DOI: 10.1186/s40658-016-0170-3Pages: 1-20

Accuracy of 177Lu activity quantification in SPECT imaging: a phantom study

1. University of British Columbia, Medical Imaging Research Group, Department of Radiology

2. University of British Columbia, Department of Physics and Astronomy

3. BC Cancer Research Centre, Department of Molecular Oncology

4. Vancouver Coastal Health Authority

5. Université Laval, Department of Physics, Engineering Physics and Optics

6. CHU de Quebec–Université Laval, Department of Medical Imaging

7. Université Laval, Department of Radiology and Nuclear Medicine

Correspondence to:
Carlos F. Uribe
Tel: (+1)-604-700-5892
Email: curibe@bccrc.ca

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Abstract

Background

The aim of the study is to assess accuracy of activity quantification of 177Lu studies performed according to recommendations provided by the committee on Medical Internal Radiation Dose (MIRD) pamphlets 23 and 26. The performances of two scatter correction and three segmentation methods were compared. Additionally, the accuracy of tomographic and planar methods for determination of the camera normalization factor (CNF) was evaluated.

Eight phantoms containing inserts of different sizes and shapes placed in air, water, and radioactive background were scanned using a Siemens SymbiaT SPECT/CT camera. Planar and tomographic scans with 177Lu sources were used to measure CNF. Images were reconstructed with our SPEQToR software using resolution recovery, attenuation, and two scatter correction methods (analytical photon distribution interpolated (APDI) and triple energy window (TEW)). Segmentation was performed using a fixed threshold method for both air and cold water scans. For hot water experiments three segmentation methods were compared as folows: a 40% fixed threshold, segmentation based on CT images, and our iterative adaptive dual thresholding (IADT). Quantification error, defined as the percent difference between experimental and true activities, was evaluated.

Results

Quantification error for scans in air was better for TEW scatter correction (<6%) than for APDI (<11%). This trend was reversed for scans in water (<10% for APDI and <14% for TEW). For hot water, the best results (<18% for small objects and <5% for objects >100 ml) were obtained when APDI and IADT were used for scatter correction and segmentation, respectively. Additionally, we showed that planar acquisitions with scatter correction and tomographic scans provide similar CNF values. This is an important finding because planar acquisitions are easier to perform than tomographic scans. TEW and APDI resulted in similar quantification errors with APDI showing a small advantage for objects placed in medium with non-uniform density.

Conclusions

Following the MIRD recommendations for data acquisition and reconstruction resulted in accurate activity quantification (errors <5% for large objects). However, techniques for better organ/tumor segmentation must still be developed.

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  • Accepted: Dec 20, 2016
  • Online: Jan 7, 2017

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