Correlation between magnetic resonance imaging of the heart and cardiac anatomy

An understanding of anatomy forms the cornerstone for accurate interpretations of pathologic alterations. In this article, we present cardiac magnetic resonance images and the corresponding sections of normal hearts obtained at autopsy and cut in planes parallel and perpendicular to the ventricular septum in addition to the standard anatomic orthogonal planes (coronal, sagittal, and transverse). This correlation demonstrates the ability of magnetic resonance imaging to display cardiac anatomy accurately and noninvasively. Because magnetic resonance imaging provides excellent contrast between flowing blood and cardiac walls and has the capacity to provide direct images in multiple planes without inherent difficulties, this procedure has advantages over other currently available imaging techniques.     

Imaging techniques in cardiac electrophysiology

Modern cardiac electrophysiology procedures include catheter-based arrhythmia ablation and transvenous device implantation, which are highly dependent on accurate, real-time cardiac imaging. With the realization that anatomic structures are critical to successful electrophysiologic procedures, accurately defining a patient's cardiac anatomy has become more important. Fluoroscopy allows for 2D imaging of cardiac structures in real-time, and is used to guide catheter and lead placement, but does not allow for visualization of soft tissues. Intracardiac echocardiography allows for both direct visualization of anatomic structures within the heart and real-time imaging during catheter placement. Despite advances in intracardiac echocardiography catheters that allow for larger windows, the ability to accurately delineate anatomic structures depends on the patient's anatomy and operator experience. Neither of these techniques allows for electrical mapping of the heart; however, both anatomic and electrical intracardiac mapping can be achieved with advanced mapping systems. These systems allow for real-time catheter localization, help elucidate cardiac anatomy, evaluate electrical activation during arrhythmias and guide catheter placement for deliverance of radiofrequency current. More recently, 3D cardiac computed tomography has been used to accurately define intracardiac anatomy; however, catheter tracking and electrical mapping cannot be performed by computed tomography. Mapping systems are now being merged with computed tomography images to produce an accurate anatomic and electrical map of the heart to guide catheter ablations. The objective of this paper is to describe the current imaging and mapping techniques used in electrophysiologic procedures.     

Imaging techniques in cardiac electrophysiology

Modern cardiac electrophysiology procedures include catheter-based arrhythmia ablation and transvenous device implantation, which are highly dependent on accurate, real-time cardiac imaging. With the realization that anatomic structures are critical to successful electrophysiologic procedures, accurately defining a patient’s cardiac anatomy has become more important. Fluoroscopy allows for 2D imaging of cardiac structures in real-time, and is used to guide catheter and lead placement, but does not allow for visualization of soft tissues. Intracardiac echocardiography allows for both direct visualization of anatomic structures within the heart and real-time imaging during catheter placement. Despite advances in intracardiac echocardiography catheters that allow for larger windows, the ability to accurately delineate anatomic structures depends on the patient’s anatomy and operator experience. Neither of these techniques allows for electrical mapping of the heart; however, both anatomic and electrical intracardiac mapping can be achieved with advanced mapping systems. These systems allow for real-time catheter localization, help elucidate cardiac anatomy, evaluate electrical activation during arrhythmias and guide catheter placement for deliverance of radiofrequency current. More recently, 3D cardiac computed tomography has been used to accurately define intracardiac anatomy; however, catheter tracking and electrical mapping cannot be performed by computed tomography. Mapping systems are now being merged with computed tomography images to produce an accurate anatomic and electrical map of the heart to guide catheter ablations. The objective of this paper is to describe the current imaging and mapping techniques used in electrophysiologic procedures.     

大脑横断面解剖与MRI对照研究

目的探讨大脑主要结构在薄层横断面上的形态及其变化规律,为此区域的影像识别与分析提供依据.方法从首例中国可视人数据集中选出大脑有关的横断面图像与相对应的MRI图像对照.结果在人体大脑横断面标本与相应的MRI轴位图像上,清楚显示出大脑主要结构的形态与影像特征.结论首例中国数字化可视人体数据集的大脑断面标本图与MRI图像有良好的对应关系,通过对照观察,可在MRI上精确识别脑沟、回及脑内结构,为临床影像诊断提供详实准确的断层形态资料,对脑内微小结构占位性病变的早期诊断提供参考依据.     

可视化肝脏横断面解剖与MR影像对照研究

目的应用数字化可视人体肝脏薄层横断面结构形态学信息,为人体肝脏断层影像学的识别与诊断提供解剖学依据.方法选取可视化人体数据集的肝脏连续横断面图像进行解剖形态学观察,与其相对应的MR图像对照研究,并完成计算机三维重建.结果在可视化肝脏横断面与其相对应的MR图像上,清晰显示肝内管道系统主支的走行分布特点,三维重建图像能清晰显示肝内管道空间结构特征,并明确肝内管道主支在肝脏横断面的最佳显示平面.结论通过对肝脏横断面解剖结构的探讨,可视化肝脏能够完整而精确地反映出该区域复杂的解剖学结构特点,为肝脏疾病的影像定性诊断及影像辅助定位治疗提供形态学依据.     

Catheter Ablation of Focal Atrial Tachycardia from the Aortic Cusp: The Role of Electroanatomic Mapping and Intracardiac Echocardiography

Catheter ablation of periatrioventricular (peri‐AV) nodal atrial tachycardias (AT) from the noncoronary aortic cusp (NCC) can be challenging due to the close proximity of the AV node In such cases, intracardiac echocardiography (ICE) together with three‐dimensional mapping system can be helpful in guiding the ablation catheter and in assessing the anatomic relationship of the aorta to the surrounding structures. We report two patients with AT originating near the AV node who underwent successful catheter ablation from the NCC. ICE proved useful in positioning the ablation catheter within the aortic cusps. Electroanatomic mapping enabled tagging the earliest activation site and renavigation back. (PACE 2013; 36:e19–e22)     

胎儿颜面部超声解剖成像研究

目的 探讨正常胎儿颜面部的超声表现与显示切面，提高超声对胎儿颜面部正常结构的认识。方法 选用20具颜面部正常的引产胎儿尸体，将其置于盛有自来水的水盆内，对胎儿尸体颜面部进行冠状、矢状及横断面超声探查，并从颌下三角探查研究硬腭与软腭的超声特征。结果 胎儿颜面部表面各个结构均能够通过常规胎儿颜面部冠状切面、矢状切面、横切面正确显示，其深部骨性结构大部分亦能清楚显示，但硬腭与软腭只有在经颌下三角探查才能清楚显示。结论 二维超声对胎儿颜面部大部分表面结构与深部骨性结构均能清楚显示，是显示胎儿颜面部结构可靠的影像学方法。     

Tissue elasticity of in vivo skeletal muscles measured in the transverse and longitudinal planes using shear wave elastography

The aim of the present study was to measure in vivo skeletal muscle elasticity in the transverse and longitudinal planes using shear wave elastography and then to compare the image stability, measurement values and measurement repeatability between these imaging planes. Thirty‐one healthy males participated in this study. Tissue elasticity (shear wave velocity) of the medial gastrocnemius, rectus femoris, biceps brachii and rectus abdominis was measured in both the transverse and longitudinal planes using shear wave elastography. Image stability was evaluated by the standard deviation of the colour distribution in the shear wave elastography image. Measurement repeatability was assessed by the coefficient of variance obtained from three measurement values. Image stability of all tested muscles was significantly higher in the longitudinal plane (P<0·001), but measurement repeatability did not differ significantly between the imaging planes (P>0·05), except in the biceps brachii (P = 0·001). Measurement values of the medial gastrocnemius, rectus femoris and biceps brachii were significantly different between the imaging planes (P<0·001). Image stability and measurement values of shear wave elastography images varied with imaging plane, which indicates that imaging plane should be considered when measuring skeletal muscle tissue elasticity by shear wave elastography.     

Three-dimensional fetal echocardiography: gated versus nongated techniques.

The purpose of this study was to compare gated with nongated three-dimensional fetal echocardiography in terms of the ability to demonstrate fetal cardiac anatomy. We examined nine fetuses in utero using conventional two-dimensional sonographic imaging equipment, an electromagnetic position sensor, and a computer-graphics workstation. Free-hand sweeps were performed through the fetal heart and great vessels in either transverse or sagittal orientations with respect to the fetal heart. Seven transverse and five sagittal sweeps were selected for reconstruction and analysis. Cardiac gating was performed by using a temporal Fourier transform to determine the fundamental frequency of cardiac motion. Two-dimensional data from each sweep were reprojected to a series of volume data sets. Each series was then condensed to a single volume, so that each two-dimensional sweep could be compared with its respective gated and nongated volume data sets. The two-dimensional data were reviewed utilizing a display with forward and backward cineloop capability. The gated and nongated volume data sets were displayed interactively as a series of three orthogonal planes, with the ability of the observer to control the location of each image plane within the volume. The gated data were animated with variable display frame rates. Conventional two-dimensional imaging provided a fairly complete evaluation of the fetal heart when scanning included the four-chamber view with a sweep across the outflow tracts. Nongated three-dimensional fetal echocardiography allowed visualization of some structures and views not demonstrated with two-dimensional ultrasonography. Gated three-dimensional fetal echocardiography provided significantly better visualization and comprehension of cardiac anatomy than nongated three-dimensional fetal echocardiography. The superiority of gated over nongated three-dimensional fetal echocardiography appears to come from both improved image quality and the anatomic clues that derive from the ability to view cardiac motion.     

Beat to beat 3-dimensional intracardiac echocardiography: theoretical approach and practical experiences

Three-dimensional (3D)-imaging provides important information on cardiac anatomy during electrophysiological procedures. Real-time updates of modalities with high soft-tissue contrast are particularly advantageous during cardiac procedures. Therefore, a beat to beat 3D visualization of cardiac anatomy by intracardiac echocardiography (ICE) was developed and tested in phantoms and animals. An electronic phased-array 5–10 MHz ICE-catheter (Acuson, AcuNav?/Siemens Medical Solutions USA/64 elements) providing a 90° sector image was used for ICE-imaging. A custom-made mechanical prototype controlled by a servo motor allowed automatic rotation of the ICE-catheter around its longitudinal axis. During a single heartbeat, the ICE-catheter was rotated and 2D-images were acquired. Reconstruction into a 3D volume and rendering by a prototype software was performed beat to beat. After experimental validation using a rigid phantom, the system was tested in an animal study and afterwards, for quantitative validation, in a dynamic phantom. Acquisition of beat to beat 3D-reconstruction was technically feasible. However, twisting of the ICE-catheter shaft due to friction and torsion was found and rotation was hampered. Also, depiction of catheters was not always ensured in case of parallel alignment. Using a curved sheath for depiction of cardiac anatomy there was no congruent depiction of shape and dimension of static and moving objects. Beat to beat 3D-ICE-imaging is feasible. However, shape and dimension of static and moving objects cannot always be displayed with necessary steadiness as needed in the clinical setting. As catheter depiction is also limited, clinical use seems impossible.     

尸体肝脏横断面解剖与CT增强影像对比研究对活体肝移植的术前评估

目的 用国人尸体肝脏薄层横断面结构形态学信息,为人体肝脏断层影像学的识别和活体肝移植提供解剖学依据。方法选取人体尸体肝脏连续横断面图像进行解剖形态学观察,与其相对应的CT增强图像对照研究,并完成计算机三维重建。结果在尸体肝脏连续横断面图像与其相对应的CT增强图像,清晰显示肝内管道系统主支的走行分布特点,三维重建图像能清晰显示肝内血管空间结构特征以及所支配区域的空间体积。结论通过对肝脏横断面解剖结构的探讨,CT增强图像能够完整而精确地反映出该区域复杂的解剖学结构特点,为活体肝移植的术前评估提供坚实的形态学基础。     

改进心脏磁共振成像的定位方法

目的探讨心脏磁共振成像定位的改进方法。方法对18例心血管病患者及82名正常志愿者行心脏MR平扫,以改进的定位方法获得美国心脏协会(AHA)推荐的标准心脏断层成像层面,包括标准水平长轴位(HLA)、垂直长轴位(VLA)及短轴位(SA)图像,在此基础上探索左、右心室流入道和流出道,主动脉弓斜矢状位及各瓣膜横断位层面图像。结果采用此法可获得标准层面的图像及左心室功能参数。结论改进的心脏磁共振成像定位方法可保证各基本成像平面及各瓣膜成像平面的标准性,为观察心脏及大血管的形态和结构提供可靠依据。     

MR imaging of tendon lesions of the hand and wrist

MR imaging of the hand and wrist tendons has greatly benefited from the use of dedicated surface coils, which allow fine depiction of the intricate anatomy of these structures, owing to high spatial resolution images as well as superb soft tissue contrast. MR imaging of the wrist and hand is obtained in the axial, sagittal, and coronal planes. The axial and sagittal planes provide most of the information necessary, however, to assess the tendons at the wrist and hand. The axial images are optimal for evaluating tendon morphology, longitudinal splits, tendon sheath fluid, and adjacent soft tissues such as overlying retinacula. The sagittal images are most useful for depicting abnormalities of the finger flexor and extensor tendons.     

Anatomic and hemodynamic imaging using a new vector phased-array intracardiac catheter.

BACKGROUND: We used a new vector, phased-array intracardiac catheter (AcuNav) with complete 2-dimensional imaging and Doppler capabilities to describe a systematic approach for a detailed anatomic and hemodynamic cardiac assessment. METHODS: In 14 dogs, the intracardiac echocardiographic catheter was inserted through an 11F venous access and placed in the right side of the heart to perform a comprehensive ultrasound examination of the heart. RESULTS: Imaging was successful in all dogs. All 4 cardiac chambers and valves were imaged clearly in multiple orientations. Additional structures seen included the vena cavae, coronary sinus, right and left appendages, interarterial septum, coronary arteries, and all 4 pulmonary veins. Intra-abdominal structures, such as the aorta, liver, and hepatic veins were also visualized. A complete Doppler examination of intracardiac and paracardiac flows was also possible. CONCLUSION: AcuNav is a unique intracardiac imaging device, which allows comprehensive structural and functional cardiac assessment.     

Combined MRI and fibreoptic colonoscopy: technical considerations and clinical feasibility

A method of fibre-optic colonoscopy with simultaneous high resolution MRI has been developed to obtain cross-sectional information of the intramural and extramural extent of lesions, for diagnostic and therapeutic purposes. An MR-compatible colonoscope with receiver coil was designed, developed and used in ex vivo studies to scan a section of large bowel in transverse and longitudinal planes with T₁ and T₂ weighted spin-echo sequences. In vivo five patients were followed-up after excision of large bowel cancer. The patients were three men and two women aged 50-77 years, (mean 65.6 years) who were studied on a 0.5 T scanner (Picker Asset, OH, USA). The coil and colonoscope were inserted into the rectum. After routine visual inspection of the colon, T₁ weighted spin-echo images and radio-frequency spoiled gradient-echo images of the bowel wall were obtained. Ex vivo: three layers of bowel wall were identified: an intermediate to high signal-intense mucosa, a high signal intensity layer on T₁ weighting which corresponded to the submucosa, and a low signal intensity muscularis propria. In vivo: On T₁ weighted images three layers could be identified that corresponded to the layers seen on the ex vivo imaging. This pilot study demonstrates that MR colonoscopy is feasible and allows delineation of bowel wall structure, thus providing a useful adjunct to conventional colonscopy.     

Development of an electrophysiology (EP)-enabled intracardiac ultrasound catheter integrated with NavX 3-dimensional electrofield mapping for guiding cardiac EP interventions: experimental studies.

OBJECTIVE: We have developed an integrated high-resolution intracardiac echocardiography (ICE) catheter for electrophysiology (EP) testing, which can be coregistered in 3-dimensional space with EP testing and ablation catheters using electrofield sensing. METHODS: Twelve open-chest pigs (34-55 kg) and 3 closed-chest pigs were studied. After introduction from the jugular or femoral venous locations, the 9F side-looking, highly steerable (0 degrees -180 degrees), 64-element array catheters could be manipulated easily throughout the right side of the heart. Multisite cardiac pacing was performed for assessing left ventricular (LV) synchrony using tissue Doppler methods. Also, in the open-chest pigs, right atrial (RA) and right ventricular (RV) ablations were performed with a separate radio frequency catheter under fluoroscopic guidance and visualized with ICE to characterize the changes. In the 3 closed-chest pigs, electrofield NavX 3-dimensional coregistration (St Jude Medical Corp, Minneapolis, MN) allowed us to test whether this additional feature could shorten the time necessary to perform 4 targeted ablations in each animal while imaging the ablation catheter and the adjacent region by ICE. RESULTS: Intracardiac anatomy, tricuspid, aortic, pulmonary, and mitral valve function, and pulmonary vein flow were all imaged reproducibly from scanning locations in the RA or RV in all animals, along with assessment of cardiac motion and the effects of multisite pacing. Three-dimensional electrofield displays detailed the spatial relationship between the ICE catheter and ablation catheters such that the time to visualize and ablate 4 sites in each of the 3 closed-chest animals was reduced. CONCLUSIONS: This new technology is a first step in the integration of ICE with EP procedures.     

Intracardiac echocardiography (9 MHz) in humans: methods, imaging views and clinical utility

A new low-frequency (9 MHz, 9 Fr) catheter-based ultrasound (US) transducer has been designed that allows greater depth of cardiac imaging. To demonstrate the imaging capability and clinical utility, intracardiac echocardiography (ICE) using this lower frequency catheter was performed in 56 patients undergoing invasive electrophysiological procedures. Cardiac imaging and monitoring were performed with the catheter transducer placed in the superior vena cava (SVC), right atrium (RA) and/or right ventricle (RV). In all patients, ICE identified distinct endocardial structures with excellent resolution and detail, including the crista terminalis, RA appendage, caval and coronary sinus orifices, fossa ovalis, pulmonary vein orifices, ascending aorta and its root, pulmonary artery, RV and all cardiac valves. The left atrium and ventricle were imaged with the transducer at the limbus fossa ovalis of the interatrial septum and in the RV, respectively. ICE was important in identifying known or unanticipated aberrant anatomy in 11 patients (variant Eustachian valve, atrial septal aneurysm and defect, lipomatous hypertrophy, Ebstein's anomaly, ventricular septal defect, tetralogy of Fallot, transposition of the great arteries, disrupted chordae tendinae and pericardial effusion) or in detecting procedure-related abnormalities (narrowing of SVC-RA junction orifice or pulmonary venous lumen, atrial thrombus, interatrial communication). In patients with inappropriate sinus tachycardia, ICE was the primary ablation catheter-guidance technique for sinus node modification. With ICE monitoring, the evolution of lesion morphology with the three imaging features including swelling, dimpling and crater formation was observed. In all patients, ICE was contributory to the mapping and ablation process by guiding catheters to anatomically distinct sites and/or assessing stability of the electrode-endocardial contact. ICE was also used to successfully guide atrial septal puncture (n = 9) or RA basket catheter placement (n = 4). Thus, ICE with a new 9-MHz catheter-based transducer has better imaging capability with a greater depth. Normal and abnormal cardiac anatomy can be readily identified. ICE proved useful during electrophysiological mapping and ablation procedures for guiding interatrial septal puncture, assessing placement and contact of mapping and ablation catheters, monitoring ablation lesion morphological changes, and instantly diagnosing cardiac complications.     

Normal MR imaging anatomy of the knee

Magnetic resonance (MR) imaging is the preferred imaging modality for evaluating internal derangement of the knee, due to its superior soft tissue contrast resolution, multiplanar imaging capability, and lack of ionizing radiation. The superb image quality facilitates learning of normal imaging anatomy and conceptualizing spatial relationships of anatomic structures, leading to improved understanding of pathologic processes, mechanisms of injury, and injury patterns, and ultimately increased diagnostic accuracy. This article depicts normal MR imaging anatomy and commonly encountered anatomic variants using representative MR images of the knee, and describes and explains the rationale of routine knee MR imaging protocol.     

Intracardiac echocardiography and acoustic radiation force impulse imaging of a dynamic ex vivo ovine heart model

Intracardiac echocardiography (ICE) has demonstrated utility in providing high-resolution cardiac ultrasound images for guidance of numerous catheter-based interventions, including radiofrequency ablations (RFA). However, the training of interventionalists and refinement of procedures involving intracardiac catheters is costly and time consuming due to necessary clinical and animal studies. As a result, research and development of ICE for other purposes is gradual and deliberate. Intracardiac acoustic radiation force impulse (ARFI) imaging has been demonstrated to be a suitable modality to monitor the progress of RFA procedures; however, a clinical protocol has been slow to develop due to the expense and demands of clinical experiments. We report on the development and use of an ex vivo heart model to evaluate ICE and intracardiac ARFI imaging. The ability of this model to provide clinically-relevant intracardiac imaging angles was investigated by inserting an intracardiac probe into the heart and imaging it from various positions and orientations. ARFI images of all four chambers also were formed. RFAs were also performed to create stiffer lesions within the right and left ventricles. Upon completion of the ablation, ARFI imaging was used to visualize the lesion and compared with images taken from pathology.The results show the ovine heart model to be a suitable apparatus for recreating several clinically-relevant intracardiac viewing angles of the heart. Also, the results indicate the potential of the heart model to be a valuable tool in the future development and refinement of a clinical protocol for intracardiac ARFI imaging based guidance and assessment of cardiac radiofrequency ablations.     

High-Resolution Anatomy from in Situ Human Brain

We have generated a spatially accurate, high-resolution three-dimensional (3D) volume of brain anatomy from cryosectioned whole human head. The head of a female cadaver was cryosectioned on a heavy duty cryomacrotome (PMV, Stockholm Sweden) modified for quantitative digital image capture. Serial images (1024², 24-bit) were captured directly from the cryoplaned specimen blockface in 500-μm intervals and reconstructed to a 3D data volume. Data were placed into the Talairach coordinate system to create a volume of brain anatomy for atlas reference. We resampled the volume at 500 μm along the sagittal, coronal, and horizontal planes and enhanced the images by digitally editing the background. The spatial resolution of the original digitized images provided sufficient anatomic detail to clearly delineate gray and white matter and neural structures, including major fiber pathways, sub-thalamic nuclei, and laminae. We developed a compact disk and controlling software program to enable the viewer to select planes of orientation, display, and copy individual sections at higher resolution. Animation proved useful in the conveyance of system anatomy as structures are shown traversing through the neuroaxis. Postmortem cryosectioning paired with this computerized presentation allowed the complete 3D volume data to be distributed and shared as an educational, clinical, and research resource.