Simultaneous in vivo positron emission tomography and magnetic resonance imaging

Positron emission tomography (PET) and magnetic resonance imaging (MRI) are widely used in vivo imaging technologies with both clinical and biomedical research applications. The strengths of MRI include high-resolution, high-contrast morphologic imaging of soft tissues; the ability to image physiologic parameters such as diffusion and changes in oxygenation level resulting from neuronal stimulation; and the measurement of metabolites using chemical shift imaging. PET images the distribution of biologically targeted radiotracers with high sensitivity, but images generally lack anatomic context and are of lower spatial resolution. Integration of these technologies permits the acquisition of temporally correlated data showing the distribution of PET radiotracers and MRI contrast agents or MR-detectable metabolites, with registration to the underlying anatomy. An MRI-compatible PET scanner has been built for biomedical research applications that allows data from both modalities to be acquired simultaneously. Experiments demonstrate no effect of the MRI system on the spatial resolution of the PET system and <10% reduction in the fraction of radioactive decay events detected by the PET scanner inside the MRI. The signal-to-noise ratio and uniformity of the MR images, with the exception of one particular pulse sequence, were little affected by the presence of the PET scanner. In vivo simultaneous PET and MRI studies were performed in mice. Proof-of-principle in vivo MR spectroscopy and functional MRI experiments were also demonstrated with the combined scanner.     

Deep-tissue anatomical imaging of mice using carbon nanotube fluorophores in the second near-infrared window

Fluorescent imaging in the second near-infrared window (NIR II, 1-1.4 μm) holds much promise due to minimal autofluorescence and tissue scattering. Here, using well-functionalized biocompatible single-walled carbon nanotubes (SWNTs) as NIR II fluorescent imaging agents, we performed high-frame-rate video imaging of mice during intravenous injection of SWNTs and investigated the path of SWNTs through the mouse anatomy. We observed in real-time SWNT circulation through the lungs and kidneys several seconds postinjection, and spleen and liver at slightly later time points. Dynamic contrast-enhanced imaging through principal component analysis (PCA) was performed and found to greatly increase the anatomical resolution of organs as a function of time postinjection. Importantly, PCA was able to discriminate organs such as the pancreas, which could not be resolved from real-time raw images. Tissue phantom studies were performed to compare imaging in the NIR II region to the traditional NIR I biological transparency window (700-900 nm). Examination of the feature sizes of a common NIR I dye (indocyanine green) showed a more rapid loss of feature contrast and integrity with increasing feature depth as compared to SWNTs in the NIR II region. The effects of increased scattering in the NIR I versus NIR II region were confirmed by Monte Carlo simulation. In vivo fluorescence imaging in the NIR II region combined with PCA analysis may represent a powerful approach to high-resolution optical imaging through deep tissues, useful for a wide range of applications from biomedical research to disease diagnostics.     

Two-Photon Time-Gated In Vivo Imaging of Dihydrolipoic-Acid-Decorated Gold Nanoclusters

Due to the unique advantages of two-photon technology and time-resolved imaging technology in the biomedical field, attention has been paid to them. Gold clusters possess excellent physicochemical properties and low biotoxicity, which make them greatly advantageous in biological imaging, especially for in vivo animal imaging. A gold nanocluster was coupled with dihydrolipoic acid to obtain a functionalized nanoprobe; the material displayed significant features, including a large two-photon absorption cross-section (up to 1.59 × 10⁵ GM) and prolonged fluorescence lifetime (>300 ns). The two-photon and time-resolution techniques were used to perform cell imaging and in vivo imaging.     

An imaging spectroscopy approach for measurement of oxygen saturation and hematocrit during intravital microscopy

OBJECTIVE: Oxygen supply and partial pressure are key determinants of tissue metabolic status and are also regulators of vascular function including production of reactive oxygen species, vascular remodeling, and angiogenesis. The objective of this study was to develop an approach for the determination of oxygen saturation and hematocrit for individual microvessels in trans- and epi-illumination intravital microscopy. METHODS: A spectral approach was used, taking advantage of the availability of commercial imaging systems that allow digital recording of intravital images at a number of predetermined wavelengths within a relatively short time. The dependence of validity and precision of saturation measurements on critical experimental variables (reference spectra, number and selection of wavelengths, exposure time, analysis area, analysis model) was evaluated. In addition, a software approach for two-dimensional analysis of images was developed. RESULTS: Exposure times per wavelength of about 200 ms and use of up to 50 wavelengths evenly spaced from 500 to 598 nm allow automatic discrimination of microvessels from tissue background (segmentation) with reliable determination of oxygen saturation (in trans- and epi-illumination) and hematocrit (in transillumination). CONCLUSIONS: The present imaging spectroscopy approach allows detailed assessment of oxygen transport and other functional parameters at the microcirculatory level.     

MRI分子与功能成像诊断胰腺癌的研究新进展

胰腺癌早期症状不显著,早期诊断缺乏特异性,因此死亡率高.近年来,分子及功能成像发展迅速,其以分子生物学为基础,在活体状态下从分子、基因水平对胰腺癌进行更早期、更特异性的诊断.磁共振成像(magneticresonance imaging,MRI)设备具有空间分辨率高、组织对比度好等优点,因此在分子及功能成像方面应用较为广泛.本文就MR分子及功能成像在胰腺癌诊断中的应用现状及发展趋势进行综述.     

Intravascular and intracardiac ultrasound imaging: current research and future directions

Intravascular and intracardiac ultrasound imaging is a newly emerging catheter-based imaging modality with considerable promise. This review article presents the rationale behind attempts at developing intravascular imaging methods, the design features of intravascular instrumentation, the knowledge obtained with in vitro studies, the in vivo experience in humans, and the potential applications of intravascular imaging in arterial atherosclerosis. The feasibility of pulmonary artery imaging and the potential applications of intracardiac echocardiography are discussed. Finally, future directions in intravascular imaging are outlined.     

颅内出血的磁共振成像

MRI的常规序列T1加权成像、T2加权成像和液体衰减反转恢复(FLAIR)序列均可敏感地检出亚急性期和慢性期颅内出血;梯度回波成像可检出各期颅内出血,但血肿信号强度与血肿存在的时间无相关性。弥散加权成像和表观弥散系数能提供更多有关血肿中心区、周围区和梗死后出血的信息。     

Comparative studies of angioscopy and ultrasound for the evaluation of arterial disease

In this in vitro investigation, we studied the histopathological basis for intravascular ultrasound image interpretation and how this technique compares with fiberoptic angioscopy in assessing atherosclerosis. This article presents the sensitivity and specificity of these techniques in the recognition of arterial abnormalities. The relevance of these data in interventional therapeutic procedures and the clinical implications of intravascular imaging methods are also discussed.     

Contrast-enhanced ultrasonographic imaging diagnosis on assessment of vascularity in liver metastatic lesions

AIM: To investigate the vasculature of rabbit liver metastatic lesions by color Doppler imaging and power Doppler imaging (PDI) techniques. METHODS: Eight New Zealand rabbits with implanted VX2 liver tumors were used. All ultrasound examinations were performed with a HP 5500 color Doppler ultrasound scanner. Before and after the injection of contrast agent, the changes of gray scale and the periphery and intralesional blood flow of the liver metastatic lesion were carefully observed by B mode ultrasound, color Doppler flow imaging (CDFI) and PDI. RESULTS: Twelve lesions were found in the eight rabbits with implanted VX2 liver tumors, whose diameter ranged from 1.6 to 4.8 cm. Echoes of these lesions were not characterized and has lack of specificity. After the injection of contrast agent, the numbers of dot or strip-like flow messages increased both at the periphery and inside of these lesions under the mode of CDFI and PDI, and were more pronounced under PDI. Morphology of intralesional vessels extended, even branched and some signals were clearly found encircling the lesion. And some vessels were found penetrating into the center of the lesion. CONCLUSION: PDI after injection of self-made echo contrast agent can show a pronounced sensitivity than that of B mode ultrasound and CDFI in diagnosis of vascularity of a metastatic lesion.     

胰腺癌影像诊断新进展

目前,胰腺癌的早期诊断受到关注.传统影像诊断技术有CT、MR和超声.新的技术已经发展起来,比如PET/CT融合和MRS,尤其是分子影像的实验研究,为今后胰腺癌的早期诊断提供新的技术手段.     

Superpenetration optical microscopy by iterative multiphoton adaptive compensation technique

Biological tissues are rarely transparent, presenting major challenges for deep tissue optical microscopy. The achievable imaging depth is fundamentally limited by wavefront distortions caused by aberration and random scattering. Here, we report an iterative wavefront compensation technique that takes advantage of the nonlinearity of multiphoton signals to determine and compensate for these distortions and to focus light inside deep tissues. Different from conventional adaptive optics methods, this technique can rapidly measure highly complicated wavefront distortions encountered in deep tissue imaging and provide compensations for not only aberration but random scattering. The technique is tested with a variety of highly heterogeneous biological samples including mouse brain tissue, skull, and lymph nodes. We show that high quality three-dimensional imaging can be realized at depths beyond the reach of conventional multiphoton microscopy and adaptive optics methods, albeit over restricted distances for a given correction. Moreover, the required laser excitation power can be greatly reduced in deep tissues, deviating from the power requirement of ballistic light excitation and thus significantly reducing photo damage to the biological tissue.     

磁共振PWI联合DWI在老年急性期脑梗死中的应用价值

目的 探讨灌注加权成像(PWI)联合弥散加权成像(DWI)对急性期脑梗死的诊断价值.方法 采用回顾性研究方法,收集56例发病时间1～72 h(其中20例为超急性期脑梗死,发病时间＜6 h;36例为急性期脑梗死,发病时间7～72 h)的老年脑梗死病人的临床及影像资料.所有病人均进行PWI和DWI检查,主要观察指标:患侧脑...     

Carotid Intima‐Media Thickness Assessment in Refinement of the Framingham Risk Score: Can It Predict ST‐Elevation Myocardial Infarction? A Pilot Study

Patients who suffer a first ST‐elevation myocardial infarction (STEMI) typically have fewer identifiable risk factors than those who suffer other types of acute coronary syndromes. As such, risk assessment tools such as the Framingham Risk Score (FRS) often fail to classify these patients as high risk. In this study, we tested the ability of assessment of carotid intima‐media thickness (CIMT) to enhance the ability to identify patients who are at risk for STEMI, using a CIMT‐derived “vascular age” in place of chronologic age in the calculation of FRS. We applied a CIMT‐based vascular age to the assessment of FRS in a cohort of patients who presented with a first STEMI. Using CIMT‐derived vascular age in place of chronologic age increased both the mean FRS and predicted 10 year cardiovascular event rate of the cohort. More importantly, the use of a CIMT‐derived vascular age in the calculation of FRS significantly improved the ability to identify patients with STEMI as high risk and candidates for statin therapy based on ATPIII criteria (19.2% vs. 57.7%, P = 0.010). The use of CIMT to derive a vascular age may improve the ability of FRS to identify patients at risk for STEMI.     

Strain and Strain Rate Imaging in Cardiomyopathy

The most common indication for an echocardiogram is for the assessment of left ventricular (LV) function and, in the evaluation of cardiomyopathy (CM), this becomes even more important. However, conventional echocardiographic measures of ventricular function are insensitive at detecting subtle perturbations in contractility. In patients with CM, the ability to detect abnormalities early in the course of the disease to establish a diagnosis can be critical and often may influence specific treatments administered as well as establish important prognostic information. Technologic advances in echocardiographic imaging during the last decade now allow for the measurement of LV strain and strain rate (SR) imaging. Strain and SR imaging allow for a more precise characterization of the mechanics of myocardial contraction and relaxation (deformation imaging) and emerging data are establishing the use of these techniques in a variety of different cardiomyopathic conditions. After establishing a common understanding of strain imaging as well as defining the methods by which these measures can be incorporated into an echocardiographic examination, we will review the accumulating information illustrating the great promise that this imaging modality has in the care of patients with CM. This review will focus on the role of strain and SR imaging in CM.     

Autofluorescence imaging and magnification endoscopy

It is well known that angiogenesis is critical in the transition from premalignant to malignant lesions.Consequently,early detection and diagnosis based on morphological changes to the microvessels are crucial.In the last few years,new imaging techniques which utilize the properties of light-tissue interaction have been developed to increase early diagnosis of gastrointestinal(GI) tract neoplasia.We analyzed several red-flag endoscopic techniques used to enhance visualization of the vascular pattern of pren...     

Evaluation of Longitudinal Tissue Velocity and Deformation Imaging in Akinetic Nonviable Inferobasal Segments of Left Ventricular Myocardium by Dobutamine Stress Echocardiography

Aim: To study tissue velocity imaging (TVI) and strain rate imaging (SRI) indices in akinetic nonviable and normal left ventricular (LV) inferobasal segment and effect of dobutamine infusion on these indices in nonviable segments. Methods: The study population consisted of two groups: 25 patients (mean age 60.75 ± 8.69 years) with left ventricular akinetic inferobasal nonviable segment determined by dobutamine stress echocardiography (DSE) and 14 normal coronaries (mean age 56.67 ± 11.90 years) with normal echocardiography as control group. The following TVI and SRI parameters were measured in patient and control group: ejection phase velocity (Sm [cm/sec]), peak systolic strain (ST [%]), and strain rate (SR [per second])). Results: Ejection fraction was significantly lower in patient group (29.40%± 5.46% vs. 55.00%± 3.39%; P < 0.001). Several differences were observed in patients with nonviable inferobasal segments compared to control group: Sm was reduced (3.58 ± 1.08 cm/sec vs. 5.56 ± 1.28 cm/sec; P < 0.001); SR and ST were significantly decreased (−0.39 ± 0.20/second vs. −1.44 ± 0.64/second, and −3.86%± 4.12% vs. −17.64%± 7.44%, respectively; P < 0.001 in both). The range of SR for nonviable segments (−0.04 to −0.77/second) did not overlap with that of the normal segments (−0.80 to −3.0/second). This range for Sm and ST overlapped with those of the normal segments. Conclusion: All TVI and SRI parameters are reduced in akinetic nonviable inferobasal compared with normal segments. According to findings of this study, resting strain rate has a potential to discriminate nonviable inferobasal from normal segments.     

DWI与PWI在急性脑梗死诊治中的应用

目的:探讨磁共振弥散成像(DWI)、灌注成像(PWI)及其后处理技术在急性脑梗死,尤其是超早期脑梗死诊断和治疗中的作用。方法:分别应用DWI、PWI和MRA等技术对临床高度怀疑急性脑梗死的患者进行扫描,并根据发病时间进行分组比较,再通过图像后处理技术对所获得图像进行分析。应用上述技术,对1999—2002年间就诊于首钢医院和法国Roger Salengro医院的59例临床诊断为急性脑梗死的患者进行分组和观察。结果:MR平扫T2加权像在发病12 h后才能隐约见到稍高信号的病灶,而DWI、PWI及后处理技术最早可在发病1.5 h发现缺血灶。此外,通过图像后处理可以看到半暗带的情况。结论:DWI、PWI与后处理技术可以明确诊断急性,尤其是超早期脑梗死,同时对治疗方案的制定与调整及评价疗效均有重要意义。     

Right Ventricular Tissue Doppler and Strain Imaging: Ready for Clinical Use?

Although tissue Doppler (TD) imaging of the left ventricle is now commonly used in clinical settings, TD imaging of the right ventricle (RV) is not routinely practiced. Yet, there are significant data on clinical uses of RV TD imaging, including established normal values using both color and spectral TD. In acute left ventricular (LV) inferior wall myocardial infarction, depressed RV TD velocities have been shown to correlate with the presence of RV impairment, and with patient outcome. In patients with LV heart failure, TD imaging has been correlated to RV ejection fraction by radionuclide angiography, and is an independent predictor of outcome. In patients with congenital heart disease, RV TD has been especially valuable for assessing RV function, and has been correlated to invasive hemodynamic indices, and RV ejection fraction by magnetic resonance imaging. The RV performance (Tei) index has been calculated and validated using TD-derived, rather than conventional pulsed Doppler time intervals. RV TD indices have been shown to be useful in the detection of subclinical and clinical disease in morbid obesity, chronic pulmonary, and systemic disease. TD-derived RV strain imaging can detect segmental myocardial dysfunction, overcoming limitations to conventional TD imaging resulting from tethering. For both TD velocity and strain imaging, however, appreciation of the limitations of these techniques is necessary for their appropriate use. Given its rapid acquisition times, reproducibility, and ease of addition to standard transthoracic echocardiographic protocols, RV TD and strain imaging are important additional modalities in the comprehensive echo-Doppler assessment of RV function.