Imaging Pearls ❯ Kidney ❯ CT Urography
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- “Our institutional CTU protocol consists of non-contrast images through the kidneys, arterial phase images from the kidneys to the bladder, venous phase images through the kidneys, and 5-7 minute excretory phase images from the kidneys to the bladder. In young patients with low riskof bladder cancer, we acquire the arterial phase only through the kidneys to reduce radiation dose. CTU is readily available across academic and community practices and across urban and rural settings. CTU is available 24 hours a day, 7 days a week, 365 days a year, and is ideal for emergency and other acute settings in addition to for routine outpatient evaluations. The examination acquisition is fast, usually in the order of 10-20 minutes, and is easily tolerated by most patients, and each phase in the CTU can be easily acquired within a single breath hold.”
MR Urography: Counterpoint-CT Provides Better Diagnostic Performance and Value Compared to MRI for Urographic Imaging.
Chu LC, Fishman EK.
AJR Am J Roentgenol. 2024 Jan 31. doi: 10.2214/AJR.24.30859. Epub ahead of print. - “CTU has higher spatial resolution, which is essential in the detection of subtle pathology (i.e., small non-obstructing stones, subtle urothelial thickening, and papillary necrosis). The submillimeter isotropic acquisition of modern CT technology can be reconstructed into 2D axial, coronal, sagittal, and 3D maximum intensity projection (MIP), volume rendering (VR), or cinematic rendering (CR) images for optimal visualization of pathology. The main drawback with CTU is radiation dose, which can be addressed with various mitigation strategies. Some centers use a split-bolus technique to reduce the number of phases phases. Other centers use dual-energy CT (DECT) to eliminate the need for a non-contrast phase in certain patients. Radiation dose can be significantly reduced with iterative reconstruction and deep learning-based reconstruction techniques. The advent of photon counting detector CT offers additional opportunities for dose reduction and improved spatial resolution.”
MR Urography: Counterpoint-CT Provides Better Diagnostic Performance and Value Compared to MRI for Urographic Imaging.
Chu LC, Fishman EK.
AJR Am J Roentgenol. 2024 Jan 31. doi: 10.2214/AJR.24.30859. Epub ahead of print. - “CTU is truly a one-stop shop examination that covers pathology from the kidneys to bladder, ranging from stones, trauma, vascular, inflammation, and neoplasms. Without a doubt, noncontrast CT is the best modality for stone detection. Small non-obstructing stones are difficult to detect on MRI. Therefore, MRU alone may miss a diagnosis that is the most common cause of hematuria. Patients with a “negative” MRU may need to undergo additional non-contrast CT to exclude stone disease, leading to redundancy. Furthermore, stone composition can be determined based on Hounsfield unit measurements or dual-energy material decomposition and may be helpful in guiding clinical management and in preventing future recurrence.”
MR Urography: Counterpoint-CT Provides Better Diagnostic Performance and Value Compared to MRI for Urographic Imaging.
Chu LC, Fishman EK.
AJR Am J Roentgenol. 2024 Jan 31. doi: 10.2214/AJR.24.30859. Epub ahead of print. - “CTU has excellent diagnostic performance in the detection of urothelial malignancy, with pooled sensitivity of 96% and pooled specificity of 99% in a meta-analysis. The subtle urothelial thickening and enhancement in patients with urothelial malignancy can be easily missed due to slice thickness or other artifacts in MRI. Previous studies comparing the diagnostic performance of CTU and MRU have shown that CTU improved visibility of urothelial structures, diagnostic confidence, and accuracy in the diagnosis of urothelial malignancy.”
MR Urography: Counterpoint-CT Provides Better Diagnostic Performance and Value Compared to MRI for Urographic Imaging.
Chu LC, Fishman EK.
AJR Am J Roentgenol. 2024 Jan 31. doi: 10.2214/AJR.24.30859. Epub ahead of print. - “Finally, in this era of value-based care, we must also consider the cost of these imaging examinations. In 2024, national Medicare non-facility price for CTU [CPT code 74178 (abdomen and pelvis CT, with and without IV contrast media)] is $343.16, whereas the nonfacility price for MRU [both CPT codes 72197 (pelvis MRI, with and without IV contrast media) and 74183 (abdomen MRI, with and without IV contrast media)] is $681.73. MRU costs twice as much as CTU by this estimation, and it does not have any proven benefit compared to CTU beyond radiation dose savings. Since MRI is a limited resource, it should be reserved for pediatric or pregnant patients, or for other clinical indications (e.g. brain, spine) in which MRI has proven diagnostic utility compared to CT.”
MR Urography: Counterpoint-CT Provides Better Diagnostic Performance and Value Compared to MRI for Urographic Imaging.
Chu LC, Fishman EK.
AJR Am J Roentgenol. 2024 Jan 31. doi: 10.2214/AJR.24.30859. Epub ahead of print. - “Given all of the stated reasons, radiology society guidelines generally endorse CTU over MRU. The American College of Radiology (ACR) Appropriateness Criteria for hematuria describes several clinical scenarios and rates the appropriateness of various imaging modalities [5]. Both CTU and MRU are rated as “Usually Appropriate” for patients presenting with gross hematuria. However, CTU (“Usually Appropriate) has a higher rating compared to MRU (“May Be Appropriate”) for patients who present with microhematuria and who have underlying risk factors for malignancy. MRU is only rated higher than CTU in the specialized scenario of imaging during pregnancy. Similarly, the American Urological Society recommends CTU and cystoscopy as first-line modalities for patients deemed high risk for malignancy. MRU is recommended in patients with contraindications to CTU, such as patients with chronic kidney disease or allergy to iodinated contrast media. In conclusion, CTU has superior diagnostic performance and is more cost effective compared to MRU and should be used as the first-line imaging modality in the evaluation of hematuria. MRU should be reserved for only a subset of patients.”
MR Urography: Counterpoint-CT Provides Better Diagnostic Performance and Value Compared to MRI for Urographic Imaging.
Chu LC, Fishman EK.
AJR Am J Roentgenol. 2024 Jan 31. doi: 10.2214/AJR.24.30859. Epub ahead of print.
- “Excretory phase imaging of CT urography can be an essential tool for detecting and appropriately characterizing urinary tract malignancies, renal papillary and medullary abnormalities, CT radiolucent stones, congenital abnormalities, certain chronic inflammatory conditions, and perinephric collections.”
What a difference a delay makes! CT urogram: a pictorial essay
Noorbakhsh A et al.
Abdominal Radiology - “Despite its routine use, there is currently no consensus protocol for performing CT urography. The most common protocol is a three-phase technique, which carries potential for substantial radiation exposure to the patient. In fitting with the ALARA (as low as reasonably achievable) principle, it is the duty of the radiologist to continually revisit and optimize protocols to achieve the lowest possible radiation dose while maintaining diagnostic image quality.”
What a difference a delay makes! CT urogram: a pictorial essay
Noorbakhsh A et al.
Abdominal Radiology - "CT urography has become the primary imaging modality for evaluation of hematuria, as well as in the staging and surveillance of urinary tract malignancies. CT urography includes a non-contrast phase and contrast-enhanced nephrographic and excretory (delayed) phases. While the three phases add to the diagnostic ability of CT urography, it also adds potential patient radiation dose. Several techniques including automatic exposure control, iterative reconstruction algorithms, higher noise tolerance, and split-bolus have been successfully used to mitigate dose.”
What a difference a delay makes! CT urogram: a pictorial essay
Noorbakhsh A et al.
Abdominal Radiology - “The CT urogram is most commonly performed as a three- phase computed tomography technique used to evaluate the kidneys and urinary collecting system. The three phases most commonly include a non-contrast phase, a nephrographic phase scanned at 80 to 120 s delay, and an excretory phase scanned at 10–15 min delay.”
What a difference a delay makes! CT urogram: a pictorial essay
Noorbakhsh A et al.
Abdominal Radiology - “Medullary sponge kidney, also known as renal tubular ectasia, is a congenital malformation of the medullary collecting ducts with cystic dilation seen on histology. Non-contrast images may only demonstrate medullary calcifications, which look similar to non-obstructing renal calculi. Contrast excretion through these abnormal collecting ducts is thought to be delayed, and results in the characteristic “paintbrush appearance” on excretory phase imaging]. While patients with medullary sponge kidney are often asymptomatic and the diagnosis discovered incidentally, medullary sponge kidney has been shown to be associated with increased risk of infection, increased renal calculus formation, and hematuria.”
What a difference a delay makes! CT urogram: a pictorial essay
Noorbakhsh A et al.
Abdominal Radiology - “On excretory phase imaging, papillary necrosis may be detected from contrast-opacified urine filling the cleft or cavity, or by contrast surrounding the sloughed necrotic tissue. Renal papillary necrosis has a wide differential of etiologies, including pyelonephritis, urinary collecting system obstruction, sickle cell disease, tuberculosis, cirrhosis, analgesic or alcohol abuse, renal vein thrombosis, diabetes mellitus, or systemic vasculitides . Other imaging findings may be relevant to narrowing the differential. A case with the classic “golf ball on tee” sign is described below, in which contrast opacifies into a central cavity—the golf ball—formed as a result of papillary necrosis.”
What a difference a delay makes! CT urogram: a pictorial essay
Noorbakhsh A et al.
Abdominal Radiology - Renal Papillary Necrosis: Causes
- pyelonephritis
- urinary collecting system obstruction
- sickle cell disease
- tuberculosis,
- cirrhosis,
- analgesic or alcohol abuse,
- renal vein thrombosis,
- diabetes mellitus
- systemic vasculitides - Ureteral Pseudodiverticulosis
Ureteral pseudodiverticulosis is a rare incidental finding typically discovered on CT urography during the work-up of other urinary tract disorders. It is seen on excretory phase imaging as multiple less than 5 mm outpouchings from the ureters. Although this entity is thought to be related to chronic inflammation, unlike ureteritis cystica, this entity is strongly associated with malignancy within the urinary tract, with one case series reporting up to 50% of cases demonstrating coexisting urothelial malignancy.
- How long is your routine delay on CT Urography?
The literature reports anywhere from 4-10 minutes
We currently use 4-5 minutes for routine CT with 8 minutes reserved for cases like suspected UPJ obstruction or where prior studies or the earlier images (arterial and/or venous) suggest a high grade obstruction - What are the advantage of a 4-5 minute delay for CT Urography?
The contrast in the pelvis and collecting systems is not too “dense/bright” causing artifact on 3D images which limit analysis of the calyceas
In a busy practice saving 5 minutes a case can provide improved throughput adding 5-10 extra slots in a 10 hour shift on a single scanner depending on study mix
- “ In our study of 1209 MDCT urography examinations, 6.8% of patients had clinically important or potentially important incidental findings requiring further investigation. Of these clinically significant results proved uncommon with acute findings diagnosed in 0.9% of patients and extraurinary malignancy confirmed in 0.4%.”
Incidental Clinically Important Extraurinary Findings at MDCT Urography for Hematuria Evaluation: Prevalence in 1209 Consecutive Examinations
Song JH et al.
AJR 2012; 199:618-622 - “ In conclusion, the prevalence of clinically important incidental extraurinary findings at MDCT urography performed for hematuria was 6.8%. Lung nodules were the most common incidental finding and malignant extraurinary neoplasm was found in 0.4% of cases.”
Incidental Clinically Important Extraurinary Findings at MDCT Urography for Hematuria Evaluation: Prevalence in 1209 Consecutive Examinations
Song JH et al.
AJR 2012; 199:618-622
- “Therefore the use of CT urography should be justified by weighing benefits versus risks, and CT urography protocols should be optimized to radiation dose. ”
Hematuria: A Problem-Based Imaging Algorithm Illustrating the Recent Dutch Guidelines on Hematuria
van der Molen AJ, Hovius MC
AJR 2012; 198:1256-1265
"Because many bladder neoplasms will not be detected by MDCT urography and more research is needed to determine the optimal technique for diagnosing bladder cancer, we think that MDCT urography cannot replace cystoscopy at present."
MDCT Urography: Exploring a New Paradigm for Imaging of Bladder Cancer
Cohan RH et al
AJR 2009; 192:1501-1508"MDCT urography now has a large role in the evaluation of patients with known and suspected bladder cancer. However, its precise role has not been established. Because many bladder neoplasms will not be detected by MDCT urography and more research is needed to determine the optimal technique for diagnosing bladder cancer, we think that MDCT urography cannot replace cystoscopy at present."
MDCT Urography: Exploring a New Paradigm for Imaging of Bladder Cancer
Cohan RH et al
AJR 2009; 192:1501-1508"3-dimensional images do provide another way of displaying the information and may be helpful in understanding complicated process (eg forniceal rupture), and anatomic relationships (eg congenital anomalies). 3-Dimensional images can also be used to help plan surgical and interventional radiology procedures."
Current Use of Computed Tomographic Urography: Survey of the Society of Uroradiology
Townsend BA et al.
J Comput Assist Tomogr 2009; 33: 96-100- CT Urography: Indications per Society of Uroradiology
- Painless gross and microscopic hematuria
- Suspected transitional cell carcinoma
- Followup of transitional cell carcinoma
- Recurrent UTI’s
- Congenital anomalies
- Renal trauma "Most uroradiologists use CT Urography in their practice today; some no longer perform IV urography. Variability in multidetector-row CT technique suggests that more research is needed to determine the optimal protocol."
Current Use of Computed Tomographic Urography: Survey of the Society of Uroradiology
Townsend BA et al.
J Comput Assist Tomogr 2009; 33: 96-100"CT Urography is essentially defined as a CT examination of the urinary tract before and after the administration of intravenous contrast material that includes excretory phase images."
What is the Current Role of CT Urography and MR Urography in the Evaluation of the Urinary Tract
Silverman SS, Leyendecker JR, Amis Jr ES
Radiology 2009; 250:309-323"Most uroradiologists perform CT urography using multidetector-row CT aline (79%) and use a 3-phase technique (52%) using a single injection (76%) of contrast media at 3 ml/sec (52%) without a compression devise (81%) and with the patient in the supine position (90%)."
Current Use of Computed Tomographic Urography: Survey of the Society of Uroradiology
Townsend BA et al.
J Comput Assist Tomogr 2009; 33:96-100"Most uroradiologists use CT urography in their practice today, some no longer perform IV urography. Variability in multidetector-row CT technique suggests that more research is needed to determine the optimal protocol."
Current Use of Computed Tomographic Urography: Survey of the Society of Uroradiology
Townsend BA et al.
J Comput Assist Tomogr 2009; 33:96-100- "The addition of a saline bolus offers no improvement, whereas the addition of enhanced CT digital radiography offers significant improvement in collecting system opacification during CT urography."
Opacification of the Genitourinary Collecting System During MDCT Urography with Enhanced CT Digital Radiography: Nonsaline versus Saline Bolus
Sudakoff GS et al.
AJR 2006:186:122-129.
- "Excretory phase CT with oral hydration opacified the calyx/infundibulum completely in 57% and nearly completely in 38%, opacified the renal pelvis completely in 94.5% and nearly completely in 3.5%."
Opacification of the Collecting System and Ureters on Excretory-Phase CT Using Oral Water as Contrast Medium
Kawamoto S, Horton KM, Fishman EK
AJR 2006; 186:136-140.
- "Excretory phase CT with oral hydration opacified the calyx/infundibulum completely in 57% and nearly completely in 38%, opacified the renal pelvis completely in 94.5% and nearly completely in 3.5%, and opacified the upper ureter completely in 78% and completely in 78% and nearly completely in 6.5%."
- Protocol
- Unenhanced CT from kidneys to bladder
- Nephrographic phase from diaphragm to iliac crests with 110 sec delay
- Excretory phase at 8 minutes from kidneys thru bladder
- Multidetector Row CT Urography in the Evaluation of Hematuria
Joffe SA et al
RadioGraphics 2003;23:1441-1456
- "At our institution, CT urography virtually replaced conventional urography in the evaluation of patients with hematuria and has proven successful in depicting a wide range of diseases affecting the urinary tract."
Multidetector CT Urography with Abdominal Compression and Three Dimensional Reconstruction
Chow LC et al.
AJR 2001;177:849-855