Nuclear Medicine
CLINICAL DECISION SUPPORT
[99mTc]Tc-diethylenetriaminepentaacetic acid, also known as
DTPA is a small molecule (393 g.mol-1), hardly chemically reactive, which freely diffuses in the extracellular space. As such, it is freely filtered in the glomeruli, not reabsorbed nor secreted. Its protein binding in plasma is low (<10%). It does not cross the brain blood barrier. Therefore, it shows the glomerular filtration, best reflect of the renal function and the extracellular space except in the brain. It crosses the alveolo-capillary membrane. It is not absorbed after ingestion.
[99mTc]Tc-DTPA is a good radiopharmaceutical to image relative renal function. In case of renal failure, because of its low extraction (20%), substitution with either DMSA or high-extraction tubular tracers ([99mTc]Tc-MAG3, [99mTc]Tc-bisicate, [123I]OIH) is recommended to achieve a high enough photon counting rate. [99mTc]Tc-DTPA gives comparable results to
[51Cr]Cr-EDTA for absolute clearance measurements.
The suggested activities to administer are
In paediatric nuclear medicine, the activities should be modified according to the EANM paediatric dosage card (https://www.eanm.org/publications/dosage-calculator/). The minimum recommended activity to administer is 20 MBq.
The effective dose for [99mTc]Tc-DTPA is 4.9 µSv/MBq in patients with normal renal function, for patients with abnormal renal function: 4.6 µSv/MBq [3].
The range in effective dose for [99mTc]Tc-DTPA is: 0.18-0.91 mSv per procedure.
Caveat:
“Effective Dose” is a protection quantity that provides a dose value related to the probability of health detriment to an adult reference person due to stochastic effects from exposure to low doses of ionizing radiation. It should not be used to quantify the radiation risk for a single individual associated with a particular nuclear medicine examination. It is used to characterize a certain examination in comparison to alternatives, but it should be emphasized that if the actual risk to a certain patient population is to be assessed, it is mandatory to apply risk factors (per mSv) that are appropriate for the gender, the age distribution and the disease state of that population."
After basic, visual assessment, the relative renal function should be measured by tracing renal ROIs and background ROIs (ideally perirenal rings) to get a corrected renogram. Quantifying methods include the Rutland-Patlak graph, which requires placing the heart into the field of view and the Integral method (area under the curve) taken between 2- and 3-min post-injection.
Global function can only be assessed from clearance measurement, requiring plasma sampling (camera-only methods are less reliable than eGFR and should be abandoned).
Care should be taken to ensure the patient is adequately hydrated before scanning
If diuresis renography is considered, prior hydration should be ensured, per os if possible, with circa 7 mL/kg body weight. When i.v. infusion must be used, a sodium-low solute must be used to ensure rapid diuresis, such as 5% glucose solution In infants, however, pure glucose solution is dangerous, and mixed saline-glucose solution is recommended
Detailed recommendations regarding the paediatric procedures are available in the The SNMMI and EANM Procedural Guidelines for Diuresis Renography in Infants and Children EANM Paediatrics Guidelines.[112]
Further information can be found in the published literature [113–116].