Department of Biomedical Imaging and Image-guided Therapy, Medical University Vienna/Vienna General Hospital, Vienna, Austria.
Department of Urology, Medical University Vienna/Vienna General Hospital, Vienna, Austria.
Eur Radiol. 2020 Aug;30(8):4295-4305. doi: 10.1007/s00330-020-06806-9. Epub 2020 Apr 3.
Previous studies have shown that split-bolus protocols in virtual non-contrast (VNC) reconstructions of dual-energy computed tomography (DE-CT) significantly decrease radiation dose in patients with urinary stone disease. To evaluate the impact on kidney stone detection rate of stone composition, size, tube voltage, and iodine concentration for VNC reconstructions of DE-CT.
In this prospective study, 16 kidney stones of different sizes (1.2-4.5 mm) and compositions (struvite, cystine, whewellite, brushite) were placed within a kidney phantom. Seventy-two scans with nine different iodine contrast agents/saline solutions with increasing attenuation (0-1400 HU) and different kilovoltage settings (70 kV/150 kV; 80 kV/150 kV; 90 kV/150 kV; 100 kV/150 kV) were performed. Two experienced radiologists independently rated the images for the presence and absence of stones. Multivariate classification tree analysis and descriptive statistics were used to evaluate the diagnostic performance.
Classification tree analysis revealed a higher detection rate of renal calculi > 2 mm in size compared with that of renal calculi < 2 mm (84.7%; 12.7%; p < 0.001). For stones with a diameter > 2 mm, the best results were found at 70 kV/Sn 150 kV and 80 kV/Sn 150 kV in scans with contrast media attenuation of 600 HU or less, with sensitivity of 99.6% and 96.0%, respectively. A higher luminal attenuation (> 600 HU) resulted in a significantly decreased detection rate (91.8%, 0-600 HU; 70.7%, 900-1400 HU; p < 0.001). In our study setup, the detection rates were best for cystine stones.
Scan protocols in DE-CT with lower tube current and lower contrast medium attenuation show excellent results in VNC for stones larger than 2 mm but have limitations for small stones.
• The detection rate of virtual non-contrast reconstructions is highly dependent on the surrounding contrast medium attenuation at the renal pelvis and should be kept as low as possible, as at an attenuation higher than 600 HU the VNC reconstructions are susceptible to masking ureteral stones. • Protocols with lower tube voltages (70 kV/Sn 150 kV and 80 kV/Sn 150 kV) improve the detection rate of kidney stones in VNC reconstructions. • The visibility of renal stones in virtual non-contrast of dual-energy CT is highly associated with the size, and results in a significantly lower detection rate in stones below 2 mm.
先前的研究表明，双能 CT（DE-CT）虚拟非对比（VNC）重建中的分段 bolus 方案可显著降低尿路结石病患者的辐射剂量。评估 VNC 重建中结石成分、大小、管电压和碘浓度对肾结石检出率的影响。
在这项前瞻性研究中，将 16 颗不同大小（1.2-4.5mm）和成分（鸟粪石、胱氨酸、羟磷灰石、碳酸磷灰石）的肾结石置于肾脏模型内。使用 9 种不同的碘造影剂/盐水溶液，具有不同的衰减（0-1400HU）和不同的千伏设置（70kV/150kV；80kV/150kV；90kV/150kV；100kV/150kV）进行 72 次扫描。两位经验丰富的放射科医生分别对图像进行评估，以判断结石的存在和不存在。使用多变量分类树分析和描述性统计来评估诊断性能。
分类树分析显示，与直径<2mm 的肾结石相比，直径>2mm 的肾结石的检出率更高（84.7%，12.7%；p<0.001）。对于直径>2mm 的结石，在衰减<600HU 的造影剂增强扫描中，70kV/Sn 150kV 和 80kV/Sn 150kV 时获得的结果最佳，灵敏度分别为 99.6%和 96.0%。管腔衰减（>600HU）较高时，检出率显著降低（91.8%，0-600HU；70.7%，900-1400HU；p<0.001）。在我们的研究方案中，胱氨酸结石的检出率最好。
DE-CT 扫描方案中采用较低的管电流和较低的对比剂衰减，对直径>2mm 的结石在 VNC 中显示出极佳的效果，但对小结石有一定的局限性。
VNC 重建的检出率高度依赖于肾盂内的对比剂衰减，应尽可能保持低衰减，因为在衰减高于 600HU 时，VNC 重建易受输尿管结石的影响而被掩盖。
较低的管电压（70kV/Sn 150kV 和 80kV/Sn 150kV）方案可提高 VNC 重建中肾结石的检出率。
双能 CT 虚拟非对比成像中肾结石的可见度与结石大小密切相关，在直径<2mm 的结石中，检出率显著降低。
