Timing and Energy Optimization of Dual-Energy CT for Brain Metastasis Conspicuity: A Prospective 24-Patient Study

Brain metastases are frequently encountered and typically evaluated by MRI, but MRI is not always available or feasible. Dual-energy CT (DECT) with virtual monochromatic reconstructions (VMRs) may offer a rapid, accessible alternative. We aimed to determine the optimal post-contrast timing and VMR energy for visualizing brain metastases using DECT.

This prospective study enrolled 24 patients with known brain metastases. DECT head scans were acquired at 90 seconds, 5 minutes, 10 minutes, and 20 minutes post-contrast using a dual-source scanner. VMR images were generated from 40 to 190 keV. For each time point, we measured lesion and background attenuation across keV, and calculated signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). Friedman and Wilcoxon tests were used to compare timing and energy effects.

Lesion conspicuity declined after the vascular phase. At 90 seconds, average CNR and SNR were 2.22 ± 0.39 (95% CI: 1.83-2.62) and 8.19 ± 0.67 (7.52-8.85), respectively. These values at 20 minutes measured 1.85 ± 0.33 and 8.34 ± 0.64. CNR peaked consistently at 40 keV, whereas SNR peaked between 70 and 100 keV depending on phase. Statistical tests confirmed significant variation across both time and energy (P < 0.001).

Optimal visualization of brain metastases on DECT is achieved at 90 seconds post-contrast using low-to-mid keV reconstructions. Although 40 keV maximized contrast, 70 to 85 keV offered a favorable balance of contrast and noise, supporting its use for interpretation and radiosurgical planning.