Activity recovery for differently shaped objects in quantitative SPECT

Area of Science:

• Nuclear Medicine
• Medical Imaging Physics

Background:

• Accurate quantification of radiotracer uptake in Single-Photon Emission Computed Tomography (SPECT) is crucial for effective diagnosis and treatment monitoring.
• Object shape can influence image reconstruction and quantitative accuracy in SPECT imaging.
• Standardized methods for assessing signal recovery across diverse geometries are needed to reduce uncertainties.

Purpose of the Study:

• To theoretically and experimentally investigate SPECT image recovery in objects of varying shapes (spheres, oblate spheroids, prolate spheroids).
• To evaluate the accuracy of volume estimation using thresholding methods for different object geometries.
• To establish a shape-independent metric for activity quantification in SPECT.

Main Methods:

• SPECT phantom inserts of spheres, oblate spheroids, and prolate spheroids were imaged using 99mTc and 177Lu on different gamma cameras.
• Signal Rate Per Activity (SRPA) was determined and analyzed as a function of volume-to-surface ratio and volume-equivalent radius.
• Experimental SRPA data were compared with analytical and numerical models, with validation using ellipsoidal phantoms.
• Threshold values for accurate volume determination were identified.

Main Results:

• Signal Rate Per Activity (SRPA) values diverged for oblate spheroids when plotted against volume-equivalent radius.
• However, SRPA values for all investigated shapes (spheres, spheroids, ellipsoids) exhibited similar behavior when plotted against the volume-to-surface ratio.
• Accurate volume estimation using thresholding was achieved for volumes exceeding 25 ml across all shapes.
• Experimental findings aligned with theoretical models.

Conclusions:

• Representing SPECT signal recovery as a function of the volume-to-surface ratio provides a shape-independent measure.
• This shape-independent approach can decrease uncertainties in estimated SPECT activities.
• Improved activity quantification accuracy holds long-term benefits for patient care in nuclear medicine.