What are the guidelines for a Nuclear Medicine (NM) kidney scan?

Guidelines for Nuclear Medicine Kidney Scan

Nuclear medicine kidney scans should include proper patient preparation, appropriate radiopharmaceutical selection, standardized imaging protocols, and follow-up recommendations based on the specific clinical indication, with particular attention to hydration status and renal function assessment prior to the procedure. 1

Patient Preparation

• Pre-scan Assessment:

  • Determine baseline renal function through serum creatinine and BUN measurements 2
  • Calculate creatinine clearance for patients with suspected renal impairment 2
  • Consider more precise GFR measurement with 99mTc-DTPA or 51Cr-EDTA for high-risk patients 2

• Hydration Requirements:

  • Ensure adequate hydration before the procedure 1
  • Oral hydration is generally sufficient (water, soft drinks)
  • IV hydration may be necessary for debilitated or fasting patients 1

• Medication Considerations:

  • Verify and document patient's current medications 1
  • Avoid nephrotoxic medications before and after nuclear studies when possible 2
  • For patients requiring contrast studies, consider N-acetylcysteine pretreatment 2

• Patient Positioning:

  • Position patient supine with arms alongside body 1
  • Use support devices (foam pallets) to reduce artifacts 1
  • Ensure patient comfort to minimize movement artifacts 1

Radiopharmaceutical Selection

Common Tracers for Kidney Imaging:

1. 99mTc-DTPA:

   • Primary use: Glomerular filtration assessment and renal perfusion 3
   • Dosage: Adjust based on patient weight and renal function 2
   • Particularly useful for GFR measurement 2

2. 99mTc-MAG3:

   • Primary use: Evaluation of urinary tract dilatations and drainage 4
   • Provides information on differential renal function 4
   • Preferred for diuretic renal scans in children 4

3. 99mTc-DMSA:

   • Primary use: Renal cortical imaging 4
   • Excellent for detecting acute pyelonephritis, renal scars, and dysplasia 4
   • Provides accurate determination of differential renal function 4

Imaging Protocol

Standard Acquisition:

• Patient Position:

  • Supine position with arms alongside body 1
  • Avoid CT truncation artifacts 1

• Field of View:

  • Extended field of view recommended for both CT and PET components 1
  • Coverage from skull vertex to toes (or at least to knees) 1

• Acquisition Direction:

  • Start from toes and proceed cranially to ensure minimal bladder filling 1
  • This reduces misalignment with CT component and minimizes scatter artifacts 1

• Timing:

  • For standard step-and-shoot PET/CT: 2-3 minutes per bed position 1
  • Adjust accordingly for continuous motion or large axial FOV PET systems 1

Special Considerations for Diuretic Renal Scans:

• Empty bladder before acquisition 1

  • Full bladder can slow drainage and increase likelihood of vesicoureteral reflux 1
  • For young children, stimulate urination by sound of running water or positioning upright 1

• Consider bladder catheterization only in specific cases (some diuretic renal scans) 1

  • Generally avoided due to risk of infection and increased patient discomfort 1

Post-Procedure Care

• Increase hydration and encourage frequent micturition throughout the day 1
• Replace diapers more frequently in pediatric patients to reduce radiation exposure 1
• Monitor for adverse reactions 2
• For therapeutic nuclear medicine procedures, complete blood count every 2-4 weeks 2

Special Considerations for Trauma Cases

• For suspected renal trauma with urinary extravasation:

  • IV contrast enhanced abdominal/pelvic CT with delayed imaging (urogram) is the first-line imaging modality for stable trauma patients 1
  • Nuclear medicine studies may be used for follow-up of complications such as urinoma 1

• For follow-up of deep renal lacerations (AAST Grade IV-V):

  • CT imaging after 48 hours is recommended 1
  • Nuclear medicine studies may help assess renal function in the affected kidney 1

Pitfalls and Caveats

• Hydration Status:

  • Inadequate hydration can lead to poor tracer excretion and false positive results 1
  • Excessive hydration may cause rapid tracer washout and false negative results 1

• Medication Interference:

  • Certain medications can affect tracer uptake and excretion 1
  • Document all medications and consider their potential impact on scan interpretation 1

• Patient Movement:

  • Movement during acquisition can cause misregistration artifacts 1
  • Consider sedation only when absolutely necessary, especially in pediatric patients 1

• Interpretation Challenges:

  • Evaluate both attenuation-corrected and non-attenuation-corrected images to detect artifacts 1
  • Review images prior to patient departure to confirm technical adequacy 1

By following these guidelines, nuclear medicine kidney scans can provide valuable diagnostic information while minimizing radiation exposure and optimizing patient comfort and safety.