Visualisation of liver tumours using hand-held real-time strain imaging: results of animal experiments

Objective

Surgical resection is the only curative option for colorectal hepatic metastases. Intra-operative localisation of these metastases during hepatic resection is performed by intra-operative B-mode imaging and palpation. Because liver metastases are stiffer than normal tissues, elastography may be a useful complement to B-mode imaging. This paper reports quantitative measures of the image quality attained during intra-operative real-time elastographic visualisation of liver metastasis.

Methods

VX2 tumours were implanted in the liver of eight rabbits and were scanned in vivo. Measurements of the tumour dimensions obtained via elastography were compared with those obtained using B-mode imaging and with gross pathology.

Results

Measurements of tumour diameters were similar when obtained by intra-operative elastography and pathological measurement methods (mean difference±standard deviation, 0.1±0.9 mm). The contrast between tumours and normal tissues was significantly higher (p<0.05) in elastograms (26±10 dB contrast) than in sonograms (1±1 dB contrast). Sensitivity and specificity for detecting tumours using intra-operative elastography were 100% and 88%, respectively, and positive and negative predictive values were 89% and 100%, respectively. In two cases elastograms were able to detect a tumour that was ambiguous in B-mode images.

Conclusion

Combined hand-held B-mode/strain imaging may provide additional information that is relevant for detection of liver metastases that may be missed by standard B-mode imaging alone, such as small and/or isoechoic tumours.Colorectal cancer is the fourth most common cancer in males and the third most common cancer in females worldwide [1,2]. Approximately half of these patients either present with hepatic metastases or develop them during the course of their disease. Although ablative therapies are frequently used, resection of liver metastases, when possible, remains the preferred therapy for potential cure [3,4]. The overall 5 year survival rates are in the range of 35–58% in several studies reporting on the results of hepatectomy conducted with curative intent [4,5]. The pre-operative and intra-operative staging of metastases is essential to remove all metastases and increase the rate of cure. At the pre-operative stage, contrast-enhanced CT is the most commonly used modality to screen for metastases. It is highly sensitive, particularly since the introduction of helical CT and multidetector systems capable of scanning the entire liver in a few seconds, allowing for several scans during the liver''s different circulatory phases [6]. MRI is very sensitive as well, and has the advantage of liver-specific contrast if required. MRI is also used for screening purposes, despite the fact that it is more time-consuming than other methodologies and may be subject to motion artefacts [7]. According to different reports, these modalities detect >90% of liver metastases if their diameter is >5 mm [7,8]. There is still a group of patients who undergo hepatic surgery without correct pre-operative diagnosis [8,9]. The use of intra-operative ultrasound (IOUS) with or without contrast agents has proved to be efficient in finding, during hepatectomy, metastases that were not detected by pre-operative examinations [9,10]. IOUS has been shown to yield significant new information, not identified on pre-operative imaging, which determines the resectability of the metastasis or changes the operative plan. IOUS is considered the gold standard, thereby achieving universal usage [9,11]. However, the rate of hepatic recurrence following apparently curative liver resection is about 40% at 3 years [12]. This underlines the limitation of IOUS itself, and the need for a more accurate imaging technique cannot be overemphasised. The missed tumours may be small, isoechoic, deeply located or positioned in regions that are difficult to image [13,14]. Therefore, surgeons also use visual and tactile sensory information intra-operatively to evaluate differences in mechanical properties between normal livers and tumours. Palpation provides tactile sensory information regarding the mechanical properties of materials intra-operatively. Palpation involves the application of a stress, with evaluation of the resultant displacement, strain and other mechanical responses that are thus subjectively evaluated. The primary mechanical property that is frequently evaluated when surgeons palpate hepatic tumours intra-operatively to assist resection is the relative stiffness of the liver when compared with a tumour. Stiffer tissues strain less than softer tissues under similar conditions, and tumours generally tend to be stiffer than normal livers. Therefore, ultrasonic elastography is an ideal imaging modality for probing the bioelasticity distribution in biological tissues [15]. The technique is based on the strain-gauge principle, according to which the stiff tissue strains less than soft tissue and when deformed externally by a mechanical compression. Because the stiffness rather than the backscatter is sensed remotely, tumours that are not detectable on sonograms might often be revealed with good resolution and good contrast in elastograms. Real-time ultrasound elastography is now used in a widespread manner in the clinic, and these systems have become commercially available [16-19].Our long-term objective is to incorporate elasticity imaging within a medical device for the treatment of liver metastases using high-intensity focused ultrasound (HIFU) for eventual clinical use. In previous studies [20,21], we have described the use of a toroidal transducer for HIFU ablation, which could represent a promising alternative for treating colorectal liver metastases. This device is designed to be used during surgery. We have also shown that elastography is useful in the evaluation of the region that has been ablated using this device [22]. In this article, we explore the feasibility of utilising hand-held real-time elastography for the visualisation of metastases. The hand-held approach was chosen to provide a straightforward complement to conventional B-mode images, which are currently used to define the extent of the metastatic disease. In vivo studies using a rabbit model of a liver tumour were conducted in order to provide quantitative measures of the image quality attained during intra-operative real-time elastographic visualisation of liver metastasis. During these experiments, the ability of extracorporeal strain images to detect these tumours was also evaluated as a secondary objective.     

Recent advances in SPECT imaging.

SPECT is a rapidly changing field, and the past several years have produced new developments in both hardware technology and image-processing algorithms. At the component level there have been improvements in scintillators and photon transducers as well as a greater availability of semiconductor technology. These devices permit the fabrication of smaller and more compact systems that can be customized for particular applications. New clinical devices include high-count sensitivity cardiac SPECT systems that do not use conventional collimation and the introduction of diagnostic-quality hybrid SPECT/CT systems. While there has been steady progress with reconstruction algorithms, exciting new processing algorithms have become commercially available that promise to provide substantial reductions in SPECT acquisition time without sacrificing diagnostic quality. Preclinical small-animal SPECT systems have become a major focus in nuclear medicine. These systems have pushed the limits of SPECT into the submillimeter range, making them valuable molecular imaging tools capable of providing information unavailable from other modalities.     

Recent topics in NMR imaging and MRI.

NMR and NMR imaging (MRI) are finding increasing use not only in the clinical and medical fields, but also in material, physicochemical, biological, geological, industrial and environmental applications. This short review is limited to two topics: (i) new techniques and pulse sequences and their application to non-clinical fields that may have clinical application; and (ii) new trends in MR contrast agents. The former topic addresses pulse sequence and data analysis; dynamics such as diffusion, flow, velocity and velocimetry; chemometrics; pharmacological agents; and chemotherapy; the latter topic addresses contrast agents (CA) sensitive to biochemical activity; CA based on water exchange; molecular interactions and stability of CA; characteristics of emerging CA; superparamagnetic CA; and macromolecular CA.     

Recent advances in imaging technologies in dentistry

Dentistry has witnessed tremendous advances in all its branches over the past three decades. With these advances, the need for more precise diagnostic tools, specially imaging methods, have become mandatory. From the simple intra-oral periapical X-rays, advanced imaging techniques like computed tomography, cone beam computed tomography, magnetic resonance imaging and ultrasound have also found place in modern dentistry. Changing from analogue to digital radiography has not only made the process simpler and faster but also made image storage, manipulation (brightness/contrast, image cropping, etc.) and retrieval easier. The three-dimensional imaging has made the complex cranio-facial structures more accessible for examination and early and accurate diagnosis of deep seated lesions. This paper is to review current advances in imaging technology and their uses in different disciplines of dentistry.     

组织多普勒应变与二维应变检测左心室壁应变可靠性对比分析

目的:评价以组织多普勒技术为基础的应变(DT-ST)及以斑点追踪技术为基础的二维应变(2D-ST)测量左室壁应变的可靠性。方法:随机抽取40例作左室壁DT-ST及2D-ST分析,并选取同期40例正常人作为对照组。左室壁应变测量由2名观察者独立完成,每名观察者对每例患者用组织多普勒应变及二维应变析各测量2次。同一名观察者测量2次间及2名观察者间测量差异用重复检测方差分析比较,一致性用组里相关系数(ICC)描述,2名观察者间测量可靠性用Cronbach’s alpha系数描述。结果:①除观察者甲冠心病组的室间隔心尖段DT-ST 2次测量结果、观察者间对照组的左室侧壁中间段、心尖段DT-ST及观察者间冠心病组左室侧壁基底段及心尖段DT-ST测量结果差异有统计学意义外(P值均<0.05),余观察者内及观察者间各节段重复测量结果之间均无显著差异;②观察者内可靠性:对照组2D-STICC与DT-STICC相近,或略大于DT-STICC;而冠心病组除观察者乙室间隔中间段ICC外,余各节段2D-ST ICC均大于DT-STICC;③观察者间可靠性:冠心病组及对照组左室壁各节段2D-ST的Cronbach’s alpha系数均大于DT-ST Cron-bach’s alpha系数。结论:组织多普勒应变及二维应变检测室壁应变均具有较高可靠性,但二维应变法具有更高的观察者间可靠性。     

介入分子影像学研究进展

近年来分子影像学迅速发展,为分子生物学、临床靶向治疗学等相关领域研究提供了有力的活体内监测手段.但目前多种分子影像技术在临床应用均存在一定的局限性,其对大动物乃至人的研究工作受到极大限制,使得分子影像学仍处于小动物基础成像或临床前研究阶段.介入分子影像学的出现,为解决这一系列问题提供了新思路,通过优化分子探针导入方式、改良现有分子成像技术装置等,使分子影像学从小动物基础研究发展为大动物研究和临床应用研究成为可能,并最终成为临床转化的重要桥梁.同时,介入分子影像学融合了分子影像诊断学与临床靶向治疗学,这无疑将成为推动临床靶向治疗及个体化治疗的重要力量,对未来临床诊治工作产生又一革命性影响,也是未来介入放射学发展的重要方向.     

Recent advances in spinal magnetic resonance imaging

The application of recent technologic innovations, such as phase-array coil technology, saturation bands in the field of view, variable bandwidth, new methods of image display, new applications of contrast agents and ultrafast spin-echo imaging, promises to improve even further the scope and versatility of magnetic resonance imaging of the spine. Several of the new methods, such as the fat-saturation and variable-bandwidth techniques, have been applied to imaging the head, but their use in imaging the spine has lagged for various technologic reasons. For other advances, such as phased-array coil technology, minor problems, including prolonged reconstruction time, have yet to be overcome. Still others, such as ultrafast spin-echo imaging, have been developed so recently that they have just begun to enter clinical trials. All of these techniques promise to improve the quality and, in some cases, the speed of spinal magnetic resonance imaging and should allow an even better understanding of the anatomy and pathology of the spine.     

Magnetic resonance imaging assessment of myocardial elastic modulus and viscosity using displacement imaging and phase-contrast velocity mapping.

Approximately half of patients experiencing congestive heart failure present with a normal left ventricular ejection fraction. Perturbations in material properties affecting ventricular pressure/volume relationships likely play an important role in the "stiff heart syndrome" yet noninvasive tools permitting the accurate assessment of myocardial elasticity are extremely limited. We developed an MRI-based technique to examine regional left ventricular stress/strain relationships by incorporating displacement-encoding with stimulated-echoes (DENSE) and phase-contrast (PC) velocity mapping and compared regional elastic moduli (EM) and viscous delay time constants (VDTCs) (N=10) with immediate postmortem direct strain gauge measurements (N=8) and global chamber compliance (literature) in normal dogs. EMs by MRI were significantly greater in papillary muscle columns when compared with lateral wall and septal locations by MRI (7.59+/-1.65 versus 3.40+/-0.87 versus 2.55+/-0.93 kPa, P<0.0001) and were in agreement with direct strain gauge measurements (3.78+/-0.93 and 2.96+/-0.88 kPa for the lateral wall and the septum, P=ns for both versus MRI). MRI-determined VDTCs were similar in the three regions (VDTC=-1.15+/-12.37 versus 3.04+/-7.25 versus 4.17+/-5.76 ms, P=ns) and did not differ from lateral and septal wall strain gauge assessment (VDTC=3.09+/-0.40 and 4.57+/-1.86 ms, P=ns for both versus MRI). Viscoelastic measurements obtained in six normal volunteers demonstrated the feasibility of this technique in humans. Noninvasive, regional assessment of myocardial stiffness using DENSE and PC velocity mapping techniques is accurate in a canine model and feasible in humans.     

应变率成像评价单纯性肥胖儿童左室局部心肌的收缩功能

目的:探讨应变及应变率成像在评价单纯性肥胖儿童心肌收缩功能方面的临床价值.方法:肥胖组儿童30人,年龄10±4岁,按年龄及性别匹配的健康儿童30人为对照组,分别进行二维及组织多普勒超声检查,应用应变率技术对局部心肌进行定量分析.结果:肥胖儿童左房内径增大(P<0.05),左室下壁、侧壁及室间隔心肌收缩期峰值应变、应变率明显低于正常儿童(P<0.05).结论:应变率成像技术可敏感的检测出单纯性肥胖儿童左心室心肌收缩功能及特性的改变.     

MR imaging of myotendinous strain.

Myotendinous strain predominantly exhibits pathognomonic MR features. Whenever a patient's musculoskeletal symptoms lack temporal correlation with exercise, MR imaging may be valuable in distinguishing strain injury from other disorders of the myotendinous unit. Compared with myotendinous strain, myositis ossificans has variable and nonspecific MR appearances that may simulate neoplasm and require biopsy for diagnosis.     

Recent advances in imaging techniques of renal masses

Multiphasic multidetector computed tomography (CT) forms the mainstay for the characterization of renal masses whereas magnetic resonance imaging (MRI) acts as a problem-solving tool in some cases. However, a few of the renal masses remain indeterminate even after evaluation by conventional imaging methods. To overcome the deficiency in current imaging techniques, advanced imaging methods have been devised and are being tested. This review will cover the role of contrast-enhanced ultrasonography, shear wave elastography, dual-energy CT, perfusion CT, MR perfusion, diffusion-weighted MRI, blood oxygen level-dependent MRI, MR spectroscopy, positron emission tomography (PET)/prostate-specific membrane antigen-PET in the characterization of renal masses.     

肝纤维化的分子成像进展

肝纤维化是各种慢性肝损伤的共同转归,肝纤维化分子成像基于病程中异常表达的靶分子,在真实完整的生理环境中通过图像直接观察细胞和分子通路。通过对病变的发生、发展过程进行成像,可做到对肝纤维化的早期诊断、早期干预及疗效评估。迄今为止,以活化的星状细胞或细胞外基质某类成分为靶分子的肝纤维化分子成像已取得一定进展。综述基于不同成像靶点的分子成像在肝纤维化中的应用进展。     

卵巢动脉的影像学研究进展及临床意义

正常卵巢动脉纤细,且起源、走行变异较多,手术时极易损伤而影响卵巢功能。卵巢动脉对子宫动脉栓塞术的技术安全和临床疗效也存在重要影响。随着各种需要保全子宫和卵巢功能的妇产科手术及血管内介入技术的广泛应用,卵巢动脉的临床意义逐渐受到重视,临床对卵巢动脉的解剖学认识也有了更高的要求。就卵巢动脉的解剖学、影像学研究及临床意义等予以综述。     

放射性核素标记的凋亡显像剂的研究进展

细胞凋亡存在于多种病理过程中, 包括神经系统变性疾病、缺血性损伤、自身免疫性疾病和多种肿瘤等。凋亡检测的可视化对疾病的诊断、新的治疗方法的开发与疗效评价具有重要意义。传统的凋亡检测方法包括光学显微镜观察、原位末端标记法分析、流式细胞仪检测等, 但其侵入性方式限制了之后的随访研究。而活体内凋亡显像有助于无创观察、直观了解凋亡发生的体内过程。PET与SPECT的发展, 以及新的针对靶点的放射性核素标记显像剂的合成, 使核医学进入了分子影像学的新时代。近年来, 细胞凋亡PET与SPECT显像剂的研发应用, 使活体内无创PET与SPECT检测细胞凋亡成为现实。笔者主要介绍用于在体凋亡显像的放射性标记探针及其最新研究应用进展。     

Recent advances in imaging of cerebrovascular disease.

The recent advances made in CT and MR imaging have led to increased accuracy in making a number of diagnoses in the emergency room setting. Increasingly, radiologists are asked to perform these studies and accurately interpret the findings, which often have a dramatic impact on triaging and treatment of the patient. Future trials need to address further the relative merits of each of the techniques outlined previously in specific settings. In addition, given the increasing number of means of obtaining diagnostic information, cost effectiveness studies are needed to better formulate an appropriate algorithm for each diagnosis.