Despite a myriad of technical advances in medical imaging, as well as the growing need to address the global impact of pulmonary diseases, such as asthma and chronic obstructive pulmonary disease, on health and quality of life, it remains challenging to obtain in vivo regional depiction and quantification of the most basic physiological functions of the lung-gas delivery to the airspaces and gas uptake by the lung parenchyma and blood-in a manner suitable for routine application in humans. We report a method based on MRI of hyperpolarized xenon-129 that permits simultaneous observation of the 3D distributions of ventilation (gas delivery) and gas uptake, as well as quantification of regional gas uptake based on the associated ventilation. Subjects with lung disease showed variations in gas uptake that differed from those in ventilation in many regions, suggesting that gas uptake as measured by this technique reflects such features as underlying pathological alterations of lung tissue or of local blood flow. Furthermore, the ratio of the signal associated with gas uptake to that associated with ventilation was substantially altered in subjects with lung disease compared with healthy subjects. This MRI-based method provides a way to quantify relationships among gas delivery, exchange, and transport, and appears to have significant potential to provide more insight into lung disease.gas exchange | pulmonary function | pulmonary ventilation

No abstract

Learning Objectives: On successful completion of this activity, participants should be able to describe (1) advantages and shortcomings of hybrid PET/MR scanners with respect to cardiovascular applications (e.g. myocardial perfusion imaging and viability imaging), (2) additional value of the MR component in cardiac imaging, and (3) technical challenges and workflow considerations regarding hybrid PET/MR scanners in the field of cardiology (e.g. attenuation correction and cardiac/respiratory/patient motion).Financial Disclosure: Dr. Schwaiger is an investigator, meeting participant, and lecturer for Siemens Medical. The authors of this article have indicated no other relevant relationships that could be perceived as a real or apparent conflict of interest. CME Credit: SNMMI is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to sponsor continuing education for physicians. SNMMI designates each JNM continuing education article for a maximum of 2.0 AMA PRA Category 1 Credits. Physicians should claim only credit commensurate with the extent of their participation in the activity. For CE credit, participants can access this activity through the SNMMI Web site (http:// www.snmmi.org/ce_online) through March 2016.PET/CT and other combined scanners have in the past decade rapidly emerged as important research tools and are proving to be invaluable for improved diagnostics in routine nuclear medicine. The design of hybrid PET/MR scanners presented a formidable technical challenge, and only recently were these instruments introduced to the market. Initial expectations of the performance of these scanners have been high, notably because of the potential for superior tissue contrast inherent in the MR modality, as well as the potential for multiparametric functional imaging in conjunction with PET. However, the additional value and potential clinical role that these new systems might bring to the cardiac field have yet to be documented. This review presents a comparative summary of the existing applications for PET and MR in the field of cardiology and suggests potential cardiac applications exploiting unique properties of the newly introduced combined instrumentation. The diverse range of imaging modalities for cardiology includes echocardiography, CT, MR imaging, SPECT, and PET, each of which offers distinct properties and advantages. The demand for combined PET/CT instrumentation in clinical nuclear medicine has grown remarkably, because of the notable advantages presented by hybrid imaging with respect to anatomic localization of lesions. Although these advantages were initially driven by the demands of oncology imaging, the resultant broader availability of PET/CT has provided the opportunity to use these scanners for indications beyond oncology, such as in the field of cardiac imaging (1). Furthermore, CT images are necessary for rapid attenuation correction, which is of particular importance for quantification in myocardial perfusion imaging. Through the use of suitable CT components a...

Purpose: To develop and test a method to noninvasively assess the functional lung microstructure. Materials and Methods: The Multiple exchange time Xenon polarization Transfer Contrast technique (MXTC) encodes xenon gas‐exchange contrast at multiple delay times permitting two lung‐function parameters to be derived: (i) MXTC‐F, the long exchange‐time depolarization value, which is proportional to the tissue to alveolar‐volume ratio and (ii) MXTC‐S, the square root of the xenon exchange‐time constant, which characterizes thickness and composition of alveolar septa. Three healthy volunteers, one asthmatic, and two chronic obstructive pulmonary disease (COPD) (GOLD stage I and II) subjects were imaged with MXTC MRI. In a subset of subjects, hyperpolarized xenon‐129 ADC MRI and CT imaging were also performed. Results: The MXTC‐S parameter was found to be elevated in subjects with lung disease (P‐value = 0.018). In the MXTC‐F parameter map it was feasible to identify regional loss of functional tissue in a COPD patient. MXTC‐F maps showed excellent regional correlation with CT and ADC (P ≥ 0.90) in one COPD subject. Conclusion: The functional tissue‐density parameter MXTC‐F showed regional agreement with other imaging techniques. The newly developed parameter MXTC‐S, which characterizes the functional thickness of alveolar septa, has potential as a novel biomarker for regional parenchymal inflammation or thickening. J. Magn. Reson. Imaging 2011;33:1052–1062. © 2011 Wiley‐Liss, Inc.

Purpose: The diagnostic gold standard for nonalcoholic fatty liver disease is an invasive biopsy. Noninvasive Cartesian MRI fat quantification remains limited to a breath-hold (BH). In this work, a novel free-breathing 3D stack-of-radial (FB radial) liver fat quantification technique is developed and evaluated in a preliminary study. Methods: Phantoms and healthy subjects (n ¼ 11) were imaged at 3 Tesla. The proton-density fat fraction (PDFF) determined using FB radial (with and without scan acceleration) was compared to BH single-voxel MR spectroscopy (SVS) and BH 3D Cartesian MRI using linear regression (correlation coefficient r and concordance coefficient r c ) and BlandAltman analysis. Results: In phantoms, PDFF showed significant correlation (r > 0.998, r c > 0.995) and absolute mean differences < 2.2% between FB radial and BH SVS, as well as significant correlation (r > 0.999, r c > 0.998) and absolute mean differences < 0.6% between FB radial and BH Cartesian. In the liver and abdomen, PDFF showed significant correlation (r > 0.986, r c > 0.985) and absolute mean differences < 1% between FB radial and BH SVS, as well as significant correlation (r > 0.996, r c > 0.995) and absolute mean differences < 0.9% between FB radial and BH Cartesian.Conclusion: Accurate 3D liver fat quantification can be performed in 1 to 2 min using a novel FB radial technique. Magn Reson Med 79:370-382,

5 TECHNICAL EFFICACY: Stage 5 J. Magn. Reson. Imaging 2018;48:13-26.

Abstract. Accurate localization and uptake quantification of lesions in the chest and abdomen using PET imaging is challenging due to the respiratory motion during the exam. The advent of hybrid PET/MR systems offers new ways to compensate for respiratory motion without exposing the patient to additional radiation. The use of self-gated reconstructions of a 3D radial stack-of-stars GRE acquisition is proposed to derive a high-resolution MRI motion model. The self-gating signal is used to perform respiratory binning of the simultaneously acquired PET raw data. Matching µ-maps are generated for every bin, and post-reconstruction registration is performed in order to obtain a motion-compensated PET volume from the individual gates. The proposed method is demonstrated in-vivo for three clinical patients. Motioncorrected reconstructions are compared against ungated and gated PET reconstructions. In all cases, motion-induced blurring of lesions in the liver and lung was substantially reduced, without compromising SNR as it is the case for gated reconstructions.

ObjectivesTo implement and evaluate a dedicated receive array coil for simultaneous PET/MR in breast cancer. MethodsThe 16 receiver channel coil design was optimized for simultaneous PET/MR. To assess MR performance, signal-to-noise ratio, parallel imaging capability and image quality was evaluated in phantoms, volunteers and patients and compared to clinical standard protocols. For PET evaluation, quantitative 18 F-FDG PET scans of phantoms and seven patients (14 lesions) were compared to scans without coil. In PET image reconstruction, a CT-based template of the coil was combined with the MR-acquired attenuation correction (AC) map of the phantom / patient. ResultsMR image quality was comparable to clinical MR-only exams. PET evaluation in phantoms showed regionally varying SUV underestimation (mean 22%) due to attenuation caused by the coil. This was improved by implementing the CT-based coil template in the AC (< 2% SUV underestimation). Patient data showed that including the coil in the AC increased SUV values in lesions (21% ± 9 %). ConclusionsUsing a dedicated PET/MR breast coil, state-of-the-art MRI was possible. In PET accurate quantification and image homogeneity could be achieved, if a CT-template of this coil was included in the attenuation correction for PET image reconstruction. KeywordsMagnetic Resonance Imaging, Positron-Emission Tomography, Breast cancer, Bilateral breast imaging, RF coil array Key Points• State-of-the-art breast MRI using a dedicated PET/MR breast coil is feasible.• A multi-channel design facilitates shorter MR acquisition times through parallel imaging.• The MR coil inside a simultaneous PET/MR system causes PET photon attenuation.• Including a coil CT-template in PET image reconstruction, accurate quantification is recovered. [2][3][4]. Although successfully applied in many oncologic applications, simultaneous PET/MR in breast cancer has so far been delayed due to the need for a dedicated breast coil, which enables prone positioning and achieves high image quality, as a precondition for state-of-the-art breast MRI [5]. However, the presence of MR related hardware, such as a breast coil, in the PET field-of-view (FOV) causes significant attenuation of the 511 keV annihilation photons, therefore hampering PET image quality [6]. Studies found, that the presence of MR head coils, which contain a substantial amount of plastic housing material, lead to 13-19% underestimation of PET activity concentration, if not accounted for during image reconstruction [7]. The attenuation effects for "lighter" or more "transparent" MR surface coils were only 4% overall, but up to 10-15% closer to the coil surface [8]. These results demonstrate that disregarding the presence of MR coils leads to substantial regional bias in PET quantification and illustrate the importance of accurate implementation of methodology for MR coil attenuation correction (AC) in simultaneous PET/MR applications. Even though MR coils are invisible in the conventional MR-acquired AC maps, it was shown that coil A...