الفهرس 
Anatomy of the kidneyOnly 14 pages are availabe for public view
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Abstract
Renal tumors account for 2–3% of all malignant diseases in adults. The vast majority of renal cancers (>90%) are various forms of renal cell carcinoma (RCC) originating from different parts of the nephron. Renal cell carcinoma (RCC) accounts for 80–90% of all renal malignancies and the overall 5 year survival rate is approximately 45%.Surgical resection is used frequently to cure RCC, detailed characterization of the tumors before operation is helpful for clinical decision and prognosis evaluation.
MRI is a powerful and versatile tool for single modality evaluation of potential renal malignancies. Among the absence of radiation exposure and the rich soft-tissue contrast, MRI has inherent three-dimensional imaging capabilities providing images in all three orthogonal planes, as well as in oblique or even double oblique orientations.
A well-planned high field MRI examination can simultaneously detect and characterize renal tumors. MRI generates the highest intrinsic soft tissue contrast of any cross-sectional imaging modality.MRU has evolved to become a serious clinical alternative to conventional IVU and CTU. There is evidence to suggest that MRI has a higher accuracy than CT in the evaluation of early lymph node spread, when venous involvement is suspected, MRI is the one used to detect. Diffusion weighted MRI is able to differentiate between normal and neoplastic renal parenchyma.
Contrast enhanced sequences (pre-contrast and post-contrast images) in arterial, corticomedullary and nephrographic phases are obtained. Gadolinium-enhanced images are used for lesion detection and characterization, detection of perinephric invasion or its absence can be improved by using fat-suppressed contrast-enhanced images, with enhancement of previously low signal intensity areas in the perinephric tissue indicating extra renal tumor extension and for evaluation of the presence and pattern of enhancement in a renal mass. Multiplanar reconstruction may be performed if necessary to delineate better the spatial relationship of the renal mass to adjacent anatomic structures
MRU is more sensitive for diagnosing the cause of urinary tract obstruction due to causes other than urolithiasis compared with unenhanced CT. Although urothelial neoplasms can be detected with MRU, its sensitivity remains to be determined and probably is lower than CT urography.
MRU, to date, has been reserved for patients who cannot receive iodinated contrast material or for whom exposure to ionizing radiation is particularly undesirable. Currently, MRU is most commonly indicated in children and pregnant patients with dilated collecting systems. . Functional data that can be obtained with MRU include renal transit time, differential renal function, and estimated GFR.
The kidney is a particularly interesting organ to study with DW MR imaging techniques because of its high blood flow and water transport functions. DW imaging can be used to differentiate solid RCCs from oncocytomas and characterize the histologic subtypes of RCC, Adding the DWI to a routine MRI protocol requires only few minutes and does not cause patient discomfort.
DWI and ADC values were helpful in the diagnosis and quantitative measurement of tumors during recent years. A malignant tumor often has a larger cell diameter and denser cellularity than normal tissue and the cell density may be indicative of tumor aggressiveness. Restriction of water diffusion is found to be a common feature of tumors. ADC values are quantitative expressions of diffusion characteristics of tissues, and ADC values are related to the proportion of extracellular and intracellular components. Since a malignant tumor often has a larger cell diameter and cellularity denser than normal tissue, Studies showed that most malignant tumors exhibit higher signal intensity and a lower ADC value than benign lesions and normal tissues, areas of restricted diffusion (eg, highly cellular tissues) will appear bright on the diffusion-weighted images and dark on the ADC map, as opposed to areas of simple T2 prolongation (eg, edema or fluid), which will demonstrate high signal intensity on both the diffusion-weighted images and the ADC map.
Despite its accuracy in staging RCC, MRI does have several disadvantages; it is limited by patient cooperation because MRI is more sensitive to motion artifact than CT. Although The most important technical challenges that we have to deal with in abdominal MRI can be summarized into signal voids, ghosting, blurring, susceptibility, and chemical shift artifacts .Various techniques have been developed to tackle with the previous problems, including signal averaging, chemical selective fat suppression, administration of negative GI contrast agents, spatially selective saturation pulses, respiratory triggering, breath-holding, and flow compensation.
To conclude, the study of renal masses should be performed with state-of-the-art equipments, using phased array coils, fast sequences, and mainly dynamic gadolinium enhanced sequences with MRU and the still progressing DWI. The main indication is to solve equivocal case in ultrasonography and computed tomography and if readily available MRI can be performed to stage renal neoplasms to differentiate benign versus malignant masses and for the follow-up of patients operated for renal tumors