Imaging in Renal Evaluation 

Renal imaging is central to diagnosing AKI, CKD, obstruction, stones, vascular disease, infection, trauma, and tumors. 

1️⃣ Ultrasound (USG) – First-Line Modality

A. Kidney Size

 High-yield:
Small kidneys + increased echogenicity = irreversible CKD

B. Cortical Thickness

Normal: 7–10 mm
Reduced thickness → chronicity marker

C. Echogenicity

• Normally cortex < liver/spleen
• Increased echogenicity → CKD

D. Hydronephrosis

Grading:

• Mild: Pelvicalyceal dilation only
• Moderate: Calyceal ballooning
• Severe: Cortical thinning

⚠ Exam pearl:USG may miss early obstruction (<24h)

E. Stones

• Hyperechoic focus
• Posterior acoustic shadow

Sensitivity less than CT.

F. Cysts

• Simple cyst: Thin wall, anechoic, posterior enhancement
• Complex cyst → requires CT characterization

2️⃣ Doppler Ultrasound

Indications

• Suspected renal artery stenosis
• Renal vein thrombosis
• Transplant kidney evaluation
• Unexplained AKI

Renal Resistive Index (RI)

RI = (Peak systolic velocity − End diastolic velocity) / Peak systolic velocity

Normal: < 0.7

0.8 → intrinsic renal disease

Renal Artery Stenosis Clues

• PSV > 180–200 cm/s
• Post-stenotic turbulence
• Kidney asymmetry

3️⃣ Non-Contrast CT (NCCT)

Gold Standard for:

➜ Urolithiasis

Sensitivity ~95–100%

Detects:

• Stone size
• Location
• Obstruction
• Secondary signs (hydroureter)

⚠ Does NOT assess function

4️⃣ Contrast-Enhanced CT (CECT)

Phases:

1. Non-contrast
2. Corticomedullary phase
3. Nephrographic phase
4. Excretory phase

Indications

A. Renal Tumor Evaluation

• Enhancement > 15–20 HU → solid tumor
• Staging

B. Pyelonephritis

• Striated nephrogram
• Abscess detection

C. Renal Trauma

• Laceration
• Hematoma
• Urine leak

D. Complicated UTI

5️⃣ CT Angiography (CTA)

Indications:

• Renal artery stenosis
• Aneurysm
• Dissection
• Fibromuscular dysplasia

High spatial resolution

6️⃣ MRI & MR Angiography

Advantages

• No radiation
• Excellent soft tissue contrast
• Alternative when iodinated contrast contraindicated

Gadolinium Risk

⚠ Nephrogenic systemic fibrosis (NSF) in severe CKD

Avoid if:

• eGFR < 30

7️⃣ Nuclear Medicine Scans

A. DTPA Scan(Diethylene Triamine Pentaacetic Acid Renography) Scan-Technetium-99m DTPA

• Cleared by: Glomerular filtration only
• NOT secreted or reabsorbed
• Measures GFR

B. MAG3 Renogram(Technetium-99m MAG3)

(Mercaptoacetyltriglycine Renography

• Tubular function,Cleared by: Tubular secretion
• Obstruction assessment

C. DMSA(Dimercaptosuccinic Acid Scan)

Binds to: Proximal tubular cortical cells

• Cortical scarring
• Reflux nephropathy (pediatrics)

8️⃣ Imaging in Acute Kidney Injury (AKI)

First test → Ultrasound

Look for:

• Obstruction
• Kidney size
• Parenchymal disease

CT only if:

• Stones suspected
• Complicated infection
• Trauma

9️⃣ Imaging in CKD

Typical USG findings:

• Small kidneys
• Increased echogenicity
• Cortical thinning

Large kidneys in CKD:

• Diabetes
• Amyloidosis
• Polycystic kidney disease

🔟 Imaging in Renal Transplant

USG + Doppler = first-line

Assess:

• Perfusion
• Arterial stenosis
• Perinephric collection
• Rejection suspicion

RI > 0.9 → poor prognosis

1️⃣1️⃣ Imaging in Specific Conditions

1️⃣2️⃣ Imaging Algorithm 

Step 1: AKI?

→ Ultrasound

Step 2: Obstruction?

→ Yes → CT if unclear

Step 3: Stone?

→ NCCT

Step 4: Mass?

→ CECT

Step 5: Vascular?

→ Doppler → CTA/MRA