找到了一个英文解释：
https://www.theonlinelearningcenter.com/Assets/CARTER/475/Do... (page 15)

Account for slice spacing [bed index – distance the bed (or table) travels during a CT acquisition] for conventional scanning

没找到确切的中文解释，似乎应该对应的是中文的“进床速度”

我不知道你的上下文，但很可能是bed utilization index，从最先的0%到后面的100%，表达的应该是来医院的病人越来越多。

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Note added at 3小时 (2020-01-07 04:49:14 GMT)
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看错了，CT扫描检查相关的，那跟床位无关。

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Note added at 3小时 (2020-01-07 05:07:02 GMT)
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更新：CT层厚、CT层间距、层间隔

一般是bed index distance连用，bed index可以缩写成BI，可以推知其答案的是slice spacing。
1）英文参考：
https://wiki.uiowa.edu/display/881886/CT Dictionary;
https://www.slideshare.net/GamalMahdaly/ct-radiation-dose-am...
Multiple Scan Average DoseMultiple Scan Average Dose  To measure radiation dose received byTo measure radiation dose received by patient from a series of CT scans,patient from a series of CT scans, between each two scans the patient isbetween each two scans the patient is moved by a bed index distance, each slicemoved by a bed index distance, each slice delivers its characteristic bell-shapeddelivers its characteristic bell-shaped dose.dose.  Finally, we have multiple consecutive bell-Finally, we have multiple consecutive bell- shaped doses.shaped doses.
A series of 7spaced scans at a constant bed index along the Z- axis is acquired to produce 7 bell- shaped dose distribution curves (TOP). Summation of these doses results in the (BOTTOM) curve.
Multi-scan average doseMulti-scan average dose (MSAD)(MSAD) CTDI can be related to the MSAD by this equation Where BI is the bed index or slice spacing (in mm), Sw is slice width (in mm), and the number of active arrays of detectors.【此句最重要】

2）中文参考：
https://zhidao.baidu.com/question/334497546.html
CT层厚指扫描层的厚度。CT层间距指指两个扫描层面中心之间的距离。CT层间隔指两层之间的距离
与床无关系，这里的bed是指扫描层。

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Note added at 3小时 (2020-01-07 05:09:25 GMT)
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补充：https://www.120ask.com/question/77511434.htm