What precautions are necessary for a patient undergoing a DTPA scan?

Precautions for Patients Undergoing a DTPA Scan

Patients undergoing a DTPA (diethylenetriamine penta-acetic acid) scan should be well-hydrated before and for at least one day after the procedure, avoid food for at least 4 hours prior to the scan, and empty their bladder immediately before imaging to minimize radiation exposure and optimize image quality. 1, 2

Patient Preparation

Pre-Scan Requirements

• Fasting: Fast for at least 4 hours before the scan 3
• Hydration:
  • Maintain adequate hydration by drinking approximately 1 liter of plain water during the 2 hours before the procedure 3, 1
  • Continue hydration for at least 1 day after the procedure to reduce radiation exposure 2, 1
• Medications:
  • Avoid nonsteroidal anti-inflammatory drugs before the procedure as they can cause transient changes in glomerular filtration rate 2
  • Discontinue medications that could transiently affect kidney function 2
  • If on somatostatin analogue therapy, this may need to be temporarily interrupted (short-acting analogues for 24 hours, long-acting preparations for 5-6 weeks) 2

Day of Scan

• Bladder emptying: Void immediately before the scan to reduce bladder activity, minimize radiation exposure, and reduce scatter artifacts 3, 1
• Positioning: Patients should be able to lie still for the duration of the scan (typically 30-45 minutes) 3
• Clothing: Remove all metallic items, including jewelry and clothing with metal components 3

Special Considerations

Medical Conditions

• Renal failure: In patients with significant renal failure, high blood pool activity may hamper visualization of uptake foci; interpretable scans can be obtained after hemodialysis 2
• Edema/ascites: Plasma clearance methods may be inaccurate in patients with edema or ascites; alternative methods should be considered 2
• Acute illness: Reschedule the scan if the patient has an acute illness that may transiently affect kidney function 2

Contrast Media

• Prior contrast studies: Wait at least 7 days after administration of iodinated contrast media before undergoing a DTPA scan to ensure complete washout 2

Pregnancy and Breastfeeding

• Pregnancy: Clinical decision is necessary to weigh benefits against possible harm in pregnant patients 2
• Breastfeeding: Should be discontinued for an appropriate period after the procedure (typically 4 days for similar radiopharmaceuticals) 2

Hydration Status Impact

Hydration status significantly affects DTPA scan results. In dehydrated states, parameters such as time to maximum activity, time from maximum activity to half activity, residual cortical activity, and mean transit time are delayed compared to adequately hydrated states 4. Dehydration can lead to false positive curve patterns on renograms, potentially resulting in misdiagnosis 4.

Radiation Considerations

• The effective dose equivalent is approximately 0.054 mSv/MBq in adults and 0.16 mSv/MBq in children 2
• Proper hydration and frequent voiding after the procedure help minimize radiation exposure 1

Common Pitfalls to Avoid

1. Inadequate hydration: Can lead to concentrated tracer in the urinary tract causing artifacts and false interpretations 3, 4
2. Recent exercise: Can alter tracer distribution; avoid strenuous exercise for at least 6 hours before the scan 3
3. Failure to empty bladder: Can increase radiation exposure and create scatter artifacts 3
4. Dehydration: May cause false positive results by altering renogram patterns 4
5. Recent contrast studies: Can interfere with scan results if performed within 7 days 2

By following these precautions, patients can ensure optimal image quality and diagnostic accuracy while minimizing radiation exposure during DTPA scans.