the corticomedullary, nephrographic, and excretory phases, with little or no respiratory or patient- motion artifacts [7]. Multiphase imaging of the kid- ney thus permits not only high-resolution imaging of the renal parenchyma but also that of its vascula- ture and collecting systems [8]. Comprehensive evaluation of renal masses by CT requires a dedicated renal CT protocol. The various phases of CT imaging of the kidney include pre- contrast, arterial (15–25 second delay), corticome- dullary (35–80 second delay), nephrographic (85–180 second delay) and excretory (3 minutes or more) phases [7]. Preliminary noncontrast scans are used to detect calcifications and allow quantifi- cation of enhancement on the postcontrast scans. However, unenhanced scans alone are inadequate for lesion characterization because no information exists regarding lesion vascularity/enhancement. In addition, the precontrast phase provides the low- est sensitivity for detecting renal masses. During the corticomedullary phase (CMP), con- trast resides in the cortical capillaries, peritubular cells, proximal convoluted tubules, and columns of Bertin [9]. Optimal time delay for the CMP phase depends on the rate of injection, the amount of contrast material administered, and the patient’s cardiac output. Advantages of the CMP include the differentiation of normal variants of renal paren- chyma from renal masses and the better depiction of tumor hypervascularity [10–12]. Peak enhance- ment of renal vessels during early CMP also provides information on vascular anatomy and pa- tency [7,9]. Two main disadvantages of the CMP are the difficulty in detecting small hypovascular lesions of the renal medulla (a low attenuation region during the CMP) (Fig. 7) and detecting small hypervascular tumors of the cortex (a high attenuation region during the CMP). Small hyper- vascular cortical RCCs may enhance to the same de- gree as the normal cortex, whereas hypovascular tumors of the medulla may not enhance during this phase [9–13]. The nephrographic phase is obtained during the passage of contrast material through the renal tubu- lar system. During the nephrographic phase, which usually begins 80 to 120 seconds after contrast injection, the renal parenchyma enhances homoge- neously. Although the duration of the nephro- graphic phase is not clearly defined, for practical reasons it may be divided into an early phase and a late phase, with the latter overlapping the excre- tory phase [7,9]. The nephrographic phase is con- sidered the optimal phase for the detection and characterization of small renal masses [14]. The excretory phase begins when contrast material is ex- creted into the collecting system, 3 to 5 minutes after contrast administration. During this phase, the nephrogram remains homogeneous but its at- tenuation is diminished. A summary of the phases of renal enhancement for MDCT, including advan- tages and disadvantages, is shown in Table 1. In many cases, the pattern of enhancement within a renal neoplasm is dense and irregular, and in such cases, subjective assessment for en- hancement is sufficient. Even if enhancement is not particularly dense but is irregular or nodular within the mass, the mass is most likely neoplastic. However, in some cases of hypovascular masses, enhancement may be more subtle and uniform. In such cases, it is useful to compare attenuation measurements between the precontrast and each of the postcontrast phases. Because enhancement of the adjacent normal renal parenchyma results in some degree of beam hardening, attenuation measurements often drift upward slightly, even in proven simple cysts. This drift is more pronounced with smaller, predominantly intrarenal lesions, Fig. 5. AML with no detectable fat. A soft tissue mass (arrow) (M) is exophytic from the posterior aspect of the right kidney (K). Although this finding was path- ologically proved to be an AML, no fat was detected at imaging, even on retrospective review. Fig. 6. Multiplanar reformation of the kidney. Isotro- pic scan acquisition and data reconstruction results in multiplanar image quality comparable to the source axial images. In this case of multicentric RCC, the dis- tribution of three renal masses (arrows) can be seen on a single coronal image. Cross-sectional Imaging Evaluation of Renal Masses 97 Imaging of Hematuria Owen J. O’Connor, MD, MRCSI a,b , Sean E. McSweeney, MB, MRCSI, FFR(RCSI) a,b , Michael M. Maher, MD,FRCSI,FFR(RCSI),FRCR a,b, * Hematuria may have a number of causes, the more common being urinary tract calculi, urinary tract infection (UTI), urinary tract neoplasms (including renal cell carcinoma and urothelial tu- mors), trauma to the urinary tract, and renal paren- chymal disease [1–5]. Hematuria is broadly divided into macroscopic and microscopic varieties [6]. He- maturia is described as macroscopic or frank when blood is visible within the urine [7,8]. A diagnosis of microscopic (occult) hematuria requires the detection of three to five red cells per high powered view, or greater than five red blood cells per 0.9 mm 3 of urine [5,9]. The prevalence of microscopic hematuria in asymptomatic individuals is approxi- mately 2.5% [10]. Investigation of hematuria The investigation of hematuria should begin with a search for bacteruria or pyuria. If either is present, a urine culture should be ordered to confirm UTI. In the absence of infection, the next step is to distin- guish glomerular and nonglomerular sources of hematuria. If the findings suggest a glomerular source of bleeding, no urologic evaluation is neces- sary, at least initially, and referral to a nephrologist is indicated [11]. Indeed, there is a body of opinion that suggests that patients aged less than 40 years and presenting with hematuria can be investigated initially by a nephrologist, as the risk of urologic malignancy is low [6]. The results of a recent study by Edwards and colleagues [6] support this policy. If a glomerular source is excluded in those with risk factors for urologic disease, urologic referral is advised [12]. Risk factors include smoking history, occupational exposure to chemicals or dyes, history of macroscopic hematuria, age greater than 40 years, previous urologic history, symptoms of irrita- tive voiding, UTIs, analgesic abuse, cyclophospha- mide intake, and history of pelvic irradiation. RADIOLOGIC CLINICS OF NORTH AMERICA Radiol Clin N Am 46 (2008) 113–132 a Department of Radiology, Cork University Hospital, Wilton, Cork, Ireland b Mercy University Hospital and University College Cork, Cork, Ireland * Corresponding author. Department of Radiology, Cork University Hospital, Wilton, Cork, Ireland. E-mail address: m.maher@ucc.ie (M.M. Maher). - Investigation of hematuria - Common urologic causes of hematuria Urinary tract calculi Malignancy Macroscopic and microscopic hematuria and prevalence of urologic disease - Imaging of hematuria Conventional radiography Intravenous urography and excretion urography Retrograde pyelography Ultrasound - Multidetector CT urography Indications for multidetector CT urography Imaging protocol Image interpretation Current status of multidetector CTurography in the evaluation of the patient with hematuria - MR urography How should we image the patient with hematuria in 2008? - Summary - References 113 0033-8389/08/$ – see front matter ª 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.rcl.2008.01.007 radiologic.theclinics.com . respiratory or patient- motion artifacts [7] . Multiphase imaging of the kid- ney thus permits not only high-resolution imaging of the renal parenchyma but also that of its vascula- ture and collecting. being urinary tract calculi, urinary tract infection (UTI), urinary tract neoplasms (including renal cell carcinoma and urothelial tu- mors), trauma to the urinary tract, and renal paren- chymal disease. of multicentric RCC, the dis- tribution of three renal masses (arrows) can be seen on a single coronal image. Cross-sectional Imaging Evaluation of Renal Masses 97 Imaging of Hematuria Owen J.