Equis ISSN 2398-2977

Kidney: scintigraphy

Synonym(s): Renal nuclear imaging studies

Contributor(s): Russel Malton, Rachel Murray

Introduction

  • Early detection of alterations in renal function or blood flow are necessary in order to implement therapeutic strategies which may prevent progression of renal disease and damage.
  • Two of the most reliable measures of renal function are glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) or effective renal blood flow (ERBF).  
  • GFR relies on measurement of a substance which is freely filtered by the glomerulus and does not undergo synthesis, metabolism, secretion or re-absorption by the kidney. The substance must also not become bound to plasma proteins.
  • Indirect estimations of ERPF and ERBF can be made by measuring plasma clearance of an inert substance which is almost completely extracted from the blood on its first pass through the kidneys.
  • Radiopharmaceuticals have been developed which allow for non-invasive and technically simple estimations of GFR and ERPF/ERBF.
  • Measurement of radioactivity present in serial blood samples taken following intravenous administration of the relevant radiopharmaceuticals allows construction of plasma disappearance curves, from which the GFR or ERPF/ERBF can be calculated using a two-compartment model.
  • Direct scintigraphic imaging of the kidneys over a finite period following rapid IV injection of radiopharmaceuticals can be used to estimate GFR or ERBF. It also has the advantage of providing information on individual kidney function. This procedure in horses is less accurate because of difficulties in correcting for background activity and attenuation owing to various kidney depths. Movement of the patient within the study period also diminishes the accuracy of the procedure.  

Radiopharmaceutical for GFR

  • 99mTc-diethylenetriaminepentaacetic acid (DTPA).

Dosage

  • Plasma clearance studies: 111-148 MBq  (3-4 mCi).
  • Gamma camera percentage uptake: approximately 10x higher because of the relative low efficiency of the gamma camera compared to the high efficiency of the well detector used for plasma clearance counting.  
  • Gamma camera studies: a known, small fraction, of the total dose given to the horse needs to be counted as the pre-dose measurement because the total dose will overwhelm the gamma camera.
  • An advantage of using low dose radiopharmaceuticals is the relative safety for handling and monitoring horses undergoing treatment.

Radiopharmaceuticals for ERPF/ERBF

  • 131I-orthoiodohippuran  (131I-OIH).
  • 99mTc-mercaptoacetyltriglycine  (99mTc-MAG3).

Dosage

  • 131I-OIH: 11.25-14.8 MBq  (300-400 mCi).
  • 99mTc-MAG3: 185-296 MBq  (5-8 mCi).

Uses

  • GFR:
    • Identification of early alterations in renal function in order to prevent progression of renal disease and damage.
    • Evaluation of response to therapy and as an aid to prognosis.
    • Detection and monitoring of sub-clinical renal disease caused by nephrotoxic agents, eg aminoglycosides   Therapeutics: aminoglycosides  .
  • ERBF:
    • Quantification of renal function and ideally detection of early dysfunction.
    • Monitoring response to therapy for primary or secondary renal dysfunction.
    • Evaluation of the influence of certain medications on renal function in metabolically compromised horses.

Requirements

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Preparation

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Procedure

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Aftercare

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Outcomes

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Prognosis

  • GFR:
    • GFR estimations may be more reproducible in horses which have lost  their functional renal reserve and the residual functional mass is constantly performing at its maximum. 
    • The accuracy of GFR estimation using 99mTc-DTPA also decreases when renal disease is severe and the GFR is very low. Other measures of renal function are of  more use in these circumstances.
  • ERBF/ERPF:
    • The radiopharmaceuticals used are not entirely removed from the blood on first pass through the kidneys resulting in measurements which under-estimate the true renal plasma flow.
    • In addition, 99mTc-MAG3 has higher protein binding capacity and a smaller volume of distribution than either 131I-OIH or PAH potentially further influencing the estimation of ERBF. 
    • 99mTc-MAG3 studies in humans, dogs and horses has however indicated similar results between the different agents used.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Woods P R, Drost W T, Clarke C R et al (2000) Use of 99mTc-mercaptoacetyltriglycine to evaluate renal function in horses. Vet Radiol 41 (1), 85-88 PubMed.
  • Matthews H K, Andrews F M, Daniel G B et al (1993) Measuring renal function in horses. Vet Med 88 (4)349-356 VetMedResource.
  • Matthews H K, Andrews F M, Daniel G B et al (1992) Comparison of standard and radionuclide methods for measurement of glomerular filtration rate and effective renal blood flow in female horses. Am J Vet Res 53 (9), 1612-1616 PubMed.
  • Walsh D M, Royal H D (1992) Evaluation of a single injection of 99mTc-labeled diethylenetriaminepentaacetic acid for measuring glomerular filtration rate in horses. Am J Vet Res 53 (5), 776-780 PubMed.
  • Held J P & Daniel G B (1991) Use of nonimaging nuclear medicine techniques to assess the effect of flunixin meglumine on effective renal plasma flow and effective renal blood flow in healthy horses. Am J Vet Res 52 (10), 1619-1621 PubMed.
  • Barthez P Y, Hornof W J, Cowgill L D et al (1998) Comparison between the scintigraphic uptake and plasma clearance of 99mTc-diethylenetriaminepentacetic acid (DTPA) for the evaluation of the glomerular filtration rate in dogs. Vet Radiol 39 (5), 470-474 PubMed.
  • Divers T J, Whitlock R H, Byars T D et al (1987) Acute renal failure in six horses resulting from haemodynamic causes. Equine Vet J 19 (3), 178-184 PubMed.
  • Hood D M, Amoss M S, Gremmel S M et al (1982) Renovascular nuclear medicine in the equine: a feasibility study. Southwestern Vet 35 (1), 19-26 VetMedResource.

Other sources of information

  • Twardock A R, Krawiec D R, Itkins R J (1996)Renal imaging I: functional renal scintigraphy.In:Handbook of Veterinary Nuclear Medicine. Eds: Berry C R & Daniel G B. North Carolina State University, Raleigh, NC. pp 122-130.
  • Twardock A R (1996)Renal imaging II: morphology scintigraphy.In:Handbook of Veterinary Nuclear Medicine. Eds: Berry C R & Daniel G B. North Carolina State University, Raleigh, NC. pp 131-132.


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