An integrated system for the non-invasive assessment of vessel wall and hemodynamic properties of large arteries by means of ultrasound.

OBJECTIVES: To integrate methods for non-invasive assessment of vessel wall properties (diastolic diameter, distension waveform and intima-media thickness) and hemodynamic properties (blood flow velocity and shear rate distribution) of large arteries by means of dedicated ultrasound signal processing. METHODS: we have developed an arterial laboratory (ART-lab) system. ART-lab consists of software running on a standard personal computer, equipped with a data acquisition card for the acquisition of radio frequency (RF) ultrasound signals obtained with a conventional echo scanner. It operates either (1) off-line or (2) in real-time. Real-time operation is restricted to the assessment of vessel wall properties because of limitations in computational power. RESULTS: This paper provides an overview of ART-lab ultrasound radio frequency data acquisition and dedicated RF-signal processing methods. The capabilities of the system are illustrated with some typical applications. CONCLUSIONS: ART-lab in real-time mode is a useful tool for monitoring arterial vessel wall dynamics, while off-line it can be employed to investigate the elastic vessel wall properties in combination with hemodynamics, such as blood flow velocity and shear rate distribution.     

Noninvasive simultaneous assessment of wall shear rate and wall distension in carotid arteries

A novel technique has been developed for the noninvasive real-time simultaneous assessment of both blood velocity profile and wall displacements in human arteries. The novel technique is based on the use of two ultrasound beams, one set at optimal angle for wall motion measurements and the other for blood velocity profile measurements. The technique was implemented on a linear array probe divided into two subapertures. A modified commercial ultrasound machine and a custom PC board based on a high-speed digital signal processor was used to process the quadrature demodulated echo signals and display results in realtime. Flow phantom experiments demonstrated the validity of the technique, providing wall shear rate (WSR) estimates within 10% of the theoretical values. The system was also tested in the common carotid arteries of 16 healthy volunteers (age 30 to 53 y). Results of simultaneous diameter distension and WSR measurements were in agreement with published data.     

Geometric accuracy of intravascular ultrasound imaging.

In spite of the current interest in and clinical application of intravascular ultrasound imaging, there is very little published information on the limitations of this modality. In vitro studies on nine phantom vessels (diameter 4.76 to 12.7 mm) and 11 human arteries (diameter 3.7 to 6.2 mm) were performed to assess the potential sources of error of diagnostic intravascular ultrasound imaging. The effects of (1) blood flow velocity, (2) temperature, (3) eccentric, noncentral catheter placement, (4) alteration of the angle of incidence by 30 degrees, and (5) the effect of imaging in different mediums--saline solution, blood, and electrode gel--were studied. Variations in blood flow velocity (from 10 to 300 ml/min) and temperature (from 22 degrees C to 37 degrees C) resulted in a < 2% change in the lumen area measured by intravascular ultrasound imaging catheters. Eccentric catheter location had little effect on phantom or human arterial lumen shape or area when imaging was performed with optimized catheters. However, with used catheters circular lumens appeared elliptical with an eccentric index for phantoms from 0.88 to 1.15, (P < 0.05), and for human arteries from 0.88 to 1.11 (P < 0.05). The area ranged from 89% to 112% (P < 0.05) in phantoms and from 90% to 110% in human arteries compared with the lumen areas measured with a central catheter position (control). A 30-degree alteration in the angle of incidence resulted in 16.3% +/- 5.5% increase in lumen area for phantoms and 14.2% +/- 8.6% for human arteries in vitro. Ultrasonic-measured wall thickness of human vessels correlated closely with the actual measured thickness (r = 0.93) when a central catheter position was used. The wall thickness measured during adjacent (< 0.2 mm) and far-wall positioning (1.9 mm) of the catheter correlated closely (r = 0.96), but the far wall thickness with a 30-degree angle of incidence resulted in a 10.6% increase from control. Studies in saline solution resulted in significantly different measures of lumen area compared with imaging in blood. Compared with images recorded in blood, images in saline solution were 7.6% to 8.2% larger and 3.9% to 7.2% smaller in gel.(ABSTRACT TRUNCATED AT 400 WORDS)     

Measurement of aortic arch distension wave with the echo-track technique

The aim of this study was to use the echo-track method for measuring aortic arch diameter, distension waveform and elastic parameters. Data were obtained from 50 healthy volunteers of 32 +/- 15 y (mean +/- 1 SD). The aortic arch was interrogated from the suprasternal position with M-mode ultrasonography using a 3.5-MHz transducer; diameter and distension waves were determined by means of an echo-track algorithm (WTS, Pie Medical); arterial blood pressure was measured in the arm with sphygmomanometry. Aortic arch diameter, distension, distensibility and compliance were 24.55 +/- 2.99 mm, 2199 +/- 726 micrometer, 3.9 +/- 1.4. 10(-3) mmHg(-1) and 1.86 +/- 0.61 mm(2). mmHg(-1), respectively. Intrasession, interobserver and intersession variability was less than 10%, 10% and 18%, respectively. It is concluded that aortic arch distension wave can be recorded noninvasively with acceptable reproducibility, allowing assessment of aortic elastic parameters, and yielding insight into pressure wave reflection within the arterial system.     

An arterial wall motion test phantom for the evaluation of wall motion software

Increasing cardiovascular disease has led to new ultrasound methods of assessing artery disease such as arterial wall motion measurement. To validate arterial wall motion software, we developed a mechanically-controlled wall motion test phantom with straight upper and lower agar tissue mimicking material layers that resemble an artery cross section. The wall separation, displacements and wall velocities and accelerations can be controlled within physiologically realistic levels. A user-definable displacement or one of several pre-defined displacement waveforms can be created by the user with custom-written software. The test phantom is then controlled using the defined waveform with a stepper motor controller. Accuracy assessment of the test phantom with a laser vibrometer yielded a positional accuracy of 36+/-2 microm. A typical application of the test phantom is demonstrated by assessing a tissue Doppler imaging (TDI) method for estimating the distension waveform. The TDI-based method was found to have a minimum resolvable displacement of 22.5 microm, and a measurement accuracy of +/-8% using a physiological wall motion movement with a peak displacement of 689 microm. The accuracy of the TDI method was found to decrease with decreasing wall displacement and increasing wall velocity.     

Toward noninvasive blood pressure assessment in arteries by using ultrasound

A new method has been developed to measure local pressure waveforms in large arteries by using ultrasound. The method is based on a simultaneous estimation of distension waveforms and velocity profiles from a single noninvasive perpendicular ultrasound B-mode measurement. Velocity vectors were measured by applying a cross-correlation based technique to ultrasound radio-frequency (RF) data. From the ratio between changes in flow and changes in cross-sectional area of the vessel, the local pulse wave velocity (PWV) was estimated. This PWV value was used to convert the distension waveforms into pressure waveforms. The method was validated in a phantom set-up. Physiologically relevant pulsating flows were considered, employing a fluid which mimics both the acoustic and rheologic properties of blood. A linear array probe attached to a commercially available ultrasound scanner was positioned parallel to the vessel wall. Since no steering was used, the beam was perpendicular to the flow. The noninvasively estimated pressure waveforms showed a good agreement with the reference pressure waveforms. Pressure values were predicted with a precision of 0.2 kPa (1.5 mm Hg). An accurate beat to beat pressure estimation could be obtained, indicating that a noninvasive pressure assessment in large arteries by means of ultrasound is feasible.(E-mail:n.bijnens@tue.nl)     

Assessment of the spatial homogeneity of artery dimension parameters with high frame rate 2-D B-mode

To elicit vessel wall inhomogeneities in diameter and distension along an arterial segment, a 2-D vessel wall-tracking system based on fast B-mode has been developed. The frame rate of a 7.5-MHz linear-array transducer (length 36 mm) is enhanced by increasing the pulse-repetition frequency to 10 kHz, decreasing the number of echo lines per frame from 128 to 64, or increasing the interspacing between echo lines with a factor of two or four. Dedicated software has been developed to extract for each echo-line the end-diastolic diameter from the B-mode image and the 2-D distension waveform from the underlying radiofrequency (RF) information. The method is validated in tubes with various focal lesion sizes. Straight segments of presumably homogeneous common carotid arteries have also been tested. The temporal and spatial SD of diameter or distension reveals inhomogeneities in time or space (i.e., inhomogeneities in artery characteristics). The method can be implemented in echo systems supporting high frame rates and real-time processing of radiofrequency data.     

Assessment of the distensibility of superficial arteries

Doppler signal processing cannot only be employed to detect the local blood velocity as function of time, but also to assess transcutaneously the displacement of the arterial walls during the cardiac cycle (distension waveform) and, hence, the time-dependent changes in arterial diameter relative to its initial diameter at the start of a cardiac cycle. The distension waveform normalized with respect to the local pulse pressure provides useful information about the local elasticity of the arterial wall. The displacement of the arterial wall can be obtained by processing the RF-signals within a sample volume coinciding with the arterial wall. To evaluate this method a dedicated high-speed memory system has been developed storing the RF-signal, as obtained with a conventional echo-imager in M-mode, over a number of successive sweeps covering a selected depth range. The data are transferred line after line to a personal computer (PC) and processed on the fly, thereby relieving the memory requirements of the PC. It can be concluded that a RF-signal memory in combination with a PC provides a useful tool to extract detailed diameter waveforms from the RF-signals obtained. Although the system does not process the signals in real-time the process can be considered to be on-line since the results become available within one minute after the acquisition of the data is completed.     

Assessment of local pulse wave velocity in arteries using 2D distension waveforms

The reciprocal of the arterial pulse wave velocity contains crucial information about the mechanical characteristics of the arterial wall but is difficult to assess noninvasively in vivo. In this paper, a new method to assess local pulse wave velocity (PWV) is presented. To this end, multiple adjacent distension waveforms are determined simultaneously along a short arterial segment, using a single 2D-vessel wall tracking system with a high frame rate (651 Hz). Each B-mode image consists of 16 echo lines spanning a total width of 15.86 mm. Dedicated software has been developed to extract the end-diastolic diameter from the B-mode image and the distension waveforms from the underlying radiofrequency (rf) information for each echo-line. The PWV is obtained by determining the ratio of the temporal and spatial gradient of adjacent distension velocity waveforms. The proposed method is verified in a phantom and in the common carotid artery (CCA) of humans. Phantom experiments show a high concordance between the PWV obtained from 2D distension velocity waveforms (4.21 +/- 0.02 m/s) and the PWV determined using two pressure catheters (4.26 +/- 0.02 m/s). Assuming linear spatial gradients, the PWV can also be obtained in vivo for CCA and averages to 5.5 +/- 1.5 m/s (intersubject variation, n = 23), which compares well to values found in literature. Furthermore, intrasubject PWV compares well with those calculated using the Bramwell-Hill equation. It can be concluded that the PWV can be obtained from the spatial and temporal gradient if the spatial gradient is linear over the observed length of the artery, i.e. the artery should be homogenous in diameter and distension and the influence of reflections must be small.     

Effects of diagnostic cardiac ultrasound on oxygen free radical production and microvascular perfusion during ischemia reperfusion

Diagnostic ultrasound (US) is reported to increase intracellular oxidative stress in vitro. Increased oxidative stress mediated ischemia-reperfusion injury in the microcirculation. To examine the effects of US in hamster cheek pouch microcirculation during baseline and ischemia and reperfusion (I/R), I/R injury was provoked in the cheek pouch under "sham" (transducer off, group 1) and active US irradiation (group 2) at baseline (15 min) and at the beginning (15 min) of the reperfusion after ischemia (30 min). US transmission was delivered in the harmonic mode (2.5 MHz) with 1.3 mechanical index (MI) and 2.0 peak negative pressure. Microvascular damage was evaluated by measuring arterial diameter, red blood cell velocity, wall shear stress, permeability, perfused capillary length and adherent leukocytes in venules. Lipid peroxides were determined in the systemic blood. US increased permeability (baseline: 0.04 +/- 0.02; after US 0.30 +/- 0.04, p < 0.01) and slightly decreased capillary perfusion by 7% during baseline (p < 0.01). Arteriolar diameter (35 +/- 7 microm vs. 20 +/- 5 microm, p < 0.05), RBC velocity (2.8 +/- 0.4 mm s(-1) vs. 0.75 +/- 0.05 mm s(-1), p < 0.05) and shear stress ( 0.76 +/- 0.09 Pa vs. 0.36 +/- 0.05 Pa, p < 0.05) decreased significantly after reperfusion. These parameters increased by 40, 64 and 33%, respectively after US. Leukocyte adhesion decreased by 31 % (p < 0.05) after US and lipid peroxides decreased by 26% and 51% during baseline and 15 min of reperfusion after US, respectively. In conclusion, diagnostic US increased microvascular permeability during baseline and reperfusion. Moreover, US enhanced wall shear stress and reduced oxidative stress during postischemic reperfusion; thus, increasing capillary perfusion.     

Pulmonary circulation of fetal sheep with lung hyperplasia following tracheal occlusion.

OBJECTIVES: To determine the alteration of blood flow velocity profile in the pulmonary arteries (PAs) of fetal sheep after tracheal occlusion (TO). METHODS: Doppler ultrasound investigations of the PAs, the pulmonary trunk and the ductus arteriosus were performed weekly in nine ewes (gestational age 92-98 days, term 145 days) with singleton pregnancies after TO (n = 5) and in control fetuses (n = 4). Histological examinations with morphometry of pulmonary arterial vessels and of airways were performed in both groups. RESULTS: In the control group the experiments lasted 38 +/- 6 days (mean +/- SD), and in the TO group 25 +/- 7 days. Relative lung weight was significantly higher in the TO group compared with the control group (14.5 +/- 3.4% and 4.0 +/- 0.5% of body weight). There were no significant differences in the Doppler parameters (pulsatility index, resistance index, the systolic peak, the diastolic minimum, time averaged maximum velocity) between groups. When the Doppler values of PAs in TO and control fetuses were combined, no significant differences between the left and right PA could be detected. The external diameter of peripheral PAs was significantly higher in the TO group as compared to control group (105.7 +/- 2.5 microm vs. 96.9 +/- 1.3 microm). CONCLUSIONS: We found a threefold increase of fetal lung volume after TO without significant changes of blood flow velocity profiles in the PAs of fetal sheep.     

Optimal region-of-interest settings for tissue characterization based on ultrasonic elasticity imaging

Pathologic changes in arterial walls significantly influence their mechanical properties. We have developed a correlation-based method, the phased tracking method, for measurement of the regional elasticity of the arterial wall. Using this method, elasticity distributions of lipids, blood clots, fibrous tissue and calcified tissue were measured by in-vitro experiments of excised arteries (mean +/- SD: lipids, 89 +/- 47 kPa; blood clots, 131 +/- 56 kPa; fibrous tissue, 1022 +/- 1040 kPa; calcified tissue, 2267 +/- 1228 kPa). It was found that arterial tissues can be classified into soft tissues (lipids and blood clots) and hard tissues (fibrous tissue and calcified tissue) on the basis of their elasticity. However, there are large overlaps between elasticity distributions of lipids and blood clots and those of fibrous tissue and calcified tissue. Thus, it was difficult to differentiate lipids from blood clots and fibrous tissue from calcified tissue by setting a threshold for a single elasticity value. Therefore, we previously proposed a tissue classification method using the elasticity distribution in each small region. In this method, the elasticity distribution of each small region of interest (ROI) (not a single pixel) in an elasticity image is used to classify lipids, blood clots, fibrous tissue and calcified tissue by calculating the likelihood function for each tissue. In the present study, the optimum size of the ROI and threshold T(o) for the likelihood function were investigated to improve the tissue classification. The ratio of correctly classified pixels to the total number of classified pixels was 29.8% when the size of a small region was 75 microm x 300 microm (a single pixel). The ratio of correctly classified pixels became 35.1% when the size of a small region was 1,500 microm x 1,500 microm (100 pixels). Moreover, a region with an extremely low likelihood with respect to all tissue components was defined as an unclassified region by setting threshold T(o) for the likelihood function to 0.21. The tissue classification of the arterial wall was improved using the elasticity distribution of a small region whose size was larger than the spatial resolution (800 microm x 600 microm) of ultrasound. In this study, the arteries used in construction of the elasticity databases were classified into each tissue using the constructed elasticity databases. Other arteries, which are not used for constructing the elasticity databases, should be classified in future work to thoroughly show the effectiveness of the proposed method.     

Effect of cadralazine on brachial artery hemodynamics and forearm venous tone in essential hypertension

Forearm venous tone and brachial artery hemodynamics, including determinations of the arterial diameter and compliance by the use of pulsed Doppler systems, were measured in 16 patients with sustained essential hypertension before and after acute oral cadralazine dosing. Systolic and diastolic blood pressures significantly decreased, whereas heart rate increased. Brachial artery diameter and vascular resistance decreased, respectively, from 0.501 +/- 0.015 to 0.485 +/- 0.015 cm (P less than 0.001) and from 124.8 +/- 13.8 to 99.3 +/- 11.9 mm Hg/ml . sec (P less than 0.01). Blood flow velocity increased (P less than 0.05) but volumic flow, pulse wave velocity, and brachial artery compliance did not change. Forearm venous tone increased but the increase was inversely related to the degree of arteriolar vasodilatation. Our results indicate that, with cadralazine, forearm vascular resistance decreased while forearm blood flow was unchanged, the dilatation of small arteries contrasted with a significant reduction in the diameter of the large brachial artery, and the decrease in blood pressure was associated with a lack of increase in arterial compliance and changes in venous tone. This suggests an overriding influence of the activation of the autonomic nervous system on the action of cadralazine on large arteries and veins.     

Carotid artery involvement in Takayasu's arteritis: evaluation of the activity by ultrasonography.

The purpose of this study was to investigate the ultrasonographic criteria for determining the activity of carotid lesions in Takayasu's arteritis. In 10 consecutive patients, common carotid arteries with active lesions (n = 8) and inactive lesions (n = 9) were included in the study. The activity of the carotid lesions was determined on the basis of clinical and laboratory findings and computed tomographic scans. Special focus was placed on thickness and echogenicity of the involved arterial wall and outer diameter of the involved arterial segment. All 17 common carotid arteries evaluated showed segmental or diffuse circumferential thickening of the involved wall. The wall thickness was 2.5 to 5.0 mm (mean +/- SD, 3.3 +/- 0.8 mm) in active lesions and 1.1 to 2.0 mm (mean, 1.6 +/- 0.4 mm) in inactive lesions. The outer diameter of the involved segment was 7.0 to 15.0 mm (mean, 10.0 +/- 2.4 mm) in active lesions and 4.9 to 9.5 mm (mean, 6.8 +/- 1.4 mm) in inactive lesions. Active lesions showed hyperechogenicity in the full thickness of the involved wall (n = 6) or concentric triple layers with a hyperechoic middle layer (n = 2). Inactive lesions showed hyperechogenicity (n = 7) or isoechogenicity (n = 2) of the involved wall. One active lesion showed intramural arteries. Although precise measurement to tenths of a millimeter is impossible with the transducer used, prominent wall thickening with a maintained outer diameter in the common carotid artery suggests an active lesion, whereas mild wall thickening with a decreased outer diameter suggests an inactive lesion. Triple layers of a thickened wall with intramural arteries can be an ultrasonographic finding of an active lesion.     

超声造影对正常动脉检测能力的实验研究

目的研究生理状态下彩色多普勒血流成像(CDFI)对不同深度血管血流的显示能力以及彩色多普勒超声造影(以下简称彩超造影)与实时灰阶谐波超声造影(以下简称谐波造影)的表现。方法动物选择普通家犬5只。使用意大利百胜Technos DU8超声诊断仪及SonoVue超声造影剂。二维超声分别显示犬的髂总动脉、髂外动脉、髂内动脉、股动脉及腋动脉,并测量内径,脉冲多普勒测量收缩期峰值流速(PSV)。人为增加血管深度,CDFI检查记录该深度状态的血流强度。至CDFI不能清晰显示血流时,分别利用彩超造影与谐波造影两种方法再次检测。彩超造影检测时记录血流强度及PSV。结果随着深度增加CDFI观察到的血流信号减弱,造影后血流信号均明显增强;造影后在同一部位检测到的PSV增加36.1%,两组数据比较有显著性差异;谐波造影显示注射造影剂后动脉管腔内回声迅速增强,能够清晰显示血管管壁与管腔的分界。结论造影剂的应用可明显提高CDFI对深部血流信号的检出,而谐波造影能更直观、准确地显示血管壁及流道的轮廓。     

Transcutaneous detection of relative changes in artery diameter

The extent of the excursions of the arterial walls during the cardiac cycle depends on both the compliance of the vessel wall and the local pressure fluctuations. Simultaneous assessment of the relative change in artery diameter in combination with the velocity distribution along the vessel cross section can reveal the cause of loss of distensibility. As will be demonstrated, a multigate pulsed Doppler system with a high spatial resolution can perform simultaneously both functions. The relative change in diameter during the cardiac cycle is obtained by taking the ratio of the distension and the diameter of the artery as observed along the ultrasound beam. It can be shown that this ratio will be angle independent. Statistical and experimental evaluations demonstrate that the system allows the assessment of the relative change in diameter of major peripheral arteries as a continuous function of time with an accuracy of about 0.5%.     

Detection and characterization of vascular lesions by intravascular ultrasound: an in vitro study correlated with histology.

High-frequency intravascular ultrasound (30 and 40 MHz) was applied to study 112 human vascular specimens. The ultrasound images were compared with histologic cross-sections. In 44 out of 58 of the histologically classified muscular arteries, a hypoechoic middle layer was seen in the vessel wall, giving it a three-layered appearance. In 10 arteries, fibrous degeneration of the muscular media resulted in a homogeneous appearance of the vessel walls, whereas atherosclerotic plaque precluded the visualization of the arterial media in four of the arteries. A three-layered appearance was seen in seven of nine histologically classified transitional arteries, and a homogeneous arterial wall was seen in two of the nine. None of the 33 elastic arteries, veins, venous bypass, and Goretex conduits showed a hypoechoic medial layer. Histologically proved fibrous intimal thickening was echographically detected in 32 of 48 specimens (67%). It was noted that these intimal lesions were easier to detect with 40 MHz than with 30 MHz transducers. Hypoechoic areas of lipid deposition were detected in 32 of 36 specimens (89%) and could be distinguished from fibrous plaques. Histologically evident calcium deposits were detected with intravascular ultrasound in 35 of 36 specimens (97%). Measurement of plaque area was only possible in cross sections with a three-layered appearance. Quantitative analysis showed a significantly larger lumen area measured from ultrasonic images (26.3 +/- 21.3 mm2) than from histologic cross-sections (21.8 +/- 16.6 mm2, p less than 0.001), probably because of tissue shrinkage during processing for histology. A significant correlation (r = 0.96, p less than 0.001) between ultrasonic and histologic measurements of lumen areas was observed, with and a negligible interobserver and intraobserver variability. Plaque area and medial thickness correlated well with histology (r = 0.87, p less than 0.001 and r = 0.93, p less than 0.001, respectively). It appears from this in vitro study that intravascular ultrasound is an accurate technique for detection and characterization of atherosclerotic lesions. Vessel lumen area can be measured in most instances, whereas plaque area and medial thickness can only be reliably assessed in muscular arteries in which the hypoechoic media serves as a reference, and shadowing by calcium or attenuation by fibrous plaque components is absent.     

彩色多普勒超声在锁骨下动脉窃血综合征及内支架置放术中的应用

目的探讨彩色多普勒超声(CDU)在锁骨下动脉窃血综合征(SSS)及内支架置放术中应用价值。方法对31例SSS的超声表现及4例内支架置放术后的超声随访结果进行回顾性分析。结果31例患者中,28例为完全性SSS,3例部分性SSS。锁骨下动脉起始处闭塞18例,均为完全性SSS;狭窄13例,内径1~3.4mm,最大流速270~430cm/s。患侧上肢动脉血流频谱为单峰、低速、低阻波形。4例内支架置放术后,锁骨下动脉起始处内支架血流通畅;椎动脉和上肢动脉血流恢复正常。结论CDU是评价SSS及内支架置放术后随访的一种有价值方法。     

Individual variations in mucosa and total wall thickness in the stomach and rectum assessed via endoscopic ultrasound

Endoscopic ultrasound is a unique tool to acquire in vivo data on alimentary tract wall thicknesses of sufficient resolution needed in radiation dosimetry studies. Through their different echo texture and intensity, five layers of differing echo patterns for superficial mucosa, deep mucosa, submucosa, muscularis externa and serosa/adventitia exist within the walls of organs composing the alimentary tract. In this study, retrospective image analyses of patient video data were made for ten examinations of the stomach and eight examinations of the rectum covering a range of patient ages. Thicknesses for stomach mucosa ranged from 1030 +/- 130 microm to 1640 +/- 80 microm (total stomach wall thicknesses from 2.80 +/- 0.12 to 4.23 +/- 0.03 mm). Measurements made for the rectal images revealed rectal mucosal thicknesses from 660 +/- 50 microm to 1130 +/- 250 microm (total rectal wall thicknesses from 2.28 +/- 0.05 to 3.55 +/- 0.43 mm). The mucosa accounted for approximately 32 +/- 7% and approximately 32 +/- 8% of the total thickness of the stomach and rectal wall, respectively. These values can thus be utilized to investigate uncertainties in alimentary tract dosimetry that are based upon fixed reference individual definitions of organ wall structure.     

Automatic recognition of the common carotid artery in longitudinal ultrasound B-mode scans

Many morphological and dynamic properties of the common carotid artery (CCA), e.g. lumen diameter, distension and wall thickness, can be measured non-invasively with ultrasound (US) techniques. As common to other medical image segmentation processes, this requires as a preliminary step the manual recognition of the artery of interest within the ultrasound image. In real-time US imaging, such manual initialization procedure interferes with the difficult task of the sonographer to select and maintain a proper image scan plane. Even for off-line US segmentation the requirement for human supervision and interaction precludes full automation. To eliminate user interference and to speed up processing for both real-time and off-line applications, we developed an algorithm for the automatic artery recognition in longitudinal US scans of the CCA. It acts directly on the envelopes of received radio frequency echo signals, eventually composing the ultrasound image. In order to properly exploit the information content of the arterial structure the envelopes are decimated, according to the two-dimensional resolution characteristics of the echo system, thereby substantially decreasing computational load. Subsequently, based upon the expected diameter range and a priori knowledge of the typical pattern in the echo envelope of the arterial wall-lumen complex, parametrical template matching is performed, resulting in the location of the lumen position along each echo line considered. Finally, in order to reject incorrect estimates, a spatial and temporal clustering method is applied. Adequate values for the parameters involved in the processing are obtained via off-line testing of the proposed algorithm on 128 echo data recordings from 45 subjects. Using those robust parameter values, correct and fast recognition of the artery is achieved in more than 98% of the 6185 processed frames. Since these results are obtained via rigorous data decimation and using a cascade of rather simple steps, the proposed automatic algorithm is suitable for real-time recognition of the CCA.