Lymphoscintigraphic imaging study for quantitative evaluation of a small field of view (SFOV) gamma camera

M.S Alqahtani,A.C Perkins,S.L Bugby,L.K Jambi,J.E Lees

doi:10.1088/1748-0221/10/07/p07011

Abstract

The Hybrid Compact Gamma Camera (HCGC) is a portable optical-gamma hybrid imager designed for intraoperative medical imaging, particularly for sentinel lymph node biopsy procedures. To investigate the capability of the HCGC in lymphatic system imaging, two lymphoscintigraphic phantoms have been designed and constructed. These phantoms allowed quantitative assessment and evaluation of the HCGC for lymphatic vessel (LV) and sentinel lymph node (SLN) detection. Fused optical and gamma images showed good alignment of the two modalities allowing localisation of activity within the LV and the SLN. At an imaging distance of 10 cm, the spatial resolution of the HCGC during the detection process of the simulated LV was not degraded at a separation of more than 1.5 cm (variation <5%) from the injection site (IS). Even in the presence of the IS the targeted LV was detectable with an acquisition time of less than 2 minutes. The HCGC could detect SLNs containing different radioactivity concentrations (ranging between 1:20 to 1:100 SLN to IS activity ratios) and under various scattering thicknesses (ranging between 5 mm to 30 mm) with high contrast-to-noise ratio (CNR) values (ranging between 11.6 and 110.8). The HCGC can detect the simulated SLNs at various IS to SLN distances, different IS to SLN activity ratios and through varied scattering medium thicknesses. The HCGC provided an accurate physical localisation of radiopharmaceutical uptake in the simulated SLN. These characteristics of the HCGC reflect its suitability for utilisation in lymphatic vessel drainage imaging and SLN imaging in patients in different critical clinical situations such as interventional and surgical procedures.

Highlights

sentinel lymph node (SLN) to Injection site (IS) ratio IS activity in 0.5 ml SLN activity in 0.1 ml activity in 4 ml 1:20 1:50 15 MBq 1:100For the melanoma phantom, the simulated injection site (i.e. Eppendorf tube) was filled with 0.5 ml of a 99mTc solution (15 MBq total) [20]
The full width at half maximum (FWHM) of the modelled lymphatic vessel remains at a steady level when the distance from the centre of the IS was more than ∼ 15 mm, reflecting the fundamental spatial resolution of each camera
A simulation technique and two lymphoscintigraphic phantoms have been illustrated and utilised to validate the capability of the Hybrid Compact Gamma Camera (HCGC) in lymphatic system imaging. The implementation of this quantitative assessment enables the practical performance of the HCGC to be evaluated for lymphatic vessel (LV) and sentinel lymph node

Summary

Introduction

The simulated injection site (i.e. Eppendorf tube) was filled with 0.5 ml of a 99mTc solution (15 MBq total) [20]. The lack of clinical data for estimated activity concentrations in LVs in the human body during lymphoscintigraphic procedures and the difficulty in performing these kinds of studies is a result of the nature of lymphatic vessels. They have varying and uncertain diameters and depths; even for a known lymphatic route, the proximal and distal parts can differ in diameter and depth [18].

Methods

Results

Conclusion