Perfusion computed tomography of the liver
Background: Perfusion CT (P-CT) is a relatively new imaging technique that permits the visual and quantitative assessment of the micro- and macrocirculation of a target organ and focal lesions. P-CT has shown promising results in the evaluation of hyper-vascular tumors such as hepatocellular carcinoma (HCC). HCC is the sixth most common cancer globally and it has a poor prognosis when discovered at a late tumor stage. Any improvement in HCC detection would be directly beneficial for patient care. This thesis aims to investigate the strengths and limitations of whole liver P-CT and to evaluate if PCT can improve the detection of hyper-vascular liver lesions in patients with chronic liver disease.
Methods: Study I: Twenty-four patients, who underwent dynamic P-CT for detection of HCC were retrospectively divided into three groups: (1) without portal-venous hypertension (PVH) (n = 8), (2) with PVH (n = 8), (3) with PVH and thrombosis (n = 8). Time to peak splenic- and peak renal enhancement (PSE resp. PRE), as well as arterial liver perfusion (ALP), portal- venous liver perfusion (PLP) and hepatic perfusion-index (HPI) of the liver and HCC derived from PSE- versus PRE- based modelling were compared between the groups. Study II: Group A (n=15) and Group B (n= 38) underwent P-CT using 50 ml contrast medium (CM). Group B underwent an additional standard multiphasic liver CT using 120ml (70-143 ml). Triple-arterial CT image sets were reconstructed from P-CT by fusing three dedicated arterial time points. Triple-arterial CT and single-arterial CT were compared by two readers (R1, R2), who assessed subjective image quality (IQ) and HCC detection rate. A third reader assessed objective IQ.Study III: Fifty study participants (Group A) were scanned with P-CT, a high CM volume protocol and bolus-tracking technique to depict ten arterial phases. Time attenuation curves were created for hyper-vascular liver lesions, liver parenchyma and hepatic vascular structures. 16 participants of Group A with lesions were further analyzed and radiation dose-neutral quadruple arterial phase image sets were created (Group A1). Group A1 was then compared to a Control Group (Group B) consisting of 16 consecutive patients undergoing standard single arterial phase scans. Lesion depiction and quantitative IQ were compared.
Results: Study I: Time to PSE was significantly delayed in PVH groups 2 and 3 (P = 0.02), whereas PRE was similar in groups 1, 2 and 3 (P > 0.05). In group 1, liver and HCC perfusion parameters were similar for PSE- and PRE-based modelling (all P > 0.05), while significant differences were seen for PLP and HPI (liver only) in group 2 and ALP in group 3 (all P < 0.05). Study II: The mean CTDIvol of triple-arterial CT and single-arterial CT was equivalent (P=0.73). Triple-arterial CT showed lower image noise and better contrast-to-noise-ratio (P<0.001, P=0.032, respectively), but no significant difference in lesion-to-liver-contrast-ratio (P=0.31). Subjective IQ was good for both protocols. The detection rate of the 65 HCC lesions was 82%/83% (R1/R2) at triple-arterial CT and 80%/77% (R1/R2) at single-arterial CT (P=0.4). Study III: Both Group A1 and B had 33 hyper-enhancing liver lesions each. The mean CTDIvol of quadruple-arterial CT and single-arterial CT was equivalent (P=0.16). The mean time to reach peak lesion-to-liver contrast (LLC) was 20.1s (±4.2s) with a range of 12.5s to 29.1s. Quadruple arterial CT performed significantly better than the Control Group in regards to LLC (P= .009), CNR (P= .002), Image Noise (P<0.001) and hepatic artery enhancement(P<0.001).
Conclusions: Study I: PSE is significantly delayed in patients with portal venous hypertension, which results in a miscalculation of P-CT parameters. Maximum-slope based P-CT could be improved by replacing the spleen with the kidney as the reference organ. The difference between time to PSE and time to PRE might serve as a non-invasive biomarker of portal venous hypertension. Study II: Radiation dose-equivalent triple arterial phase imaging is feasible and showed superior image quality and similar HCC detection rate as standard single arterial phase CT despite a substantially smaller CM volume. Study III: The optimal scan delay at single arterial phase CT for depiction of hyper-vascular liver lesions occurs at 20 s, when using a high iodine dose CM protocol and bolus-tracking. Fused quadruple arterial phase CT significantly increases lesion depiction, quantitative IQ and hepatic artery enhancement as compared to standard single arterial phase CT, without elevating the total radiation dose.
List of scientific papers
I. Fischer MA, Brehmer K, Svensson A, Aspelin P, Brismar TB. Renal versus splenic maximum slope based perfusion CT modelling in patients with portal-hypertension. Eur Radiol. 2016;26(11):4030-4036.
https://doi.org/10.1007/s00330-016-4277-7
II. Brehmer K, Brismar TB, Morsbach F, Svensson A, Stål P, Tzortzakakis A, Voulgarakis N, Fischer MA. Triple Arterial Phase CT of the Liver with Radiation Dose Equivalent to That of Single Arterial Phase CT: Initial Experience. Radiology. 2018;289(1):111-118.
https://doi.org/10.1148/radiol.2018172875
III. Brehmer K, Fischer MA, Svensson-Marcial A, Stål P, Brismar TB. Multiple-arterial phase CT scanning for visualization of focal arterialized liver lesions. [Manuscript]
History
Defence date
2022-05-20Department
- Department of Clinical Science, Intervention and Technology
Publisher/Institution
Karolinska InstitutetMain supervisor
Brismar, TorkelCo-supervisors
Fischer, Michael; Stål, PerPublication year
2022Thesis type
- Doctoral thesis
ISBN
978-91-8016-609-6Number of supporting papers
3Language
- eng