3001 - Quantitative Assessment of Virtual Monoenergetic Imaging on Metal-Induced Blooming in Photon-Counting CT Using Edge-Profile MTF

Purpose/Objective(s):

Photon-counting CT (PCCT) enables reconstruction of virtual monoenergetic images (VMI), offering an advantage in suppressing metal-induced blooming artifacts. The improved image quality and enhanced edge sharpness at implant-tissue interfaces allow more accurate delineation of implant contours without dimension overestimation. Previous studies have demonstrated high keV VMI effectively mitigates blooming effect around metal implants. This study evaluates the edge sharpness degradation caused by metal-induced blooming artifacts, using modulation transfer function (MTF) derived from edge profiles in a phantom with titanium (Ti) and steel plugs, with an illustrative patient case with metal implant.

Materials/Methods:

A tissue characterized phantom containing various material plugs, including a large metal plug (Ti/steel) simulating an implant, was scanned on PCCT at 120kVp. VMIs were generated at low (50 keV) and high (190 keV) keV levels, with iterative metal artifact reduction (iMAR) applied, and referenced with T3D images that are equivalent to conventional CT images. Twenty edge profiles were drawn perpendicular to the metal–water-equivalent material interface and processed to obtain MTFs. MTF50 was used as the indicator for edge sharpness. In the patient case, MTF50 was analyzed similarly from profiles focused on the metal–tissue interface.

Results:

High keV VMI (190keV) yielded the highest MTF50 values among all scenarios, with mean values of 0.3713 lp/mm and 0.3094 lp/mm for the Ti and steel plug, respectively, and 0.4812 lp/mm in the patient case. The results indicate improved edge sharpness under high keV VMI.

Conclusion:

The edge profile derived MTF analysis demonstrates that high keV VMI in PCCT substantially improves edge sharpness compared to T3D image and suppresses blooming effect. The finding supports the routine clinical use of contouring metal implant on high keV VMI for better accuracy and minimizing overestimation of implant dimensions.

Table 1. MTF50 values at high and low keV VMI levels in phantom (Ti/Steel plug) and patient cases, averaged over 20 profiles.

Case	Image sets	MTF50 (lp/mm) (mean ± SD)
Phantom with Ti plug	50 keV VMI	0.2917 ± 0.0496
	190 keV VMI	0.3713 ± 0.0925
	T3D	0.3083 ± 0.0607
Phantom with Steel plug	50 keV VMI	0.2416 ± 0.1294
	190 keV VMI	0.3094 ± 0.0454
	T3D	0.3020 ± 0.0342
Patient with metal implant	50 keV VMI	0.3728 ± 0.0548
	190 keV VMI	0.4812 ± 0.0966
	T3D	0.3550 ± 0.1776