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Multimodal medical image synthesis is an important task. Previous efforts mainly focus on the task domain of medical image synthesis using the complete source data and have achieved great success. However, data collection with completeness in real life might be prohibitive due to high expenses or other difficulties, particularly in brain imaging studies. In this paper, we address the challenging and important problem of medical image synthesis from incomplete multimodal data sources. We propose to learn the modal-wise representations and synthesize the targets accordingly. Particularly, a surrogate sampler is derived to generate the target representations from incomplete observations, based on which an interpretable attention-redistribution network is designed. The experimental results synthesizing PET images from MRI images demonstrate that the proposed method can solve different missing data scenarios and outperforms related baselines consistently. 

Positronium Lifetime Image (PLI) reconstruction is a technique used in time-of-flight (TOF) Positron emission tomography (PET) imaging that involves measuring the lifespan of positronium, which is a metastable electron-positron pair that arises when a PET molecule releases a positron, prior to its annihilation. In our previous work, we demonstrated that our proposed maximum likelihood (ML) algorithm for PLI reconstruction can generate quantitatively accurate lifetime images for a 570 ps TOF PET system. In this study, we conducted further investigations into the statistical properties of the algorithm, including the variability of the reconstruction results, the sensitivity of the algorithm to the number of acquired PLI events and its robustness to hyperparameter choices. Our findings indicate that the proposed ML method produces sufficiently stable lifetime images to enable reliable distinction of regions of interest and the number of PLI events required to produce quantitatively accurate lifetime images is computationally plausible. These results demonstrate the potential of our ML algorithm for advancing the capabilities of TOF PET imaging. 

This chapter provides an overview of the procedures and methods employed for coring operations and in the shipboard laboratories of the R/V JOIDES Resolution during International Ocean Discovery Program (IODP) Expedition 397. The laboratory information applies only to shipboard work described in the Expedition Report section of the Expedition 397 Proceedings of the International Ocean Discovery Program volume that includes the shipboard sample registry, imaging and analytical instruments, core description tools, and the Laboratory Information Management System (LIMS) database. The shipboard workflow followed standard IODP procedures (as previously described by, e.g., Huber et al., 2019; Winckler et al., 2021; Planke et al., 2023), with revisions and refinements as described in this chapter. Methods used by investigators for shore-based analyses of Expedition 397 data will be documented in separate publications. All shipboard scientists contributed to this volume with the following primary responsibilities (authors are listed in alphabetical order; see Expedition 397 scientists for contact information): Summary chapter: Expedition 397 Scientists Methods and site chapters: Background and objectives: F. Abrantes, D. Hodell Operations: C.A. Alvarez Zarikian, K. Grigar Lithostratigraphy: H.L. Brooks, J.M. Link, J. McManus, C. Pallone, X. Pang, E. Salgueiro, V. dos Santos Rocha, J. Yu Biostratigraphy: C.A. Alvarez Zarikian, W. Clark, J.-A. Flores, M. Peral, K. Verma Paleomagnetism: L. Dauchy-Tric, C. Xuan Geochemistry: S. Hines, B. Mitsunaga, L. Nana Yobo, J. Wu Physical properties and downhole measurements: H.-H.M. Huang, H. Ikeda, J. Kuroda, S. Sanchez Stratigraphic correlation: T. Herbert, H.-H.M. Huang, S. Kaboth-Bahr This introductory section provides an overview of drilling and coring operations, core handling, curatorial conventions, depth scale terminology, and the sequence of shipboard analyses. Subsequent sections of this chapter document specific laboratory instruments and methods in detail. 

During International Ocean Discovery Program Expedition 397, we recovered a total of 6176.7 m of core (104.2% recovery) at four sites (U1586, U1587, U1385, and U1588) from the Promontório dos Príncipes de Avis, a plateau located on the Portuguese continental slope that is elevated above the Tagus Abyssal Plain and isolated from the influence of turbidites. The drill sites are arranged along a bathymetric transect (4692, 3479, 2591, and 1339 meters below sea level [mbsl], respectively) to intersect each of the major subsurface water masses of the eastern North Atlantic. Multiple holes were drilled at each site to ensure complete spliced composite sections, which will be further refined postcruise by a campaign of X-ray fluorescence core scanning. At Site U1586 (4692 mbsl), the deepest and farthest from shore, a 350 m sequence was recovered in four holes that extend as far back as the middle Miocene (14 Ma), which is nearly twice as old as initially predicted from seismic stratigraphy. Sedimentation rates are lower (averaging 5 cm/ky in the Quaternary) at Site U1586 than other Expedition 397 sites, and a few slumped intervals were encountered in the stratigraphic sequence. Despite these limitations, Site U1586 anchors the deep end-member of the bathymetric transect and provides an important reference section to study deepwater circulation, ventilation and carbon storage in the deep eastern North Atlantic. At Site U1587 (3479 mbsl), the second deepest site along the depth transect, we recovered a 567 m sequence of late Miocene to Holocene sediments that accumulated at rates between 6.5 and 11 cm/ky. The high sedimentation rates and long continuous record at this site will permit climate reconstruction at high temporal resolution (e.g., millennial) for the past 7.8 My. The Messinian Stage (7.25–5.33 Ma) was recovered, which provides a valuable opportunity to study the Messinian Salinity Crisis in an open marine setting adjacent to the Mediterranean. Site U1385 (Shackleton site) was a reoccupation of a position previously drilled during Integrated Ocean Drilling Program Expedition 339. Expedition 339 Site U1385 has yielded a remarkable record of millennial-scale climate change for the past 1.45 My (Marine Isotope Stage 47). During Expedition 397, we deepened the site from 156 to 400 meters below seafloor, extending the record to near the base of the Pliocene (5.3 Ma). Sedimentation rates remained high, averaging between 9 and 11 cm/ky throughout the sequence. The newly recovered cores at Expedition 397 Site U1385 will permit the study of millennial climate variability through the entire Quaternary and Pliocene, prior to the intensification of Northern Hemisphere glaciation. Site U1588 is the shallowest, closest to shore, and youngest site drilled during Expedition 397 and is also the one with the highest sedimentation rate (20 cm/ky). The base of the 412.5 m sequence is 2.2 Ma, providing an expanded Pleistocene sequence of sediment deposited under the influence of the lower core of the Mediterranean Outflow Water (MOW). Together with other Expedition 339 sites, Site U1588 will be important for determining how the depth and intensity of the MOW has varied on orbital and millennial timescales. In addition, it also provides a marine reference section for studying Quaternary climate variability at very high temporal resolution (millennial to submillennial). A highlight of the expedition is that sediment at all sites shows very strong cyclicity in bulk sediment properties (color, magnetic susceptibility, and natural gamma radiation). Particularly remarkable are the precession cycles of the Pliocene that can be correlated peak-for-peak among sites. These cyclic variations will be used to derive an orbitally tuned timescale for Expedition 397 sites and correlate them into classic Mediterranean cyclostratigraphy. The cores recovered during Expedition 397 will form the basis of collaborative postcruise research to produce benchmark paleoclimate records for the late Miocene through Quaternary using the widest range of proxy measurements. It will take many years to complete these analyses, but the records will lead to major advances in our understanding of millennial and orbital climate changes and their underlying causes and evolving contextuality. Outreach during Expedition 397 was highly productive, reaching a record number of students and the general public across the world through several diverse platforms, including live ship-to-shore events, webinars, social media, videos, radio pieces, blog posts, and in-person activities. 

Site U1587 is the second farthest from shore drilled during Expedition 397 and located at a water depth of 3479 meters below sea level (mbsl) (Figures F1, F2, F3). It is the second deepest site along the bathymetric transect and is bathed today by a mixture of ~75% North Atlantic Deep Water (NADW) and 25% Lower Deep Water (LDW) sourced from the Southern Ocean (Figure F4) (Jenkins et al., 2015). The mixing ratio of these water masses and their vertical position in the water column has changed in the past, which has implications for ventilation and carbon storage in the deep Atlantic Ocean. The location of Site U1587 was motivated by the clear expression of millennial climate variability in proxy records of oxygen isotopes and sea-surface temperature in nearby Piston Core MD95-2042 (Shackleton et al., 2000, 2004; Bard et al., 2000; Pailler and Bard, 2002; Davtian and Bard, 2023). Isotopic, organic biomarker, and pollen results from this core demonstrated the potential of correlating Iberian margin sediments with ice cores from Greenland and Antarctica and with European terrestrial sequences (e.g., Sánchez-Goñi et al., 2000; Margari et al., 2010, 2014, 2020). The sediment record from Site U1587 provides the opportunity to develop sediment proxy records for the Greenland and Antarctic ice cores to the base of the Quaternary and beyond. The piston core (JC089-04-2P) recovered near Site U1587 is 10.7 m long and has a sedimentation rate of 17 cm/ky (Figure F5). Ca/Ti and Zr/Sr show strong evidence of millennial variability during the last glacial cycle. The objective for Site U1587 is to study such variability for older glacial cycles throughout the Quaternary. Site U1587 is located at the intersection of Seismic Lines JC089-6 and JC089-7 (Figure F6). Although mass transport deposits or disturbed intervals are developed nearby, the continuity of reflections is good at Site U1587 (Figures F7, F8). The Upper Miocene to Quaternary sequence at Site U1587 is expanded relative to Site U1586 and is more than 500 m thick. Sedimentation rates are estimated to average ~10 cm/ky at Site U1587, or about twice that of Site U1586. We had permission from the Environmental Protection and Safety Panel (EPSP) to drill to 500 meters below seafloor (mbsf), but we requested and were granted permission to drill an additional 50 m to extend the record well into the late Miocene. Site U1587 provides an expanded sequence of late Miocene to Quaternary sediments with which to address the following objectives: Document how millennial climate variability evolved during the glacial cycles of the Quaternary and Pliocene as boundary conditions changed with the progressive intensification of Northern Hemisphere glaciation (NHG). Reconstruct the history of changing local dominance of northern-sourced versus southern-sourced deep water, as well as ventilation and carbon storage in the deep Atlantic Ocean. Determine interhemispheric phase relationships (leads/lags) by comparing the timing of proxy variables that monitor surface (Greenland) and deepwater (Antarctic) components of the climate system. Investigate climate during past interglacial periods, including the warm Pliocene period prior to the intensification of NHG. Link terrestrial, marine, and ice core records by analyzing pollen and terrestrial biomarkers that are delivered to the deep-sea environment of the Iberian margin. Recover a complete record of the time leading up to, during, and following the Messinian Salinity Crisis, which complements objectives of International Ocean Discovery Program (IODP) Expedition 401 (Flecker et al., 2023) and will permit evaluation of the causes and consequences of this remarkable event in Earth's history. Develop an orbitally-tuned age model for Site U1587 by correlating physical properties to eccentricity-modulated precession and tying them into the record of Mediterranean cyclostratigraphy.