European Radiology: Application of photon counting detector CT to reduce metal artifacts in cranial images

At this stage, brain computed tomography (CT) is still one of the essential tests for the diagnosis and treatment of
a large number of brain diseases.
In addition to limitations of radiation exposure and inadequate soft-tissue contrast, CT imaging can be affected by a large number of artifacts caused by metal implants, particularly after
intracranial aneurysm intravascular platinum coil embolization.
Because these coil-related artifacts can limit the diagnostic value of subsequent CT recordings, particularly in the detection of acute cerebral hemorrhage or low-density ischemic stroke areas around intravascular platinum coils, several acquisition and post-processing techniques have been clinically introduced in the past few years to improve image quality, Reduce image artifacts
.

At this stage, the photon counting detector CT (PCD-CT)
has been introduced clinically.
Compared to the energy integration detectors (EIDs) currently in use in clinical CT scanners, this new technique is able to convert X-ray photons directly into electronic signals without the intermediate step
of converting photons into visible light like scintillators.
PCD-CT offers the advantages of reduced radiation exposure, improved spatial resolution, correction of beam hardening artifacts, and the use of alternative contrast agents, while creating opportunities
for quantitative imaging.
In addition, PCD-CT itself provides spectral information, which further increases the potential
for metal artifact reduction (MAR).
So far, only limited studies have explored metal-related imaging artifacts as well as MAR options
in PCD-CT.

Recently, a study published in the journal European Radiology evaluated imaging artifacts caused by neurovascular platinum coils and the MAR effect of PCD-CT compared to EID-CT in an experimental in vitro model using standard brain imaging protocols, providing technical support
for further improving image quality and diagnostic accuracy.

In this study, a nodular rubber latex resembling a brain aneurysm was filled with a neurovascular platinum coil and then inserted into a brain imaging model
.
Image acquisition and reconstruction
were repeated for PCD-CT and EID-CT (n=10, respectively) using standard brain imaging protocols.
In addition, linear interpolation MAR
was performed on PCD-CT and EID-CT images.
The degree of artifacts was analyzed both quantitatively (standard deviation for regions of interest) and qualitative (analysis on a 5-point scale).


Quantitative and qualitative analysis showed that EID-CT images had a lower degree of metallic artifacts compared to total energy PCD-CT images (e.
g.
, 82.
99 ± 7.
89 Hounsfield (HU) vs.
90.
35 ± 6.
28 HU; P <0.
001), there was no quality difference between the high-energy chamber PCD-CT images and the EID-CT images (4.
18 ± 0.
37 and 3.
70 ± 0.
64; P = 0.
575).

After MAR, PCD-CT images had a more pronounced reduction in artifacts compared to EID-CT images in both analyses (e.
g.
, 2.
35±0.
43 and 3.
18±0.
34; p<0.
001).
<b20>

Figure Schematic of an experimental in vitro model resembling a platinum coil embolized aneurysm of a cerebral artery, whose average attenuation is similar to that of brain tissue in a brain imaging model

The results of this study show that there is no difference in the degree of platinum coil-related artifacts between high-energy chamber PCD-CT images and traditional EID-CT images, while both low-energy chamber PCD-CT and total energy PCD-CT images show higher degree of artifacts
.
However, linear interpolation MAR is able to reduce coil-related artifacts in total energy PCD-CT images, which differ from EID-CT images
.
Therefore, in this in vitro study, combining PCD-CT with MAR provides an improved option
for clinical reduction of coil-related artifacts in brain imaging.

Original source:

Niclas Schmitt,Lena Wucherpfennig,Lukas T Rotkopf,et al.
Metal artifacts and artifact reduction of neurovascular coils in photon-counting detector CT versus energy-integrating detector CT - in vitro comparison of a standard brain imaging protocol.
DOI:10.
1007/s00330-022-09073-y