Preamble.

This guideline is a special requirement for energy spectrum imaging technology in X-ray computed tomography (CT) equipment. Applicants for registration should combine with the characteristics of the declared products, according to this guideline to improve the relevant content of the registration declaration, on the inapplicable part of the technical characteristics of the product should be based on the reasons.

As a supplement to the ‘X-ray computed tomography equipment registration technical review guidelines’ [1] (hereinafter referred to as CT guidelines), is the specific requirements for spectral imaging technology. CT products with the function of energy spectrum imaging, its registration declaration information should comply with the requirements of this guiding principle in addition to the requirements of the CT guiding principle.

Scope of application

This guideline is applicable to CT products with spectral imaging function. According to the Catalogue of Classification of Medical Devices, this product belongs to subcategory 06 Medical Imaging Devices, with primary product category 02 X-ray computed tomography equipment (CT) and secondary product category 01 X-ray computed tomography equipment (CT), and is managed as Class III medical devices. For other X-ray imaging equipment with spectral imaging function and medical image processing software involving CT spectral images, the relevant content of its registration declaration information can also refer to the requirements of this guideline. At present, CT products with spectral imaging function usually provide spectral applications based on dual-energy imaging, and this guideline also describes the registration requirements for dual-energy CT spectral imaging technology.

Technical breakdown

CT energy spectrum imaging refers to the imaging technology that uses the change of CT value of substances under different energy (keV) X-ray irradiation to improve the image quality or provide additional image information during CT imaging.

Currently, the spectral imaging techniques applied to CT products can be divided into two categories: those based on the ray source end and those based on the detector end. According to the differences in realisation methods and hardware, these two types of spectral imaging techniques can be further divided into the following different technology routes:

Ray source-based spectral imaging: two scans with different tube voltages;
Spectral imaging based on the ray source: periodic tube voltage switching;
Spectral imaging based on the ray source: fast tube voltage switching;
Ray source-based spectroscopic imaging: use of spectrally separated filter plates;
Spectral imaging based on ray source: dual source scanning with different tube voltages;
Detector-based spectroscopic imaging: double-layer detectors;
Detector-based spectral imaging: photon counting detectors.
The CT spectral imaging function involves image scanning, reconstruction and post-processing functions based on the different CT spectral imaging routes described above. CT spectral imaging technology can be used to achieve CT spectral imaging, so as to obtain different types of CT spectral images, usually including virtual monochrome images, effective atomic number images, electron density images, substance separation images, substance concentration distribution images and substance identification images.  

Key points of registration review

1. Product Technical Requirements

For CT products with spectroscopic imaging function, it is necessary to add performance indexes and test methods related to spectroscopic imaging function in the technical requirements of the product, as a supplement to the content of product technical requirements in the CT guidelines, see Annex 1-1 for the specific content of the increase.

The added content involves the evaluation and requirements for the dose level and imaging performance of the spectral imaging function of the product. For the evaluation of CT spectral imaging performance, the types of images involved include spectral images provided by the spectral imaging function and images used for routine diagnosis. The spectral images include virtual monochrome images, effective atomic number images, electron density images, substance separation images, substance concentration distribution images, and substance identification images. The image for routine diagnosis includes a high-energy image and a low-energy image obtained by reconstruction based on high-energy and low-energy CT data, and a monoenergetic CT-like image equivalent to a single-energy CT image of the same object. The applicant shall provide relevant content according to the technical characteristics of the product's energy spectrum imaging technology, in conjunction with the product's energy spectrum imaging function, and shall provide the reasons for not applying the performance indexes that are not applicable.

For different types of energy spectrum images, the validation substances listed in Annex 1-1 are those that are more frequently used in the energy spectrum imaging function at present, such as iodine and calcium in the image of substance concentration distribution. If the energy spectrum imaging function of the declared product involves the energy spectrum images of other substances, such as the concentration distribution images of HAP, iron and other substances, the applicant can refer to the existing contents in Annex 1-1 to supplement the relevant performance indexes and test methods according to the product function. Further, if the declared product has other functions based on energy spectrum imaging technology other than those listed above, the applicant may formulate corresponding performance indexes and test methods according to the product functions.

According to Annex 1-2 in the appendix to the product technical requirements to provide product specifications and product configuration information of the components involved in the spectral imaging function, as a supplement to the ‘product configuration table’ in the CT guidelines.

2. Product performance study

3.Radiation safety study

Provide information on the dose evaluation study of the energy spectrum imaging function. Describe the dose control method and realisation method of energy spectrum imaging. For the dose value of typical energy spectrum imaging scanning protocols, explain the reference and formulation of the basis and submit relevant supporting information.

4.Software research

With reference to the ‘Guiding Principles for the Review of Medical Device Software Registration’ [3], the software research information in the software study provides information on the software functions and core algorithms involved in the energy spectrum imaging function. For brand new algorithms, it is necessary to provide algorithm research reports.

If it involves the use of deep learning algorithms and other artificial intelligence technology, should refer to the ‘Artificial Intelligence Medical Device Registration Review Guidelines’ [4] to submit the corresponding information.

Clinical evaluation information

For CT with spectral imaging function, the applicant for registration shall submit clinical evaluation information containing clinical evaluation of spectral imaging function according to the requirements of the ‘Guiding Principles for Clinical Evaluation of Medical Devices’ [5] and the ‘Guiding Principles for Technical Guidance on Clinical Evaluation Report for Medical Device Registration and Declaration’ [6].