MRI of the kidney and urinary tract

Abstract

MRI of the kidney and urinary tract has evolved with advancements in MR technology combined with further radiologic experience. A combination of simple pulse sequences and the use of gadolinium (Gd) allow a comprehensive evaluation of the genitourinary system and facilitate the detection and accurate characterization of renal and urinary tract masses. In this review an MRI technique used to evaluate the kidneys and urinary tract is presented with an emphasis on the characterization of renal masses. RECENT TECHNOLOGICAL ADVANCES have expanded the role of MRI in evaluating the kidney and the urinary tract. The high spatial resolution and intrinsic tissue contrast of MRI have resulted in superb detection and characterization of renal and urinary tract anatomy and pathology. Recently, new imaging methods (such as parallel imaging) have resulted in sequences with higher spatial resolution that are performed during shorter breath-holds. Gadolinium (Gd) can be administered to patients without concern for contrastinduced nephrotoxicity, and is well tolerated by patients with a history of iodinated-contrast allergy. The superior safety profile of Gd combined with the lack of ionizing radiation makes MRI an ideal modality for evaluating the genitourinary system, especially in patients who have renal disease or have undergone nephrectomy or partial nephrectomy. In this review the MRI findings of the kidneys and urinary system are discussed with an emphasis on differentiating renal masses and evaluating the collecting system. TECHNIQUEA comprehensive examination of the kidneys and collecting system includes an evaluation of the renal vasculature, parenchyma, and collecting system. Unenhanced imaging includes axial breath-hold T1-weighted gradient-echo (GRE) (performed in and out of phase), coronal or axial breath-hold T2-weighted half-Fourier single-shot fast spin-echo (FSE), and breath-hold frequency-selective fat-suppressed 3D T1-weighted spoiled GRE (Table 1) sequences. The 3D fat-suppressed T1-weighted sequence is also performed at multiple time points after intravenous Gd administration, and may be used to produce MR angiographic, venous, parenchymal, and excretory phase images. If it is necessary to determine the renal arterial anatomy (e.g., in patients about to undergo partial nephrectomy), this sequence should be performed in the oblique-coronal plane during an arterial phase. Using the proper scan delay and acquiring the low-spatial-frequency (high contrast) lines of k-space during peak arterial enhancement are critical for minimizing venous contamination and preventing scanning before sufficient contrast reaches the aorta. The arterial phase may be optimized with the use of fluoroscopic triggering (1), an automated bolus detection technique (2), a timing run (3), or a "best-guess" method. With improved gradient strength, pulse sequences, and parallel imaging methods, a "time-resolved" approach can also be used, which will obviate the need for a timing strategy (4). Scanning with rapid temporal resolution (approxi...

Diffusion-weighted magnetic resonance imaging: new perspectives in the diagnostic pathway of non-complicated acute pyelonephritis

“…Gradient echo MRI has a semeiotics and diagnostic accuracy at least comparable to that of CT in the evaluation of morphological and functional impairment in renal inflammation and its complications [26]. Some downsides, however, must be noted.…”

Usefulness of Diffusion-Weighted MRI in Diagnosis of Upper Urinary Tract Cancer

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G e n it o u r i n a r y I m ag i ng • O r ig i n a l R e s e a rc h A combination of morphologic imaging techniques using iodinated radiocontrast media, such as excretory urography and conventional CT, has been used for diagnosing upper urinary tract cancer [1][2][3][4][5]. Recently, MDCT urography has emerged as a method for assessing the upper urinary tract and has improved detection of urothelial lesions, with sensitivity of 89% in a retrospective review [6,7].

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Dynamic magnetic resonance imaging in acute pyelonephritis

“…Of these, 279 were diagnostic and 163 were performed as follow-up studies (153 in patients with native kidneys and mezzo di contrasto organo-iodato, oltrechè l'evoluzione della tecnologia, hanno sicuramente contribuito al crescente consenso che negli ultimi anni la RM ha guadagnato nello studio delle infezioni delle vie urinarie, proponendola in alternativa alla TC, soprattutto nelle pazienti gravide o in età fertile e nei pazienti in cui l'uso di mezzo di contrasto organo-iodato sia controindicato [9,12]. La RM dinamica con chelati del gadolinio (GD-DTPA) consente infatti, al pari della TC, la valutazione morfologica e funzionale della compromissione flogistica renale e delle sue potenziali complicanze [13]. Il , followed by a 20-ml bolus of saline solution -delayed acquisitions in the axial and coronal planes with T1-weighted GRE sequences obtained 5-10 min after the beginning of contrast infusion The signs evaluated on diagnostic MRI to confirm or rule out the clinical suspicion of APN were: -change in renal volume (typically increased in the presence of inflammatory oedema) -preservation, decrease or loss of the corticomedullary gradient -focal or diffuse signal alterations on baseline scans -areas of nonenhancement after contrast administration (single, multiple, unilateral or bilateral) -phase of the examination during which nonenhancement was evident -site(s) of the signal alterations (upper renal pole, middle third, lower pole) -presence of abscess foci -extrarenal spread of the inflammatory process (perirenal and/or pararenal) -urinary tract dilatation (unilateral or bilateral)…”

“…L'assenza di radiazioni ionizzanti e dell'impiego di with CT, dynamic MRI with gadolinium chelates [gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA)] allows for morphological and functional evaluation of inflammatory renal disease and its potential complications [13]. The rationale for the systematic use of CT and MRI in APN lies in the fact that early diagnosis and monitoring of inflammation significantly influences both medical treatment and the duration and cost of hospitalisation.…”