超低辐射剂量心脏CT血管造影是可行的

芝加哥——使用以模型为基础的迭代重建(MIBR)技术，在超低辐射剂量下(0.2 mSv)进行冠脉计算机断层(CT)血管造影可达到诊断性成像质量，并且这种技术具有临床可行性。苏黎世大学医院的Julia Stehli医生在北美放射学会(RSNA)年会上说，这意味着，与标准冠脉CT血管造影相比，辐射剂量降低了大约80%。


Julia Stehli医生

关于辐射暴露的顾虑促进了前瞻性ECG触发装置的使用，使辐射剂量由20 mSv降低至2 mSv甚至更低。一些供应商也开发了新的以原始数据为基础的迭代重建算法，目的为进一步降低辐射剂量，但可能要为此付出影像噪音增加的代价。MIBR算法(GE医疗集团)已显示颇具前景的噪音降低结果，这种技术也被称为Veo，目前已在美国、欧洲和亚洲被用于腹部CT扫描，但因为ECG触发装置的复杂性增加，尚未进入心脏扫描市场。

Stehli医生报告了该医院首项关于连续25例前瞻性入选的接受标准低剂量冠脉CT血管造影(CCTA)的可疑冠心病患者的MIBR临床应用经验，这些患者于同日在配备有前瞻性ECG触发装置的64层CT扫描仪上进行低剂量CCTA 。根据体重指数调整管电压和电流，包含的范围为18.4 kg/m2~40.2 kg/m2。根据体表面积调整造影剂体积和流速。对于20例患者，在CCTA前使用静脉受体阻滞剂治疗。依照医院常规实践，使用30%的适应性统计学迭代重建(ASIR)技术重建标准CCTA，同时将超低剂量影像发送至供应商，进行MIBR重建。研究中的多数患者表现为胸痛(72%)，其中56%为吸烟者，44%患有动脉高血压，36%有心血管疾病家族史，患者的平均年龄为58岁。

结果显示，标准CCTA组和超低剂量CCTA组的有效辐射剂量分别为1.3 mSv和0.2 mSv(P＜0.001)，处于报告的胸部后-前位和侧位X线检查范围之内。由两位不知情的独立阅读者使用4分Likert量表（1分为无法诊断，2分为良好，3分为充分，4分为优秀）对总共100枝血管和330个冠状动脉节段进行了半定量评估。不同观察者对影像质量评价的一致性Kappa数值为0.8。标准CCTA组和超低剂量MBIR组每个节段的平均影像质量评分分别为3.3和3.4(P＜0.05)，她说。两组分别有319(97%)和317个节段(96%)达到诊断性影像质量（评分为2~4分）。对于超低剂量方案的最终检验将是临床结局数据，预期将于2014年报告。研究者拒绝透露关于临床结局的详情，但指出，新方案的敏感性和特异性良好。

该研究结论为，使用模型为基础的迭代重建技术，可以在超低辐射剂量水平进行冠脉CT血管造影，且可达到诊断性影像质量。作者称，在不久的将来，这一技术可进入临床应用。

Stehli医生及其合作者披露无相关利益冲突。

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By: PATRICE WENDLING, Cardiology News Digital Network

CHICAGO – Coronary computed tomography angiography with diagnostic image quality is feasible at an ultralow radiation dose of 0.2 millisievert using model-based iterative reconstruction.

This represents roughly an 80% reduction in radiation dose compared with standard coronary CT angiography, Dr. Julia Stehli said at the annual meeting of the Radiological Society of North America.

Increasing concerns about radiation exposure have prompted the use of prospective ECG triggering to reduce radiation doses from 20 mSv to 2 mSv or less. Several vendors also have developed new raw-data–based iterative reconstruction algorithms to further reduce radiation doses, but the trade-off can be increased image noise.

The model-based iterative reconstruction (MIBR) algorithm (GE Healthcare), however, has shown promising results for noise reduction, said Dr. Stehli of University Hospital Zurich. The technology, known as Veo, is already in use in the United States, Europe, and Asia for abdominal CT scans but is not yet commercially available for cardiac scans because of the added complexity of ECG triggering.

Dr. Stehli reported on the hospital’s first clinical experience with MIBR in 25 consecutive prospectively enrolled patients with suspected coronary artery disease who underwent standard low-dose coronary CT angiography (CCTA) and same-day ultralow-dose CCTA on a 64-slice CT scanner with prospective ECG triggering. Tube voltage and current were adapted to body mass index, which covered a wide range from 18.4 kg/m2 to 40.2 kg/m2. Contrast media volume and flow rate were adapted to body surface area. Intravenous beta-blockers were used prior to CCTA in 20 patients.

Standard CCTA was reconstructed using 30% of adaptive statistical iterative reconstruction (ASIR) according to usual hospital practice, while the ultralow-dose images were sent to the vendor for reconstruction with MIBR.

The effective radiation dose was 1.3 mSv with standard CCTA and 0.2 mSv in the ultralow-dose CCTA group (P less than .001), which is in the range reported for a postero-anterior and lateral chest X-ray, Dr. Stehli said.

A total of 100 vessels and 330 coronary artery segments were semiquantitatively assessed by two blinded, independent readers using a 4-point Likert scale, with 1 being nondiagnostic, 2 good, 3 adequate, and 4 excellent. The Kappa value for interobserver agreement of image quality was 0.8.

The average image quality score per segment was 3.3 with standard CCTA vs. 3.4 with ultralow-dose MBIR (P less than .05), she said.

Diagnostic image quality (score 2-4) was found in 319 segments (97%) and 317 segments (96%), respectively.

"These numbers are quite revolutionary," session comoderator Dr. Konstantin Nikolaou, professor of radiology at the University of Munich, said in an interview. "We’ve heard about 1.0 [mSv], so 0.2 [mSv] is great."

Still, more details are needed on exactly how the protocol works and the need to send images to the vendor for MBIR reconstruction, he said.

During a discussion of the results, Dr. Stehli said that reconstruction by the vendor typically took about 15 minutes, but Dr. Nikolau said that "it’s hard to say if that is feasible in routine clinical practice."

The ultimate test for the ultralow-dose protocol will be the clinical outcomes data, expected to be reported in 2014.

"If that proves to be robust and works in many patients and rates a good diagnostic accuracy, it would be great," Dr. Nikolau said.

The investigators would not release details on the clinical outcomes but said sensitivity and specificity for the new protocol are good.

"We believe this will have clinical applications in the near future," Dr. Stehli said in an interview.

Most patients in the study presented with chest pain (72%), and 56% were smokers, 44% had arterial hypertension, and 36% had a family history of cardiovascular disease. Their mean age was 58 years.

Dr. Stehli and her associates reported having no financial disclosures.