大野 良治

キヤノンメディカルシステムズ社にて新たに開発された"Compressed SPEEDER"および人工知能を用いた再構成法である"Advanced intelligent Clear-IQ Engine(以下AiCE)"を藤田医科大学病院では積極的に臨床応用を進めている。Compressed SPEEDERは最新の高速撮像技術であり、AiCEはDeep Learning技術を用いたデノイズ再構成技術である。両技術の開発は新たなMRI診療を発展させていくための要素技術の革新であると信ずる。(著者抄録)

＜文献概要＞破裂脳動脈瘤と未破裂脳動脈瘤では画像検査の目的が異なるため,それに応じて最適な手法を選択する必要がある.脳動脈瘤の疾患背景を理解することは,脳動脈瘤の破裂リスク評価に役立つ.本稿では,ルーチン検査で役立つ破裂/未破裂脳動脈瘤の基礎知識と,最新のCT,MRI技術について解説する.

呼吸器疾患の画像診断において胸部単純X線写真(CXR)やコンピュータ断層撮影(CT)の臨床的有用性はゆるぎないものであり、日常臨床にて一般的に用いられている。また、近年の多列検出器型CT(MDCT)の臨床応用により、形態診断においては薄層CT(TSCT)や造影TSCTなどが用いられている。また、肺結節の鑑別診断や肺癌などの腫瘍性疾患における病期診断などにおいて糖代謝をもとにしたフルデオキシグルコースによる陽電子放射断層撮影(PET)やPETとCTの融合画像(PET/CT)も頻用されつつある。このような状況下において胸部疾患における正常と異常のさらなる評価を行うための画像診断機器としては核磁気共鳴画像(MRI)が挙げられる。本稿では胸部画像の正常と異常を見極めるための画像診断機器として、MRIの臨床応用に関して述べる。(著者抄録)

慢性閉塞性肺疾患(COPD)の臨床における画像診断法としては、CTによる形態診断、換気血流シンチグラフィなどの核医学検査による機能診断が肺機能検査と併せて用いられている。しかし、2000年以降においてはMR装置や撮像法の進歩により、ガドリニウム造影剤、超偏極希ガス、あるいは100%酸素などを用いたMRIはCOPDを評価するために新たな肺機能画像として発展しつつある。本稿においてはMRIによるCOPD定量解析に関する最新動向に関して述べたい。(著者抄録)

Since the clinical introduction of magnetic resonance imaging (MRI), the chest has been one of its most challenging applications, and many physicists and radiologists have tried since the 1980s to use MR for assessment of different lung diseases as well as mediastinal and pleural diseases. Since then, however, technical advances in sequencing, scanners, and coils, adaptation of parallel imaging techniques, utilization of contrast media, and development of postprocessing tools have been reported by many basic and clinical researchers. As a result, state-of-the-art thoracic MRI is now substituted for traditional imaging techniques and/or plays a complementary role in the management of patients with various chest diseases, and especially in the detection of pulmonary nodules and in thoracic oncology. In addition, MRI has continued to be developed to help overcome the limitations of computed tomography (CT) and nuclear medicine examinations. It can currently provide not only morphological, but also functional, physiological, pathophysiological, and molecular information at 1.5T with a gradual shift from 1.5T to 3T MR systems. In this review, we focus on these recent advances in MRI for pulmonary nodule detection and pulmonary nodule and mass evaluation by using noncontrast-enhanced and contrast-enhanced techniques as well as new molecular imaging methods such as chemical exchange saturation transfer imaging for a comparison with other modalities such as single or multidetector row CT, 18F-fluoro-2-deoxyglucose positron emission tomography (FDG-PET), and/or PET/CT. LEVEL OF EVIDENCE: 4 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1437-1458.

The Fleischner Society Guidelines for management of solid nodules were published in 2005, and separate guidelines for subsolid nodules were issued in 2013. Since then, new information has become available; therefore, the guidelines have been revised to reflect current thinking on nodule management. The revised guidelines incorporate several substantive changes that reflect current thinking on the management of small nodules. The minimum threshold size for routine follow-up has been increased, and recommended follow-up intervals are now given as a range rather than as a precise time period to give radiologists, clinicians, and patients greater discretion to accommodate individual risk factors and preferences. The guidelines for solid and subsolid nodules have been combined in one simplified table, and specific recommendations have been included for multiple nodules. These guidelines represent the consensus of the Fleischner Society, and as such, they incorporate the opinions of a multidisciplinary international group of thoracic radiologists, pulmonologists, surgeons, pathologists, and other specialists. Changes from the previous guidelines issued by the Fleischner Society are based on new data and accumulated experience. © RSNA, 2017 Online supplemental material is available for this article. An earlier incorrect version of this article appeared online. This article was corrected on March 13, 2017.

OBJECTIVE: This article discusses the basics of unenhanced MR angiography (MRA) and MR venography (MRV), time-resolved contrast-enhanced (CE) MRA and dynamic first-pass CE perfusion MRI, and unenhanced and CE MRV, in addition to assessing the clinical relevance of these techniques for evaluating patients with suspected pulmonary thromboembolism and deep venous thrombosis. CONCLUSION: Since the 1990s, the efficacy of MRA or MRV and dynamic perfusion MRI for patients with suspected pulmonary thromboembolism and deep venous thrombosis has been evaluated. On the basis of the results of single-center trials, comprehensive MRI protocols, including pulmonary unenhanced and CE MRA, perfusion MRI, and MRV, promise to be safe and time effective for assessing patients with suspected pulmonary thromboembolism, although future multicenter trials are required to assess the real clinical value of MRI.

The increase in the radiation exposure from CT examinations prompted the investigation on the various dose-reduction techniques. Significant dose reduction has been achieved and the level of radiation exposure of thoracic CT is expected to reach the level equivalent to several chest X-ray examinations. With more scanners with advanced dose reduction capability deployed, knowledge on the radiation dose reduction methods has become essential to clinical practice as well as academic research. This article reviews the history of dose reduction techniques, ongoing changes brought by newer technologies and areas of further investigation.

While the inauguration of national low dose computed tomographic (LDCT) lung cancer screening programs has started in the USA, other countries remain undecided, awaiting the results of ongoing trials. The continuous technical development achieved by stronger gradients, parallel imaging and shorter echo time has made lung magnetic resonance imaging (MRI) an interesting alternative to CT. For the detection of solid lesions with lung MRI, experimental and clinical studies have shown a threshold size of 3-4mm for nodules, with detection rates of 60-90% for lesions of 5-8mm and close to 100% for lesions of 8mm or larger. From experimental work, the sensitivity for infiltrative, non-solid lesions would be expected to be similarly high as that for solid lesions, but the published data for the MRI detection of lepidic growth type adenocarcinoma is sparse. Moreover, biological features such as a longer T2 time of lung cancer tissue, tissue compliance and a more rapid uptake of contrast material compared to granulomatous diseases, in principle should allow for the multi-parametric characterization of lung pathology. Experience with the clinical use of lung MRI is growing. There are now standardized protocols which are easy to implement on current scanner hardware configurations. The image quality has become more robust and currently ongoing studies will help to further contribute experience with multi-center, multi-vendor and multi-platform implementation of this technology. All of the required prerequisites have now been achieved to allow for a dedicated prospective large scale MRI based lung cancer screening trial to investigate the outcomes from using MRI rather than CT for lung cancer screening. This is driven by the hypothesis that MRI would reach a similarly high sensitivity for the detection of early lung cancer with fewer false positive exams (better specificity) than LDCT. The purpose of this review article is to discuss the potential role of lung MRI for the early detection of lung cancer from a technical point of view and to discuss a few of the possible scenarios for lung cancer screening implementation using this imaging modality. There is little doubt that MRI could play a significant role in lung cancer screening, but how and when will depend on the threshold needed for positive screens (e.g. lesion volume and required diagnostic accuracy), cost-effectiveness and improved patient outcomes from a reduction in the need to follow up benign nodules. Potential applications range from lung MRI as the first choice screening modality to the role of an ad hoc on site test for the detailed evaluation of a subgroup of positive screening results.

With the development of functional imaging modalities we now have the ability to study the microenvironment of lung cancer and its genomic instability. Radiomics is defined as the use of automated or semi-automated post-processing and analysis of large amounts of quantitative imaging features that can be derived from medical images. The automated generation of these analytical features helps to quantify a number of variables in the imaging assessment of lung malignancy. These imaging features include: tumor spatial complexity, elucidation of the tumor genomic heterogeneity and composition, subregional identification in terms of tumor viability or aggressiveness, and response to chemotherapy and/or radiation. Therefore, a radiomic approach can help to reveal unique information about tumor behavior. Currently available radiomic features can be divided into four major classes: (a) morphological, (b) statistical, (c) regional, and (d) model-based. Each category yields quantitative parameters that reflect specific aspects of a tumor. The major challenge is to integrate radiomic data with clinical, pathological, and genomic information to decode the different types of tissue biology. There are many currently available radiomic studies on lung cancer for which there is a need to summarize the current state of the art.

The pulmonary vasculature and its role in perfusion and gas exchange is an important consideration in many conditions of the lung and heart. Currently the mainstay of imaging of the vasculature and perfusion of the lungs lies with CT and nuclear medicine perfusion scans, both of which require ionizing radiation exposure. Improvements in MRI techniques have increased the use of MRI in pulmonary vascular imaging. Here we review MRI methods for imaging the pulmonary vasculature and pulmonary perfusion, both using contrast enhanced and non-contrast enhanced methodology. In many centres pulmonary MR angiography and dynamic contrast enhanced perfusion MRI are now well established in the routine workflow of patients particularly with pulmonary hypertension and thromboembolic disease. However, these imaging modalities offer exciting new directions for future research and clinical use in other respiratory diseases where consideration of pulmonary perfusion and gas exchange can provide insight in to pathophysiology.

東芝メディカルシステムズにおける3T核磁気共鳴(Magnetic Resonance:MR)装置は、当初は60cm Open Boreを有する研究用システムである「Vantage 3T」として開発されたが、2010年以降は71cm Open Boreを有する臨床用3T MR装置「Vantage Titan 3T」として臨床導入が世界的に推進されてきた。Vantage Titan 3Tには(1)ガントリシステムとしてはPianissimoシステムやConformテクノロジーを有し、(2)グラディエントシステムとしてはSlim gradientコイルを採用している。そして、Maximum gradientは30mT/mであり、Slew rate maxが203mT/m/msである。また、(3)RFシステムとしてMultiphase Transmissionを採用し、(4)128 element RF receive systemおよびParallel imagingとしてAtlas SPEEDERを採用したコイルシステムを有している。そして、2016年に新たなSaturn Technologyを採用したグラディエントシステムを有する新たなVantage Titan 3Tが臨床導入された。本講演では、このSaturn Technologyを採用したグラディエントシステムを有する新たなVantage Titan 3Tに関して概要を述べるとともに、2010年以降のVantage Titan 3Tの最新臨床応用に関しても述べる。(著者抄録)

This review focuses on the state-of-the-art of the three major classes of gas contrast agents used in magnetic resonance imaging (MRI)-hyperpolarized (HP) gas, molecular oxygen, and fluorinated gas--and their application to clinical pulmonary research. During the past several years there has been accelerated development of pulmonary MRI. This has been driven in part by concerns regarding ionizing radiation using multidetector computed tomography (CT). However, MRI also offers capabilities for fast multispectral and functional imaging using gas agents that are not technically feasible with CT. Recent improvements in gradient performance and radial acquisition methods using ultrashort echo time (UTE) have contributed to advances in these functional pulmonary MRI techniques. The relative strengths and weaknesses of the main functional imaging methods and gas agents are compared and applications to measures of ventilation, diffusion, and gas exchange are presented. Functional lung MRI methods using these gas agents are improving our understanding of a wide range of chronic lung diseases, including chronic obstructive pulmonary disease, asthma, and cystic fibrosis in both adults and children.