Chest CT at a dose below 0.3 mSv: impact of iterative reconstruction on image quality and lung analysis.

BACKGROUND: In chest computed tomography (CT), iterative reconstruction (IR) algorithms maintain diagnostic image quality (IQ) while significantly reducing the dose. PURPOSE: To evaluate the impact of IR on IQ of chest CT at effective doses below 0.3 mSv. MATERIAL AND METHODS: Twenty chest CT scans performed at effective dose below 0.3 mSv (CT1) were reconstructed varying three parameters: filtered back-projection and IR iDose(4) algorithms; 512 × 512 and 768 × 768 matrices; and sharp and soft kernels, thus generating eight series per patient. The qualitative evaluation of the IQ was performed by ranking series from 1 to 8 (8 corresponding to the highest rank) which was subsequently compared to quantitative assessment of IQ by using an appropriated merit formula. Intra- and inter-reader IQ ranking reliability was also evaluated using Cohen's kappa. Analysis of lung findings was finally compared between the best CT1 series and the reference CT (CT0). RESULTS: The best series in terms of qualitative and quantitative IQ was obtained using IR, 512(2) matrix and soft kernel. The best CT1 series detected nodules greater than 4 mm with an almost perfect match with CT0. CONCLUSION: Chest CT performed at effective doses below 0.3 mSv may be used to confidently diagnose lesions greater than 4 mm using iDose(4), soft kernel and 512 × 512 matrix.

All-in-one interictal presurgical imaging in patients with epilepsy: single-session EEG/PET/(f)MRI.

PURPOSE: In patients with pharmacoresistant focal epilepsy, resection of the epileptic focus can lead to freedom from seizures or significant improvement in well-selected candidates. Localization of the epileptic focus with multimodal concordance is crucial for a good postoperative outcome. Beyond the detection of epileptogenic lesions on structural MRI and focal hypometabolism on FDG PET, EEG-based Electric Source Imaging (ESI) and simultaneous EEG and functional MRI (EEG-fMRI) are increasingly applied for mapping epileptic activity. We here report presurgical multimodal interictal imaging using a hybrid PET/MR scanner for single-session FDG PET, MRI, EEG-fMRI and ESI. METHODS: This quadrimodal imaging procedure was performed in a single session in 12 patients using a high-density (256 electrodes) MR-compatible EEG system and a hybrid PET/MR scanner. EEG was used to exclude subclinical seizures during uptake of the PET tracer, to compute ESI on interictal epileptiform discharges and to guide fMRI analysis for mapping haemodynamic changes correlated with interictal epileptiform activity. RESULTS: The whole multimodal recording was performed in less than 2 hours with good patient comfort and data quality. Clinically contributory examinations with at least two modalities were obtained in nine patients and with all modalities in five patients. CONCLUSION: This single-session quadrimodal imaging procedure provided reliable and contributory interictal clinical data. This procedure avoids multiple scanning sessions and is associated with less radiation exposure than PET-CT. Moreover, it guarantees the same medication level and medical condition for all modalities. The procedure improves workflow and could reduce the duration and cost of presurgical epilepsy evaluations.

Sequential whole-body PET/MR scanner: concept, clinical use, and optimisation after two years in the clinic. The manufacturer's perspective.

PET and MRI are established clinical tools which provide complementary information, but clinical workflow limits widespread clinical application of both modalities in combination. The two modalities are usually situated in different hospital departments and operated and reported independently, and patients are referred for both scans, often consecutively. With the advent of PET/MR as a new hybrid imaging modality there is now a possibility of addressing these concerns. There are two different design philosophies for integrated PET/MR imaging-positioning PET inside the MRI magnet or in tandem, similar to PET/CT. The Ingenuity TF PET/MR by Philips Healthcare is a sequential PET/MR tomograph combining state-of-the-art time-of-flight PET and high-field MRI with parallel transmission capabilities. In this review article we describe the technology implemented in the system, for example RF and magnetic shielding, MR-based attenuation correction, peculiarities in scatter correction, MR system optimisation, and the philosophy behind its design. Furthermore, we provide an overview of how the system has been used during the last two years, and expectations of how the use of PET/MR may continue in the years to come. On the basis of these observations and experiences we discuss the utility of the system, clinical workflow and acquisition times, and possible ways of optimization.

Approaches for the optimization of MR protocols in clinical hybrid PET/MRI studies.

Magnetic resonance imaging (MRI) is the examination method of choice for the diagnosis of a variety of diseases. MRI allows us to obtain not only anatomical information but also identification of physiological and functional parameters such as networks in the brain and tumor cellularity, which plays an increasing role in oncologic imaging, as well as blood flow and tissue perfusion. However, in many cases such as in epilepsy, degenerative neurological diseases and oncological processes, additional metabolic and molecular information obtained by PET can provide essential complementary information for better diagnosis. The combined information obtained from MRI and PET acquired in a single imaging session allows a more accurate localization of pathological findings and better assessment of the underlying physiopathology, thus providing a more powerful diagnostic tool. Two hundred and twenty-one patients were scanned from April 2011 to January 2012 on a Philips Ingenuity TF PET/MRI system. The purpose of this review article is to provide an overview of the techniques used for the optimization of different protocols performed in our hospital by specialists in the following fields: neuroradiology, head and neck, breast, and prostate imaging. This paper also discusses the different problems encountered, such as the length of studies, motion artifacts, and accuracy of image fusion including physical and technical aspects, and the proposed solutions.

Fat-constrained 18F-FDG PET reconstruction in hybrid PET/MR imaging.

UNLABELLED: Fusion of information from PET and MR imaging can increase the diagnostic value of both modalities. This work sought to improve (18)F FDG PET image quality by using MR Dixon fat-constrained images to constrain PET image reconstruction to low-fat regions, with the working hypothesis that fatty tissue metabolism is low in glucose consumption. METHODS: A novel constrained PET reconstruction algorithm was implemented via a modification of the system matrix in list-mode time-of-flight ordered-subsets expectation maximization reconstruction, similar to the way time-of-flight weighting is incorporated. To demonstrate its use in PET/MR imaging, we modeled a constraint based on fat/water-separating Dixon MR images that shift activity away from regions of fat tissue during PET image reconstruction. PET and MR imaging scans of a modified National Electrical Manufacturers Association/International Electrotechnical Commission body phantom simulating body fat/water composition and in vivo experiments on 2 oncology patients were performed on a commercial time-of-flight PET/MR imaging system. RESULTS: Fat-constrained PET reconstruction visibly and quantitatively increased resolution and contrast between high-uptake and fatty-tissue regions without significantly affecting the images in nonfat regions. CONCLUSION: The incorporation of MR tissue information, such as fat, in image reconstruction can improve the quality of PET images. The combination of a variety of potential other MR tissue characteristics with PET represents a further justification for merging MR data with PET data in hybrid systems.

Clinical applications of hybrid PET/MRI in neuroimaging.

PURPOSE: We tested the performance and clinical applicability of combined protocols for brain imaging studies acquired on a new whole-body hybrid PET/MR scanner. PATIENTS AND METHODS: Fifteen patients [6 male and 9 female patients; mean (SD) age, 51 (30) y; range, 6-89 y] were scanned on a Philips Ingenuity TF PET/MR. Standard imaging protocols of both modalities were combined, using a "head coil" and contrast-enhanced fully diagnostic MR protocols. Attenuation correction of the PET images was performed using tissue segmentation of the MR image and incorporation of attenuation templates measured for coils and table.The clinical indications evaluated are as follows: patients with cognitive disturbance of suspected neurodegenerative origin, presurgical evaluation of drug-refractory epilepsy, and brain tumor staging. For the first 2 indications, FDG PET imaging was performed, whereas for the last, fluoroethyltyrosine, an amino acid tracer, was used. RESULTS: In all cases (4 patients with neurodegenerative disease, 6 patients with epilepsy, and 5 patients with high-grade tumor), we obtained full diagnostic quality of both modalities and the total duration of the examination remained within a tolerable range (<2 hours). Twelve subjects had pathological findings: 11 of which were confirmed by clinical follow-up as true positive and 1 was confirmed as a false-positive result. For the 3 normal studies, the clinical follow-up confirmed the imaging findings as true-negative. CONCLUSIONS: Acquiring both PET and MR in a single session on a hybrid system minimized patient discomfort while maximizing clinical information and optimizing registration of both modalities. In addition, in comparison to PET/CT, the effective dose (related to CT) was reduced, and this is particularly beneficial in the pediatric population.