Ultrasound imaging in three and four dimensions

Three-dimensional (3D) reconstruction of ultrasound images was first demonstrated nearly 15 years ago, but only now is becoming a clinical reality. In the meantime, methods for 3D reconstruction of CT and MRI images have achieved an advanced state of development, and 3D imaging with these modalities has been applied widely in clinical practice. 3D applications in ultrasound have lagged behind CT and MRI, because ultrasound data is much more difficult to render in 3D, for a variety of technical reasons, than either CT or MRI data. Only in the past few years has the computing power of ultrasound equipment reached a level adequate enough for the complex signal processing tasks needed to render ultrasound data in three dimensions. At this point in time, the clinical application of 3D ultrasound is likely to advance rapidly, as improved 3D rendering technology becomes more widely available. This article is a review of the present status of 3D ultrasound imaging. It begins by comparing the characteristics of CT, MRI, and ultrasound image data that either make these data amenable or not amenable to 3D reconstruction. The article then considers the technical features involved with acquiring an ultrasound 3D data set and the mechanisms for reconstructing the images. Finally, the article reviews the literature that is available regarding clinical application of 3D ultrasound in obstetrics, ultrasound, the abdomen, and blood vessels.     

Ultrasound virtual endoscopic imaging

Volume data acquisition, three dimensional (3D) imaging, and multiplanar reformatting have become widely used for computed tomography (CT) and magnetic resonance imaging (MRI). As an extension of this technology, virtual endoscopic visualization of hollow organs has become a reality that is now finding its way into clinical CT practice. The same methods of computer processing as are used for CT and MRI can be applied to an ultrasound (US) volume image data set with the same potential output; namely, 3D, multiplanar, and virtual endoscopic images. The use of this image processing technology for US applications has lagged behind the CT and MRI applications, but considerable progress in applying these methods to US has occurred in recent years. As a result, US virtual endoscopic imaging now can be performed on a clinical basis by using standard US instruments and commercially available computer software. The use of newer US imaging methods, such as tissue harmonic and power Doppler imaging, has enhanced the potential for US virtual endoscopy. This article reviews the technology of US virtual endoscopy. In addition, our preliminary experience of using this method for abdominal and vascular diagnosis is described. Finally, we speculate on technical improvements and potential applications that are likely in the future.     

舌癌的超声诊断研究

目的：探讨超声诊断舌癌的临床应用价值。方法：采用高频超声经皮舌骨上区舌检查法诊断舌占位性病变和舌癌患者85例,并行术后随访观察。其中51例原发性舌癌超声检查（US）与核磁共振检查（MR）、临床检查及病理检查结果进行对照。结果：原发性舌癌超声显示率为98．0％,诊断准确率为92．2％。术前原发性舌癌超声、MR和临床检查T分期诊断准确率分别为90．2％、90．0％和80．4％。结论舌癌超声诊断法对舌癌术前分期诊断和术后随访均具有重要的临床应用价值。     

超声图像分割研究现状

目前,医学图像作为临床检测以及放疗引导的重要参考依据,在医学的发展中起着关键作用。医学图像主要包括计算机断层扫描（CT）、核磁共振（MRI）、X射线、超声（US）等,超声相对前三者价格较低,对软组织成像效果较好且对人体基本无伤害,在现阶段应用已越来越广泛。超声图像分割对后期图像分析有很大的作用,可以给临床诊断及放疗摆位等提供一定的参考,本文就超声图像的分割的传统方法、基于形变模型的分割方法和结合深度学习方法的研究情况进行阐述。     

Freehand 3-D Ultrasound Imaging: A Systematic Review

Two-dimensional ultrasound (US) imaging has been successfully used in clinical applications as a low-cost, portable and non-invasive image modality for more than three decades. Recent advances in computer science and technology illustrate the promise of the 3-D US modality as a medical imaging technique that is comparable to other prevalent modalities and that overcomes certain drawbacks of 2-D US. This systematic review covers freehand 3-D US imaging between 1970 and 2017, highlighting the current trends in research fields, the research methods, the main limitations, the leading researchers, standard assessment criteria and clinical applications. Freehand 3-D US systems are more prevalent in the academic environment, whereas in clinical applications and industrial research, most studies have focused on 3-D US transducers and improvement of hardware performance. This topic is still an interesting active area for researchers, and there remain many unsolved problems to be addressed.     

~(18)F-FDG PET显像在诊断消化道良恶性肿瘤和术后随访中的应用价值

目的 通过18F-FDG PET显像在消化道良恶性肿瘤鉴别诊断和随访结果,与CT/MR和手术病理结果的对比研究,以评价PET在消化道肿瘤中的临床应用价值。方法 消化道恶性肿块13例(胰腺癌10例,直肠癌2例和肝癌1例)、良性肿块5例和恶性肿瘤(胃癌5例,直肠癌4例和肝癌1例)手术治疗后10例共28例患者进行~(18)F-FDG PET全身显像,采用双盲法将PET诊断结果与同期的CT/MR影像结果进行比较。结果 13例消化道恶性肿块PET和CT/MR均见原发灶病变,10例PET显像结果与CT/MR相同,另外3例胰腺癌患者PET显像见腹腔淋巴结和脊柱转移。5例良性消化道占位性病变PET全身显像均阴性,其中1例病例病理诊断为直肠腺瘤。10例消化恶性肿瘤术后随访中有3例PET阳性结果与CT/MR相同,4例PET全身显像阴性,另外3例PET显像见其他部位病灶。结论 ~(18)F-FDG PET显像对原发性恶性肿瘤的诊断、良恶性肿块的鉴别诊断具较高的准确性和特异性,对恶性肿瘤治疗后随访确认或排除肿瘤残留和复发以及发现全身部位的转移等具有良好的临床应用价值,其对全身转移病灶的定性和定位诊断优于CT/MR。     

Renal complex cysts in adults: contrast-enhanced ultrasound

Contrast-enhanced ultrasound (CEUS) has been proved to be a useful imaging modality to characterize complex renal cysts using the Bosniak classification in a similar way as Computed Tomography (CT). CEUS helps not only in the characterization of complex cysts detected on baseline US but also in the characterization of indeterminate cystic lesions on CT or Magnetic Resonance (MR).     

MRI in the evaluation of hepatocellular nodules: role of pulse sequences and contrast agents

Magnetic resonance (MR) imaging is more useful than computed tomography (CT) in the evaluation of hepatocellular nodules based on the excellent soft-tissue image contrast of MR imaging. In addition, recent MR units have allowed various fast MR imaging techniques (i.e., parallel imaging or echo-planar imaging) to dramatically improve image quality and image contrast. A variety of liver-specific MR contrast agents are also currently available or have been evaluated in clinical trials to improve the contrast between the liver parenchyma and hepatocellular nodules.     

Blood-Brain Barrier (BBB) Disruption Using a Diagnostic Ultrasound Scanner and Definity® in Mice

The objective of this work was to determine whether diagnostic ultrasound and contrast agent could be used to transcranially and nondestructively disrupt the blood-brain barrier (BBB) in mice under ultrasound image guidance and to quantify that disruption using magnetic resonance imaging (MRI) and magnetic resonance (MR) contrast agent. Each mouse was placed under isoflurane anesthesia and the hair on top of its skull was removed before treatment. A diagnostic ultrasound transducer was placed in a water bag coupled with gel on the mouse skull. Definity (ultrasound [US] contrast) and Magnevist (MR contrast) were injected concurrent with the start of a custom ultrasound transmission sequence. The transducer was translated along the rostral-caudal axis to insonify three spatial locations (2 mm apart) along one half of the brain for each sequence. T1-weighted MR images were used to quantify the volume of tissue over which the BBB disruption allowed Magnevist to enter the brain, based upon increases in MR contrast-to-noise ratio (CNR) compared with the noninsonified portions of the brain. Ultrasonic frequency, pressure and pulse duration, as well as Definity dose and injection time were varied. Preliminary results suggest that a threshold exists for BBB opening dependent upon both pressure and pulse duration (consistent with reports in the literature performed at lower frequencies). A range of typical diagnostic frequencies (e.g., 5.0–8.0 MHz) generated BBB disruption. Comparable BBB opening was noted with varied delays between Definity injection and insonification (0–2 min) for a range of Definity concentrations (400-2400 μL/kg). The low-pressure, custom sequences (mechanical index [MI] ≤ 0.65) had minimal blood cell extravasation as determined by histologic evaluation. This study has shown the ability of a diagnostic ultrasound system, in conjunction with Definity, to open the BBB transcranially in a mouse model for molecules approximately 0.5 kDa in size. Opening was achieved at higher frequencies than previously reported and was localized under ultrasound image guidance. A typical, ultrasound imaging mode (pulsed wave [PW] Doppler) with specific settings (transmit frequency = 5.7 MHz, gate size = 15 mm, pulse repetition frequency = 100 Hz, system power = 15%) successfully opened the BBB, which facilitates implementation using the most of commercially available clinical diagnostic scanners. Localized opening of the BBB may have potential clinical utility for the delivery of diagnostic or therapeutic agents to the brain. (Email: kdf2@duke.edu)     

Emergency department ultrasound for hemothorax after blunt traumatic injury

Diagnosing hemothorax after blunt trauma may be aided by emergency department (ED) ultrasound (US). Various prior studies have evaluated ED US using different gold standards. A prospective study of blunt trauma patients who underwent computed tomography (CT) scan of the chest, abdomen, or both, was performed. Before CT scan, an US examination was performed specifically to identify free fluid in the thorax. The CT scan findings were used as the gold standard for validation of US results. From July 1998 to June 1999, 142 of 155 patients who underwent US and CT scan for evaluation of blunt trauma were included in this study. The CT scan identified 16 cases of hemothorax among these patients. ED US resulted in 2 true-positive, 2 false-positive, 14 false-negative, and 124 true-negative findings. ED US was 12.5% sensitive and 98.4% specific. ED US did not detect small-volume hemothorax identified by CT scan. Future research should focus on further defining the size of hemothorax appreciable with ED US, with increased attention paid to the type of gold standard implemented for its evaluation.     

MR evaluation of solid renal masses

After diagnosis of a suspicious renal mass on ultrasound or CT, renal MR imaging typically is ordered to characterize the mass further, stage the mass, or resolve discordant ultrasound and CT results. MR imaging may also be ordered in cases in which ultrasound is poor or in instances in which contrast-enhanced CT may be ill advised.     

Does oral radiocontrast affect image quality of abdominal sonography?

Objective

Emergency Department patients with abdominal pain may require both an ultrasound (US) and computed tomography (CT) for an accurate diagnosis. Patients are often asked to drink oral radiocontrast while awaiting ultrasound, in order to better expedite a CT in the case of a non-diagnostic US. The impact of oral radiocontrast on US image quality has not been studied. We compared the quality of US images obtained before and after the ingestion of oral radiocontrast in healthy adult volunteers.

Deformable registration of preoperative MR,pre-resection ultrasound,and post-resection ultrasound images of neurosurgery

Purpose

Sites that use ultrasound (US) in image-guided neurosurgery (IGNS) of brain tumors generally have three sets of imaging data: preoperative magnetic resonance (MR) image, pre-resection US, and post-resection US. The MR image is usually acquired days before the surgery, the pre-resection US is obtained after the craniotomy but before the resection, and finally, the post-resection US scan is performed after the resection of the tumor. The craniotomy and tumor resection both cause brain deformation, which significantly reduces the accuracy of the MR–US alignment.

Method

Three unknown transformations exist between the three sets of imaging data: MR to pre-resection US, pre- to post-resection US, and MR to post-resection US. We use two algorithms that we have recently developed to perform the first two registrations (i.e., MR to pre-resection US and pre- to post-resection US). Regarding the third registration (MR to post-resection US), we evaluate three strategies. The first method performs a registration between the MR and pre-resection US, and another registration between the pre- and post-resection US. It then composes the two transformations to register MR and post-resection US; we call this method compositional registration. The second method ignores the pre-resection US and directly registers the MR and post-resection US; we refer to this method as direct registration. The third method is a combination of the first and second: it uses the solution of the compositional registration as an initial solution for the direct registration method. We call this method group-wise registration.

Results

We use data from 13 patients provided in the MNI BITE database for all of our analysis. Registration of MR and pre-resection US reduces the average of the mean target registration error (mTRE) from 4.1 to 2.4 mm. Registration of pre- and post-resection US reduces the average mTRE from 3.7 to 1.5 mm. Regarding the registration of MR and post-resection US, all three strategies reduce the mTRE. The initial average mTRE is 5.9 mm, which reduces to 3.3 mm with the compositional method, 2.9 mm with the direct technique, and 2.8 mm with the group-wise method.

Conclusion

Deformable registration of MR and pre- and post-resection US images significantly improves their alignment. Among the three methods proposed for registering the MR to post-resection US, the group-wise method gives the lowest TRE values. Since the running time of all registration algorithms is less than 2 min on one core of a CPU, they can be integrated into IGNS systems for interactive use during surgery.

     

Right colonic diverticulitis: MR appearance

Background: We evaluated the magnetic resonance (MR) features of right colonic diverticulitis. Methods: This prospective study was based on five patients selected from a group of 156 patients admitted to the radiology department for further evaluation because of clinically suspected appendicitis. All five patients had ultrasound (US) and MR studies, and four patients also had computed tomography (CT). Results: In all five patients, right-side diverticulitis was seen as an outpouching of the right colon with associated circumferential wall thickening of the colon and surrounding inflammatory changes. Conclusions: Our results suggest that MR imaging can be useful in the diagnosis of right colonic diverticulitis. An inflamed diverticulum with adjacent colonic wall thickening and surrounding inflamed fat are characteristic MR signs. MR imaging can be a valuable alternative to CT in young or pregnant patients who have suspected appendicitis and an equivocal US result.     

Hepatocellular carcinoma: Prospective assessments of the T-factor with CT, US, and MR imaging

The capabilities of computed tomography (CT), ultrasonography (US), and magnetic resonance (MR) imaging were studied in order to determine the role of each of these noninvasive examinations for estimating the T-factor of hepatocellular carcinomas (HCCs). Fifty-one patients with surgically proven HCCs received CT (50 patients), US (46 patients), and MR (44 patients). The images of CT, US, and MR were prospectively evaluated for main tumor size, intrahepatic metastases, and vascular invasion, which compose the T-factor of HCC, and compared to pathological results. The sizes of the main tumor were estimated correctly by all examinations. For estimating intrahepatic metastases, US (74%) and MR (73%) were superior to CT (65%). For estimating portal invasion, CT (79%) was superior to US (70%) and MR (66%), because CT could demonstrate the segmental staining caused by portal invasion. The estimates of hepatic venous invasion were difficult during any of the examinations. We conclude that presurgical evaluations of the T-factor require the use of US and CT or MR and CT.     

Non-iterative partial view 3D ultrasound to CT registration in ultrasound-guided computer-assisted orthopedic surgery

Purpose

In image-guided orthopedic surgery, rigid registration of intra-operative ultrasound (US) to a pre-operative plan, developed using computed tomography (CT) scans, is an important step for providing real time surgical guidance. The ability to perform this registration accurately, automatically, and in real time is critical for enabling more effective image guidance and anatomic restoration in a number of orthopedic procedures. Several surface-based and intensity-based registration methods have been proposed before to align the US and CT data. Although relatively successful results were reported, both methods require accurate segmentation or localization of the bone surface in US data, which is a challenging task. Furthermore, typically, only partial views of the three-dimensional (3D) bone anatomy are visible in US data, and registration would only converge if a good estimation of the initial alignment between the US and CT datasets is known.

Methods

We propose a 3D rigid CT to US registration method based on the alignment of local phase bone image projections. The registration is achieved by transforming the local phase bone features, calculated using 3D Log-Gabor filters, to a projection space obtained using 3D Radon transform. Validation experiments show the capability of the method in registering partial view US volumes to full view CT volume.

Results

Feasibility experiments, carried out on a phantom and ten volunteer subjects, show an average surface registration, in the region where the US scans were acquired, of 0.42 and 0.78  mm, respectively.

Conclusions

The proposed US to CT registration method is fully automatic, non-iterative and requires no initial alignment between the two registering datasets.     

虚拟导航超声造影定位检出肝脏局灶性病变的价值

目的探讨虚拟导航超声造影定位检出肝脏局灶性病变的价值。方法 47个CT/MR提示但常规超声无法显示的肝脏局灶性病变,使用虚拟导航将病灶的CT/MR和超声图像对位融合后,行超声造影检查,观察图像融合的成功率和所需时间,以及虚拟导航超声造影检出病灶的情况及检出率。结果所有病例中虚拟导航均能成功对位,对位融合所需时间为3～10min,平均(4.4±1.5)min。虚拟导航超声造影能显示病灶37个,检出率为78.7%(37/47)。结论虚拟导航超声造影对于常规超声无法显示的肝脏局灶性病变具有较高的定位检出率,是一种具有临床应用前景的新技术。     

MR imaging of pulmonary and mediastinal malignancies

The primary goal of performing cross-sectional imaging of the chest in the radiologic evaluation of lung cancer is to obtain information about the character and magnitude of the neoplasm. Patient prognosis and therapy decisions depend directly on identifying the size and full extent of the tumor. The ideal imaging modality therefore should provide reliable information that can be used to assist in accurately staging the malignancy. Traditionally, CT scanning has been used exclusively as part of the preoperative evaluation of primary lung carcinomas. Recent advances in CT scanning technology have greatly improved image acquisition times and image quality and consequently have enhanced the role of CT imaging in the evaluation of bronchogenic carcinomas. Single-breath CT acquisitions of the chest can now be accomplished in a matter of seconds. These rapid acquisitions improve image quality by decreasing respiratory motion, while enhancing patient compliance and throughput. Clearly, CT scanning has matured into an efficient and accurate diagnostic tool to stage primary lung malignancies noninvasively. In its present state of development, MR imaging has one distinct disadvantage that makes it significantly less attractive as a routine lung cancer examination, namely the inability to produce images of the lung that are high in spatial resolution. Also, the sensitivity and specificity of MR imaging, which are similar to those of CT scanning in identifying mediastinal and hilar metastases, offer no clinical advantages. Longer image acquisition times and time constraints force most MR imaging examinations to be abbreviated and limited in coverage. As a result, the necessary exclusion of important anatomic areas routinely visualized by CT scanning may limit the diagnostic power of MR imaging. Finally, MR imaging requires greater physician supervision than CT scanning to direct imaging and to maintain examination quality and thoroughness. Although MR imaging can contribute significantly to the radiologic evaluation of patients with lung cancer, its role is somewhat limited, and it is most useful as a complement to CT scanning. The additional versatility offered by pulse sequences that take advantage of the intrinsic relaxation of tissues greatly facilitates identification of tumor, particularly when local invasion is present. By virtue of the short T1 value of fat, MR imaging may improve the detection of mediastinal disease, particularly in cases in which the sensitivity of CT scanning cannot be optimized because of allergies to contrast or renal insufficiency. MR imaging is superior to CT scanning in demonstrating musculoskeletal anatomy and the neurovascular structures of the neck and mediastinum. Although MR imaging has a potential usefulness in the radiographic evaluation of lung carcinoma, technical shortcomings relegate this modality to a role that is primarily complementary to CT scanning. With time, technological improvements will undoubtedly redefine the role of MR imaging in the radiographic evaluation and staging of bronchogenic carcinomas.     

影像学技术定量诊断脂肪肝的实验研究

目的 利用ROC曲线比较生化、超声、CT、质子磁共振波谱(1H MRS)定量诊断脂肪肝的应用价值.方法 选用45只健康新西兰大白兔,高脂高糖饲料加酒精饮料建立不同程度脂肪肝模型,应用生化、超声、CT及1H MRS多种.临床诊断方法,共观测18个变量指标,在每种诊断方法所观测的指标中,选取与脂肪肝分级相关性最高的指标,并以此进行受试者操作特征(ROC)曲线分析和ROC曲线下面积Z检验,比较这几种诊断方法的应用价值.结果 在所有18个观测指标中,血清胆固醇、超声衰减系数、肝CT值和1H MRS脂肪波峰下面积分别是生化、超声、CT、1H MRS诊断方法中与脂肪肝分级相关性最高的观测指标,相关系数分别为0.886(P=0.000)、0.483(P=0.002)、-0.764(P=0.000)、0.558(P=0.001);ROC曲线分析和Z检验显示:上述各指标ROC曲线下面积分别为0.981,0.581,0.810,0.713,除1H MRS脂肪波峰下面积与超声衰减系数、肝CT值之间差异无统计学意义外(P>O.05),其他两两之间差异均有统计学意义(P1H MRS>超声;生化测定血清胆固醇水平对判断脂肪肝程度可能具有重要的意义,值得进一步研究.     

Comparison of extended field of view and dual image ultrasound techniques: accuracy and reliability of distance measurements in phantom study

This study was undertaken to investigate and compare the accuracy and reliability of dual image and extended field-of-view (EFOV) ultrasound (US) techniques in distance measurements using acoustic phantoms. Ten tissue phantoms were constructed and were scanned twice with an interval of 3 days by two operators. Measurements of various known distance (ranging from 4.6 to 7.2 cm) in the phantoms were made with dual image and EFOV US. Results showed that both dual image and EFOV US have a high accuracy and reliability in distance measurements, with the EFOV US (r = 0.997 to 0.998, reproducibility = 99.8%, repeatability = 98.2 to 99.8%) being slightly more accurate and reliable than dual image US (r = 0.948 to 0.981, reproducibility = 94.6%, repeatability = 89.6 to 97.9%). EFOV US has a higher accuracy and reliability than dual image US in distance measurements. However, the dual image US is a useful alternative with a high accuracy and reliability when EFOV US is not available.