Non-Invasive Mycobacterium avium Detection Using 99mTc-GSA on Single-Photon Emission Computed Tomography

<b>Background</b>: The prevalence of nontuberculous mycobacteria (NTM) infection is on the rise, surpassing that of pulmonary tuberculosis in Japan. Current standard therapy for NTM infection involves long-term treatment of at least 1.5 years, with low success rates and a high relapse rate. ^99mTc-diethylenetriaminepentaacetic acid-galactosyl-human serum albumin (^99mTc-GSA) is used for human liver imaging. In this study, we utilized ^99mTc-GSA as a probe to detect <i>Mycobacterium avium</i> (<i>M. avium</i>), a major pathogen in NTM pulmonary diseases (NTM-PDs). Our aim was to investigate the non-invasive detection of <i>M. avium</i> using ^99mTc-GSA on Single-Photon Emission Computed Tomography (SPECT). <b>Methods</b>: The accumulation of ^99mTc-GSA in <i>M. avium</i> was investigated in vitro. In vivo, SPECT images were obtained after the administration of ^99mTc-GSA to an <i>M. avium</i> thigh infection model. Subsequently, the contrast difference in accumulated ^99mTc-GSA between infected and non-infected thighs was calculated using SPECT imaging. Furthermore, SPECT images were obtained for thighs infected with varying bacterial loads, and the accumulation was compared between them. <b>Results</b>: In vitro, we observed that ^99mTc-GSA accumulates in <i>M. avium</i>. In vivo, SPECT images demonstrated the specific accumulation of ^99mTc-GSA at the infection site, with this accumulation being correlated with the bacterial load. <b>Conclusions</b>: ^99mTc-GSA specifically accumulates in <i>M. avium</i>, and SPECT can be used to monitor the distribution and quantity of <i>M. avium</i> in animals. By utilizing these measures, ^99mTc-GSA can be targeted to the site of infection and used as a bacterial probe.