Attenuation smear: A ‘paradoxical’ increase in counts due to attenuation artifact

Background: Attenuation is a well recognized cause of reconstruction artifacts in SPECT imaging. Occasionally, we have noted an increase in activity extending from the apical septal portion of the ventricle in women with significant breast attenuation. Although the idea that attenuation can produce an increase in activity on the reconstructed images seems paradoxical at first, it is consistent with the process of filtered back projection. Methods: We filled a cardiac phantom with 1 mCi of Technetium-99m, placed it in a water filled anthropomorphic torso phantom and imaged it over a 180° orbit. Next, a breast phantom designed to simulate a significant degree of breast attenuation was placed on the torso phantom and imaging was repeated. The images were reconstructed first using conventional filtered back projection then with maximum likelihood. Results: When the phantoms with and without breast attenuation were reconstructed using filtered back projection and compared, the phantom with breast attenuation had a large ‘smear’ of activity extending anteriorly from the apical septal wall which was very similar to the abnormalities previously noted in clinical images; the phantom without breast attenuation had no such defect. This artifact was significantly less prominent when the images were reconstructed using the maximum likelihood technique. Conclusions: Attenuation artifact can also produce a seemingly paradoxical increase in counts on the reconstructed image but this phenomenon is consistent with the workings of filtered back projection.     

Ultrasonic speed of sound dispersion imaging

The feasibility for speed of sound dispersion (SOSD) imaging was investigated here. A through transmission new method for measuring the SOSD was utilized. With this method a long pulse comprising of two frequencies one being the double of the other is transmitted through the object and detected on its other side. SOSD projection images were obtained by scanning objects immersed in water using a raster mode utilizing a computerized scanning system. Using this approach SOSD projection images were obtained for solids and fluids as well as for a tissue mimicking breast phantom and an in vitro soft tissues phantom. The results obtained here, have clearly demonstrated the feasibility of SOSD projection imaging. SOSD may serve as a new contrast source and potentially may aid in breast diagnosis.     

Scanning acoustic-photoacoustic microscopy using axicon transducers

A dual mode scanning acoustic microscope is investigated, yielding simultaneously images with optical and acoustical contrast. Short laser pulses are used to excite acoustic waves in a sample for the photoacoustic imaging mode. At the same time the pulses irradiate a conical target generating limited diffraction acoustic waves (X-waves) for large depth of field ultrasound imaging. For photoacoustic as well as for ultrasound imaging a focusing, ring shaped detector is applied. First phantom experiments demonstrate the possibility to acquire data for both imaging modes in a single scan, by separating images due to their different time of flight.     

A Dual-Chamber,Thick-Walled Cardiac Phantom for Use in Cardiac Motion and Deformation Imaging by Ultrasound

Determination of the mechanical properties of the myocardium is crucial for cardiac diagnosis. Cardiac strain and strain rate imaging may enable such quantification. To further develop these methodologies, an experimental setup allowing the recording of ultrasonic deformation data in a reproducible manner is necessary. Such setup with biventricular polyvinyl alcohol heart phantoms has been built. To test this setup, segmental longitudinal, radial and circumferential displacement, velocity, strain and strain rate in the phantoms were measured using a clinical ultrasound scanner and commercially available deformation imaging algorithms (based on both tissue velocity imaging and speckle tracking). The model deformation was close to that observed in the human left ventricular wall and was highly reproducible (e.g., the average peak longitudinal strain for the mid- and apical phantom segments equals −15.32 ± 0.53% and −19 ± 6% for the ventricle wall). The experimental setup is a valuable source of data for the development of algorithms for deformation estimation. (E-mail: b.lesniak-plewinska@mchtr.pw.edu.pl)     

Ultrasonic Nakagami Imaging: A Strategy to Visualize the Scatterer Properties of Benign and Malignant Breast Tumors

Previous studies have demonstrated the usefulness of the Nakagami parameter in characterizing breast tumors by ultrasound. However, physicians or radiologists may need imaging tools in a clinical setting to visually identify the properties of breast tumors. This study proposed the ultrasonic Nakagami image to visualize the scatterer properties of breast tumors and then explored its clinical performance in classifying benign and malignant tumors. Raw data of ultrasonic backscattered signals were collected from 100 patients (50 benign and 50 malignant cases) using a commercial ultrasound scanner with a 7.5 MHz linear array transducer. The backscattered signals were used to form the B-scan and the Nakagami images of breast tumors. For each tumor, the average Nakagami parameter was calculated from the pixel values in the region-of-interest in the Nakagami image. The receiver operating characteristic (ROC) curve was used to evaluate the clinical performance of the Nakagami image. The results showed that the Nakagami image shadings in benign tumors were different from those in malignant cases. The average Nakagami parameters for benign and malignant tumors were 0.69 ± 0.12 and 0.55 ± 0.12, respectively. This means that the backscattered signals received from malignant tumors tend to be more pre-Rayleigh distributed than those from benign tumors, corresponding to a more complex scatterer arrangement or composition. The ROC analysis showed that the area under the ROC curve was 0.81 ± 0.04 and the diagnostic accuracy was 82%, sensitivity was 92% and specificity was 72%. The results showed that the Nakagami image is useful to distinguishing between benign and malignant breast tumors.     

Contrast Biases the Autocorrelation Phase Shift Estimation in Doppler Tissue Imaging

Quantitative assessment of regional myocardial function at rest and during stress with Doppler tissue imaging (DTI) plays an important role in daily routine echocardiography. However, reliable visual analysis is largely dependent on image quality and adequate border delineation, which still remains a challenge in a significant number of patients. In this respect, an ultrasound contrast agent (UCA) is often used to improve visualization in patients with suboptimal image quality. The knowledge of how DTI measurements will be affected by UCA present in the tissue is therefore of significant importance for an accurate interpretation of local myocardial motion. The aim of this paper was to investigate how signal contribution from UCA and nonlinear wave propagation influence the performance of the autocorrelation phase shift estimator used for DTI applications. Our results are based on model experiments with a clinical 2-D grayscale scanner and computational simulations of the DTI velocity estimator for synthetically-derived pulses, simulated bubble echoes and experimentally-sampled RF data of transmitted pulses and backscattered contrast echoes. The results show that destruction of UCA present in the tissue will give rise to an apparent bidirectional velocity bias of individual velocity estimates, but that spatial averaging of individual velocity measurements within a region-of-interest will result in a negative bias (away from the transducer) of the estimated mean or mean peak velocity. The UCA destruction will also have a significant impact on the measured integrated mean velocity over time, i.e., displacement. To achieve improved visualization with UCA during DTI-examinations, we either recommend that it is performed at low acoustic powers, mechanical index ≤0.3, thereby minimizing the effects from bubble rupture, or that each Doppler pulse package is preceded by a destruction burst similar to “Flash imaging” to clear the target area of contrast microbubbles. (E-mail: marcus.ressner@imt.liu.se)     

Preliminary Results of Acoustic Radiation Force Impulse (ARFI) Ultrasound Imaging of Breast Lesions

The aim of this study was to determine the appearance of breast lesions using acoustic radiation force impulse imaging (ARFI) and to correlate the ARFI values with the pathologic results. The area ratio (AR) and virtual touch tissue quantification (VTQ) values were analyzed in 86 patients (mean age 45.6 years, range 17-78 years) with 92 breast lesions (65 benign, 27 malignant; mean size 25.7 mm). The diagnostic performance of ultrasound (US) alone and US plus ARFI values were compared with respect to sensitivity, specificity and area under the curve (AUC) using a receiver operating characteristic curve analysis. The mean AR of the benign lesions (1.08 ± 0.21) differed from that of the malignant lesions (1.99 ± 0.63; p < 0.0001), as did the mean VTQ values (3.25 ± 2.03 m/s vs. 8.22 ± 1.27 m/s; p < 0.0001). In conclusion, ARFI provides quantitative elasticity measurements, which may complement B-mode US and potentially improve the characterization of breast lesions.     

Age-Related Ultrasonic Properties of Breast Tissue In Vivo

The aim of the current work was to quantify the ultrasonic properties of the whole breast in vivo as a function of age. Forty-four women were scanned using a computerized ultrasonic scanner developed in our laboratory. Raster scans in two orthogonal views, mediolateral and craniocaudal, were obtained using the ultrasonic through-transmission method. By combining the information from the two views, we estimated two acoustic properties: speed of sound and attenuation coefficient. On the basis of the results, both the attenuation coefficient and the speed of sound follow a three-phase age-related pattern. During the first phase, which corresponds to ages 20 to 35 y, both properties decrease with time and then remain roughly unchanged until about 55 y. During the third phase corresponding to ages >55 y, values decrease again with time. The mean speed of sound decreases from 1504 ± 35 m/s at <30 y to 1452 ± 9 m/s at >60 y (p < 0.01), and the attenuation coefficient decreases from 1.27 ± 0.32 to 0.96 ± 0.13 dB/cm/MHz (p < 0.03), respectively. In conclusion, both the ultrasonic speed of sound and the attenuation coefficient of breast tissue are age related. Both parameters decrease during life, markedly during the first and third phases. These changes may be attributed to anatomic and physiologic changes associated with reproductivity and menopause.     

Cardiac gated breath-hold black blood MRI of the coronary artery wall: an in vivo and ex vivo comparison

Background: High resolution magnetic resonance (MR) imaging of the coronary artery wall in vivo has been limited by the cardiac and respiratory motion, flow artifacts as well as the relatively small size of the coronary arteries. We sought to validate in vivo black blood MR imaging of the coronary artery wall using a double inversion recovery fast spin echo MR imaging sequence with limited breath-holding and cardiac gating for suppression of motion artifacts by comparison with ex vivo MR imaging. Methods: Yorkshire albino swine (n = 6) were used in this study and coronary lesions were induced with balloon angioplasty. Four weeks after balloon injury of the coronary arteries MR imaging of the coronary artery lesions was performed. High resolution in vivo and ex vivo images of the coronary artery wall and lesions were obtained using a double inversion recovery fast spin echo sequence in a 1.5 T MR system. There was a statistically significant agreement (p < 0.0001) between measurements of vessel wall area (r = 0.87, slope = 0.87) and maximal wall thickness (r = 0.84, slope = 0.88) from in vivo and ex vivo MR images of the coronary arteries. The mean differences between in vivo and ex vivo measurements were 0.56 ± 1.98 mm² for vessel wall area and 0.02 ± 0.36 mm for maximal wall thickness. Conclusions: Using breath-holding and cardiac gating, it is possible to perform high resolution MR imaging of the coronary artery wall in vivo with good suppression of motion artifacts with a double inversion recovery fast spin echo black blood imaging sequence.     

Oil Gel-Based Phantom for Evaluating Quantitative Accuracy of Speed of Sound Measured in Ultrasound Computed Tomography

To evaluate the quantitative accuracy of the measured speed of sound in ultrasound computed tomography for breast imaging, it is necessary to use a phantom with inclusions whose speed of sound is known. Accordingly, a phantom with known-speed-of-sound inclusions (e.g., containing water and saltwater solution) under the control of temperature was developed. In addition, an oil gel was used as the phantom material for mimicking wave refraction from fatty breast tissue to dense breast tissue. The oil gel was generated by adding SEBS (styrene-ethylene/butylene-styrene, 10% w/w) to paraffin oil. The oil gel-based phantom has a cylindrical shape and contains rod-shaped inclusions that can be filled with water or saltwater solution (3.5% w/w sodium chloride in water). When temperature increases, the speed of sound in the water increases, while that in the oil gel decreases; in particular, the speed of sound in the oil gel was higher than that in the water at temperatures <20.6°C, while the speed of sound in the oil gel was lower than that in the water at temperatures >20.6°C. It has been reported that the speed of sound in dense breast tissue is higher than that in water, while that in fatty breast tissue is lower than that in water. Ultrasound is refracted owing to the difference between the speed of sound in the breast tissue and that in the background water. By controlling the temperatures of the oil gel and water, the oil gel-based phantom simulates the refraction of an ultrasound wave from fatty breast tissue to dense breast tissue. For 43 d, the variation ranges of the speed of sound and attenuation in the oil gel in the reconstructed images were 0.7 m/s and 0.03 dB/MHz/cm, respectively. The concentration of the saltwater solution in the polyacrylamide gel-based phantom decreased from 1% (w/w) to 0.48% (w/w) after 24 h, while that in the oil-gel-based phantom was constant. In addition, magnetic resonance imaging of the oil gel-based phantom revealed that NiSO₄ solution was stably contained in the phantom for 42 d. It is therefore concluded that the liquid cannot penetrate the oil gel. This oil gel-based phantom with such high temporal stability is suitable for multicenter distribution and may be used for standardization of data acquisition and image reconstruction across centers.     

Acoustic characterization of tissue-mimicking materials for ultrasound perfusion imaging research

Materials with well-characterized acoustic properties are of great interest for the development of tissue-mimicking phantoms with designed (micro)vasculature networks. These represent a useful means for controlled in-vitro experiments to validate perfusion imaging methods such as Doppler and contrast-enhanced ultrasound (CEUS) imaging. In this work, acoustic properties of seven tissue-mimicking phantom materials at different concentrations of their compounds and five phantom case materials are characterized and compared at room temperature. The goal of this research is to determine the most suitable phantom and case material for ultrasound perfusion imaging experiments. The measurements show a wide range in speed of sound varying from 1057 to 1616 m/s, acoustic impedance varying from 1.09 to 1.71 × 10⁶ kg/m²s, and attenuation coefficients varying from 0.1 to 22.18 dB/cm at frequencies varying from 1 MHz to 6 MHz for different phantom materials. The nonlinearity parameter B/A varies from 6.1 to 12.3 for most phantom materials. This work also reports the speed of sound, acoustic impedance and attenuation coefficient for case materials. According to our results, polyacrylamide (PAA) and polymethylpentene (TPX) are the optimal materials for phantoms and their cases, respectively. To demonstrate the performance of the optimal materials, we performed power Doppler ultrasound imaging of a perfusable phantom, and CEUS imaging of that phantom and a perfusion system. The obtained results can assist researchers in the selection of the most suited materials for in-vitro studies with ultrasound imaging.     

Spectral near‐infrared fluorescence imaging of curved surfaces using projection reconstruction algorithms

In vivo spectral fluorescence imaging has made it possible to non‐invasively visualize superficial curved structures as well as structures deep to the skin. However, the defocus created by blurring has been an obstacle to creating anatomically interpretable surface images. Herein we present a methodology to correct for blurring induced by curved structures during spectral fluorescence imaging using signal intensity projection algorithms. In a phantom and an animal model in which the lymphatic system was visualized after the interstitial injection of quantum dots with emission spectra in the near‐infrared (NIR) range, the planes of focus were sequentially adjusted to obtain a z‐stack of images which contains images acquired from multiple focal points. Maximum, minimum, median and average intensity projections were applied to the resulting images. Using the phantom, the minimum and the median intensity projection images demonstrated improved deblurring whereas during in vivo imaging the median intensity projection images more clearly visualized important structures than did the other projection techniques. Image stacking with subsequent application of appropriate projection techniques provides a simple method for deblurring in vivo optical images obtained from curved surfaces, thus improving their anatomic resolution. Copyright © 2007 John Wiley & Sons, Ltd.     

Relationship between retention of a vascular endothelial growth factor receptor 2 (VEGFR2)-targeted ultrasonographic contrast agent and the level of VEGFR2 expression in an in vivo breast cancer model.

OBJECTIVE: The aim of this study was to characterize the relationship between retention of a vascular endothelial growth factor receptor 2 (VEGFR2)-targeted ultrasonographic contrast agent (UCA) and VEGFR2 expression in tumor vasculature of breast cancer. METHODS: 67NR breast cancer tumors implanted in mice were evaluated in vivo with both VEGFR2-targeted and nontargeted UCAs, and a high-frequency ultrasound system. A bolus of the UCA was injected and allowed to circulate for 4 minutes to allow binding of targeted microbubbles. After that, 2 sets of images before and after a high-power ultrasonic destruction sequence were acquired. The average video intensity of predestruction and postdestruction images was measured and used as a relative measure of retention of the UCA in the tumor. Levels of VEGFR2 expression and tumor vascular density were quantified by immunohistochemical staining and compared with retention of the VEGFR2-targeted UCA. RESULTS: Retention of VEGFR2-targeted microbubbles in tumors was significantly higher than retention of nontargeted microbubbles (mean +/- SD, 47.75+/-9.85 versus 18.5+/-5.46 dB; P< .001). Retention of the VEGFR2-targeted UCA was found to correlate with the level of VEGFR2 expression in the studied tumors (r(2)=0.41). In contrast, retention of the nontargeted UCA was not correlated with the level of VEGFR2 expression (r(2)=0.08). Furthermore, retention of the VEGFR2-targeted UCA was not correlated with the level of tumor vascularity. CONCLUSIONS: The magnitude of the molecular ultrasonographic signal from a VEGFR2-targeted UCA retained by tissue correlates with VEGFR2 expression. These results validate the use of molecular ultrasonography for in vivo detection and quantification of VEGFR2 expression in this breast cancer model.     

Acoustic radiation contrast in MR images for breast cancer diagnostics--initial phantom study

Acoustic radiation contrast in magnetic resonance images is an approach to visualize the changes in ultrasonic loss and viscoelastic changes of the sample with the resolution of a magnetic resonance imaging (MRI) system. By irradiating ultrasound (US) into a tissue-mimicking sample, a displacement along the US beam path caused by the acoustic radiation force is obtained. This displacement varies with the US intensity, the duration of irradiation, the US attenuation and the viscoelastic properties of the sample. US pulses of 2.5 MHz with a duration of 20 ms and an intensity of <17 W/cm² are used. An MRI sequence was programmed to produce images in which the magnitude of the displacement is visualized by gray value changes. In addition, a finite element simulation of the measurements was performed to demonstrate the feasibility of the method. Through examination of the measurements and the simulations, information about viscoelastic changes was achieved. In this work, measurements on different breast phantoms are presented. (E-mail: marcus.radicke@gmx.de)     

Development of a digital breast phantom for photoacoustic computed tomography

Photoacoustic (PA) imaging provides morphological and functional information about angiogenesis and thus is potentially suitable for breast cancer diagnosis. However, the development of PA breast imaging has been hindered by inadequate patients and a lack of ground truth images. Here, we report a digital breast phantom with realistic acoustic and optical properties, with which a digital PA-ultrasound imaging pipeline is developed to create a diverse pool of virtual patients with three types of masses: ductal carcinoma in situ, invasive breast cancer, and fibroadenoma. The experimental results demonstrate that our model is realistic, flexible, and can be potentially useful for accelerating the development of PA breast imaging technology.     

Acoustic Radiation Force Impulse Imaging for Reactive and Malignant/Metastatic Cervical Lymph Nodes

The aim of this study was to compare lymph node stiffness using acoustic radiation force impulse (ARFI) imaging in patients with cervical lymph node swelling. Forty-two cervical lymph nodes (reactive, n = 22; metastatic, n = 20) from 19 patients (13 men, 6 women; mean age, 63.68 ± 14.9 y; range, 23–85 y) were examined between September 2011 and March 2012. The shear wave velocity (SWV, m/s) of each lymph node was evaluated by ARFI imaging. SWV of reactive lymph nodes was 1.52 ± 0.48 m/s, and that of metastatic/malignant lymph nodes was 2.46 ± 0.75 m/s. A SWV > 1.9 m/s was very useful metastatic lymph node classification, with 95.0% specificity, 81.8% sensitivity and 88.0% overall accuracy. The area under the receiver operating characteristic curve was 0.923 (95% confidence interval, 0.842–1.000). ARFI imaging can be useful in the differentiation of reactive and malignant/metastatic cervical lymph nodes.     

Ultrasound contrast imaging based on a novel algorithm combined pulse inversion with wavelet transform

In this article, an ultrasound contrast imaging method that combines the pulse-inversion technique with wavelet transform has been proposed to enhance the contrast between bubbles and surrounding tissues. In this technique, wavelet transform is utilized to analyze the correlation between mother wavelet and the received echoes from a pair of inverted transmit pulses, respectively. To obtain a better correlation, a new mother wavelet named “bubble wavelet” is constructed according to the modified Herring equation. Radio-frequency (RF) data were acquired from a modified digital diagnostic ultrasound system that transmits two identical pulses with opposite polarity. The proposed method was validated by simulations. Experiments were performed on an ultrasound flow phantom and results showed that the contrast-to-tissue ratio (CTR) was improved by up to 28 dB depending on types of mother wavelet, scales and depths, compared with that obtained using pulse-inversion-based second-harmonic imaging. Experiments in vivo were also conducted out using kidneys of rabbits and results showed that the signals of surrounding tissues can be well suppressed compared with that of bubbles. The proposed method was compared with the quadratic pulse inversion (QPI) imaging on the same set of experimental data. Further improvements might be achieved with optimized bubble wavelet and imaging algorithm.     

Application of MAGnetic resonance imaging compilation in acute ischemic stroke

BACKGROUNDSynthetic magnetic resonance imaging (MRI) MAGnetic resonance imaging compilation (MAGiC) is a new MRI technology. Conventional T1, T2, T2-fluid-attenuated inversion recovery (FLAIR) contrast images, quantitative images of T1 and T2 mapping, and MAGiC phase sensitive inversion recovery (PSIR) Vessel cerebrovascular images can be obtained simultaneously through post-processing at the same time after completing a scan. In recent years, studies have reported that MAGiC can be applied to patients with acute ischemic stroke. We hypothesized that the synthetic MRI vascular screening scheme can evaluate the degree of cerebral artery stenosis in patients with acute ischemic stroke.AIMTo explore the application value of vascular images obtained by synthetic MRI in diagnosing acute ischemic stroke.METHODSA total of 64 patients with acute ischemic stroke were selected and examined by MRI in the current retrospective cohort study. The scanning sequences included traditional T1, T2, and T2-FLAIR, three-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA), diffusion-weighted imaging (DWI), and synthetic MRI. Conventional contrast images (T1, T2, and T2-FLAIR) and intracranial vessel images (MAGiC PSIR Vessel] were automatically reconstructed using synthetic MRI raw data. The contrast-to-noise ratio (CNR) values of traditional T1, T2, and T2-FLAIR images and MAGiC reconstructed T1, T2, and T2-FLAIR images in DWI diffusion restriction areas were measured and compared. MAGiC PSIR Vessel and TOF MRA images were used to measure and calculate the stenosis degree of bilateral middle cerebral artery stenosis areas. The consistency of MAGiC PSIR Vessel and TOF MRA in displaying the degree of vascular stenosis with computed tomography angiography (CTA) was compared.RESULTSAmong the 64 patients with acute ischemic stroke, 79 vascular stenosis areas showed that the correlation between MAGiC PSIR Vessel and CTA (r = 0.90, P < 0.01) was higher than that between TOF MRA and CTA (r = 0.84, P < 0.01). With a degree of vascular stenosis > 50% assessed by CTA as a reference, the area under the receiver operating characteristic (ROC) curve of MAGiC PSIR Vessel [area under the curve (AUC) = 0.906, P < 0.01] was higher than that of TOF MRA (AUC = 0.790, P < 0.01). Among the 64 patients with acute ischemic stroke, 39 were scanned for traditional T1, T2, and T2-FLAIR images and MAGiC images simultaneously, and CNR values in DWI diffusion restriction areas were measured, which were: Traditional T2 = 21.2, traditional T1 = -6.7, and traditional T2-FLAIR = 11.9; and MAGiC T2 = 7.1, MAGiC T1 = -3.9, and MAGiC T2-FLAIR = 4.5.CONCLUSIONThe synthetic MRI vascular screening scheme for patients with acute ischemic stroke can accurately evaluate the degree of bilateral middle cerebral artery stenosis, which is of great significance to early thrombolytic interventional therapy and improving patients’ quality of life.     

选择一体化PET/MR小病灶图像重建方案

目的 观察不同重建条件组合对不同大小病灶图像质量的影响，提出一体化PET/MR对于小病灶的最佳图像重建方案。方法 采用GE SIGNA TOF PET/MR系统对符合国际电工协会（IEC）推荐标准的PET图像质量（IQ）发射体模进行扫描，并对列表模式PET原始数据按照以下条件分别组合进行重建：有序子集最大期望值（迭代子集：28；迭代次数：1~9次）；重建矩阵（128×128，192×192，256×256）；高斯低通滤波器，半高宽（FWHM）（1~6 mm）；单独使用飞行时间（TOF）技术；单独使用点扩散函数（PSF）；同时使用TOF和PSF（TOF+PSF）；不使用TOF和PSF（NOTOF+NOPSF）。分析不同重建条件下图像对比度恢复（CR）、背景变化率（BV）和信噪比（SNR），评估图像质量。结果 10 mm和13 mm小球在OSEM（3次迭代，28个子集）、192×192矩阵、2 mm高斯滤波半高宽、TOF+PSF重建组合下信噪比最高，分别为13.31%、21.73%，13.31%、21.73%，25.74%、35.80%和26.25%、46.01%。结论 3次迭代、28个子集、192×192矩阵、TOF+PSF为本研究条件下一体化PET/MR对于模拟小病灶的最佳图像重建方案。     

3M和5M液晶显示器对不同分辨率乳腺体模图影像显示质量的研究

目的比较不同分辨率乳腺机获得的专用模体测试结果,评估3M与5M医用专业显示器对乳腺影像显示质量的影响。方法使用70μm和100μm分辨率乳腺机分别拍摄对比度细节乳腺摄影(CDMAM)。由4名放射诊断医师和2名技师在标准和放大显示模式下,评估2种显示器所能显示的最小圆盘直径(Di)与厚度(Ci,th),并计算出影像质量因子反数值(IQFinv)。2种显示器及2种显示模式的比较均采用配对t检验。结果在使用100μm分辨率乳腺影像数据时,无论是标准显示模式还是放大显示模式,2种显示器的影像细节显示能力相仿(P>0.05);使用70μm分辨率乳腺影像数据时,在标准显示模式下,5M显示器可识别最小直径为(0.130±0.000)mm,小于3M显示器的(0.155±0.012)mm(P=0.004)。5M显示器的IQFinv值显著高于3M显示器(P=0.036)。在放大显示模式下,3M与5M显示器的可识别最小直径相同[(0.125±0.012)mm],5M显示器的IQFinv值高于3M显示器,但差异无统计学意义(P>0.05)。无论哪种分辨率图像与显示器组合,在放大模式下阅片的影像质量均优于标准模式(P=0.010)。结论 70μm分辨率数据配备5M显示器可获得高质量图像,利用阅读时的放大模式在一定程度上可改善3M显示器对各种细节的显示。