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Introduction to Renal CT Scan Protocol

Hisham AlKhatib, M.D.Consultant Radiologist

Common Clinical Problems in the Kidney • suspected renal calculus

• suspected renal infection

• r/o renal mass

• evaluate renal mass (cyst vs. tumor)

• stage renal cancer

• evaluate hematuria

• trauma

• ? renal artery stenosis

• ? renal vein thrombosis

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Patient preparation and technique

Before study

• Fasting 4 hours

• Creatinine level

• Pertinent history to decide the protocol needed

• Protocol design

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What are the risk factors for contrast induced acute

renal failure?

• preexisting renal failure

• diabetes mellitus

• dehydration

• cardiovascular disease and diuretics

• age over 75 years

• multiple myeloma (in dehydrated person)

• hypertension

• uricosuria

Scanning phases

• precontrast phase

• arterial

• corticomedullary phase

• nephrographic phase

• excretory phase

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Noncontrast scan

• baseline density measurements for evaluating renal masses or renal cysts

• urolithiasis, nephrolithiasis, renal calcifications

• in patients unable to receive intravenous contrast (i.e., contrast allergy, poor renal function, etc.).

Unenhanced CT of the Kidney

• Optimal Phase For Detection of-- Calculus- Cyst versus mass (HDRC versus solid tumor)- High density renal cyst- Identify location of the kidneys to define coverage

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arterial phase

• is a short phase that occurs about 15–25 seconds after the start of intravenous contrast medium injection and is marked by maximum opacification of the renal arteries.

• The renal veins also usually opacify in the late arterial phase.

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corticomedullary (angionephrographic) phase

• The starts at about 30–40 seconds after the start of contrast medium injection.

• There is intense enhancement of the renal cortex due to preferential arterial flow to the cortex and glomerular filtration of the contrast material, while the medulla remains relatively less enhanced.

• This is also the best phase for maximum opacification of the renal veins.

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nephrographic phase

• begins at 80–120 seconds after the start of contrast medium injection.

• Tubular filtration of contrast material produces homogeneous enhancement of the renal parenchyma.

• the best phase for detection of subtle parenchymal lesions.

Nephrographic Phase

• (60-140 sec):

• Optimal Phase For Detection of-- Renal lesion detection- Pyelonephritis- Tumor invasion (renal vein/IVC)- Characterize lesion density- Perfusion changes- Renal vein or IVC thrombus

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excretory or urographic phase

• starts at 180 seconds (3 minutes) after the start of contrast medium injection.

• Excretion of the contrast material allows opacification of the calyces, renal pelvises, and ureters, while the intensity of the nephrogram progressively declines.

• routinely acquire excretory phase images at 4–5 minutes to ensure opacification of the ureters.

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Excretory (pyelogram)Phase

• delayed scans ( 3-5 minutes)

• Contrast in calyces ,pelvis and ureters

• Excretory Phase Imaging is optimal for detecting;

– pathology in the renal pelvis or collecting system

– visualization of the renal parenchyma

– pathology in the ureter

CT Urography: Indications per Society of Uroradiology

•

- Painless gross and microscopic hematuria- Suspected transitional cell carcinoma- Follow up of transitional cell carcinoma- Recurrent UTI’s- Congenital anomalies- Renal trauma

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Ct urogram

Split Bolus Technique for CT Urography

- Scan without contrast from top of kidneys thru the base of the bladder- Inject 50 ml of iodixanol at 3 cc/sec- Wait 5 minutes- Inject 80 ml of iodixanol at 3 cc/sec- Wait 100 seconds and then scan the patient from the top of the kidneys thru the pelvis (combined nephrographic and excretory phase)

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