gms | German Medical Science

Objective: The major goal of preoperative imaging in patients with pituitary tumors is to delineate tumor and to assess cavernous sinus invasion. Until now, MRI is the gold standard imaging modality. However, MRI is limited regarding sufficient information about the bony anatomy. 3D-information about the sphenoid sinus and the sella facilitates the surgical approach in selected cases. Moreover, the number of patients with cardiac pacemakers that limit their access to preoperative MRI is rising. Standard CT of the pituitary gland provides excellent information of the bony anatomy. However, the soft tissue contrast of standard CT is inferior to MRI and patients often undergo preoperative CT and MRI diagnostic. Contrast enhanced dual-energy CT (DECT) enables the calculation of so-called monoenergetic (ME) images between 40-190 keV. Low keV images significantly increase contrast due to the high photon absorption. Thus, the purpose of this feasibility study was to evaluate low keV monoenergetic DECT images as a potential one-stop-shop preoperative modality in patients with pituitary tumours.

Methods: 14 patients with different pituitary gland lesions were prospectively enrolled in this study. All patients underwent contrast enhanced DECT imaging (FORCE, Siemens Healthineers). Imaging data was calculated from 40-190 keV in 10 keV intervals. In addition, a standard 120 kV polyenergetic CT dataset was reconstructed as a standard CT reference method. Objective image quality was evaluated by measuring pituitary gland attenuation and image noise in a standardized region of interest (ROI) on all 34 available datasets. The signal to noise ratio (SNR) was calculated for each dataset by dividing attenuation and image noise. Image quality was evaluated by a neurosurgeon and a radiologist. Both were asked to select 1. best diagnostic image dataset, 2. dataset with best delineation of the cavernous sinuous and 3. best dataset for delineation of cystic tumour areas out of the 34 available datasets.

Results: The ME datasets of 50 and 40 keV showed a higher difference between tumor and sinus cavernosus attenuation (TSAD) when compared to the standard 120 keV CT protocol. The TSAD for the reference polyenergetic 120 keV protocol was 67 HU, for the 50 keV ME 106 HU and for the 40 keV ME 163 HU. Of all datasets, the 40 and 50 keV ME images were preferred regarding overall best image quality by the neurosurgeon as well as by the radiologist.

Conclusion: ME datasets at low keV between 50 and 40 keV significantly improve objective and subjective image quality when compared to standard CT. These findings are explained by the physical k-edge of iodine that leads to an increasing tissue/iodine absorption. Thus, DECT may become the CT imaging technique of choice for pituitary lesions since it allows full flexibility of keV settings and the calculation of virtually non-contrast enhanced images.