Soft Reconstruction Kernels Improve HCC Imaging on a Photon-Counting Detector CT.

RATIONALE AND OBJECTIVES: Hepatocellular carcinoma (HCC) is the only tumor entity that allows non-invasive diagnosis based on imaging without further histological proof. Therefore, excellent image quality is of utmost importance for HCC diagnosis. Novel photon-counting detector (PCD) CT improves image quality via noise reduction and higher spatial resolution, inherently providing spectral information. The aim of this study was to investigate these improvements for HCC imaging with triple-phase liver PCD-CT in a phantom and patient population study focusing on identification of the optimal reconstruction kernel. MATERIALS AND METHODS: Phantom experiments were performed to analyze objective quality characteristics of the regular body and quantitative reconstruction kernels, each with four sharpness levels (36-40-44-48). For 24 patients with viable HCC lesions on PCD-CT, virtual monoenergetic images at 50 keV were reconstructed using these kernels. Quantitative image analysis included contrast-to-noise ratio (CNR) and edge sharpness. Three raters performed qualitative analyses evaluating noise, contrast, lesion conspicuity, and overall image quality. RESULTS: In all contrast phases, the CNR was highest using the kernels with a sharpness level of 36 (all p < 0.05), with no significant influence on lesion sharpness. Softer reconstruction kernels were also rated better regarding noise and image quality (all p < 0.05). No significant differences were found in image contrast and lesion conspicuity. Comparing body and quantitative kernels with equal sharpness levels, there was no difference in image quality criteria, neither regarding in vitro nor in vivo analysis. CONCLUSION: Soft reconstruction kernels yield the best overall quality for the evaluation of HCC in PCD-CT. As the image quality of quantitative kernels with potential for spectral post-processing is not restricted compared to regular body kernels, they should be preferred.

Photon-counting detector CT improves quality of arterial phase abdominal scans: A head-to-head comparison with energy-integrating CT.

PURPOSE: Photon-counting detector (PCD)-CT is expected to have a substantial impact on oncologic abdominal imaging. We compared subjective and objective image quality between PCD-CT and conventional energy-integrating detector (EID-)CT arterial phase abdominal scans. METHODS: This study included 84 patients undergoing both types of abdominal CT. EID-CT scans were acquired with a tube voltage of 100 kVp. With PCD-CT, acquired with 120-kVp, we reconstructed polychromatic T3D images and virtual monoenergetic images (VMIs) in 10-keV intervals from 40 to 90 keV. Quantitative image analysis included noise and contrast-to-noise ratio (CNR) of hepatic vessels, kidney cortex, and hypervascular liver lesions to liver parenchyma. Three raters used a 5-point Likert scale for qualitative image analysis of image noise and contrast, lesion conspicuity, and overall image quality. Radiation dose exposure (CT dose index) was compared between the two CT types. RESULTS: Mean CT dose index and effective dose were respectively 18 % and 26 % lower with PCD-CT versus EID-CT. Compared with EID-CT, CNRs of kidney cortex and vessel to liver parenchyma were significantly higher in PCD-CT VMIs at energies ≤ 60 keV and in polychromatic T3D images (p < 0.004). Overall image quality of PCD-CT VMIs at 50 and 60 keV was rated as significantly better (p < 0.01) than the EID-CT images (inter-reader agreement alpha = 0.80). Lesion conspicuity was significantly better in low-keV VMIs (p < 0.03) and worse in > 70-keV VMIs. CONCLUSIONS: With low-keV VMI, PCD-CT yields significantly improved objective and subjective quality of arterial phase oncological imaging compared with EID-CT. This advantage may translate into higher diagnostic confidence and lower radiation dose protocols.

Hyperpolarized 1H long lived states originating from parahydrogen accessed by rf irradiation.

Hyperpolarization has found many applications in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). However, its usage is still limited to the observation of relatively fast processes because of its short lifetimes. This issue can be circumvented by storing the hyperpolarization in a slowly relaxing singlet state. Symmetrical molecules hyperpolarized by Parahydrogen Induced Hyperpolarization (PHIP) provide straightforward access to hyperpolarized singlet states because the initial parahydrogen singlet state is preserved at almost any magnetic field strength. In these systems, which show a remarkably long (1)H singlet state lifetime of several minutes, the conversion of the NMR silent singlet state to observable magnetization is feasible due to the existence of singlet-triplet level anti-crossings. Here, we demonstrate that scaling the chemical shift Hamiltonian by rf irradiation is sufficient to transform the singlet into an observable triplet state. Moreover, because the application of one long rf pulse is only partially converting the singlet state, we developed a multiconversion sequence consisting of a train of long rf pulses resulting in successive singlet to triplet conversions. This sequence is used to measure the singlet state relaxation time in a simple way at two different magnetic fields. We show that this approach is valid for almost any magnetic field strength and can be performed even in the less homogeneous field of an MRI scanner, allowing for new applications of hyperpolarized NMR and MRI.