An investigation of simulated umbilical artery Doppler waveforms. II. A comparison of three Doppler waveform quality indices

Three Doppler waveform quality indices based upon assessment of the noise of the maximum frequency envelope of simulated umbilical artery waveforms were investigated. These indices were: an estimate of the correlation between successive waveforms (QI1), a local linearity measure (QI2) and a ratio of two regions of the Fourier transform amplitude spectrum of the maximum frequency envelope (QI3). Simulated umbilical artery waveforms were acquired from a physiological flow phantom. A test population was used consisting of a large number of waveforms where one of three physical variables had been adjusted to produce waveforms of varying quality. These three physical variables were: beam-vessel angle, beam-vessel axial misalignment and attenuator thickness. For this group of waveforms the accuracy of estimation of the maximum frequency envelope and pulsatility index (PI) were known. All three quality indices gave good separation of high- and low-quality waveforms based upon threshold values of the accuracy of PI and maximum frequency envelope. The dependence of each quality index on fetal breathing, waveform length and waveform pulsatility was investigated. QI2, the local linearity measure, showed most promise in its independence from these variables.     

An investigation of simulated umbilical artery Doppler waveforms. III. The effect of noise reduction algorithms on the maximum frequency envelope and on the pulsatility index.

The effect of two noise reduction algorithms on the accuracy of estimation of the maximum frequency envelope and pulsatility index (PI) of simulated umbilical artery Doppler waveforms was investigated. The algorithms were: first, smoothing of the envelope from unfiltered Doppler spectra using a double window modified trimmed mean (DWMTM) filter and second, speckle and noise reduction of the Doppler spectrum using an image processing method. The test population consisted of waveforms were the degree of beam-vessel misalignment had been varied. The accuracy of estimation of the maximum frequency envelope and the PI was calculated by comparing each set of waveforms with the gold-standard maximum frequency envelope from the ensemble averaged waveform obtained with no misalignment. Speckle reduction gave rise to PI values that were low by approximately 0.1 (3%-4%). When there was no background noise present the improvements in envelope estimation were factors of 1.27 and 1.24, respectively, for the DWMTM method and the spectral filter, whereas the factors were 1.56 and 2.07 when background noise was present. For estimation of PI the DWMTM filter was superior. For no background noise the DWMTM filter gave a factor of 3.36 improvement whereas there was no improvement with the spectral filter. When background noise was present the factors for improvement in PI estimation were 2.39 and 4.16.     

A comparison of single- and dual-beam methods for maximum velocity estimation.

The purpose of this study was to compare the precision and accuracy of maximum velocity estimation when the target direction is known (a string phantom), and when the target direction is unknown (a flow model of arterial stenosis with stenoses of 0-80% by area). Maximum velocity was estimated using single- and dual-beam methods. A linear-array system was used to acquire Doppler spectra from a single-beam direction. The same array was used for sequential acquisition of Doppler spectra from 2 beam directions; the velocity estimates from these were then compounded in a vector manner. The variation of estimated maximum velocity with beam-string angle over the range 40-80 degrees was 27% for conventional Doppler, 2.6% for angle correction from the edge of the array and 1.6% for the vector Doppler. In the stenosis model, for the single-beam methods, the highest frequency shift was obtained just prior to the point of minimum lumen. At this location, the variation with beam-vessel angle over the range 40-80 degrees was 35% for conventional Doppler, 7.4% for the correction factor method and 6.9% for correction from the edge of the array. For the vector method, the maximum velocity is obtained from within the poststenotic jet, the variation was 2% over the range 40-80 degrees. It is recommended that existing Doppler systems use the correction-factor method to reduce variation in measured maximum velocity. The use of the vector technique by future generations of Doppler systems may lead to angle-independent velocity estimation.     

Measurement of volume flow with time domain and M-mode imaging: in vitro and in vivo validation studies.

Color velocity imaging quantification is a commercially available technique that estimates volume flow within vessels by combining velocity data, acquired by time domain correlation, with vessel diameter measurements obtained by M-mode imaging. By integrating the velocity profile over time, quantitative volume flow calculations may be made. To investigate the accuracy of this system, we used two flow phantoms over a range of steady and pulsatile flows for in vitro evaluation, and the common carotid artery of 10 women on five consecutive occasions was insonated for in vivo assessment. In flow phantom studies, accuracy was within 8% for flows above 200 ml/min, but decreased at lower flows depending on the depth, beam-vessel angle used, and steering of the beam. At angles greater than 70 degrees, velocity errors made quantitative measurement of flow unreliable, whereas at angles less than 30 degrees, the increased error in calculating vessel diameter led to large errors of area estimation, and hence made flow measurements unreliable. For the in vivo studies on the carotid artery the intraoperator repeatability values for the three operators were 9.92% (A), 13.74% (B), and 13.24% (C). The interoperator repeatability for the group was 15.30%. This study suggests that the color velocity imaging quantification technique is an accurate and reproducible method of assessing volume flow in vessels. However, in our experience, obtaining volume flow data is more time consuming and operator dependent than traditional Doppler techniques. The color velocity imaging quantification system may be of use in monitoring conditions in which changes in volume flow in a vessel or to an organ is an important part of the disease process.     

Echogenicity of hepatic versus portal vein walls revisited with histologic correlation.

The portal vein wall typically is hyperechoic over a wide range of beam-vessel angles, whereas the hepatic vein wall is hyperechoic only when the incident beam and the vessel are perpendicular. This has been attributed to marked discrepancies in mural thickness, collagen content, or perivascular fat between portal and hepatic veins. We evaluated histologically the walls of portal and hepatic veins using three cadaveric livers. For vessels with luminal diameter above 2 to 3 mm, hepatic vein and portal vein wall thicknesses were similar such that portal vein walls were not more than 50% thicker than those of hepatic veins of comparable size. Hepatic vein walls were mostly composed of parallel, tightly packed collagen fibers. In contrast, portal vein walls were composed of loosely arrayed, nonparallel connective tissue fibers which were separated by multiple intervening spaces and only a minority of which were collagenous. Perivascular fat was not identified adjacent to intrahepatic vessels beyond the liver hilus. The marked differences in echogenicity between portal vein and hepatic vein walls typically observed at ultrasonography thus cannot be attributed to differences in mural thickness, collagen content, or perivascular fat between these vessels. Rather, the distinct composition of the hepatic vein wall renders it a specular reflector, which is hyperechoic only when the angle between the ultrasound beam and the vessel wall is close to 90 degrees, whereas the composition of the portal vein wall enables it to appear hyperechoic at a wide range of beam-vessel angles.     

Implementation of spectral width Doppler in pulsatile flow measurements

In this paper, we present an automatic beam-vector (Doppler) angle and flow velocity measurement method and implement it in pulsatile flow measurements using a clinical Doppler ultrasound system. In current clinical Doppler ultrasound flow velocity measurements, the axis of the blood vessel needs to be set manually on the B-scan image to enable the estimation of the beam-vector angle and the beam-vector angle corrected flow velocity (the actual flow velocity). In this study, an annular array transducer was used to generate a conical-shaped and symmetrically focused ultrasound beam to measure the flow velocity vectors parallel and perpendicular to the ultrasound beam axis. The beam-vector angle and flow velocity is calculated from the mode frequency (f(d)) and the maximum Doppler frequency (f(max)) of the Doppler spectrum. We develop a spectrum normalization algorithm to enable the Doppler spectrum averaging using the spectra obtained within a single cardiac cycle. The Doppler spectrum averaging process reduces the noise level in the Doppler spectrum and also enables the calculation of the beam-vector angle and flow velocity for pulsatile flows to be measured. We have verified the measurement method in vivo over a wide range of angles, from 52 degrees to 80 degrees, and the standard deviations of the measured beam-vector angles and flow velocities in the carotid artery are lower than 2.2 degrees and 12 cm/s (about 13.3%), respectively.     

Differentiation of hepatic tumors by color Doppler imaging: role of the maximum velocity and the pulsatility index of the intratumoral blood flow signal

Doppler spectral analysis using color Doppler ultrasonography (US) was performed in a total of 133 patients with 135 hepatic tumors, including 88 hepatocellular carcinomas (HCCs), 30 metastatic hepatic cancers, 15 hemangiomas and 2 focal nodular hyperplasias (FNHs). Mean +/- SD of maximum velocity (Vmax) in hemangiomas (15.0 +/- 16.0 cm/s) was significantly lower than in HCCs (34.9 +/- 26.7 cm/s) and in metastases (37.9 +/- 17.4 cm/s). Mean +/- SD of the pulsatility index (PI) in hemangiomas (0.45 +/- 0.41) was significantly lower than in HCCs (1.52 +/- 0.71) and metastases (1.44 +/- 0.43). Mean +/- SD of Vmax and PI in FNH was 20.0 +/- 11.3 cm/s and 0.90 +/- 0.35, respectively. HCC showed a wide spectrum in terms of Vmax and PI; however, 18% of the HCC nodules had relatively high PI (>2.0). Specificity of Vmax more than >60 cm/s and PI more than 2.0 for the diagnosis of HCC were 92 and 94%, respectively. On the other hand, 87% of hemangiomas showed relatively lower Vmax (<30 cm/s) and 87% of hemangiomas showed relatively low PI (<1.0 cm/s). Specificity of Vmax less than 30 cm/s and PI less than 1.0 for the diagnosis of hemangioma were 47 and 78%, respectively. When taking account of both parameters, Vmax and PI, diagnostic efficacy for hemangioma and HCC was greatly improved (sensitivity, specificity, accuracy, positive predictive value and negative predictive value of 80, 86, 85, 41 and 97%, respectively, in hemangioma, and 38, 85, 54, 83 and 58%, respectively, in HCC) as compared with the results with Vmax or PI alone. In conclusion, in addition to the information obtained by Vmax, simultaneous measurement of PI adds valuable information useful in the noninvasive differentiation among hepatic tumors by Doppler spectral analysis at color Doppler US.     

Angle-independent estimation of maximum velocity through stenoses using vector Doppler ultrasound

Categorisation for arterial stenoses treatment is determined primarily by the degree of occlusion, which is often estimated ultrasonically from blood velocity measurements. In current single-beam ultrasound (US) systems, this estimate can suffer from gross errors due to angle-dependence. The purpose of this study was to find out if an experimental dual-beam US system could reduce the angle-dependence of the velocity estimates. We compared four dual-beam velocity estimation algorithms on both a string phantom and straight tube wall-less flow phantoms incorporating symmetrical and asymmetrical stenoses from 0% to 91% by area. The estimated maximum velocity varied, on average, by 7.6% for beam-vessel angles from 40 degrees to 80 degrees. The fluctuation in the magnitude estimate was reduced by a factor of 2.6 using a hybrid single-dual-beam algorithm. We conclude that, when the true velocity lies in the scan plane, the dual-beam system reduces the angle-dependence and, thus, has the potential to improve categorisation of patients with arterial stenoses.     

Improved transverse flow estimation using differential maximum Doppler frequency

Conventional Doppler technique can only provide the axial component of the blood flow vector, which is actually a three dimensional (3-D) quantity. To acquire the complete flow vector, estimations of the other two velocity components are essential. For the two dimensional (2-D) Doppler-bandwidth-based transverse estimation, however, accuracy is generally limited because of the complex dependence of the Doppler spectral shape on the flow variation within the sample volume. Two factors that may lead to the Doppler spectral change were considered in this study. One is the position offset of the sample volume and the other is the length of the sample volume. Simulations were performed and experimental data were also collected. Results indicate that the position offset may result in severe underestimation of Doppler shift frequency. Consequently, Doppler bandwidth is overestimated when it is determined by the difference between Doppler shift frequency and maximum Doppler frequency. Compared with the position offset, influence of the length of sample volume on the Doppler bandwidth is minor. To overcome this problem, a novel method, which is based on the differential maximum Doppler frequency, is proposed. Specifically, two beams with different beam widths are simultaneously generated to observe the blood flow and the difference between the corresponding maximum Doppler frequencies is used to estimate the transverse velocity. It is demonstrated that the accuracy and stability of transverse estimation are significantly improved by the proposed method even when the position offset is present.     

Quantitative flow measurements for classification of ovarian tumors by transvaginal color Doppler sonography in postmenopausal patients.

Color Doppler and Duplex measurements were obtained in 83 (42 benign, 41 malignant) ovarian tumors in postmenopausal patients. An ATL UM9/HDI was used. The following flow criteria were analyzed: lowest resistance index (RI) and pulsatility index (PI), total number of arteries and number of central arteries and the maximum, mean and sum of systolic, end-diastolic and time-averaged maximum velocities of all intratumoral vessels. In 98% of malignant and in 85% of benign lesions, vessels were detected. All flow criteria showed highly significant differences between benign and malignant tumors (p < 0.0001). However, there was a considerable overlap between benign and malignant tumors (e.g. the median of the lowest RI was 0.62 (range 0.26-1.0) for benign and 0.40 (0.22-0.66) for malignant tumors; the median of the maximum systolic velocity was 17.5 cm/s (range 5.2-61.5 cm/s) for benign and 47.05 cm/s (14.6-105.0 cm/s) for malignant tumors).Differentiation of malignant tumors by the lowest RI and PI, number of arteries and maximum of systolic flow velocities gave a sensitivity of 77-85%, specificity of 77-83% and accuracy of 80-84%. Differentiation was superior by calculation of the maximum end-diastolic velocities and by the summation of the systolic, end-diastolic and time-averaged maximum flow velocities: sensitivity 90-9.5% specificity 83-86% and accuracy 87-91%. This study confirms that a single measurement is not sufficient for an accurate differentiation of ovarian lesions and, besides the measurement of minimum RI and PI, the measurements of flow velocities as Doppler criteria play an important role.     

Foot placement angle and arch type: effect on rearfoot motion

The purpose of the study was to describe the relationship between foot placement angle, arch type, and rearfoot motion during running. Twenty women were filmed in the frontal plane at 100 fps. Subjects displaying a variety of foot placement angles were chosen. Before data collection, arch indices were calculated. Each subject ran five trials at a pace of 3.5 m/sec. All subjects wore the same type of shoe. All trials were digitized to determine rearfoot angles throughout foot contact. The following mean values were obtained: total rearfoot was 10.09 degrees, maximum pronation was -9.63 degrees, foot placement angle was 7.58 degrees and arch index (AI) was 0.23 cm2. Non-linear regression was used to predict the relationship between maximum pronation and total rearfoot motion using foot placement angle and AI. Foot placement angle was the best single predictor of total rearfoot motion. When using both foot placement angle and arch type as predictors of total rearfoot motion, r2 was .35. Less abduction was associated with more total rearfoot motion. Arch type exhibited a quadratic relationship with total rearfoot motion. Normal-arched individuals (.21 cm2 less than AI less than .26 cm2) exhibited less total rearfoot motion than high-arched (AI greater than .26 cm2) and flat-arched (AI less than .21 cm2) individuals. For maximum pronation, foot placement angle was the only significant predictor (r2 = .13). Greater foot placement angles (more abduction) were associated with less maximum pronation.     

Angle-dependence and reproducibility of dual-beam vector doppler ultrasound in the common carotid arteries of normal volunteers

Dual-beam vector Doppler has the potential to improve peak systolic blood velocity measurement accuracy by automatically correcting for the beam-flow Doppler angle. Using a modified linear-array system with a split receive aperture, we have assessed the angle-dependence over Doppler angles of 40 degrees -70 degrees and the reproducibility of the dual-beam blood maximum velocity estimate measured in the common carotid arteries (CCA) 1 to 2 cm prior to the bifurcation of 9 presumed-healthy volunteers. The velocity magnitude estimate was reduced by approximately 7.9% as the angle between the transmit beam and the vessel axis was increased from 40 degrees to 70 degrees. With repeat measurements made, on average, approximately 6 weeks apart, the 95% velocity magnitude limits of agreement were as follows: Intraobserver -41.3 to +45.2 cm/s; interobserver -29.6 to +46.8 cm/s. There was an 8.6 cm/s interobserver bias in velocity magnitude. We conclude that the dual-beam vector Doppler system can measure blood velocity within its scan plane with low dependence on angle and with similar reproducibility to that of single-beam systems.     

Temperature elevations computed for three-layer and four-layer obstetrical tissue models in nonlinear and linear ultrasonic propagation cases.

The authors computed temperature elevations in a three-layer and a four-layer tissue model, assuming the crucial obstetrical case when the ultrasonic pulse propagating through the abdominal wall and the fluid-filled bladder penetrates into soft fetal tissues. To consider nonlinear propagation, the authors applied a new theory of nonlinear increase of absorption recently developed by the first author. Computations were carried out for pulses with a carrier frequency of 3 MHz, duration time of 1.33 micros, and pulse repetition frequency of 3.3 kHz. Similar computations were carried out for a four-layer tissue model corresponding to the third trimester of gestation. The ceramic piezoelectric transducer 2 cm in diameter radiated the ultrasonic beam focused at a distance of 6.5 cm. The intensities at the radiating transducer (at the source) were I(SAPA) = 10 and 5 W/cm2. Temperature elevations and distributions were determined numerically for various values of low-amplitude absorption coefficients assumed to be the same as attenuation coefficients. It was shown in the three-layer tissue model that the maximum temperature elevation can be about 50% higher for nonlinear than for linear propagation.The maximum fetal temperature elevation in this case was 2.36 degrees C for nonlinear and 1.84 degrees C for linear propagation. The temperature elevation in the abdominal wall was lower than those temperatures when the attenuation of the abdominal wall was assumed to be a low value of 0.05 Np/cm.MHz (0.45 dB/cm.MHz). However, when it was increased to 0.16 Np/cm.MHz (1.4 dB/cm.MHz), the temperature elevation of the abdominal wall reached 3.2 degrees C and the maximum fetal elevation was 1.65 degrees C. In such cases, the abdominal wall became the principal source of heat production. In this case, the difference between fetal temperature elevations for nonlinear and linear propagation was only about 10%. The results obtained in the four-layer tissue model, in which the uterus tissue also was represented, show that temperature elevations in this case are about 3.6 times lower than in the three-layer tissue model, with comparable attenuation of the abdominal wall. Differences between nonlinear and linear propagation in the four-layer tissue model are negligible. The temperature elevations obtained were proportional to the pulse repetition frequency, without changing temperature distributions in the ultrasonic beam. In this manner, fetal temperature elevations can be reduced by reducing the repetition frequency.     

大脑中动脉狭窄对颅外段颈内动脉血流动力学的影响

目的研究不同程度的大脑中动脉(MCA)狭窄对颅外段颈内动脉(ICA)血流动力学的影响。方法本研究纳入单侧MCA狭窄或闭塞的患者98例,根据狭窄程度分为对照组(MCA中度狭窄,N=46)与观察组(MCA重度狭窄或闭塞,N=52),使用彩色多普勒超声测量两侧颅外段ICA的收缩期峰值流速(Vp)、舒张末期流速(Vd)、平均流速(Vm)、搏动指数(PI)。结果与对照组相比,观察组患侧ICA的Vp、Vm及Vd较健侧明显降低(41.17cm/s vs48.76cm/s,21.22cm/s vs 28.23cm/s,11.82cm/s vs 17.92cm/s,P均<0.05),而患侧PI值明显高于健侧(1.43vs1.20,P<0.01),PI值差值显著增大(0.28vs 0.06,P<0.05)。结论颅外段颈内动脉血流动力学的改变在一定程度上提示了大脑中动脉狭窄的严重程度,能够有效提高TCD对于大脑中动脉狭窄或闭塞进行诊断的准确性。     

Vector Doppler imaging of a spinning disc ultrasound Doppler phantom

Vector Doppler methods are used to obtain angle independent in-plane velocity information. Velocity magnitude as well as direction are reconstructed from regular steered colour flow and from split-aperture Doppler acquisitions. Spatially resolved in-plane velocity was obtained through Doppler colour flow mode and subsequent data triangulation. A depth-invariant constant Doppler angle was achieved by using a depth expanding transmit-receive Doppler aperture. Velocities of up to 50 cm s(-1) and 360 degrees vector velocity directions were measured. This was achieved by creating a spinning solid disc phantom. Such a phantom was built to allow underwater mounting and spinning of a solid disc-shaped ultrasound phantom (maximum velocity of 50 cm s-1). Doppler triangulation was realised by steered Doppler and by a split-aperture approach. Results of both imaging methods are shown. Split-aperture results showed errors of less then 10% for velocity magnitude estimation and less then 2.5 degrees for directional information.     

Intraobserver variation in Doppler ultrasound indices of placental perfusion derived from different numbers of waveforms.

Continuous-wave ultrasound is used to obtain records of Doppler-shifted frequencies from arteries. Indices using the maximum frequency envelope are usually derived from a number of selected waveforms on each record and averaged. Analysis of variance was performed on indices obtained from repeated Doppler ultrasound waveform records of uterine and umbilical perfusion in late pregnancy. Intraobserver variation was minimal when derived from six (consecutive) waveforms and was less than 10% for each index.     

Fetal depth and ultrasound path lengths through overlying tissues

Measurements of minimum thicknesses, in a four-layer, overlying tissue model, on 22 pregnancies between 15 and 20 weeks gestation, yielded a global minimum and a mean of the minimum total thickness per patient of 1.7 and 2.9 cm, respectively, and a minimum and mean subcutaneous fat thickness of 0.7 and 1.4 cm. Conservative calculations of the minimum attenuation per patient, at 3.5 MHz indicated that less than 2.5% of 15 to 20 week pregnancies should fall below the lower 95% prediction line of: Attenuation (dB) = 0.10 X Maternal Weight (kg) - 3.0. The smallest calculated attenuation for any of the 21 subjects was 0.8 dB MHz-1 indicating just under a factor of two protection at 3.5 MHz of proximal fetal tissues compared with ultrasound intensities measured in water. This value is lower than those generally used in the past. The knowledge of distributions of transducer-to-fetal distances and thicknesses of overlying tissues is also important for improvement of image quality. Measurement of minimum depth of the anterior fetal thorax in 57 examinations of 25 to 40 week fetuses yielded minimum and mean values of 2.5 and 4.1 cm, respectively.     

Determination of the optimal elbow axis for evaluation of placement of prostheses

OBJECTIVE: To present a method to determine the position and orientation of the mean optimal flexion axis of the elbow in vivo to be used in clinical research. DESIGN: Registering the movements of the forearm with respect to the upper arm during five cycles of flexion and extension of the elbow using a 6 degrees-of-freedom electromagnetic tracking device. BACKGROUND: Loosening of elbow endoprostheses could be caused by not placing the prostheses in a biomechanically optimal way. To evaluate the placement of endoprostheses with regard to loosening, a method to determine the elbow axis is needed. METHODS: The movements of the right forearm with respect to the upper arm during flexion and extension were registered with a 6 degrees-of-freedom electromagnetic tracking device. A mean optimal instantaneous helical axis of 10 elbows was calculated in a coordinate system related to the humerus. RESULTS: The average position of the flexion/extension axis was 0.81 cm (SD 0.66 cm) cranially and 1.86 cm (SD 0.72 cm) ventrally of the epicondylus lateralis. The average angle with the frontal plane was 15.3 degrees (SD 2 degrees). CONCLUSIONS: A useful estimation of the position and orientation of a mean optimal flexion axis can be obtained in vivo.     

Esophageal temperature monitoring during radiofrequency catheter ablation: experimental study based on an agar phantom model

Although previous studies have established the feasibility of monitoring esophageal temperature during radiofrequency cardiac ablation using an esophageal temperature probe (ETP), some questions remain regarding its efficacy. The aims of this study were to study the effect of the location of the ETP on the temperature reached, and to test the characteristics of ETP as used in clinical practice. We constructed an agar phantom to model the thermal and electrical characteristics of the biological tissues (left atrium, esophagus and connective tissue). The ETP was positioned at 6.5 mm from an ablation electrode and at distances of 0, 5, 10, 15, 20 mm from the catheter axis. A thermocouple was located on the probe to measure the actual temperature of the external esophageal layer during the ablations (55 degrees C, 60 s). The mean temperatures reached at the thermocouple were significantly higher than those measured by the ETP (48.3 +/- 1.9 degrees C versus 39.6 +/- 1.1 degrees C). The temperature values measured with the ETP were significantly lower when the probe was located further from the catheter axis (up to 2.5 degrees C lower when the distance from the probe-catheter axis was 2 cm). The dynamic calibration of the ETP showed a mean value for the time constant of 8 s. In conclusion, the temperature measured by the ETP always underestimates the temperature reached in the thermocouple. This fact can be explained by the distance gap between the thermocouple and probe and by the dynamic response of the ETP. The longer the distance between the ETP and catheter axis, the higher is the temperature difference.     

Noninvasive temperature estimation using sonographic digital images.

OBJECTIVE: The purpose of this study was to develop and evaluate a speckle-tracking method for tissue temperature estimation due to heating fields using digital sonographic images. METHODS: The temperature change estimation method is based on the thermal dependence of the ultrasound speed and the thermal expansion of the medium. Local changes in the speed of sound due to changes in the temperature produce apparent displacement of the scatterers, and the expansion introduces physical displacement. In our study, a new technique has been introduced in which the axial physical displacements were obtained from digital sonographic images. The axial speckle pattern displacement was determined with a cross-correlation algorithm. The displacement data were then used for computing the temperature changes. To monitor the temperature in real time, the computational time was decreased by restricting the search region in the cross-correlation algorithm and carrying out the cross-correlation function in the frequency domain via a fast Fourier transform algorithm. RESULTS: Experiments were performed on tissue-mimicking phantoms. The imaging probe was a commercial linear array working at 10 MHz. In addition, the temperature changes during heating were measured invasively by negative temperature coefficient thermistors. There was good agreement between ultrasonic temperature estimations and invasive temperature measurements. CONCLUSIONS: The proposed method verifies the capability of the speckle-tracking algorithm for determining both the magnitude and direction of displacement. The average error was 0.2 degrees C; the maximum error was 0.53 degrees C; and the SD was 0.19 degrees C. Therefore, the proposed algorithm is capable of extracting the temperature information from sonographic digital images.