低剂量未加强的CT 在诊断盲肠炎方面与标准剂量CT相当


  July 23, 2009 — 根据发表于7月美国X光射线学期刊研究,低剂量未加强的计算机断层(CT)降低大约50%的放射线,不过可以和标准剂量显影剂CT一样有效诊断盲肠炎。
  
  韩国首尔国立大学医学院的Hyobin Seo医师等人写道,有关盲肠炎的CT技术要用哪里种一直有所争论。越来越多使用CT作为疑似盲肠炎患者的评估,许多是年轻病患。现代超薄型扫描仪则需要增加辐射剂量。
  
  本研究的目的在于,比较低剂量加强型CT与标准剂量静脉注射显影剂加强型CT,以滑动厚片射线总和回顾盲肠炎诊断影像。
  
  Seo医师等人写道,虽然静脉或肠道显影剂加强之利益被广为评估,但少有研究聚焦在影像重建或影像回顾技术,这对判断正常或发炎盲肠很重要。以许多CT工作站所有的薄片与滑动厚片射线总和技术回顾,发现可以准确地判断盲肠的病理状况。
  
  该研究中,207名疑似盲肠炎的成人接受平均有效剂量4.2 mSv (低剂量)和8.0 mSv (标准剂量)的CT。由两名放射师滑动5mm厚的放射总和厚片回顾影像。以5分级距排序盲肠炎的可能性,以3分级距排序盲肠影像,他们可提出其它诊断。
  
  总共有78名病患发现盲肠炎。第一位放射师使用低剂量未加强方法可以正确确认其中77个案例(敏感度98.7%),使用标准剂量加强方法可以确认全部78个案例(敏感度100%)。第二位放射师用两种方法都可以确认全部78个案例(敏感度100%)。
  
  第一位放射师在这两种方法的专一度分别是95.3%和93.0% (P = .25),第二位放射师是96.9%和96.9%。第一位放射师在低剂量和标准剂量分别误判5.4%和3.9%的正常盲肠(P = .63),第二位放射师是3.9%和2.3%(P = .50)。这些病患的盲肠被误为有盲肠炎。
  
  研究作者写道,低剂量未加强CT诊断信度、盲肠可见度、其它诊断等并不逊色,而判读者对于盲肠诊断的信心则有显著差异(P = .004)。
  
  这两项技术在诊断盲肠穿孔方面相当。
  
  虽然研究者发现,低剂量未加强CT的诊断表现并不比标准剂量显影剂加强CT差,但他们并无法断言使用低剂量可加强CT的整体临床利益,因为样本少且追踪期短,这也是作者指出的研究限制。
  
  他们结论表示,其结果认为,低剂量未加强CT有潜力运用于盲肠炎的诊断,但是需要更大型的前溯研究,以确定其并用滑动厚片射线总和诠释法时的可用性。
  
  研究接受韩国政府的资金。
  

Low-Dose Unenhanced CT Rivals Standard-Dose CT for Diagnosing Appendicitis

By Fran Lowry
Medscape Medical News

July 23, 2009 — Low-dose unenhanced computed tomography (CT) that delivers approximately 50% less radiation is just as effective in diagnosing appendicitis as standard-dose contrast-enhanced CT, according to a study published in the July issue of the American Journal of Roentgenology.

"There is controversy about which appendiceal CT technique is optimal," write Hyobin Seo, MD, from Seoul National University College of Medicine, Korea, and colleagues. "CT is increasingly used for evaluation of patients with suspected appendicitis, many of whom are young. Acquiring thinner sections with modern scanners may further increase the radiation dose."

The purpose of this study was to compare low-dose enhanced CT with standard-dose intravenous contrast-enhanced CT using an image review with sliding slab ray-sum in the diagnosis of appendicitis.

"Although the potential advantages of [intravenous] or enteric contrast enhancement have been intensively evaluated, few studies have been focused on image reconstruction or image review techniques, which are important in visualizing a normal or inflamed appendix," Dr. Seo and colleagues write. "Review of thin sections with sliding slab ray-sum technique, which is available on many CT workstations, has been found accurate for visualization of pathologic conditions in the appendix."

In the study, 207 adults with suspected appendicitis underwent CT with mean effective doses of both 4.2 mSv (low dose) and 8.0 mSv (standard dose). Thin-section images were retrospectively reviewed by sliding a 5-mm-thick ray-sum slab by 2 radiologists. They rated the likelihood of appendicitis on a 5-point scale and appendiceal visualization on a 3-point scale, and they proposed alternative diagnoses.

A total of 78 patients were found to have appendicitis. The first radiologist was able to correctly identify 77 of 78 cases of appendicitis using the low-dose unenhanced method (sensitivity, 98.7%) and all of the cases of appendicitis using the standard-dose enhanced method (78 of 78; sensitivity, 100%). The second radiologist was able to correctly identify appendicitis in all 78 patients using both methods (sensitivity, 100%).

Specificity was 95.3% and 93.0%, respectively, for reader 1 (P = .25) and 96.9% and 96.9% for reader 2. A normal appendix was missed in 5.4% of low-dose and 3.9% of standard-dose techniques by reader 1 (P = .63) and in 3.9% and 2.3%, respectively, by reader 2 (P = .50). None of the patients whose appendix was not visualized had appendicitis.

Diagnostic confidence, visualization of the appendix, and alternative diagnoses tended to be compromised with low-dose unenhanced CT, showing a significant difference for a reader's confidence in the diagnosis of appendicitis (P = .004), the study authors write.

The 2 techniques were comparable in the diagnosis of appendiceal perforation.

Although the researchers found that the diagnostic performance of low-dose unenhanced CT is not significantly impaired compared with that of standard-dose contrast-enhanced CT, they could not affirm the overall clinical benefit of using low-dose unenhanced CT because of the small sample size and limited follow-up period, the authors state, citing limitations of their study.

They conclude that their results suggest that low-dose unenhanced CT is potentially useful in the diagnosis of appendicitis but that a larger prospective study is needed to ascertain its utility when combined with sliding slab ray-sum interpretation.

The study was supported by a grant from the government of Korea.

Am J Roentgenol. 2009;193:96–105.

    
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