光谱CT 虚拟单能量图像在尿路结石检出中的应用研究

Objective To explore the value of low-level virtual monoenergetic images （VMI）in the detection of small urinary stones at the specific window settings and to further explore the effects of radiation dose and reconstructed slice thickness on stone detection.Methods Forty-eight calcified stones （length and width smaller than 8 mm ）were prospectively included and placed in a 32 cm standard phantom filled with water.Spectral computed tomography （CT）scanning protocols were performed with low dose and conventional dose.Images were reconstructed as conventional images （120 kVp）and VMI （40，50，60 and 70 keV）ones with slice thickness and increment of 1 mm.In addition，the 120 kVp，40 keV and 70 keV VMI were reconstructed with slice thickness （increment）of 2 mm and 5 mm，respectively.The number of stone and detection confidence were independently evaluated by two physicians on before-mentioned images both at the bone window and soft tissue window settings. Differences in the detection rate of urinary stone were compared using Fisher’s exact test.Results All the 48 stones were detected on the 40—70 keV VMI and 120 kVp images.Among them，the detection confidence of urinary stones at the soft tissue window settings was all 4 points，while the confidence of detection on the 40 keV VMI and the conventional dose 50 keV VMI at the bone window settings was 4 points；the detection confidence of the other images decreased.VMI images and 120 kVp images with slice thickness of 1 mm and 2 mm could detect all stones with detection confidence of 3 points or more，while the stone detection and detection confidence of the corresponding images with 5 mm were significantly reduced.Radiation dose had no effect on stone detection or confidence.Conclusion Low-level VMI at low dose can detect urinary stones，especially in combination with soft tissue window settings.For not affecting the detection of stones，it is recommended to use slice thickness of 1-2 mm for image reconstruction.