PCCT virtual monoenergetic imaging (VMI) improved visualization of hypovascularized liver metastases, with the greatest lesion conspicuity and CNR achieved at the low end of the keV spectrum. At 40 keV, tumor-to-liver ratio (TLR) reached 0.37, while CNR peaked at 6.88.
Compared with conventional EID-CT, PCCT showed lower image noise at 70 keV (15.4 vs. 17.1 HU), while VMI below 70 keV produced higher lesion CNR and greater tumor-to-liver contrast.
The advantage was particularly relevant in patients with higher BMI: around the clinically relevant 60–80 keV range, PCCT maintained image noise and largely preserved CNR despite a more moderate CTDI upregulation than EID-CT.
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Figure 4. Example of PCD-VMIs (40–190 keV) in a patient with hypovascularized liver metastases of pleura mesothelioma. Hypovascularized metastasis in segment VI (arrow).
Protocol
Detail | Value |
|---|
Scanner (PCCT) | NAEOTOM Alpha |
Scanner (EID-CT) | SOMATOM AS20 |
Application | Contrast-enhanced abdominal oncologic CT; hypovascularized liver metastases |
Study population | 100 patients with liver metastases: PCCT n = 50, EID-CT n = 50 |
PCCT acquisition mode | QuantumPlus with spectral information |
Detector energy thresholds | 20, 35, 65, 70 keV |
Scan direction | Craniocaudal |
Patient position | Supine |
Scan range | Diaphragm or upper thoracic aperture to symphysis |
Breath-hold | Single breath-hold |
Tube voltage (PCCT) | 120 kVp |
Tube current modulation | CARE Dose4D |
IQ level | 145 |
Rotation time | 0.25 s |
Pitch | 0.8 |
Collimation | 144 × 0.4 mm |
Reconstruction kernel | Qr40 |
Iterative reconstruction | QIR 3 |
Slice thickness | 1.0 mm |
Reconstruction increment | 1.0 mm |
Spectral postprocessing | SPP spectral series |
VMI levels | 40, 45, 50, 55, 60, 70, 80, 90, 100, 110, 130, 150, 170, 190 keV |
Contrast agent | Iopromide (Ultravist 300 mg I/mL) |
Contrast volume | 120 mL |
Saline chaser | 30 mL |
Flow rate | 4.0 mL/s |
Bolus triggering | 120 HU in ascending aorta |
Post-trigger delay | 45 s |
EID-CT tube voltage | Auto-kV; 100 kVp in 46 patients, 120 kVp in 4 patients |
EID-CT rotation time | 0.5 s |
EID-CT pitch | 1.05 |
EID-CT collimation | 1.5 × 16 × 1.2 mm |
EID-CT reconstruction | I31f, SAFIRE level 3 |
Primary endpoints | Image noise, tumor-to-liver ratio (TLR), contrast-to-noise ratio (CNR), BMI-dependent performance |
Key Results
Parameter | Main finding |
|---|
Optimal lesion conspicuity | Greatest at low-keV VMI; TLR was lowest at 40 keV (0.37) |
CNR | Maximum at the low end of the spectrum: 6.88; CNR was significantly higher at ≤70 keV than >70 keV |
Image noise | At 70 keV, PCCT had lower noise than EID-CT: 15.4 vs. 17.1 HU |
70-keV comparison | TLR and CNR were broadly comparable between PCCT and EID-CT |
<70-keV advantage | PCCT provided higher CNR and greater lesion conspicuity than EID-CT |
BMI effect | At 70 keV, PCCT maintained similar noise in high- vs. low-BMI patients (15.8 vs. 15.3 HU) |
Dose/BMI relationship | CTDI increased with BMI on both systems, but the increase was more pronounced with EID-CT |
Main implication | Spectral PCCT allows low-keV VMI to increase iodine contrast and improve visualization of hypovascularized liver metastases while maintaining favorable noise characteristics, with a particular advantage in larger patients. |
Source:
Bette S, Decker JA, Braun FM, Becker J, Haerting M, Haeckel T, Gebhard M, Risch F, Woźnicki P, Scheurig-Muenkler C, Kroencke TJ, Schwarz F. Optimal Conspicuity of Liver Metastases in Virtual Monochromatic Imaging Reconstructions on a Novel Photon-Counting Detector CT—Effect of keV Settings and BMI. Diagnostics. 2022;12(5):1231. doi:10.3390/diagnostics12051231.
