Aims and objectives
- to explain how to choose the most appropriate combination of reconstruction type/filter on CT scan types of equipment for calculation of the emphysema index (EI).
In histology,
macroscopic emphysema is defined as cavities in the lung with a dimension of ≥ 1 mm.
We propose the same goal on a CT scan: to detect holes in the lung ≥ 1 mm.
Methods and materials
Equipment: iCT,
IntellispacePortal Workstation with COPD density software (Philips,
Best,
the Netherlands)
Catphan phantom (1) and CT-performance phantom (2): both phantoms are scanned with the scan protocol of the thorax with 100 kV.
The field of view (FOV) in the catphan phantom was 10 cm (goal: optimal resolution) and in the CT-performance phantom 35 cm (standard FOV for CT scan of the thorax).
Reconstructions are made with Filtered Back Projection (FBP),
iterative reconstructions (IR) and model-based IR (MBIR) in combination with a hard filter and...
Results
(1): The density plot line in IMR-BSP reaches the minimum peak-value the fastest when compared to iDose4-L and FBP-L.
The density plot line in reconstructions with soft filters reaches the minimum peak value later than in hard ones.
All combinations start to detect the low pixel values too late (Fig 2).
(2): Cavities of 1.00 mm are not detected.
The cavity of 1.25 mm is detected in IMR-BSP,
1.75 mm is detected by iDose4-L and FBP-L.
Reconstructions derived from soft filters,
regardless of the reconstruction...
Conclusion
On an iCT type of equipment,
EI is most reliable,
but still underestimated in reconstructions with IMR-BSP because:
a change in density is detected the fastest,
but not instantaneous
only cavities >1.25 mm are detected.
References
http://physics.indiana.edu/∼courses/p551/f13/Experiments_files/Modus_DeskCAT_LM3_P551.pdf Published 2013.
Accesses Dec 6,
2018
Friedmann SN,
Fung GS,
Siewerden JH,
Tsui BM.
A simple approach to measure computed tomography (CT) modulation transfer function (MTF) and noise-power spectrum (NPS) using the American College of Radiology (ACR) accreditation phantom.
Med Phys 2013;(40)5:051907