Tissue analysis by dual-energy computed tomography

A straightforward method of tissue analysis from dual-energy computed tomography (CT) is presented which does not rely on previous inaccurate or incorrect formulations of the X-ray attenuation coefficient. The attenuation coefficients of tissue and bone were represented by a mixture of two reference materials. For convenience, water and calcium chloride were chosen. After careful calibration of the CT scanner, a dual-energy CT scan yields the water and calcium chloride in units of kg/kg multiplied by the specific gravity of the tissue. For an error of +/- 2 HU on dual-energy scans at 140 kVp and 87 kVp on an EMI CT5005 general-purpose scanner, the error on the calcium chloride coefficients is +/- 0.004 kg/kg. Fat concentrations greater than 25% by weight may be detected when the coefficients are averaged over at least 200 pixels. Bone mineral content could be measured with a precision of 0.01 (in units of kg/kg multiplied by specific gravity) for averaging regions of 24 pixels. Iodine concentrations in tissue can be deduced if water and iodine are chosen as the reference materials. Clinical examples are presented to illustrate the technique for scans of both the head and the abdomen.     

Tissue signatures with dual-energy computed tomography.

By providing information on two parameters, dual-energy computed tomography can offer clinically useful tissue signatures for metallic deposits (Ca) or injected iodine, as well as for different normal and abnormal types of brain parenchymal tissues and CSF. Cerebral CT was performed on 36 patients and tissue differences analyzed using Hounsfield notation.     

Evaluation of non-linear blending in dual-energy computed tomography

Dual-energy CT scanning has significant potential for disease identification and classification. However, it dramatically increases the amount of data collected and therefore impacts the clinical workflow. One way to simplify image review is to fuse CT datasets of different tube energies into a unique blended dataset with desirable properties. A non-linear blending method based on a modified sigmoid function was compared to a standard 0.3 linear blending method. The methods were evaluated in both a liver phantom and patient study. The liver phantom contained six syringes of known CT contrast which were placed in a bovine liver. After scanning at multiple tube currents (45, 55, 65, 75, 85, 95, 105, and 115 mAs for the 140-kV tube), the datasets were blended using both methods. A contrast-to-noise (CNR) measure was calculated for each syringe. In addition, all eight scans were normalized using the effective dose and statistically compared. In the patient study, 45 dual-energy CT scans were retrospectively mixed using the 0.3 linear blending and modified sigmoid blending functions. The scans were compared visually by two radiologists. For the 15, 45, and 64 HU syringes, the non-linear blended images exhibited similar CNR to the linear blended images; however, for the 79, 116, and 145 HU syringes, the non-linear blended images consistently had a higher CNR across dose settings. The radiologists qualitatively preferred the non-linear blended images of the phantom. In the patient study, the radiologists preferred non-linear blending in 31 of 45 cases with a strong preference in bowel and liver cases. Non-linear blending of dual energy data can provide an improvement in CNR over linear blending and is accompanied by a visual preference for non-linear blended images. Further study on selection of blending parameters and lesion conspicuity in non-linear blended images is being pursued.     

双能CT成像在直肠癌术前分期评估中的应用进展

双能CT成像(DECT)利用单能量成像、物质分离成像和能谱曲线等对直肠癌肿瘤病灶、肠周脂肪组织及肠周淋巴结的碘基质及能谱曲线特征进行定性定量分析,更加精确地鉴别肠周脂肪受侵与否以及转移性与非转移性淋巴结。可以与常规影像检查方法互补进一步提高直肠癌术前分期的准确性。就DECT成像的原理及其在评估直肠癌术前分期方面的应用进展进行综述。     

Accuracy of vertebral mineral determination by dual-energy quantitative computed tomography

Quantitative computed tomography is an established method for the non-invasive assessment of bone mineral content. Scanning with two different X-ray energies allows material-selective image reconstruction and separation on the basis of differing atomic numbers. As proven by chemophysical analysis of 45 bone samples, dual-energy quantitative computed tomography with basis material decomposition allows highly accurate measurement of bone mineral density with an error of 1.4%, independent of fat and soft tissue content.This work is dedicated to Prof. Dr. W. Wenz, University of Freiburg, Germany, for his 65th birthday     

双源双能量CT心肌灌注成像的研究进展

近年来,双源双能量CT心肌灌注成像在临床中的应用及研究逐渐增多,能够反映心肌微循环状况,定性及定量地评价心肌血流状态,检测心肌微循环及心肌活性,并且可以在评估冠状动脉的同时评估由于心肌缺血导致的心肌受损情况。其诊断心肌损伤的灵敏度、特异度、阴性预测值和阳性预测值与组织病理学检查的一致性好。相对于其他检查技术,双能量心肌灌注成像能便捷地提供更丰富的临床信息。笔者对双源双能量CT心肌灌注成像的研究进展进行综述。     

Material differentiation in forensic radiology with single-source dual-energy computed tomography

The goal of this study was to investigate the use of dual-energy computed tomography (CT) in differentiating frequently encountered foreign material on CT images using a standard single-source CT scanner. We scanned 20 different, forensically relevant materials at two X-Ray energy levels (80 and 130 kVp) on CT. CT values were measured in each object at both energy levels. Intraclass correlation coefficient (ICC) was used to determine intra-reader reliability. Analysis of variance (ANOVA) was performed to assess significance levels between X-Ray attenuation at 80 and 130 kVp. T test was used to investigate significance levels between mean HU values of individual object pairings at single energy levels of 80 and 130 kVp, respectively. ANOVA revealed that the difference in attenuation between beam energies of 80 kVp compared to 130 kVp was statistically significant (p < 0.005) for all materials except brass and lead. ICC was excellent at 80 kVp (0.999, p < 0.001) and at 130 kVp (0.998, p < 0.001). T test showed that using single energy levels of 80 and 130 kVp respectively 181/190 objects pairs could be differentiated from one another based on HU measurements. Using the combined information from both energy levels, 189/190 object pairs could be differentiated. Scanning with different energy levels is a simple way to apply dual-energy technique on a regular single-energy CT and improves the ability to differentiate foreign bodies with CT, based on their attenuation values.     

双能量CT痛风石成像的研究进展

痛风是因尿酸钠盐沉积在关节、软组织、软骨和肾脏而引起组织的异物炎性反应。临床上常需综合典型的临床症状以及血、尿中尿酸盐水平的测定和常规影像检查(如X线、MRI、B超等)进行诊断,但不典型痛风的诊断仍存在困难。双能量CT通过区分尿酸盐结晶和钙质的不同衰减特性来诊断痛风,并采用特定的体积计算软件对痛风石进行准确定量。随着双能量痛风石成像的广泛应用,其在临床工作中的应用价值将不断扩展及深化,并有望成为确诊和管理痛风的重要手段。     

Characterization of ureteral stents by dual-energy computed tomography: Clinical implications

Dual-energy computed-tomography (DECT) has been suggested as the method of choice for imaging urinary calculi due to the modality’s high sensitivity for detecting stones and its capability of accurately differentiating between uric-acid (UA) and non-UA (predominantly calcium) stones. The clinical significance of the latter feature relates to the differences in management of UA vs non-UA calculi. Like calculi, ureteral stents are assigned color by the dual-energy post-processing algorithm, which may lead to improved or worsened stone visualization based on the resulting stent/stone contrast. Herein we depict the case of a nephrolithiasis patient with bilateral stents, each with different color, clearly displaying the effect of stent color on stone visualization. Further, three-dimensional reconstruction of the DECT images illustrates advantages of this enhancement compared to conventional two-dimensional computed tomography. The resulting stent/stone contrast produces an unanticipated potential advantage of DECT in patients with urolithiasis and stents and may promote improved management decision-making.     

双能CT虚拟去钙技术评估骨髓损伤的应用研究

目的:探讨双能CT(dual energy CT,DECT)在评估骨髓损伤中的应用价值。方法:收集11例病史完整的急性关节损伤患者的MRI和DECT资料。由2位副高级职称的骨关节系统影像科医师(Z和X)采用双盲法对DECT虚拟去钙图像进行评级(4级法),以骨髓水肿作为骨髓损伤的图像指标,参照MRI平扫(含抑脂T2WI)图像,评级一致后纳入统计分析。结果:在11例中,纳入统计253个区域。将1级定为阳性,阅片人Z判定DECT图像对骨髓水肿诊断灵敏度、特异度、阳性预测值、阴性预测值分别为73.3%、93.8%、83.30%、89.2%,准确度为87.8%,K=0.681;阅片人X判定相应各值为67.9%、90.9%、76.8%、86.4%,准确度为83.8%,K=0.607。将1级和2级定为阳性,阅片人Z相应各值为55.7%、90.6%、83.1%、71.0%、74.7%,K=0.475;阅片人X相应各值为52.2%、88.4%、78.9%、68.9%、71.9%,K=0.418。测量各分区CT值,差异均有统计学意义(均P0.05)。使用CT值绘制ROC曲线,若将1级图像定为阳性,则胫骨上段及股骨下段AUC值分别为0.883和0.941。若将1级和2级图像定为阳性,则胫骨上段及股骨下段AUC值分别为0.786和0.943。结论:DECT虚拟去钙技术可去除骨中的钙质,直观显示骨髓水肿,提示骨髓损伤;CT值可作为骨髓水肿程度的定量参数。     

Initial experience with visualizing hand and foot tendons by dual-energy computed tomography

PurposeTo assess the feasibility of visualizing hand and foot tendons by dual-energy computed tomography (CT).Methods and materialsTwenty patients who suffered from hand or feet pains were scanned on dual-source CT (Definition, Forchheim, Germany) with dual-energy mode at tube voltages of 140 and 80 kV and a corresponding ratio of 1:4 between tube currents. The reconstructed images were postprocessed by volume rendering techniques (VRT) and multiplanar reconstruction (MPR). All of the suspected lesions were confirmed by surgery or follow-up studies.ResultsTwelve patients (total of 24 hands and feet, respectively) were found to be normal and the other eight patients (total of nine hands and feet, respectively) were found abnormal. Dual-energy techniques are very useful in visualizing tendons of the hands and feet, such as flexor pollicis longus tendon, flexor digitorum superficialis/profundus tendon, Achilles tendon, extensor hallucis longus tendon, and extensor digitorum longus tendon, etc. It can depict the whole shape of the tendons and their fixation points clearly. Peroneus longus tendon in the sole of the foot was not displayed very well. The distal ends of metacarpophalangeal joints with extensor digitoium tendon and extensor pollicis longus tendon were poorly shown. The lesions of tendons such as the circuitry, thickening, and adherence were also shown clearly.ConclusionDual-energy CT offers a new method to visualize tendons of the hand and foot. It could clearly display both anatomical structures and pathologic changes of hand and foot tendons.     

The role of dual-energy computed tomography in the assessment of pulmonary function

The assessment of pulmonary function, including ventilation and perfusion status, is important in addition to the evaluation of structural changes of the lung parenchyma in various pulmonary diseases. The dual-energy computed tomography (DECT) technique can provide the pulmonary functional information and high resolution anatomic information simultaneously. The application of DECT for the evaluation of pulmonary function has been investigated in various pulmonary diseases, such as pulmonary embolism, asthma and chronic obstructive lung disease and so on. In this review article, we will present principles and technical aspects of DECT, along with clinical applications for the assessment pulmonary function in various lung diseases.     

Quantification of recalcification of irradiated vertebral body osteolyses by dual-energy computed tomography

In 12 patients with osteolyses of the spine, the change of the vertebral mineral content after radiotherapy was quantified by Dual-Energy Computed Tomography (CT). In 11 of the patients, recalcification of radiated vertebral body metastases could already be detected at the completion of a 4 week course of radiotherapy. However, the amount of recalcification varied considerably between the patients. The methodological approach is described and the different reactions of the vertebral body osteolyses to radiotherapy are discussed.     

Pulmonary blood volume imaging with dual-energy computed tomography: spectrum of findings

Dual-energy (DE) pulmonary blood volume (PBV) computed tomography (CT) has recently become available on clinical CT systems. The underlying physical principle of DECT is the fact that the photoelectric effect is strongly dependent on the CT energies resulting in different degrees of x-ray attenuation for different materials at different energy levels. DECT thus enables the characterization and quantification of iodine within tissues via imaging at different x-ray energies and analysis of attenuation differences. Technical approaches to DECT include dual-source scanners acquiring two scans with different energy levels simultaneously, and single-source CT scanners using sandwich detectors or rapid voltage switching. DE PBV CT enables the creation of iodine maps of the pulmonary parenchyma. Experience to date shows that these studies can provide additional physiological information in patients with acute or chronic pulmonary embolism beyond the pure morphological assessment a standard CT pulmonary angiography (CTPA) provides. It appears also to be promising for the evaluation of patients with obstructive airways disease. This article reviews the physics and technical aspects of DE PBV CT as well as the appearance of normal and abnormal lung tissue on these studies. Special consideration is given to pitfalls and artefacts.     

Prediction of infarction development after endovascular stroke therapy with dual-energy computed tomography

Objectives

After intraarterial recanalisation (IAR), the haemorrhage and the blood-brain barrier (BBB) disruption can be distinguished using dual-energy computed tomography (DECT). The aim of the present study was to investigate whether future infarction development can be predicted from DECT.

Methods

DECT scans of 20 patients showing 45 BBB disrupted areas after IAR were assessed and compared with follow-up examinations. Receiver operator characteristic (ROC) analyses using densities from the iodine map (IM) and virtual non-contrast (VNC) were performed.

Results

Future infarction areas are denser than future non-infarction areas on IM series (23.44?±?24.86 vs. 5.77?±?2.77; p?<?0.0001) and more hypodense on VNC series (29.71?±?3.33 vs. 35.33?±?3.50; p?<?0.0001). ROC analyses for the IM series showed an area under the curve (AUC) of 0.99 (cut-off: <9.97 HU; p?<?0.05; sensitivity 91.18 %; specificity 100.00 %; accuracy 0.93) for the prediction of future infarctions. The AUC for the prediction of haemorrhagic infarctions was 0.78 (cut-off >17.13 HU; p?<?0.05; sensitivity 90.00 %; specificity 62.86 %; accuracy 0.69). The VNC series allowed prediction of infarction volume.

Conclusions

Future infarction development after IAR can be reliably predicted with the IM series. The prediction of haemorrhages and of infarction size is less reliable.

Key Points

? The IM series (DECT) can predict future infarction development after IAR. ? Later haemorrhages can be predicted using the IM and the BW series. ? The volume of definable hypodense areas in VNC correlates with infarction volume.

     

双源CT双能量心肌血池成像的应用及研究进展

缺血性心脏病已经成为威胁人类健康的高发疾病,判断供血区心肌灌注情况以及冠脉是否有狭窄对预防、治疗缺血性心脏病有重要意义。双能量CT心肌灌注检查在临床上多用于静态评估心肌血池,用于冠心病或心肌梗死的检查。笔者将近年来双源CT双能量心肌血池成像的原理、扫描方法、图像采集及临床应用做一综述。