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.
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.
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.
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.
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.
Hybrid PET/MRI imaging techniques are become more readily available, and its role in viability assessment appears promising.
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 timeof-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. PET/ MR is rapidly emerging as a promising new hybrid imaging modality. Among several differentiating features when compared with PET/CT, the combination of PET with MR imaging can potentially benefit from reduced radiation for the patient and predominantly from the wider range of tissue characteristics generated by appropriate MR imaging sequences and their multiparametric combinations (1). MR provides anatomic imaging with better soft-tissue depiction and more dedicated tissue contrast than CTand furthermore offers insight into a variety of aspects of human physiology with the potential to image metabolic processes and physiologic function (2-4), complementing metabolic and molecular information afforded by PET for better assessment of the underlying physiopathology (5). Beyond these diagnostic aspects, in the hybrid setting with PET, MR data are also used to estimate tissuedependent photon attenuation and scatter to improve the quantitative accuracy of PET images (6-8). The MR-based motion correction of PET reconstruction to improve PET image quality is also supported (9,10).Spatial resolution and quantification accuracy in PET imaging are limited by the low detector spatial resolution and poor photon counting statistics. Early developments in PET reconstruction techniques have addressed this limitation by modeling the underlying photon generation statistics and taking advantage of the physics of coincidence detection to find an app...
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