## 2 Materials and Methods  
In July 2023, two researchers ([PERSON], 12 years of experience, and [PERSON], 4 years of experience) employed National Library of Medicine databases, including PubMed, NLM catalog, MeSH, and Bookshelf, for the research using the following keywords: \"phantomless quantitative\". Titles and abstracts of all the papers were analyzed by the two researchers. Papers were included for further in-depth review if the focus was on PL-QCT to investigate osteoporosis or osteopenia (Figure 2). The references of the eligible studies were screened manually to identify additional studies of potential interest. The characteristics and major findings of the studies included are summarized in Tables 1 and 2. Figure 2: Flowchart for study search and selection. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Year** & **First Author** & **Technique** & **Results** \\ \hline
**2010** & **[PERSON] et al.** & PB-BMD vs. PL-BMD T12-L4** &
\begin{tabular}{c} A minor BMD bias of 0.9 mg/cm\({}^{3}\) for the \\ PL-BMD option was found \\ \end{tabular} \\ \hline
**2011** & **[PERSON] et al.** & \
\begin{tabular}{c} T12-L5 levels assessed using \\ both PL-QCT and \\ straightforward non-angled \\ ROI MDCT attenuation \\ measures \\ \end{tabular} &
\begin{tabular}{c} For BMD screening at CTC, both PL-QCT and \\ straightforward ROI attenuation \\ measurements of the lumbar spine are useful, with excellent sensitivity for osteoporosis as determined by the DXA T-score \\ \end{tabular} \\ \hline
**2015** & **[PERSON] et al.** & \
\begin{tabular}{c} PB-QCT vs. PL-QCT approach \\ in LI-L5 \\ \end{tabular} &
\begin{tabular}{c} Excellent agreement was seen in the linear \\ regression of lumbar vBMD produced from the \\ PB vs. PL calibrations \\ \end{tabular} \\ \hline
**2017** & **[PERSON] et al.** & \
\begin{tabular}{c} Spine and hip analysis using \\ air and either hip adipose \\ tissue or aortic blood as \\ calibrating reference materials \\ \end{tabular} &
\begin{tabular}{c} Calibrated measurements using phantoms and \\ PL were equivalent \\ \end{tabular} \\ \hline
**2018** & **[PERSON] et al.** & \
\begin{tabular}{c} PL internal tissue calibration \\ performed on 3 consecutive \\ vertebrae from TI2 to L4 \\ \end{tabular} &
\begin{tabular}{c} The PL technique has a higher intra-operator \\ variability (5.8\%) than the PB method (1.8\%) \\ and a higher inter-operator variability (5.8\%) \\ than the PB method (1.8\%) \\ \end{tabular} \\ \hline
**2019** & **[PERSON] et al.** & \
\begin{tabular}{c} PL HU-to-BMD conversion \\ using a multiple linear \\ regression model \\ \end{tabular} &
\begin{tabular}{c} Significant correlations between the BMD \\ values calculated using the suggested \\ HU-to-BMD conversion and those obtained \\ using the reference phantom \\ \end{tabular} \\ \hline
**2022** & **[PERSON] et al.** & \
\begin{tabular}{c} Newly developed automatic \\ PL-QCT system \\ \end{tabular} &
\begin{tabular}{c} According to the findings of the BMD test, the \\ autonomous PL-QCT system exhibited more \\ precision than earlier studies that used QCT \\ while still being able to detect osteoporosis \\ similarly to DXA and PB-QCT \\ \end{tabular} \\ \hline
**2022** & **[PERSON] et al.** & \
\begin{tabular}{c} PL-QCT system \\ \end{tabular} &
\begin{tabular}{c} PL-QCT can predict osteoporosis with a fair \\ amount of precision and accuracy \\ \end{tabular} \\ \hline
**2023** & **[PERSON] et al.** & \
\begin{tabular}{c} QCT using CNN \\ \end{tabular} &
\begin{tabular}{c} The proposed-method-measured BMDs were \\ higher than QCT-measured BMDs in a cohort \\ of study \\ \end{tabular} \\ \hline
**2023** & **[PERSON] et al.** & \
\begin{tabular}{c} PL-QCT using automatic \\ calibration technique \\ \end{tabular} &
\begin{tabular}{c} Preoperative BMD was an independent risk \\ factor for postoperative cage subsidence after \\ extreme lateral interbody fusion \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main characteristics and findings of the analyzed single-energy CT studies included in the review.