CT perfusion and dual energy CT of head and neck cancer

2.1. Background & purpose The recent introduction of new technical innovations such as CT perfusion (CTP) and dual energy CT (DECT) increases the diagnostic abilities of CT for imaging of the head and neck (H&N). The aim of this work was to evaluate the role of CTP and DECT in head and neck imaging. The first part tests whether CTP can differentiate between malignant H&N tumors and surrounding muscle, and discusses the impact of arterial input selection and tumor region of interest (ROI) on CTP of H&N cancer. The second part of the study evaluates radiation dose and image quality of DECT of the H&N. Finally the use of DE derived weighted averaging to improve lesion delineation and image quality is discussed. 2.2. Patients and methods CT perfusion Retrospective analysis of CTP was done for a total number of 55 cases of H&N tumors. Perfusion parameters were calculated for 33 cases of squamous cell carcinoma (SCC) and compared to those of muscles. CTP parameters of 50 cases of H&N tumors calculated using different arterial input functions were compared. CTP was calculated for 28 SCC cases using the single dynamic CT section that shows maximal tumor dimension compared to using average values obtained from all tumor-containing dynamic CT sections. Dual energy CT of head and neck This prospective part of the study was further divided into 2 parts. In the first part 32 consecutive patients underwent DECT of the H&N and were compared to a standard single energy CT (SE) control group. Radiation doses were compared. Weighted-average images from raw data of the 2 DE tubes (weighting factor 0.3 from 80 kVp and 0.7 from 140 KVp) were compared to SE images. Image noise was compared at 5 anatomic levels. Two blinded readers compared subjective overall image quality on a 5-point grading scale. In the second part 35 proved SCC cases underwent DECT of the neck. Pure 140 kVp and 80 kVp image datasets as well as weighted-average images from raw data of the 2 DE tubes at weighting factors 0.3, 0.6, 0.8 (30%, 60% and 80% from 80 kVp raw data respectively) were reconstructed. Objective image noise, contrast to noise ratio (CNR) and subjective image quality were compared between the 5 image datasets. Results CT perfusion Tumor perfusion parameters were significantly higher than those of muscle (p 0.05) were observed between perfusion parameters obtained using internal carotid artery (ICA) versus external carotid artery (ECA) and ipsilateral versus contralateral ICA. High correlation was observed between perfusion parameters calculated using one section with maximal tumor dimension and the average of multiple sections. Differences between the means were non significant, p values>0.05. The 95% limits of agreement between repeated measurements using average of multiple sections were slightly narrower for blood volume and permeability than those of repeated measurements using one section. Dual energy CT of head and neck CTDIvol was 12% lower with DE than SECT (p0.05). There were no significant differences between DE- and SECT in attenuation measurements, all p values >0.05. No significant differences in subjective image quality scores were observed between DE- and SECT at any of the 5 anatomic levels (p >0.05). At weighting factor 0.6 the lesion CNR was significantly higher than at weighting factor 0.3 and at pure 140 kVp image dataset (p 0,05) beobachtet. CT Perfusionsparameter, die aus einem Bildausschnitt mit maximaler Tumordimension errechnet wurden, wiesen keinen signifikanten Unterschied zu Durchschnittswerten aus mehreren Bildabschnitten (p > 0,05) auf. Allerdings wurde insgesamt eine hohe Korrelation zwischen den 2 verschiedenen Methoden beobachtet. Die 95%ige Übereinstimmung zwischen den Durchschnittswerten für Blutvolumen und Perfusion, die aus wiederholten Messungen von mehreren Bildausschnitten gewonnen wurden, war etwas kleiner als die 95%ige Übereinstimmung bei wiederholten Messungen in einem Bildausschnitt. Dual Energy CT von Kopf und Hals Das CTDIvol war im DECT 12% niedriger als mit single energy CT (p 0,05). Ebenfalls wurden keine signifikanten Unterschiede zwischen DECT und single energy CT in den Schwächungsmessungen festgestellt (p> 0,05). Es fanden sich auch keine signifikanten Unterschiede in der subjektiven Bildqualität zwischen DECT und single energy CT in der Evaluation der 5 anatomischen Ebenen (p> 0,05). Im DECT zeigte sich bei Gewichtungsfaktor 0,6 ein signifikant höherer CNR im Vergleich zu Gewichtungsfaktor 0,3 und dem reinen 140 kV Datensatz (p