Contrast-enhanced sonography of the spleen

OBJECTIVE: Combined use of low-mechanical-index technologies and non-air-filled contrast media allows real-time sonographic assessment of the spleen. This pictorial essay focuses on several aspects of contrast-enhanced sonography of the spleen, including examination technique, clinical indications, normal findings obtained through all vascular phases, abnormal findings (splenomegaly, infarction, abscess, benign tumors, lymphoma, metastasis, injuries, and accessory spleen), limitations, and pitfalls. CONCLUSION: Real-time, contrast-enhanced sonography is a novel technique allowing depiction of a wide range of splenic abnormalities.     

Comparison of diagnostic performance of unenhanced vs SonoVue - enhanced ultrasonography in focal liver lesions characterization. The experience of three Italian centers

PURPOSE: To evaluate the diagnostic performance of contrast-enhanced US with SonoVue (Bracco, Milan, Italy) compared to baseline US in focal hepatic lesions characterization. MATERIALS AND METHODS: A comprehensive number of four operators from 3 hospitals evaluated 57 consecutive patients with 60 focal hepatic lesions (28 hepatocellular carcinomas, 11 metastases, 13 hemangiomas, 1 hepatocellular adenoma and 7 focal nodular hyperplasias) by baseline gray-scale ultrasound (US) and color Doppler US. The same lesions were subsequently scanned by contrast-enhanced US after intravenous bolus administration of 2,4-4,8 ml of SonoVue by employing intermittent high or continuous low transmit power imaging. The diagnosis of lesions nature (benign or malignant) and histotype proposed by the on-site operator was finally compared to the definite diagnosis reached by reference procedures (multiphasic contrast-material enhanced helical-computed tomography or magnetic resonance in 24 lesions and fine needle US guided biopsy in 36 lesions). Diagnostic performance (sensitivity, specificity and overall accuracy expressed by the agreement with the reference procedures) of baseline and contrast enhanced US were compared. RESULTS: Differences in sensitivity (baseline vs contrast-enhanced US: 13/39 [33%] vs 32/39 [82%]), specificity (baseline vs contrast-enhanced US: 12/21 [57%] vs 16/21 [76%]) and overall accuracy (baseline vs contrast-enhanced US: 25/60 [41%] vs 47/60 [78%]) were significant (p<0.05; McNemar test). CONCLUSIONS: SonoVue-enhanced US determined a significant improvement in diagnostic performance in the characterization of focal liver lesions if compared to baseline US.     

眼眶分区及CT、MRI征象在眼眶占位性病变中的诊断价值

目的 探讨眼眶分区及CT、MRI征象在鉴别眼眶良、恶性占位性病变的诊断价值.方法 收集201例经病理证实的眼眶占位性病变临床及CT、MRI资料,按4分区法统计分析病变在眼眶各区的分布情况及病变部位、形态、边界、与周围结构关系、MRI信号、CT密度、钙化、眶壁骨质改变等指标在鉴别眼眶良、恶性占位的诊断价值.结果 (1)病变分布:①眼眶良、恶性占位性病变总体在各区的分布差异有统计学意义(χ2总=48.93,P=0.000).病变仅位于骨膜外区18例、神经鞘区4例、肌锥内区39例均为良性.肌锥外区病变103例,良性(64%,66/103)多于恶性(36%,37/103).②眼眶良、恶性占位性病变在单区及混合区的分布差异有统计学意义(χ2=25.559,P=0.000).164例单区病变,良性(77%,127/164)多于恶性(23%,37/164);37例混合区病变,恶性(65%,24/37)多于良性(35%,13/37).(2)CT、MRI征象:201例病变,140例良性,61例恶性,其中(良性/恶性):形态规则(93/10),边界清楚(108/24),包绕眼球(24/39),骨质破坏(4/11).病变形态、边界、包绕眼球、骨质破坏在眼眶良、恶性病变之间有差异.钙化、T1WI/T2WI信号、眼球变形移位及是否单双侧发病在眼眶良、恶性病变中无差异.结论 眼眶占位性病变在眼眶各区的分布及其CT、MRI征象有一定规律, 根据眼眶分区及征象特点有助于诊断.     

CT-guided biopsy of pelvic masses

CT-guided fine-needle puncture (FNP) was carried out in 74 patients with pelvic masses and resulted in a correct diagnosis in 36/45 patients (80%) with malignant disease. FNP was true-positive in 66.7% and false-negative in 20%. In benign and inflammatory pelvic space-occupying lesions, FNP confirmed the suspected CT diagnosis in all cases by cytology and bacteriology. CT-guided puncture should always be used complementary to CT when a mass of unclear etiology is present.     

Value of contrast-enhanced sonography for the characterization of focal hepatic lesions in patients with diffuse liver disease: receiver operating characteristic analysis

OBJECTIVE: Our aim was to assess the diagnostic performance of contrast-enhanced agent detection sonographic imaging to characterize focal hepatic lesions in patients with diffuse liver disease in comparison with baseline sonographic images and to determine whether agent detection imaging can reduce the necessity of further diagnostic workup for lesion characterization. MATERIALS AND METHODS: Contrast-enhanced sonography using 4 g of Levovist at a concentration of 300 mg/mL was performed on 75 focal hepatic lesions in 75 patients with diffuse liver disease. Interval reviews for both baseline without and with contrast-enhanced sonography were performed independently by two radiologists. They were requested to determine the malignity of focal hepatic lesions using a 5-point confidence level and to record the specific diagnoses and the necessity for further imaging for lesion characterization. Radiologists' performances for lesion differentiation using baseline and contrast-enhanced sonography were evaluated using receiver operating characteristic (ROC) analysis. Interobserver agreement was also analyzed. RESULTS: When contrast-enhanced sonography was used, ROC analysis revealed a significant improvement for both reviewers (area under the receiver operating characteristic curve [A(z)] = 0.753 and 0.830 and 0.971 and 0.974 at baseline sonography and contrast-enhanced sonography, respectively; p < 0.002) for differentiating malignant and benign focal liver lesions. Contrast-enhanced sonography also improved specificity from 12% to 91% for reviewer 1 and from 26% to 85% for reviewer 2 compared with baseline sonography. Furthermore, excellent interobserver agreement was achieved for contrast-enhanced sonography (weighted kappa = 0.919), whereas only good agreement was achieved for baseline sonography (weighted kappa = 0.656). A better result for specific diagnosis was obtained by contrast-enhanced sonography (79% and 75%) than by baseline sonography (37% and 48%, p < 0.05). Contrast-enhanced sonography (72% and 63%) outperformed baseline sonography (35% and 28%, p < 0.05) as a confirmatory imaging technique. CONCLUSION: Contrast-enhanced agent detection sonography can be used to characterize focal hepatic lesions in patients with diffuse liver disease reliably and with a higher diagnostic confidence than baseline sonography. Furthermore, contrast-enhanced sonography reduced the need for further diagnostic workups for focal hepatic lesion characterization.     

The complementary role of SPECT in the diagnosis of cavernous hemangioma of the liver

Cavernous hemangiomas are the most common benign tumors of the liver. Although their clinical course is usually uncomplicated, an accurate diagnosis may be important to exclude conditions that need treatment, (or to avoid an unnecessarily risky percutaneous biopsy). Although blood pool scintigraphy using planar gamma camera imaging is a reliable examination for the diagnosis of liver hemangiomas, it may fail to depict small, deeply seated lesions, and hence miss the diagnosis. Two cases are reported in which SPECT demonstrated delayed pooling in small, deep, space-occupying lesions, which were poorly seen on planar images, and therefore made a cavernous hemangioma the most likely diagnosis.     

New sonographic criteria for recommending fine-needle aspiration biopsy of nonpalpable solid nodules of the thyroid

OBJECTIVE: The purpose of our study was to provide new sonographic criteria for fine-needle aspiration biopsy of nonpalpable solid thyroid nodules. MATERIALS AND METHODS: Sonographic scans of 155 nonpalpable thyroid nodules in 132 patients were prospectively classified as having positive or negative findings. Sonographic findings that suggested malignancy included microcalcifications, an irregular or microlobulated margin, marked hypoechogenicity, and a shape that was more tall than it was wide. If even one of these sonographic features was present, the nodule was classified as positive (malignant). If a nodule had none of the features described, it was classified as negative (benign). The final diagnosis of a lesion as benign (n = 106) or malignant (n = 49) was confirmed by fine-needle aspiration biopsy and follow-up (>6 months) in 83 benign nodules, by fine-needle aspiration biopsy and surgery in 44 malignant and 15 benign lesions, and by surgery alone in five malignant and eight benign lesions. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated on the basis of our proposed classification method. RESULTS: Of 82 lesions classified as positive, 46 were malignant. Of 73 lesions classified as negative, three were malignant. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy based on our sonographic classification method were 93.8%, 66%, 56.1%, 95.9%, and 74.8%, respectively. CONCLUSION: Considering the high level of sensitivity of our proposed sonographic classification, fine-needle aspiration biopsy should be performed on thyroid nodules classified as positive, regardless of palpability.     

Morphology and diagnosis of acquired bladder deformities

Acquired displacements of the urinary bladder refer to intrapelvic pathological anatomy. These alterations of the bladder are predominantly detected via an initial radiologic study with intravenous urography or suprapubic pelvic ultrasonography. According to their clinical incidence displacements of the bladder can occur in: pelvic space-occupying lesions; displacements in musculo-fascial defects of supporting structures as well as in extirpation cavities of the small pelvis; extrapelvic space-occupying lesions. Herniation, prolapse and descensus of the bladder can be accurately diagnosed by correct examination via intravenous urography. The diagnostics of pelvic and extrapelvic pathogenetic causes require the complex application of all methods of diagnostic imaging, the value of which is determined by clinical diagnosis and by the choice of an appropriate therapy.     

Importance of evaluating all vascular phases on contrast-enhanced sonography in the differentiation of benign from malignant focal liver lesions

OBJECTIVE: Our objective was to evaluate the accuracy of a blood-pool sonographic contrast agent in the late phase compared with the three vascular phases for differentiation between benign and malignant focal liver lesions. SUBJECTS AND METHODS: In 152 patients (105 with chronic liver disease), 152 solid focal liver lesions characterized either by fine-needle biopsy or by dynamic CT or MRI were studied. The final diagnoses were metastasis for 24, hepatocellular carcinoma for 75, focal nodular hyperplasia for 13, regenerating or dysplastic nodule for 14, hemangioma for 22, cholangiocarcinoma for two, and another focal liver lesion for two. Real-time sonography was performed after a bolus injection of 2.4 mL of SonoVue, using a low mechanical index (< 0.2). All lesions were evaluated in the arterial, portal, and late phases; classified as benign or malignant; and correlated with final diagnoses. RESULTS: For discrimination between malignant and benign focal liver lesions, evaluation of all vascular phases improved the sensitivity from 78.4% to 98% and the accuracy from 80.9% to 92.7%, compared with evaluation of the late phase alone. The increase in accuracy was higher in patients with chronic liver disease (16.3%) than in those without (2.1%). CONCLUSION: Evaluation of SonoVue enhancement in all three vascular phases is superior to evaluation of SonoVue enhancement in the late phase alone, especially in patients with chronic liver disease.     

Ultrasound-guided fine-needle puncture of the thyroid

If properly performed, modern high-resolution real-time ultrasonography will disclose subtle differences in the texture of thyroid tissue and thereby enable the examiner to suggest a diagnosis. Nevertheless, there is often a need for a more specific diagnosis of solid or semisolid thyroid lesions - especially when the lesion might be malignant. Ultrasonically guided fine-needle aspiration biopsy (UG-FNB) allows a final cytological and/or histological diagnosis to be made in patients with benign or malignant space-occupying growths even if they are small. In its simplest form, thyroid nodules (diameter greater than 1.5 cm) with a uniform sonographic texture are punctured blind after determination of the site and size of the lesion on the basis of ultrasonic imaging. When the lesion is small and deeply situated (diameter less than or equal to 1.5 cm), this method will not be sufficiently accurate and more precise needle guidance is mandatory. In ultrasonically guided fine-needle puncture, the idea is to place the tip of an appropriate needle safely and accurately in the suspect lesion, so that representative specimens of solid tissue or fluid can be obtained and technical failures reduced. The main indication for biopsy of the thyroid gland is to differentiate between benign and malignant tumors. To compare the accuracy of conventional puncture techniques and ultrasonically guided puncture methods, 835 patients with benign or malignant space-occupying growth (even the small ones) were examined simultaneously with conventional and ultrasonically guided fine-needle aspiration biopsy over a period of 3 years (prospectively). Our results showed a significant difference in the sensitivity between conventional puncture without sonographic guidance and ultrasonically guided puncture techniques performed on patients with small and very small lesions (phi less than 2 cm). The size, macroscopic structure, and topographic-anatomical localization of the lesions were found to influence the diagnostic accuracy of the puncture techniques. UG-FNB is an excellent, effective, safe and painless method of treating uncomplicated thyroid cysts; it should be considered an alternative to surgery, if there are no clinical and cytological findings indicating malignancy and no severe space-occupying complications. Since the tip of the needle can be visualized on the scan, the needle may be advanced or withdrawn during aspiration so it is possible to empty the cyst completely. The use of ultrasound in the follow-up of patients with thyroid cyst puncture is mandatory to evaluate the results. Surgical therapy should be reserved for large cysts causing space-occupying complications.     

MR动态增强减影技术对乳腺良恶性病灶鉴别的价值

目的:评价MR动态增强减影技术对乳腺良恶性病灶鉴别的价值。方法:收集进行乳腺MR动态增强减影扫描并有明确病理结果的56例67个病灶作为研究对象进行回顾性分析。结果:乳腺良恶性病灶在MR动态增强形态、强化时间-信号强度曲线、强化峰值时间、血管分布形态、腋窝淋巴结五个指标上表现不同。结论:MR动态增强减影技术对乳腺良恶性病灶具有较高的鉴别诊断价值。     

Vascular thrombosis and homocystinuria

Hepatic hemangiomas are the most common benign tumors of the liver and commonly present as incidental findings on sonographic examination of the abdomen. To chart more precisely the natural course of the sonographic appearance of hepatic hemangiomas, 47 patients with 68 hemangiomas were rescanned 1-6 years after the initial study. Fifty-six lesions (82%) showed an identical appearance on follow-up study. However, 12 (18%) of the lesions had an appreciably changed sonographic appearance. Three lesions could not be found, seven were less obvious (less echogenic), one was larger, and one smaller. This study shows that once hemangiomas are identifiable sonographically in adults, they have reached a stable size and change in size or appearance only rarely. They do not continue to grow slowly over time. Furthermore, this study also confirms that the sonographic appearance in the appropriate patient can differentiate these hemangiomas relatively reliably from metastases.     

Automated water-path full-breast sonography: correlation with histology of 176 solid lesions

A comparative study with mammography and physical examination showed that automated water-path whole-breast sonography contributed to the care of at least one-half of 786 study patients (separate report). Clinical application then followed in an additional 2530 women in whom there were 107 biopsy-proven cancers, 69 discrete biopsied benign lesions, and 121 biopsies of poorly defined lesions, usually some form of fibrocystic disease without a discrete mass. Breast sonography demonstrated 72% of the cancers and detected six cancers not seen on mammography. Although there was considerable overlapping of sonographic characteristics of benign and malignant diseases, most lesions were differentiated. Only 10% of the solid benign lesions had some characteristic of malignancy, and in 90% of the infiltrating duct carcinomas, findings suggested the histologic diagnosis. While breast sonography must be considered a complement to physical examination and mammography, the procedure can reliably differentiate the histologic types of at least 83% of discrete benign lesions and 75% of cancers. In 90% of all solid breast lesions, sonography differentiated benign and malignant processes.     

超声造影对肾脏小占位的诊断分析

目的:探讨不同病理类型肾脏肿瘤的造影特点,评价超声造影诊断肾脏良恶性肿瘤的应用价值,为临床诊断提供依据。方法:应用声学造影剂声诺维对27例超声诊断为肾脏占位病变或可疑肾脏占位病变的患者进行超声造影检查,分析其造影增强图像特点。结果:27例患者均满意获得清晰的肿瘤动态造影灌注图像,大部分与其正常肾组织回声等强,10例肾恶性肿瘤的造影显像比其正常肾组织快,3例肾良性肿瘤造影显像为"同进慢出";4例肾柱肥大造影后与正常肾组织造影剂显像一致;2例肾囊肿内无造影剂显示。结论:超声造影成像技术能清晰显示肾肿瘤的血流灌注特点,对肾脏肿瘤的诊断具有一定实用价值。     

Ultrasonographic contrast agent: evaluation of time-intensity curves in the characterisation of solitary thyroid nodules

PURPOSE: To evaluate whether the time-intensity curve can improve characterisation of solitary thyroid nodules. MATERIAL AND METHODS: From June to December 2000 we studied 61 patients (16 men and 45 women, mean age 46 years) with solitary thyroid nodules that were not associated with any important hormonal alteration and that showed poor tracer uptake at scintigraphy. We evaluated the Power Doppler vascular pattern before and after a 60" intravenous injection of 2.5 g of Levovist (diluted in 7 ml). The study lasted 5 minutes from the beginning of the infusion. Finally, the time-intensity curves were processed. All the nodules underwent fine needle aspiration biopsy (FNAB) and excision biopsy. RESULTS: Histology revealed 43 benign lesions and 18 malignant lesions. At contrast-enhanced Power Doppler 83.4% (15/18) of the malignant nodules were found to be hypervascularized, while 16.6% (3/18) were hypovascularized. Of the benign lesions, 90.7% (39/43) were hypervascularized, 9.3% (4/43) were hypovascularized. All the nodules, both hyper- and hypovascularized, displayed rapid and intense wash-in curves. By contrast, the wash-out curves were regular and monophasic in 40/43 (93%) benign lesions (36 hypervascularized and 4 hypovascularized lesions) and irregular and polyphasic in 16/18 (89%) malignant lesions (13 hypervascularized and 3 hypovascularized lesions); 3/43 (7%) benign nodules showed polyphasic wash-out and 2/18 malignant lesions (11%) showed monophasic wash-out. DISCUSSION AND CONCLUSIONS: Time-intensity curves, and particularly wash-out curves, provide useful information for the characterisation of solitary thyroid nodules. 93% of benign nodules (with regular vascularization) showed a monophasic pattern of the wash-out curve, while 89% of malignant nodules ("anarchical" vascularization) had polyphasic wash-out curves. This behaviour was observed in both hypervascularized and hypovascularized lesions. Our method proved to have a sensitivity of 88% and a specificity of 93%. The study of time-intensity curves could therefore enable us to differentiate between benign and malignant lesions and characterise hypovascularized malignant nodules which would not be observed without contrast agent.     

Late-phase pulse-inversion sonography using the contrast agent levovist: differentiation between benign and malignant focal lesions of the liver

OBJECTIVE: We assessed the ability of contrast-enhanced sonography to reveal differences between benign and malignant focal hepatic lesions. SUBJECTS AND METHODS: We examined 67 patients with focal hepatic lesions in a prospective study. The causes of the lesions were confirmed by histology, CT, MR imaging, or scintigraphy. The liver was screened for focal lesions using sonography. Thereafter, 2 g of Levovist (300 mg/mL; 1 mL/sec) was injected IV as a bolus. After a delay of at least 2.5 min without scanning, the liver was examined via three different scans using pulse-inversion sonography. RESULTS: For the discrimination of malignant versus benign liver lesions, contrast-enhanced sonography improved sensitivity from 85% to 100% and specificity from 30% to 63%, as compared with baseline sonography. Receiver operating characteristic analysis revealed a significant improvement in this discrimination (A(z) = 0.692 +/- 0.065 at baseline sonography, A(z) = 0.947 +/- 0.037 with contrast-enhanced sonography, p < 0.001). Furthermore, a lower interobserver variability was found for contrast-enhanced sonography (weighted kappa = 0.947), as compared with baseline sonography (weighted kappa = 0.469). All lesions that had homogeneous enhancement in the late phase of Levovist enhancement were benign. In distinction, 90% of lesions without contrast enhancement in the late phase were malignant. All lesions were malignant that were isoechoic (invisible) on baseline sonography but visible because of lack of enhancement after injection. CONCLUSION: Contrast-enhanced sonography has greater specificity and sensitivity than baseline sonography for the differentiation of benign and malignant liver lesions.     

Hepatocellular carcinoma treated with radiofrequency ablation: comparison of pulse inversion contrast-enhanced harmonic sonography, contrast-enhanced power Doppler sonography, and helical CT.

OBJECTIVE: The purpose of this study was to compare the efficacy of contrast-enhanced pulse inversion harmonic imaging with contrast-enhanced power Doppler sonography and helical CT to determine incomplete local treatment after radiofrequency ablation in patients with hepatocellular carcinoma. MATERIALS AND METHODS: Thirty-five consecutive patients (24 men and 11 women; mean age, 64 years) with 43 hepatocellular carcinomas (3.6 +/- 1.1 cm) were treated using internally cooled radiofrequency ablation therapy. Therapeutic response was evaluated at 4 months with dual-phase contrast-enhanced helical CT, conventional power Doppler Sonography, and pulse inversion harmonic imaging using a sonographic contrast agent (SH-508). CT and sonographic studies were reviewed separately in random order by four radiologists at different consensus conferences. Sensitivity and specificity of the sonographic methods were determined using CT as a gold standard and results were compared using the McNemar test. RESULTS: CT examinations identified residual tumor in 12 lesions (27.9%). Although conventional contrast-enhanced power Doppler sonography identified residual viable tumor foci in four incompletely treated lesions (9.3%), contrast-enhanced pulse inversion harmonic imaging identified residual tumoral enhancement in 10 lesions (23.3%). Thus, the sensitivity of pulse inversion harmonic imaging (83.3%) was significantly greater (p < 0.05) for detecting residual nonablated tumor compared with conventional contrast-enhanced power Doppler sonography. CONCLUSION: Our study suggests that contrast-enhanced pulse inversion harmonic imaging may enable the detection of residual nonablated tumor in more cases than contrast-enhanced power Doppler sonography and may ultimately prove to be a useful adjunct for percutaneous ablation therapies. Nevertheless, contrast-enhanced axial imaging (CT or MR imaging) is currently the most sensitive test for managing thermal ablation for patients with hepatocellular carcinoma.     

Doppler power with contrast media in the characterization of renal masses

PURPOSE: To report the results of a prospective study investigating the potentials of contrast-enhanced power Doppler in the diagnosis of expansive renal lesions. MATERIAL AND METHODS: From 1997 to October 30, 1999, we studied 59 expansive renal lesions (28 malignant, 31 benign) in 48 patients (mean age 55 years, range 10-79) with power Doppler US before and after the administration of an echo-enhancing agent (Levovist, Schering AG, Berlin, Germany). We identified 5 patterns of vascular architecture of the lesions, both before and after contrast agent administration, following the classification by Jinzaki e Coll. RESULTS AND DISCUSSION: Power Doppler US showed vascular structures in 34 patients. The administration of Levovist revealed vessels in 12/25 lesions which had none at baseline studies and in 6 cases vascularity was particularly evident. Color signals were enhanced in all the 34 vascularized lesions, which allowed better definition of vascular patterns. The characterization of vascular patterns with baseline power Doppler US helped improve diagnostic accuracy compared to gray-scale US (58% versus 32%) for hyperechoic lesions, complex cysts and pseudomasses. Independent of contrast agent administration, the integration of gray-scale and power Doppler modes increased diagnostic accuracy even further (76% correct diagnoses). CONCLUSIONS: In our series, the US contrast agent did not increase the diagnostic accuracy of power Doppler in the differential diagnosis of hyperechoic renal lesions; conversely, Levovist can be advantageous for the characterization of suspected pseudomasses and complex cysts.     

螺旋CT及MRI在鉴别肾脏囊性占位病变中的作用

目的分析肾脏囊性占位病变的CT与MRI表现,并评价其对鉴别良恶性病变的临床意义。方法 151例由手术病理证实的肾脏囊性占位病变患者,包括多发囊肿125例,海绵状血管瘤16例及囊性肾癌10例,均经CT与MRI平扫及增强扫描。比较了CT与MRI对肾脏囊性占位病变的诊断能力。结果 151例中,CT诊断肾囊肿118例,血管瘤16例,以及囊性肾癌17例,其诊断敏感性,特异性及准确性分别为58.8%,95.0%及95.4%;MRI诊断肾囊肿122例,血管瘤16例,以及囊性肾癌13例,其诊断敏感性,特异性及准确性分别为76.9%,98.8%及98.0%。CT对肾良性病变低估7例,对恶性病变高估了7例,而MRI对肾良性病变低估3例,对恶性病变高估3例。结论 CT与MRI二者都能对血管瘤作出正确诊断,而在肾囊肿与囊性肾癌的诊断及鉴别诊断中,MRI明显优于CT。