Imaging of the renal donor and transplant recipient

Vascular imaging in renal donors

Imaging plays a crucial role in pre-transplant evaluation to enhance the probability of a successful outcome. Its aim is to define kidney and vascular anatomy and to assess potential pathologies. Each modality has advantages and disadvantages. Computed tomography angiography (CTA) is the most commonly used imaging modality, however, magnetic resonance angiography (MRA) can be used in selected cases. The purpose of this review article is to provide an overview of available imaging modalities, their benefits, risks, advantages, and disadvantages. Imaging findings that indicate particular anomalies and pathologies that may affect living renal donor selection will be discussed.

Functional Evaluation of Transplanted Kidneys with Reduced Field-of-View Diffusion-Weighted Imaging at 3T

Objective

To determine the feasibility of reduced field-of-view diffusion-weighted imaging (rFOV DWI) with multi-b values to detect functional variability in transplanted kidneys.

Materials and Methods

Using a 3T MRI scanner, multi-b rFOV DWI of transplanted kidney or native kidney was performed in 40 renal transplantation recipients and 18 healthy volunteers. The patients were stratified, according to an estimated glomerular filtration rate (eGFR): Group 1, eGFR ≥ 60 mL/min/1.73 m²; Group 2, eGFR ≥ 30 mL/min/1.73 m² and < 60 mL/min/1.73 m²; Group 3, eGFR < 30 mL/min/1.73 m². Total apparent diffusion coefficient (ADC_T), perfusion-free ADC (ADC_D) and perfusion fraction (F_P) of kidneys were calculated and compared among the four groups. Correlations between the imaging results and eGFR were assessed.

Results

All volunteers had eGFR ≥ 60 mL/min/1.73 m², while 16, 16, and 8 patients were included in Groups 1, 2, and 3, respectively. In the renal cortex, ADCT was higher in Group 1 ([1.65 ± 0.13] × 10^-3 mm²/s) than Group 3 ([1.44 ± 0.11] × 10^-3 mm²/s) (p < 0.05), and the inter-group differences of F_P values were significant (all p < 0.05) (0.330 ± 0.024, 0.309 ± 0.019, 0.278 ± 0.033, and 0.250 ± 0.028 for control group, Groups 1, 2, and 3, respectively). Renal cortical ADC_T, ADC_D, F_P, and renal medullary ADC_T and F_P correlated positively with eGFR (r = 0.596, 0.403, 0.711, 0.341, and 0.323, respectively; all p < 0.05). When using 0.278 as the cutoff value, renal cortical F_P had a sensitivity of 97.1% and a specificity of 66.7% for predicting decreased renal function.

Conclusion

Multi-b rFOV DWI presents transplanted kidneys with high resolution, which is a promising functional tool for non-invasively monitoring function of transplanted kidneys.

Metabolomic Profiling in Individuals with a Failing Kidney Allograft

BACKGROUND

Alteration of certain metabolites may play a role in the pathophysiology of renal allograft disease.

METHODS

To explore metabolomic abnormalities in individuals with a failing kidney allograft, we analyzed by liquid chromatography-mass spectrometry (LC-MS/MS; for ex vivo profiling of serum and urine) and two dimensional correlated spectroscopy (2D COSY; for in vivo study of the kidney graft) 40 subjects with varying degrees of chronic allograft dysfunction stratified by tertiles of glomerular filtration rate (GFR; T1, T2, T3). Ten healthy non-allograft individuals were chosen as controls.

RESULTS

LC-MS/MS analysis revealed a dose-response association between GFR and serum concentration of tryptophan, glutamine, dimethylarginine isomers (asymmetric [A]DMA and symmetric [S]DMA) and short-chain acylcarnitines (C4 and C12), (test for trend: T1-T3 = p<0.05; p = 0.01; p<0.001; p = 0.01; p = 0.01; p<0.05, respectively). The same association was found between GFR and urinary levels of histidine, DOPA, dopamine, carnosine, SDMA and ADMA (test for trend: T1-T3 = p<0.05; p<0.01; p = 0.001; p<0.05; p = 0.001; p<0.001; p<0.01, respectively). In vivo 2D COSY of the kidney allograft revealed significant reduction in the parenchymal content of choline, creatine, taurine and threonine (all: p<0.05) in individuals with lower GFR levels.

CONCLUSIONS

We report an association between renal function and altered metabolomic profile in renal transplant individuals with different degrees of kidney graft function.

Computed Tomography in the Preoperative and Postoperative Evaluation of Kidney Transplant Patients

OBJECTIVES

Computed tomography is required for selection of living donors for kidney transplant. We assessed the diagnostic relevance and effectiveness of multiphase contrast-enhanced computed tomography angiography for evaluating patients before and after transplant.

MATERIALS AND METHODS

Thirty-two potentially living kidney donors (15 men and 17 women) underwent multiphase computed tomography angiography for evaluation before kidney transplant and 2 posttransplant recipients under went this test owing to abnormal vascularization. Computed tomography angio graphy was used to determine parenchymal blood-flow conditions and vascular architecture of the kidney grafts. All of the 34 patients underwent prestudy Doppler ultrasonography.

RESULTS

Additional renal arteries were found in 11 patients (32.3%). From them, a single additional renal artery, situated from the aorta to the lower segment of the kidney, was observed in 8 (72.7%) patients; dual additional renal arteries with equivalent caliber trunks were observed in 3 (27.3%) patients. An additional renal artery occurred more often in women in 6 (54.5%) donors. Concomitant renal pathology was detected in 3 (9.3%) of 32 donors: simple cysts in 2 donors and hydro nephrosis transformation in 1 donor. These 3 cases represented an accidental discovery and were therefore excluded from the list of donors. In addition, all donors underwent excretory-phase computed tomography, and their renal function and urinary collecting system results were evaluated. Two recipients with graft dysfunction presented with decreased venous return and delayed arterial filling of the renal arteries that manifested as delayed contrast in the kidney graft medulla. Renal parenchymal ischemic zones were consistent with microvasculature thrombosis, the most common cause of vascular complications in these recipients.

CONCLUSIONS

Multiphase computed tomography angiography is a necessary tool for assessing the structure and condition of vascular architecture in kidney donors and recipients. Individuals with ambiguous Doppler results, this test should be required; it is also warranted when renal graft vascular complications are suspected.

Experiences with the use of iteratively reconstructed dose-modified MDCT angiography examinations of living renal donors

PURPOSE

To evaluate the performance of iteratively reconstructed (IR) dose-modified (DM) multidetector computed tomography (MDCT) angiography (CTA) examinations of renal donors in comparison to standard dose filtered back projection (FBP) images.

MATERIALS AND METHODS

Eighty-five potential donors who underwent dual-phase CTA on 16-/64-MDCT scanners were retrospectively reviewed. Images from a 16-MDCT scanner were reconstructed with filtered back projection (group A, 47) and examinations from 64-MDCT with IR (group B, 38). Scan parameters were constant for both groups except for higher noise index (× 1.3) in group B. Images were interpreted for the relevant anatomy and IQ by 2 readers. Surgical report served as reference standard for operated kidneys, whereas for nonoperated kidneys, interobserver agreement was evaluated.

RESULTS

Radiation dose was 36% lower in group B compared to group A. All CTA examinations were rated for diagnostic quality with comparable IQ scores. In 48 operated kidneys, 10 surgically confirmed vascular anomalies were correctly identified by both readers. In the remaining 122 nonoperated kidneys, there was an excellent interobserver agreement.

CONCLUSIONS

Iteratively reconstructed technique preserves high image quality and diagnostic performance at significantly lower radiation doses in DM kidney donor CTA examinations.

CT angiography for surgical planning in face transplantation candidates

SUMMARY

Facial allotransplantation replaces missing facial structures with anatomically identical tissues, providing desired functional, esthetic, and psychosocial benefits far superior to those of conventional methods. On the basis of very encouraging initial results, it is likely that more procedures will be performed in the near future. Typical candidates have extremely complex vascular anatomy due to severe injury and/or multiple prior reconstructive attempts; thus, each procedure is uniquely determined by the defects and vascular anatomy of the candidate. We detail CT angiography vascular mapping, noting the clinical relevance of the imaging, the angiosome concept and noninvasive delineation of the key vessels, and current controversies related to the vascular anastomoses.

Renal transplant ultrasound: a pictorial review

Renal transplantation is considered the optimal treatment in patients with end-stage renal disease. Ultrasound is usually the first choice imaging modality for evaluating renal transplant anatomy and perfusion. It is important to be aware of how to image a renal transplant, the normal sonographic appearances and relevant pathological processes. Renal transplant ultrasound imaging includes duplex vascular evaluation and the operator must have a sound knowledge of both normal and abnormal Doppler waveforms. Complications following renal transplantation are usually assessed with ultrasound. The time frame in which complications can occur stretches from the immediate postoperative period to months or years following transplantation. A knowledge of the anticipated complications relative to that timescale helps to focus the examination. This pictorial review aims to demonstrate the appearances of the normal renal transplant as well as potential complications. These include vascular (renal vein thrombosis, renal artery stenosis, pseudoaneurysm and arteriovenous fistulae), parenchymal (acute rejection, acute tubular necrosis and malignancy) and urological (ureteric stricture and renal calculi) complications.

Multidetector computed tomography with triple-bolus contrast medium administration protocol for preoperative anatomical and functional assessment of potential living renal donors

OBJECTIVE

To evaluate multidetector computed tomography (MDCT) with a triple-bolus contrast administration protocol for preoperative anatomical and functional assessment of living renal donors.

METHODS

Fifty-five potential living renal donors underwent MDCT of which 27 proceeded to donor nephrectomy. A triple-bolus contrast administration protocol was used for simultaneous acquisition of arterial, nephrographic, and excretory phases. MDCT images were independently reviewed in random order by two radiologists blinded to surgical anatomy findings. Diagnostic accuracy for anatomical variants was quantified by sensitivity and specificity. Differential renal function (DRF) was derived from MDCT for 54 patients and compared with technetium-99 m dimercaptosuccinic acid renography (Tc-99 m DMSA).

RESULTS

All triple-bolus MDCT examinations were technically adequate. Accessory renal arteries and veins were identified at surgery in 33% (n = 9/27) and 22% (n = 6/27) of donor kidneys. The mean difference between MDCT-derived DRF and DMSA was 0.8% (95% CI 0.1-1.6) with 95% limits of agreement of -4.6% (95% CI -3.3 to -5.9) to 6.3% (95% CI 5.0-7.6). MDCT delivered a mean (SD, range) radiation dose of 9.5 (3.6, 3.6-17.3) mSv.

CONCLUSION

MDCT with a triple-bolus contrast administration provides accurate anatomical and functional evaluation of living renal donors.