Artificial intelligence (AI) shows tremendous promise in the field of medical imaging, with recent breakthroughs applying deep‐learning models for data acquisition, classification problems, segmentation, image synthesis, and image reconstruction. With an eye towards clinical applications, we summarize the active field of deep‐learning‐based MR image reconstruction. We review the basic concepts of how deep‐learning algorithms aid in the transformation of raw k‐space data to image data, and specifically examine accelerated imaging and artifact suppression. Recent efforts in these areas show that deep‐learning‐based algorithms can match and, in some cases, eclipse conventional reconstruction methods in terms of image quality and computational efficiency across a host of clinical imaging applications, including musculoskeletal, abdominal, cardiac, and brain imaging. This article is an introductory overview aimed at clinical radiologists with no experience in deep‐learning‐based MR image reconstruction and should enable them to understand the basic concepts and current clinical applications of this rapidly growing area of research across multiple organ systems.

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OBJECTIVE.-The objective of this article is to show how artificial intelligence (AI) has impacted different components of the imaging value chain thus far as well as to describe its potential future uses. CONCLUSION.-The use of AI has the potential to greatly enhance every component of the imaging value chain. From assessing the appropriateness of imaging orders to helping predict patients at risk for fracture, AI can increase the value that musculoskeletal imagers provide to their patients and to referring clinicians by improving image quality, patient centricity, imaging efficiency, and diagnostic accuracy.

The unparalleled velocity achieved by overhead throwers subjects the shoulder to extreme forces, resulting in both adaptive changes and pathologic findings that can be detected at imaging. A key biomechanical principle of throwing is achieving maximum external rotation, which initially leads to adaptive changes that may result in a pathologic cascade of injuries. In addition to the well-established concepts of glenohumeral internal rotation deficit and internal impingement, osseous and soft-tissue injuries of the shoulder unique to overhead athletes are illustrated. The epidemiology and biomechanics of throwing injuries are reviewed, and examples from the authors' institutional experience with competitive, collegiate, and professional baseball players are provided to demonstrate the constellation of unique imaging findings seen in overhead throwing athletes. Given the widespread popularity of baseball, and other sports relying on overhead throwing motions at all playing levels from recreational to professional, it is important for radiologists in various practice settings to be familiar with the special mechanisms, locations, and types of shoulder injuries seen in the overhead throwing population. RSNA, 2018.

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The replaced shoulder is increasingly encountered by the radiologist, both on a dedicated and incidental basis, in this era of the growing population of aging patients wishing to preserve their mobility and function. Knowledge of the normal biomechanics of the glenohumeral joint-particularly the function of the rotator cuff and the unique relationship of the humeral head to the glenoid-is essential for understanding the need for shoulder replacement and its subsequent complications, because the intent of shoulder arthroplasty is to approximate the normal joint as closely as possible. The most common indications for shoulder arthroplasty are osteoarthritis, inflammatory arthritis, proximal humerus fractures, irreparable rotator cuff tears, rotator cuff arthropathy, and avascular necrosis of the humeral head. Knowledge of the key imaging features of these indications helps facilitate a correlative understanding between the initial diagnosis and the choice of which type of arthroplasty is used-total shoulder arthroplasty, reverse total shoulder arthroplasty, or partial joint replacement (humeral head resurfacing arthroplasty or hemiarthroplasty). The preoperative requirements and usual postoperative appearance of each arthroplasty type are summarized, as well as the complications of shoulder arthroplasty, including those unique to or closely associated with each type of arthroplasty and those that can be encountered with any type of shoulder arthroplasty.

Soft-tissue augmentation and implants are increasingly seen by the radiologist as more techniques emerge for a variety of indications and locations. Some surgical and implant procedures are performed for purely cosmetic reasons in otherwise healthy patients seeking to improve their body image, and some are performed for reconstruction after cancer or other chronic illnesses. Abdominoplasty, liposuction, and autologous fat grafting can be performed for abdominal and gluteal contouring. Injection of liquid injectable silicone has historically been fraught with legal issues, although it continues to be used for augmentation in a variety of anatomic locations. Newer solid silicone implants have revolutionized cosmetic and reconstructive muscular contouring. Subdermal implants placed by nonmedical professionals are relatively new and unrecognized within the medical establishment, although such implants have been described in the popular culture. Perhaps the most rapidly increasing segment of cosmetic procedures, however, is minimally invasive cosmesis in the form of soft-tissue fillers in the hands and face. Finally, the major principles of breast augmentation and penile implants are also reviewed. Regardless of the location and the type of implant, complications of plastic surgery and soft-tissue implants can generally be classified into the following categories: seroma, hematoma, infection, migration, vascular or nerve compression, fibrosis, foreign-body reaction, and rupture or breakdown. Key concepts include knowing the appropriate anatomic location and the normal postoperative appearance so that complications can be properly detected. A broad range of approved, off-label, and illicit plastic surgical and implant procedures are described and their complications illustrated with cases with classic imaging findings. RSNA, 2017.

ObjectivesDespite significant progress, artifact-free visualization of the bone and soft tissues around hip arthroplasty implants remains an unmet clinical need. New-generation low-field magnetic resonance imaging (MRI) systems now include slice encoding for metal artifact correction (SEMAC), which may result in smaller metallic artifacts and better image quality than standard-of-care 1.5 T MRI. This study aims to assess the feasibility of SEMAC on a new-generation 0.55 T system, optimize the pulse protocol parameters, and compare the results with those of a standard-of-care 1.5 T MRI.Materials and MethodsTitanium (Ti) and cobalt-chromium total hip arthroplasty implants embedded in a tissue-mimicking American Society for Testing and Materials gel phantom were evaluated using turbo spin echo, view angle tilting (VAT), and combined VAT and SEMAC (VAT + SEMAC) pulse sequences. To refine an MRI protocol at 0.55 T, the type of metal artifact reduction techniques and the effect of various pulse sequence parameters on metal artifacts were assessed through qualitative ranking of the images by 3 expert readers while taking measured spatial resolution, signal-to-noise ratios, and acquisition times into consideration. Signal-to-noise ratio efficiency and artifact size of the optimized 0.55 T protocols were compared with the 1.5 T standard and compressed-sensing SEMAC sequences.ResultsOverall, the VAT + SEMAC sequence with at least 6 SEMAC encoding steps for Ti and 9 for cobalt-chromium implants was ranked higher than other sequences for metal reduction (P < 0.05). Additional SEMAC encoding partitions did not result in further metal artifact reductions. Permitting minimal residual artifacts, low magnetic susceptibility Ti constructs may be sufficiently imaged with optimized turbo spin echo sequences obviating the need for SEMAC. In cross-platform comparison, 0.55 T acquisitions using the optimized protocols are associated with 45% to 64% smaller artifacts than 1.5 T VAT + SEMAC and VAT + compressed-sensing/SEMAC protocols at the expense of a 17% to 28% reduction in signal-to-noise ratio efficiency. B1-related artifacts are invariably smaller at 0.55 T than 1.5 T; however, artifacts related to B0 distortion, although frequently smaller, may appear as signal pileups at 0.55 T.ConclusionsOur results suggest that new-generation low-field SEMAC MRI reduces metal artifacts around hip arthroplasty implants to better advantage than current 1.5 T MRI standard of care. While the appearance of B0-related artifacts changes, reduction in B1-related artifacts plays a major role in the overall benefit of 0.55 T.