CHEST: Spectral CT Flashcards
(32 cards)
What is the conventional 120kVp image in spectral CT and what is its clinical relevance?
The conventional 120kVp image allows accurate HU measurements on true conventional 120kVp images. Its clinical relevance is providing accurate HU measurements that are comparable to standard CT imaging.
What are MonoE (monoenergetic) images and what energy range do they cover?
MonoE images display the quantified attenuation that would have been obtained from a pure monochromatic beam of X keV. The energy range is 40-200 keV.
What are the 6 main clinical benefits of MonoE images?
- Boost of iodine conspicuity at low keV’s
- Improves lesion visualization and characterization
- Improvement in contrast to noise ratio - better visualization of grey/white matter
4.Reduces beam hardening artifacts at high keV’s
- Reduces metal artifact reduction at high keV’s
- Provides consistent CT numbers independent of patient size
What is the crucial warning when measuring HU values on MonoE images?
Beware measuring HU’s at different keV’s – they change. HU values are energy-dependent in monoenergetic images.
What is “Iodine no water” imaging and what does it highlight?
An image that displays iodine quantifications for all voxels above the water line based on water/iodine pair. It highlights the distribution of iodine in the body, excluding regions that resemble water.
What important technical detail should be understood about “no water” suppression?
While technically based on iodine-water material decomposition, the “no water” image doesn’t only remove pure water – it suppresses any tissue whose attenuation closely matches that of water across the energy spectrum.
What 4 types of structures remain visible on iodine no water images and why?
- Blood vessels - Iodine-rich blood enhances
- Enhancing tumors - Iodine uptake present
- Perfused organ segments - Active contrast delivery
- Hypervascular lesions - Strong iodine signal
What 5 types of structures are suppressed on iodine no water images and why?
- Edema - Behaves like water in attenuation curve
- CSF/Ventricular fluid - Very similar to water – subtracted
- Serous fluid/ascites/pleural effusion - Water based → removed
- Unenhanced soft tissue (muscle, brain, parenchyma, liver without contrast) - Not “pure-water”, but close enough in attenuation to be mostly suppressed
- Necrotic tumor core - Often fluid like → diminished signal
What is the difference in purpose between iodine density and iodine no water imaging?
Iodine density: Measures how much iodine is present
Iodine no water: Shows where iodine is, hides water-like tissue
How do the outputs differ between iodine density and iodine no water?
Iodine density: Quantitative (mg/ml)
Iodine no water: Qualitative (visual-only map)
What are the suppression differences between iodine density and iodine no water?
Water suppression: Iodine density = No, Iodine no water = Yes
Bone suppression: Both = Yes
What are the different clinical applications for iodine density vs iodine no water?
Iodine density: Tumor perfusion, delayed contrast mapping
Iodine no water: Highlighting active enhancement
How do iodine density and iodine no water images appear differently?
Iodine density: Color map or grayscale overlay (with HU)
Iodine no water: High-contrast “iodine-only” map
What is “iodine quantification” in spectral CT?
How much iodine (contrast) is present in each voxel, measured in mg/mL.
What does “water/iodine pair” refer to in spectral CT processing?
The algorithm that compares each voxel’s attenuation to how water and iodine behave at different energies.
What does “above the water line” mean in iodine imaging?
Only includes voxels that behave more like iodine than water (i.e. have contrast enhancement).
Why is bone excluded in iodine quantification algorithms?
Bone has such high attenuation it can confuse the algorithm, so it’s excluded from iodine analysis.
In the PE case, what was the initial imaging problem and what caused it?
The patient performed a Valsalva maneuver during CT acquisition, causing poor quality opacification of pulmonary arteries. The conventional 120kVp images showed no clot from proximal to peripheral vessels.
How did spectral CT help in the PE case and what energy was used?
Monochromatic images at 45 keV revealed a clot in a peripheral pulmonary artery that was not visible on conventional CT. Note the increased contrast level in pulmonary vessels compared to conventional 120kVp images.
What was observed on conventional CT in the lung cancer workup case?
A right upper lung nodule containing a high-density structure where differentiation between calcium and iodine was not obvious.
What was the pathology result and what did spectral CT reveal in the lung cancer case?
Pathology revealed right upper lobe lung adenocarcinoma (ADK). Iodine uptake was noted in the right upper lung nodule (1.44 mg Iodine/ml) and right mediastinal adenopathy (0.58 mg Iodine/ml). This coarse calcification type can be observed in lung cancer.
What additional information was provided by the Z effective map in the lung cancer case?
The same iodine uptake information was displayed in color on the Z effective map, providing another way to visualize the enhancement pattern.
What was found on conventional and 70 keV monoenergetic images in the patient with thyroid cancer history?
A small lung nodule was observed in the left upper lobe on conventional CT. The 70 keV monoenergetic image showed the same image quality as 120kV but didn’t achieve further characterization of the lung nodule.
How did iodine density help in the thyroid cancer case?
Iodine density application showed a significant iodine uptake difference, helping to characterize the lung nodule that couldn’t be further characterized with conventional or 70 keV images.
