Introduction:

Bone metastasis is the third most common metastasis in cancer patients, causing intractable pain and debilitating complications. However, studies have shown that conventional single-energy computed tomography (SECT) has limitation in detecting subtle bone metastases without obvious osteolysis/osteosclerosis. We hypothesize that dual-energy computed tomography (DECT) can distinguish different composition in tumors and in healthy bone marrow, facilitating the detection of bone marrow metastases.

Methods:

We constructed 51 semi-anthropomorphic lumbar spine phantoms embedded with 75 simulated tumors (25 mild lytic, 25 isodense, and 25 mild sclerotic). These phantoms were initially scanned without outer torso phantom encasement, and then scanned again with outer torso phantom encasement under the same machine setting in a rapid-kilovoltage-switching DECT scanner. Two radiologists independently reviewed the virtual monochromatic reconstruction in 70 keV and material decomposition images (hydroxyapatite-water, water-hydroxyapatite, cortical bone-water, water-cortical bone). We recorded reviewer’s response regarding the presence of tumors, tumor conspicuity score and image quality using 3-point Likert scales. The sensitivity and specificity of different reconstruction algorithms were evaluated with McNemar test. Wilcoxon signed rank test was used to evaluate the tumor conspicuity and image quality of different algorithms. Then we validate our testing algorithms by retrospectively reviewing patients’ images in our institution.

Results:

Hydroxyapatite-Water material decomposition algorithm achieved higher sensitivity in detecting isodense lesions as compared to the 70 keV reconstruction (without torso phantom encasement: 94% vs 82%, p=0.031; with torso phantom encasement: 38% vs 18%, p=0.013). Hydroxyapatite-Water material decomposition algorithms also possessed higher tumor conspicuity score (p<0.0001) compared to 70 keV reconstruction, and was less affected by CT artifacts.

Conclusion:

DECT with hydroxyapatite-water material decomposition may help detect spine marrow metastases, especially for subtle isodense tumors. Further study in prospective clinical scans is warranted.