained.
Postprocessing of 3D Data Sets
All MR images were digitally transported, processed, and evaluated on a
workstation (Advantage Windows [version 3.1], GE Healthcare). Various
reconstructions were created from both the MR angiography and the MR
venography examinations. Coronal oblique maximum-intensity-projection images
were formatted parallel to the right and left renal vasculature with a field
of view of 150 mm, a slice width of 5 mm, and a distance of 2.5 mm between
views. Coronal anteroposterior maximum-intensity-projection images were
constructed to show both kidneys with a field of view of 200 mm and using the
same slice width and increment. Oblique radially reformatted
maximum-intensity-projection images were obtained parallel to the aorta and
using the aorta or the inferior vena cava as the center with a slice thickness
of 10 mm and a 2° angle between every view over 360°. Multiplanar
reconstruction images were obtained interactively during interpretation along
different angles using different partial fields of view and variable
thicknesses. In addition, when an arterial stenosis was suspected, axial
images perpendicular to the renal arteries were obtained to evaluate the grade
of stenosis.
Image Evaluation
All source and reconstructed images of contrast-enhanced MR angiography
were evaluated digitally by an experienced vascular radiologist and a
dedicated researcher who was also a radiology resident. The observers were
blinded to the results of the digital subtraction angiography examination and
to the results of the extensive workup for kidney donation including
sonography. Another experienced vascular radiologist and the radiology
resident, who were blinded to the results of the contrast-enhanced MR
angiography images and the workup including sonography, evaluated the digital
subtraction angiography images. These were viewed both digitally and on hard
copy in subtracted and unsubtracted modes. The reviewers evaluated the
examination results together and formed a consensus about the following points
for the contrast-enhanced MR angiography and digital subtraction angiography
images: presence of parenchymal abnormality, duplication or obstruction of the
collecting system, number and localization of renal arteries, presence of
renal artery stenosis, any findings suggesting fibromuscular dysplasia, and
the number and localization of renal veins.
For contrast-enhanced MR angiography, consensus was formed about the following points: number and size of cysts, characterization of parenchymal abnormalities, the distance from the aorta to the branching of the main renal artery and its relationship to the lateral side of the inferior vena cava, the presence of retrocaval right renal artery branching, the presence of a retroaortic left renal vein, the caliber of the left spermatic or ovarian vein draining into the left renal vein, and the presence of the adrenal and lumbar veins draining into the renal vein.
Impact on Decision Making
Separate evaluations of contrast-enhanced MR angiography and digital
subtraction angiography, in that order, took place for making decisions. These
evaluations were performed after the image evaluations and before nephrectomy.
This design was possible because the entire donor procedure takes several
months to complete and limited capacity for transplantation procedures creates
a waiting list. While making decisions regarding nephrectomy using the
contrast-enhanced MR angiography images, the reviewers were blinded to the
digital subtraction angiography images. The reviewers were also blinded to the
outcome because the evaluations took place before the nephrectomy
procedures.
The contrast-enhanced MR angiography images with the reported findings of the image evaluation and information about the age and sex of the potential donor, who was unknown to the surgeon, were presented to the transplantation surgeon by an experienced vascular radiologist or a dedicated radiology researcher who was also a radiology resident. If the resident researcher presented the findings, he had in all cases discussed the findings with the vascular radiologist before presentation to the transplantation surgeon. During the evaluation, the surgeon and radiologist (or resident researcher) together determined which side should be chosen for nephrectomy and the reasons for that choice. Usually the right side is preferred for laparoscopic harvesting of a donor kidney, but the presence of supernumerary vessels or vascular anomalies, renal artery stenosis, retrocaval right renal artery branching, parenchymal abnormalities, or an abnormal renal collecting system may influence the decision. In addition, the necessity of and reason for an additional digital subtraction angiography examination were determined. At least 2 months later, the digital subtraction angiography images were similarly presented, with the surgeon and presenter blinded to the contrast-enhanced MR angiography findings and to the outcome; discussed; and used to decide which side should be chosen for nephrectomy.
After the evaluations using separate images for this study had been completed, the combined information from the contrast-enhanced MR angiography and digital subtraction angiography examinations was evaluated. The decisions regarding the side of nephrectomy and whether an additional digital subtraction angiography examination that had been regarded as necessary did indeed provide the expected additional information were determined on the basis of all the information available from both imaging procedures.
Data Analysis
The agreement between the number of renal arteries detected on
contrast-enhanced MR angiography and that detected on digital subtraction
angiography was analyzed using a weighted kappa analysis
[26]. The frequency of
abnormality of the renal parenchyma, abnormality of the collecting system,
presence of renal venous anomalies, and presence of an adrenal vein or a
lumbar vein found with contrast-enhanced MR angiography were calculated. The
presence of renal artery stenosis was calculated and compared among donors
younger and older than 60 years using the chi-square test. Agreement between
contrast-enhanced MR angiography and digital subtraction angiography for
detecting supernumerary renal vasculature and renal artery stenosis was
analyzed using the kappa statistic. The level of agreement for the decisions
of whether to donate and which side to harvest was analyzed for overall
marginal homogeneity using the Stuart-Maxwell test.
Cost Analysis
The main purpose of our economic evaluation was to quantify differences in
the use of resources and costs of diagnostic tests incurred for each of the
diagnostic tests. For the cost analysis, we collected information concerning
all relevant items of health care in the preoperative evaluation of potential
renal donors to calculate the cost for an imaging test and to calculate the
diagnostic imaging cost per patient. The cost of diagnostic imaging included
the costs of the imaging test; the hospital costs after the imaging test; and
costs incurred as a result of test procedure complications, if they occurred.
The costs were computed from the hospital perspective according to a
standardized methodology of economic evaluations
[27].
The costs of the imaging test included personnel costs, the costs for
supplies such as film, the investment costs for the equipment used, costs for
equipment servicing, construction costs, costs of supporting departments,
costs to rent hospital floor space, and overhead costs. Personnel costs were
computed using the measured time spent on a diagnostic imaging test or a
percutaneous intervention for each involved personnel category and the mean
wage rates from our hospital. Social security (37% of the wage) was added in
accordance with national guidelines. The costs of the supplies used in
diagnostic procedures were based on cost prices and summed. The annuitized
costs of the radiologic equipment and the annual equipment servicing costs
were summed and divided by the proportion of the total available room time.
All elective examinations were performed within the time of our regular
workweek, which is 40 hr, and the room was estimated to be used 80% of the
time [27]. Information about
the costs of supporting departments was obtained from records of our financial
and economics department. The costs to rent hospital floor space were computed
for the involved radiologic rooms by multiplying the floor space by the rental
cost of 
204/m2 per year. The overhead costs for
contrast-enhanced MR angiography and digital subtraction angiography were
estimated to be 15% of directly assignable costs
[27].
The cost of the hospital stay and visits (i.e., routinely after digital
subtraction angiography or when hospital stay or visits were necessary because
of complications of an imaging test) was included, and the associated costs
were calculated using national estimates of hospital stay
[27]. All costs were reported
in euros at year 2000 prices and were converted into U.S. dollars (prevailing
exchange rate: 1.00 = $1.24 [July 15, 2004]). The costs of radiologic
equipment, equipment servicing, construction, and contrast agents were
validated using a small survey of these costs from five national
hospitals.
We compared the costs of the following diagnostic strategies: contrast-enhanced MR angiography; digital subtraction angiography; and, an additional theoretic strategy, contrast-enhanced MR angiography followed by digital subtraction angiography only if necessary. For the last strategy, the mean cost of the strategy was computed taking into account the number of additional digital subtraction angiography procedures that were found to be necessary after contrast-enhanced MR angiography findings were inconclusive.
Results
No complications from either contrast-enhanced MR angiography or digital subtraction angiography were noted. Figure 1 illustrates all anomalies found on contrast-enhanced MR angiography in our study (Table 1): supernumerary arteries, retrocaval branching of the right renal artery, supernumerary renal veins, retroaortic (Fig. 2) or circumaortic left renal vein, left spermatic or ovarian vein draining into left renal vein, and left lumbar vein draining into left renal vein. Contrast-enhanced MR angiography depicted renal parenchymal or adrenal abnormality in 50% of the cases (21/42) (Table 1). There was one case of fetal lobulation, one of congenital hypoplasia, another of unilateral undefined partial unenhanced parenchyma, and one coincidental finding of a pheochromocytoma. In 17 cases, simple cysts were found. In one case, a duplicated collecting system was found. Renal artery stenosis was found on contrast-enhanced MR angiography or digital subtraction angiography in 17% of the donors older than 60 years, which did not differ significantly from the frequency in donors 60 years old or younger.
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Diagnostic Agreement
The agreement between contrast-enhanced MR angiography and digital
subtraction angiography for the detection of supernumerary arteries was
excellent (weighted 
= 0.82) (Table
2). Contrast-enhanced MR angiography detected more supernumerary
arteries than digital subtraction angiography. Digital subtraction angiography
missed four cases of double arterial supply and one accessory artery in a case
with triple arterial supply. The agreement between contrast-enhanced MR
angiography and digital subtraction angiography for the presence of arterial
stenosis was moderate ( = 0.41).
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Impact on Decision Making
Based on only the contrast-enhanced MR angiography images, the decision as
to which kidney to use for donation could be made in 40 (95%) of the 42 cases,
whereas based on only the digital subtraction angiography images, the decision
could be made in 37 (88%) of the 42 cases (Tables
3 and
4). The overall difference
between the decisions based on contrast-enhanced MR angiography and those
based on digital subtraction angiography—that is, whether a decision was
possible and which side to harvest—was not statistically significant
(p = 0.07). In five cases (12%), the decision could not be made with
exclusively digital subtraction angiography, and in two cases (5%) a decision
was not possible based solely on contrast-enhanced MR angiography. In the two
cases for which the decision could not be made based on contrast-enhanced MR
angiography, digital subtraction angiography also was not helpful in deciding
which kidney to resect.
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In 22 cases (52%), right-sided nephrectomy (the preferred side) was chosen with contrast-enhanced MR angiography; the alternative, left-sided nephrectomy, was chosen in 18 cases (43%). Based on digital subtraction angiography, the right side was chosen in 23 cases (55%) and the left side, in 14 cases (33%). In four cases, the decision was based on parenchymal findings on MR images: In one case, physicians decided not to harvest a kidney with a large simple cyst; in one case, they decided to harvest the kidney on the side of an incidental pheochromocytoma, which was resected first; in one case, they chose to harvest a hypoplastic kidney; and in one case, they decided to resect a kidney that showed an infarct.
A decision could not be made with digital subtraction angiography in five cases. In one case, this was due to an insufficiently angulated projection; in three cases, the digital subtraction angiography examination was incomplete because of failure of selective catheterization and overprojection of arteries; and in one case, digital subtraction angiography was inconclusive with respect to whether branching of the right renal artery was located retrocavally. Contrast-enhanced MR angiography did not lead to a decision in two cases: because of technical failure shortly after introducing the protocol in one case and because of movement artifacts of the donor in the other, both of which led to poor image quality.
Additional digital subtraction angiography was requested in 10 cases (24%) after contrast-enhanced MR angiography (Table 5). In two, a decision could not be made because of poor image quality, whereas in the other eight a preliminary decision could be made on the basis of contrast-enhanced MR angiography but digital subtraction angiography was requested to increase confidence in that decision. Five of the 10 requested digital subtraction angiography examinations provided new information. In one case, fibromuscular dysplasia of the renal artery was found and had been unsuspected on the basis of the contrast-enhanced MR angiography findings. In one case, a stenosis at the origin of the renal artery was found, and grading the stenosis on contrast-enhanced MR angiography would have been impossible. In one case, the distance between the origin and retrocaval branching of the right renal artery was shown to be sufficiently long, and in two cases, possible vessel wall irregularities detected on contrast-enhanced MR angiography were excluded.
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Among the 32 patients in whom digital subtraction angiography was not considered necessary but digital subtraction angiography was performed according to the research protocol, digital subtraction angiography showed new findings in only one case. This donor had early retrocaval branching of the right renal artery that was shown on contrast-enhanced MR angiography and an accessory left renal artery that was too large to be sacrificed that was shown on digital subtraction angiography. On the basis of contrast-enhanced MR angiography and digital subtraction angiography together, the right kidney was chosen for nephrectomy.
Cost Analysis
After undergoing digital subtraction angiography in an outpatient setting
and being observed for 4 hr after the procedure, all patients were discharged.
Contrast-enhanced MR angiography was less expensive from the hospital's
perspective (346 [$429]) than digital subtraction angiography (435
[$539]) for imaging potential renal donors
(Table 6). For
contrast-enhanced MR angiography, the costs per examination were determined
mainly by the large investment in scanning equipment and the cost of
gadolinium contrast material. For digital subtraction angiography, the costs
were highly dependent on the costs of hospital stay for observation,
personnel, and materials (catheters and contrast agent). The mean total
diagnostic imaging cost of the diagnostic strategy to perform
contrast-enhanced MR angiography and then perform digital subtraction
angiography only if necessary—that is, the cost of contrast-enhanced MR
angiography plus the cost of digital subtraction angiography when considered
necessary—was higher (449 [$557]) than that of digital subtraction
angiography.
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In this prospective clinical study, we evaluated the agreement between contrast-enhanced MR angiography and digital subtraction angiography in the preoperative imaging workup of living renal donors and their impact on decision making and costs. Contrast-enhanced MR angiography was superior to digital subtraction angiography in detecting renal vascular anomalies and depicting parenchymal abnormalities, did not lead to a significantly different choice of kidney for harvesting, and was less expensive than digital subtraction angiography. If subtle arterial abnormality such as fibromuscular dysplasia is suspected on the basis of contrast-enhanced MR angiography or if the image quality is poor, additional imaging needs to be performed using digital subtraction angiography.
Whereas the authors of most published studies have reported the accuracy of contrast-enhanced MR angiography in the preoperative diagnostic workup of living renal donors [11–14, 22–24], we analyzed its performance from a health policy perspective. Given the previously reported high accuracy of contrast-enhanced MR angiography, we believe that it was important to measure the agreement with digital subtraction angiography, the impact on decision making, and the hospital costs.
In the analysis concerning the detection of arterial stenosis, all types and degrees of renal artery stenoses were grouped into one category. The rationale is that a stenosis, whether significant or insignificant, can potentially be progressive and may eventually lead to renal hypertension and renal insufficiency [28, 29]. Our results support previously published findings that contrast-enhanced MR angiography can fail to depict subtle renal artery stenosis and that additional imaging is necessary to diagnose or exclude stenoses when contrast-enhanced MR angiography has poor image quality [30]. Contrast-enhanced MR angiography can yield false-negative or false-positive findings in this respect: In our series, one case of fibromuscular dysplasia was missed on contrast-enhanced MR angiography, whereas signs of fibromuscular dysplasia detected on contrast-enhanced MR angiography could not be confirmed on digital subtraction angiography in one case (Fig. 3A, 3B).
Contrast-enhanced MR angiography did not always provide high-quality images of the arterial lumen because of suboptimal resolution and artifacts caused by patient movement [31]. High spatial resolution is a prerequisite to depict small arteries and branches and to show delicate abnormality such as fibromuscular dysplasia [32]. Also, a high contrast-to-noise ratio plays a role; this may somewhat compensate for the lower spatial resolution of MR angiography compared with digital subtraction angiography. Leaving an asymptomatic donor with one kidney with fibromuscular dysplasia could be harmful because this can progress to symptomatic renal artery stenosis, but such a kidney may be acceptable for donation [33].
Given the low probability of fibromuscular dysplasia and the uncertainty about the long-term outcome in either renal donor or recipient, the debate as to whether contrast-enhanced MR angiography suffices as the imaging test in renal donors continues [11, 20, 34]. Nevertheless, a cost-effectiveness analysis taking into account the long-term outcome suggested that noninvasive imaging studies are sufficient [35]. Instead of CT angiography, we chose to perform a noninvasive imaging technique without exposing patients to radiation: contrast-enhanced MR angiography. Moreover, when an additional digital subtraction angiography examination is necessary, the healthy donor would not be exposed to radiation twice.
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We showed that a choice could be made in 95% of the cases after contrast-enhanced MR angiography versus 88% after digital subtraction angiography. Two of the five indecisive cases with digital subtraction angiography were because of early branching of the right renal artery, where digital subtraction angiography could not show whether the branching was retrocaval (Fig. 5A, 5B, 5C). These cases require cross-sectional imaging such as MR angiography to show the relationship of the artery and its branches to the inferior vena cava. When a renal artery branches retrocavally, the surgeon is unable to reach the main renal artery laparoscopically and the situation is equivalent to the presence of two renal arteries.
Several limitations of our study should be mentioned. One limitation is that we did not consider a strategy in which all donors would undergo digital subtraction angiography followed, if necessary, by contrast-enhanced MR angiography. More specifically, we did not determine how many times contrast-enhanced MR angiography would be requested after digital subtraction angiography. We can, however, estimate this number by recognizing that in five cases a decision could not be made based on the digital subtraction angiography images. Performing digital subtraction angiography in all donors followed if necessary by contrast-enhanced MR angiography would, however, imply performing an invasive imaging workup in all donors and would lead to higher costs and is therefore an unattractive strategy.
Another limitation is a possible bias toward MR angiography, which could potentially have been present. We tried to limit this bias by involving both a vascular radiologist and a transplantation surgeon in the decision-making evaluations.
Another limitation of our study is that we examined the decisions from the perspective of harvesting all kidneys laparoscopically. The images were not used to decide which technique should be used—open versus laparoscopic nephrectomy. Two donors underwent open surgery, one because of the habitus of the donor and the other because the laparoscopic technique was converted to an open technique as a result of venous bleeding. Although a limitation, our chosen perspective at the same time is currently probably the most applicable and also provides a perspective on the problem that differs from those already published.
Furthermore, a limitation was our choice of perspective for the cost analysis. Our interest was to evaluate the impact of contrast-enhanced MR angiography on clinical practice; therefore, we performed a cost evaluation from the hospital's perspective. In contrast to reimbursements and charges, hospital costs inform us about the health care resources used for a specific health care service and can guide our choices in the setting of constrained resources [38]. Although a societal perspective is advocated for cost-effectiveness analyses, such an analysis would require consideration of the long-term outcomes, which were not the focus of this study. Finally, costs were expressed in euros to reflect the West European background of this study. Although West European health care costs are lower than those in the United States [39, 40], the ratio of the costs between various imaging examinations is likely to be similar.
Compared with digital subtraction angiography, contrast-enhanced MR angiography alone was less expensive and the strategy of contrast-enhanced MR angiography plus digital subtraction angiography if necessary was similar in expense. The cost of digital subtraction angiography depends highly on the necessity of hospital stay, personnel, and supplies, whereas the cost for contrast-enhanced MR angiography depends on the investment for the scanning equipment and the price of gadolinium contrast material. Expenses for MRI can be reduced by scanning without contrast material, but this also reduces the accuracy [41]. Furthermore, the expense could potentially be reduced by increasing the number of hours that the machine is in operation or by increasing throughput.
In conclusion, compared with digital subtraction angiography, contrast-enhanced MR angiography is superior in detecting vascular anomalies, better depicts parenchymal abnormalities, does not lead to significantly different preoperative decisions, and is less costly. Our results suggest that living renal donors should initially be evaluated with contrast-enhanced MR angiography. If contrast-enhanced MR angiography does not provide sufficient information to make a confident preoperative decision, an additional digital subtraction angiography examination should be performed.
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