Activity recovery for differently shaped objects in quantitative SPECT

Pablo Mínguez Gabiña; Teresa Monserrat Fuertes; Inés Jauregui; Cristina Del Amo; Emilia Rodeño Ortiz de Zarate; Johan Gustafsson

doi:10.1088/1361-6560/acd982

Activity recovery for differently shaped objects in quantitative SPECT

Phys Med Biol. 2023 Jun 16;68(12). doi: 10.1088/1361-6560/acd982.

Authors

Pablo Mínguez Gabiña^{1

2}, Teresa Monserrat Fuertes^{3

4}, Inés Jauregui⁵, Cristina Del Amo⁵, Emilia Rodeño Ortiz de Zarate⁶, Johan Gustafsson⁷

Affiliations

¹ Department of Medical Physics and Radiation Protection, Gurutzeta-Cruces University Hospital/ Biocruces Bizkaia Health Research Institute, Plaza Cruces s/n, E-48903 Barakaldo, Spain.
² Faculty of Engineering, Department of Applied Physics, UPV/EHU, Bilbao, Spain.
³ Department of Medical Physics and Radiation Protection, Central University Hospital of Asturias, Oviedo, Spain.
⁴ Faculty of Medicine and Nursing, Department of Surgery, Radiology and Physical Medicine, UPV/EHU, Bilbao, Spain.
⁵ 3D Printing and Bioprinting Laboratory, Biocruces Bizkaia Health Research Institute, Plaza Cruces s/n, E-48903 Barakaldo, Spain.
⁶ Department of Nuclear Medicine, Gurutzeta-Cruces University Hospital/ Biocruces Bizkaia Health Research Institute, Plaza Cruces s/n, E-48903 Barakaldo, Spain.
⁷ Medical Radiation Physics, Lund, Lund University, Lund, Sweden.

PMID: 37236207
DOI: 10.1088/1361-6560/acd982

Abstract

Objective.The aim was to theoretically and experimentally investigate recovery in SPECT images with objects of different shapes. Furthermore, the accuracy of volume estimation by thresholding was studied for those shapes.Approach.Nine spheres, nine oblate spheroids, and nine prolate spheroids phantom inserts were used, of which the six smaller spheres were part of the NEMA IEC body phantom and the rest of the inserts were 3D-printed. The inserts were filled with^99mTc and¹⁷⁷Lu. When filled with^99mTc, SPECT images were acquired in a Siemens Symbia Intevo Bold gamma camera and when filled with¹⁷⁷Lu in a General Electric NM/CT 870 DR gamma camera. The signal rate per activity (SRPA) was determined for all inserts and represented as a function of the volume-to-surface ratio and of the volume-equivalent radius using VOIs defined according to the sphere dimensions and VOIs defined using thresholding. Experimental values were compared with theoretical curves obtained analytically (spheres) or numerically (spheroids), starting from the convolution of a source distribution with a point-spread function. Validation of the activity estimation strategy was performed using four 3D-printed ellipsoids. Lastly, the threshold values necessary to determine the volume of each insert were obtained.Main results.Results showed that SRPA values for the oblate spheroids diverted from the other inserts, when SRPA were represented as a function of the volume-equivalent radius. However, SRPA values for all inserts followed a similar behaviour when represented as a function of the volume-to-surface ratio. Results for ellipsoids were in agreement with those results. For the three types of inserts the volume could be accurately estimated using a threshold method for volumes larger than 25 ml.Significance.Determination of SRPA independently of lesion or organ shape should decrease uncertainties in estimated activities and thereby, in the long term, be beneficial to patient care.

Keywords: 3D-printing; partial-volume effects; quantitative SPECT; recovery.

MeSH terms

Humans
Phantoms, Imaging
Tomography, Emission-Computed, Single-Photon*