Background <p>[^99mTc]Tc-NTP 15 − 5 showed affinity for joint cartilage proteoglycans on preclinical studies but has not been tested in humans. This phase I trial (CARPECT: NCT04481230) aims to define the optimal of [^99mTc]Tc-NTP 15 − 5 injected activity to obtain the best visual contrast of cartilage, without toxicity. Quantitative analyses of cartilage, periarticular uptakes, biodistribution, pharmacokinetic and dosimetry of this new tracer were also studied.</p> Results <p>Between November 2020 and June 2022, five patients with unilateral knee osteoarthritis or breast cancer treated with hormonal therapy inducing cartilage disease were injected with [^99mTc]Tc-NTP 15 − 5, at increasing activity levels: 5, 10 and 15 MBq/kg. No major toxicity was reported, according to NCICTC 4.0 scale. With an activity of 15 MBq/Kg, the median rate of joint uptakes higher than diaphysis’ one on whole body planar scintigraphy was 80.6% (80.60–85.45) at 2&#xa0;h p.i. and increased with time. S/N ratio with muscular background measured on SPECT-CT was superior to 3 from 2h30 p.i for cartilage. Uptake evolution depending on time from 1h00 to 6h30 p.i. permitted to discriminate cartilage and pooled proteoglycan structures from background and cartilage from ligaments + tendons for all examination times (<i>p</i> &lt; 0.001), and cartilage from bursa at 1&#xa0;h p.i. (<i>p</i> &lt; 0.05). Pharmacokinetic, biodistribution and dosimetry were in line with preclinical studies.</p> Conclusions <p>This study confirms the usability and accuracy of [^99mTc]Tc-NTP 15 − 5 for cartilage human functional imaging 2&#xa0;h after injection, at 15 MBq/kg.</p> Trial registration <p>Clinicaltrials.gov: NCT04481230. <a href="https://clinicaltrials.gov/ct2/show/NCT04481230">https://clinicaltrials.gov/ct2/show/NCT04481230</a>. Registration date: November, 12th, 2020.</p>