（阅读笔记 ） CT灌注扫描时间

• Method
• • Patient
  • Image Protocol
  • Image PostProcessing
  • Simulation of Shorter Scans
• Results
• • Relation Between Optimal Scan Duration and VOF Parameters
• 其他

by HPC_ZY

期刊论文《Optimal Computed Tomographic Perfusion Scan Duration for Assessment of Acute Stroke Lesion Volumes》[1] 阅读笔记

Although magnetic resonance (MR) imaging has been the reference standard for assessment of the ischemic core and penumbra for many years, recent studies have demonstrated comparable results with CTP and MR imaging.9–11 In comparison with MR, CTP has several advantages: it is quicker, cheaper, more widely available, and can be applied in patients who are claustrophobic or have other MR contraindications such as pacemakers.12–14

尽管磁共振（MR）成像多年来一直是评估缺血核心和半暗带的参考标准，但最近的研究表明CTP和MR成像的结果具有可比性。不过CTP有几个优点：它更快、更便宜、更广泛地适用于患者患有幽闭恐怖症或有其他MR禁忌症，如起搏器

Recommendations about the optimal scan acquisition parameters, such as scan duration, differ between studies.15–17 Consequently, CTP scan times vary considerably between imaging centers and are as short as 40 seconds at some centers and as long as 90 seconds at others.2,11,17–22 Short scan times can result in truncation of the concentration measurements and resultant inaccurate CTP results.23–25 On the contrary, long scan times can expose patients to unnecessary radiation with no additive accuracy of CTP results.

关于最佳扫描采集参数（如扫描时间）不同的研究给出不同结果。

短扫描时间会导致浓度测量值的截断，从而导致CTP结果不准确；相反，长扫描时间会使患者暴露在不必要的辐射下，而CTP结果没有额外的准确性。

Because the assessment of ischemic tissue on CTP is based on contrast bolus passage characteristics, it is intuitive that the optimal CTP scan duration depends on the arrival time and the shape of the contrast bolus.

由于CTP对缺血组织的评估是基于对比剂团通过特性，因此，最佳CTP扫描持续时间取决于到达时间和造影剂团的形状。

To identify the optimal scan duration, we sequentially truncated the length of the acquired CTP scan in a cohort of patients with a relatively long scan duration (90 seconds) and recorded the impact of truncation on measurements of the ischemic core and penumbra volumes.

为了确定最佳扫描持续时间，RapidAI在一组扫描持续时间相对较长（90秒）的患者中，依次缩短获得性CTP扫描的长度，并记录截短对测量缺血核心和半暗带体积的影响。

Method

Patient

Image Protocol

Image PostProcessing

Postprocessing of CTP images was performed using a customized research version of the RAPID (iSchemaView, Menlo Park, CA) perfusion software program.5,26–29 RAPID allows for fully automated processing of CTP images, including automatic arterial input function (AIF) detection and motion correction.

CTP图像的后处理是使用定制的研究版本的RAPID（iSchemaView，Menlo Park，CA）灌注软件程序执行的。可以完成CTP图像的全自动处理，包括AIF检测和运动校正等。

We used the VOF as a representation for the bolus shape in each CTP study because it is the most easy-to-determine signal and, because of the large venous dimensions, less susceptible to partial volume effects than the AIF.

我们在每项CTP研究中使用VOF作为一种代表，因为它是最容易确定的信号，而且由于静脉尺寸大，比AIF更不容易受到部分容积效应的影响。

We parameterized the VOF by curve ftting using a gamma variate function as described by Madsen.30 For each scan, we used the ft to determine the following: (1) the bolus arrival time (T0), defned as the time at which 0.1% of the area under the VOF curve ft was reached, and (2) the width of the VOF, defned as the full width at half maximum of the ftted gamma variate function. Although T0 can also be determined directly from one of the ftted parameters, we empirically found that the 0.1% criterion yielded a more accurate measure of T 0. 31

我们使用Madsen描述的伽马变量函数，通过曲线ftting来参数化VOF。对于每次扫描，我们使用ft来确定以下内容：

（1）bolus到达时间（T0），定义为达到VOF曲线下0.1%面积的时间，

（2）VOF的宽度，定义为ftted gamma变量函数半最大值处的全宽。

虽然T0也可以直接从ftted参数中确定，但我们从经验上发现，0.1%的标准可以更精确地测量T0。31

Simulation of Shorter Scans

Results

Relation Between Optimal Scan Duration and VOF Parameters

For the 59 scans that were volumetrically stable, the median optimal scan time was 32.7 seconds (90th percentile 52.6 seconds; 100th percentile 68.9 seconds) and the median relative height of the ftted VOF at the optimal scan times was 0.39 (90th percentile 0.02; 100th percentile 0.00).

对于59次容积稳定的扫描，最佳扫描时间中位数为32.7秒（第90百分位52.6秒；第100百分位68.9秒），最佳扫描时间时ftted VOF的中位数相对高度为0.39（第90百分位0.02；100百分位0.00；如下表）。

下图为扫描持续时间（s）与缺血性病变体积（mL）估计值之间的关系。

其中，静脉输出功能（VOF）曲线ft显示为蓝色曲线。

严重低灌注组织（Tmax>6 s）的体积估算用绿色圆圈表示。

绿色虚线表示最后6帧中Tmax>6s病变的平均体积（稳定性尾）。

绿色虚线代表边界（平均体积±10毫升），超过该界限，病变体积被视为不可靠。

缺血核心（rCBF<30%）的体积估计用粉红色圆圈表示。

The optimal scan time was T0 plus 1.6 times the width of the VOF (P<0.001; R2 =0.49). The 95% prediction interval of this function ranged from -25.6 to 25.6 seconds.

最佳扫描时间为T0加上VOF宽度的1.6倍（P<0.001；R2=0.49）。该函数的95%预测区间为-25.6到25.6秒。

下图显示了平均VOF曲线ft（T0标准化为10秒）和彩色编码区域，这些区域表明CTP体积的可靠范围。

其他

[1] Kasasbeh A S, Christensen S, Straka M, et al. Optimal computed tomographic perfusion scan duration for assessment of acute stroke lesion volumes[J]. Stroke, 2016, 47(12): 2966-2971.