MR imaging of renal transplants

MRI for diagnosis of post-renal transplant complications: current state-of-the-art and future perspectives

Kidney transplantation has developed into a widespread procedure to treat end stage renal failure, with transplantation results improving over the years. Postoperative complications have decreased over the past decades, but are still an important cause of morbidity and mortality. Early accurate diagnosis and treatment is the key to prevent renal allograft impairment or even graft loss. Ideally, a diagnostic tool should be able to detect post-transplant renal dysfunction, differentiate between the different causes and monitor renal function during and after therapeutic interventions. Non-invasive imaging modalities for diagnostic purposes show promising results. Magnetic resonance imaging (MRI) techniques have a number of advantages, such as the lack of ionizing radiation and the possibility to obtain relevant tissue information without contrast, reducing the risk of contrast-induced nephrotoxicity. However, most techniques still lack the specificity to distinguish different types of parenchymal diseases. Despite some promising outcomes, MRI is still barely used in the post-transplantation diagnostic process. The aim of this review is to survey the current literature on the relevance and clinical applicability of diagnostic MRI modalities for the detection of various types of complications after kidney transplantation.

Magnetic resonance imaging T1- and T2-mapping to assess renal structure and function: a systematic review and statement paper

This systematic review, initiated by the European Cooperation in Science and Technology Action Magnetic Resonance Imaging Biomarkers for Chronic Kidney Disease (PARENCHIMA), focuses on potential clinical applications of magnetic resonance imaging in renal non-tumour disease using magnetic resonance relaxometry (MRR), specifically, the measurement of the independent quantitative magnetic resonance relaxation times T₁ and T₂ at 1.5 and 3Tesla (T), respectively. Healthy subjects show a distinguishable cortico-medullary differentiation (CMD) in T₁ and a slight CMD in T₂. Increased cortical T₁ values, that is, reduced T₁ CMD, were reported in acute allograft rejection (AAR) and diminished T₁ CMD in chronic allograft rejection. However, ambiguous findings were reported and AAR could not be sufficiently differentiated from acute tubular necrosis and cyclosporine nephrotoxicity. Despite this, one recent quantitative study showed in renal transplants a direct correlation between fibrosis and T₁ CMD. Additionally, various renal diseases, including renal transplants, showed a moderate to strong correlation between T₁ CMD and renal function. Recent T₂ studies observed increased values in renal transplants compared with healthy subjects and in early-stage autosomal dominant polycystic kidney disease (ADPKD), which could improve diagnosis and progression assessment compared with total kidney volume alone in early-stage ADPKD. Renal MRR is suggested to be sensitive to renal perfusion, ischaemia/oxygenation, oedema, fibrosis, hydration and comorbidities, which reduce specificity. Due to the lack of standardization in patient preparation, acquisition protocols and adequate patient selection, no widely accepted reference values are currently available. Therefore this review encourages efforts to optimize and standardize (multi-parametric) protocols to increase specificity and to tap the full potential of renal MRR in future research.

MR Imaging of Renal Transplant Rejection

The results of 62 consecutive MR examinations were correlated with the subsequent clinical course and histologic results. Twenty-six cases of rejection showed a marked diminution of cortico-medullary differentiation (CMD). The renal parenchymal vascular pattern and visibility of renal sinus fat were not markedly altered in rejection and there was no difference between normal and rejected allograft shape. The ability of MR imaging to diagnose renal transplant rejection is only based on CMD, which, however, is non-specific. In 2 cases of severe acute rejection, T2 weighted images showed an abnormal signal intensity of the cortex due to renal infarction. Our preliminary results in 8 patients with Gd-DOTA injection showed 2 cases with necrosis seen as areas with absent contrast enhancement. This technique seems to be promising in the detection of perfusion defects.

Acute abdominal pain: is there a potential role for MRI in the setting of the emergency department in a patient with renal calculi?

Acute flank pain is a frequent clinical presentation encountered in emergency departments, and a work-up for obstructive urolithiasis in this setting is a common indication for computed tomography (CT). However, imaging alternatives to CT for the evaluation of renal colic are warranted in some clinical situations, such as younger patients, pregnancy, patients that have undergone multiple prior CT exams and also patients with vague clinical presentations. MRI, although relatively insensitive for the direct detection of urinary calculi, has the ability to detect the secondary effects of obstructive urolithiasis. Using rapid, single shot T2-weighted sequences without and with fat saturation provides an abdominopelvic MR examination that can detect the sequelae of clinically active stone disease, in addition to alternate inflammatory processes that may mimic the symptoms of renal colic. In addition, MR nephro-urography (MRNU) has the ability to provide quantitative analysis of renal function that has the potential to direct clinical management in the setting of obstructing calculi. This review describes the potential utility and limitations of MRI in the emergency setting for diagnosing causes of flank pain and renal colic, particularly in patients with unusual presentations or when an alternative to CT may be warranted.

Kidney transplantation: structural and functional evaluation using MR Nephro-Urography

End-stage-renal disease (ESRD) is a major health issue in the United States, and the Medicare costs of ESRD totaled nearly USD 21 billion in 2005. Renal transplantation has emerged as the treatment of choice in this patient population, providing improved quality of life and lower healthcare costs compared with other treatment options. Imaging evaluation of a graft kidney plays a critical role in the postoperative care of the renal transplant patient. In the past, diagnostic evaluation of the transplant kidney has depended upon a combination of ultrasonography, computed tomography, MRI, and biopsy, used in conjunction with the patient's clinical presentation. However, new and developing advances in MR technology has lead to the development of MR Nephro-Urography (MRNU), which provides both anatomic and functional evaluation of the kidney in a single examination. It is expected that the increasing use of MRNU will have a significant impact on the management of renal transplant patients. This review describes MRNU methodology, examines known posttransplant complications, and highlights the utility of MRNU as a comprehensive imaging examination to diagnose both surgical and medical complications of the transplant kidney.

Contribution of 99Tcm-DMSA scintigraphy to aetiological diagnosis in renal transplant recipients with impaired renal function

Routine 99Tcm-dimercaptosuccinic acid (DMSA) scintigraphy was performed in a series of 24 kidney transplant recipients with impaired renal function. Diagnostic findings on planar and tomoscintigraphic acquisitions obtained 3 and 4 h after the injection of 130-140 MBq 99Tcm-DMSA were compared with the diagnosis established by fine-needle biopsy in 13 patients and by clinical course and other examinations (ultrasonography, bacteriology) in 11 patients. Renal scintigraphy demonstrated segmental defects in patients with rejection (n = 2/6), immunosuppressor nephrotoxicity (n = 2/6), acute pyelonephritis (n = 3/3), renal artery stenosis (n = 1/1) and obstructive lymphocele (n = 1/1). Diffuse lack of uptake was observed in one patient with severe renal failure. The scintigram was normal in 14 patients, including three with lesions histologically compatible with graft rejection or immunosuppressor nephrotoxicity. 99Tcm-DMSA was thus found to contribute little to the differential diagnosis between graft rejection and immunosuppressor nephrotoxicity. However, it may be useful for identifying specific disease states, particularly acute pyelonephritis, seen as well-delimited systematized defects. 99Tcm-DMSA scintigraphy could also be used in late follow-up after pyelonephritis in renal transplant recipients.

Loss of corticomedullary demarcation on magnetic resonance imaging: an index of biopsy-proven acute renal transplant dysfunction

A prospective study of 19 cadaveric renal allograft recipients with suspected graft rejection was undertaken to compare the histological findings of the renal transplant biopsy with the results of magnetic resonance imaging (MRI). All 19 patients underwent a biopsy of the transplant allograft. Biopsy results included acute cellular rejection, acute vascular rejection, chronic vascular rejection (CVR), and acute tubular necrosis (ATN). Recipients of cadaveric renal allografts with normal function served as controls. The control showed distinct corticomedullary demarcation (CMD) on T1-weighted imaging. In contrast, CMD was absent or diminished in all the patients with suspected allograft rejection. Unfortunately, the loss of CMD did not correlate with a specific biopsy diagnosis. Patients with biopsy evidence of acute and chronic rejection or ATN demonstrated loss of CMD with similar image patterns. In conclusion, MRI is capable of detecting renal allograft dysfunction, but does not permit the determination of a specific cause.

Non-obstructive kidney transplant dysfunction: magnetic resonance evaluation

The value of magnetic resonance imaging in the differential diagnosis of non-obstructive dysfunction of renal allografts was studied in a series of 58 examinations at 0.5 T. Four parameters were evaluated: the corticomedullary differentiation; the relative thickness of the cortex; the evolution, with echo number, of the relative signal intensities of kidney parenchyma and adjacent fatty tissue on images generated by a long time to repeat multiecho sequence; and the proximal vascularization. The loss of corticomedullary differentiation is the major finding in acute rejection, but it is not specific as it is also observed in chronic rejection and in the much rarer acute glomerulonephritis. Thickening of the cortex is helpful for the detection of rejected transplants with visible corticomedullary delineation (26% of the cases). Uncomplicated acute tubular necrosis appears as a normal transplant.

Magnetic resonance imaging of renal transplants: initial experience

Magnetic resonance imaging (MRI) was used in 45 renal transplant investigations (38 patients) using a Picker 0.15 T resistive system and a localized surface coil. An attempt was made to define optimal sequences in the evaluation of both normal and pathological transplants. Three sequences were found to be of value; a T1 weighted sequence (IR2180/700/40) to assess corticomedullary differentiation and its loss in acute rejection and acute tubular necrosis, a T2 weighted sequence (SE2000/80) for assessment of renal vessels and disturbances in blood supply, and a STIR (short tau inversion recovery) sequence (IR800/100/40) to define further the distended collecting system in obstruction and the presence of any perirenal collection. Encouraging results have been obtained, particularly in cases of acute rejection. It is suggested that the MRI scan is a useful screening test in cases of clinical doubt and may even obviate biopsy in some cases.