Monitoring of liver metastases after stereotactic radiotherapy using low-MI contrast-enhanced ultrasound—initial results

The purpose of this study was to monitor liver metastases after radiotherapy using contrast-enhanced ultrasound (CEUS). In 15 patients, follow-up examinations after stereotactic, single-dose radiotherapy were performed using CEUS (low mechanical index (MI), 2.4-ml SonoVue) and computed tomography (CT). Besides tumor size, the enhancement of the liver and the metastases was assessed at the arterial, portal venous, and delayed phases. The sizes of the tumor and of a perifocal liver reaction after radiotherapy measured with CEUS significantly correlated with those measured at CT (r=0.93, p<0.001). CEUS found a significant reduction of the arterial vascularization in treated tumors (p<0.05). In the arterial phase, the perifocal liver tissue was hypervascularized compared to the treated tumor (p<0.001); in the late phase, it was less enhanced than the liver (p<0.001) and more than the tumor (p<0.01). The perifocal liver reaction was also seen in CT, but with a variable enhancement at the arterial (50% hyperdense compared to normal liver tissue), venous, or delayed phase (each with 70% hyperdense reactions). CEUS allows for the assessment of tumor and liver perfusion, in addition to morphological tumor examination, which was comparable with CT. Thus, changes of tumor perfusion, which may indicate tumor response, as well as the perifocal liver reaction after radiotherapy, which must be differentiated from perifocal tumor growth, can be sensitively visualized using CEUS.     

Assessment of the vascularization of neuroendocrine tumors by stimulated acoustic emission of SH U 508A ultrasound contrast agent and color or power Doppler sonography

RATIONALE AND OBJECTIVES: To assess the vascularization of neuroendocrine tumors by stimulated acoustic emission (SAE) of SH U 508A during the blood pool phase in comparison with contrast-enhanced Doppler sonography. METHODS: Thirty-six patients with neuroendocrine tumors received contrast-enhanced Doppler sonography and 21, an additional SAE. To classify tumor perfusion on Doppler sonography, a 4-step rating score was introduced: (1) no vessels (hypoperfusion); (2) one feeding or central vessel (hypoperfusion); (3) some vessels (hyperperfusion); and (4) disseminated vessels (hyperperfusion). In 36 patients, 1 pancreatic primary tumor, 33 liver metastases, 1 splenic metastasis, and 1 lymph node metastasis were examined. Results were correlated with biphasic spiral CT (n = 35) and angiography (n = 2). RESULTS: Arterial-phase CT and digital subtraction angiography revealed 18 hyper- and 18 hypoperfused lesions. Contrast-enhanced Doppler correctly classified 15 of 18 patients (83%) with hyperperfused lesions as well as 16 of 18 (89%) hypoperfused tumors by applying the rating score. SAE correctly identified 4 of 9 hyperperfused lesions (44%), 2 were isoperfused compared with normal liver tissue (22%), and 3 were hypoperfused (33%). Of 12 hypoperfused lesions, 11 were classified correctly (92%), and 1 showed isoperfusion. Hence, the positive and negative predictive values for SAE were 80% and 69%, respectively. For contrast-enhanced Doppler sonography, positive and negative predictive values were 88% and 84%, respectively. CONCLUSIONS: Blood pool SAE failed to determine subtle tumor perfusion correctly. The rating score for contrast-enhanced Doppler sonography characterized tumor perfusion with high accuracy. The use of a contrast agent significantly improved perfusion characterization.     

Evaluation of neovascularization with spectral computed tomography in a rabbit VX2 liver model: a comparison with real-time contrast-enhanced ultrasound and molecular biological findings

Objective:

To validate the feasibility of using the parameters of spectral CT and CT perfusion and the dynamic features of real-time contrast-enhanced ultrasound (CEUS) to evaluate the vascularization of VX2 hepatic tumours.

Methods:

Spectral CT imaging, CT perfusion and CEUS analysis were performed on rabbits implanted with VX2 hepatic tumours, 7 and 14 days after implantation. The perfusion parameters of CT, normalized iodine concentration (NIC) and dynamic features of CEUS were measured in the rim of the tumour (TR) and the normal liver region. The expression of vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2) was also determined.

Results:

Increased perfusion parameters of CT were found in the TR. In addition, the NIC was elevated in TR during the arterial phase, and the peak intensity of the CEUS of the TR was reached significantly earlier than that on normal liver region. At 14 days, the perfusion parameters of CT (blood volume, permeability surface and hepatic arterial fraction) offered higher accuracy and stability in differentiating the TR from the normal liver region. Furthermore, CEUS was more accurate in diagnosing tumours <1.0 cm in diameter. In addition, VEGF and FGF2 expression was higher in the TR and were positively correlated with CT and CEUS parameters, except mean transit time, rise time, washout time and peak time.

Conclusion:

Use of spectral CT with perfusion techniques, iodine-based material-decomposition analysis and dynamic CEUS changes may reflect the angiogenesis and haemodynamic information of hepatic tumours.

Advances in knowledge:

It is feasible to assess vascularization in hepatic cancer using CT or CEUS.     

乏血供肝转移瘤超声造影与CT增强扫描的对比研究

目的:探讨乏血供肝转移瘤超声造影(CEUS)血流灌注特点及其与CT增强扫描的差异。方法:选择CT增强扫描提示为乏血供肝转移瘤的12例(20个病灶)行常规超声及造影检查。二维超声观察病灶的部位、大小、边界、内部回声;CEUS观察病灶各期的强化模式、强化水平,重点观察动脉期(0～25s),并与CT增强扫描进行比较。结果:12例共20个病灶,CT增强扫描动脉期:1个病灶轻度增强(5%),11个环形强化(55%),2个不均匀强化(10%),6个无强化(30%)。CEUS动脉期:11个病灶弥漫性均匀强化(55%),7个环形强化(35%),2个不均匀强化(10%)。结论:CEUS显示乏血供肝转移瘤动脉期血供情况优于CT增强扫描;对于CT增强扫描怀疑为乏血供肝转移瘤患者,尤其是单发转移瘤,CEUS检查对临床诊断和治疗有很大帮助。     

应用DSA、CT和经肠系膜上动脉门静脉灌注CT成像研究肝转移瘤的血液供应

目的 探讨DSA、CT和经肠系膜上动脉门静脉灌注CT成像对肝转移瘤的血液供应显示状况.方法 回顾性分析100例原发病灶经手术和(或)病理证实的肝转移瘤患者资料,均进行了CT平扫、多期CT增强扫描、选择性腹腔动脉和超选择性肝固有动脉DSA检查,其中,56例还经肠系膜上动脉插管行肠系膜上动脉的门静脉灌注CT成像(P(1TAP)检查,计算转移瘤中心区域、肿瘤边缘、门静脉和正常肝实质的时间-密度曲线(TDC)灰度密度(K值),观察肝转移瘤血液供应来源.DSA图像用Photoshop软件进行定量分析,CT图像用去卷积灌注软件进行分析.结果 DSA表现:肝固有动脉造影TDC显示肿瘤中心K值峰值平均为(67±12)%,肿瘤边缘K值峰值平均为(76±15)%,正常肝实质K值峰值平均为(51±10)%.腹腔动脉造影TDC显示,肿瘤中心及肿瘤边缘K值表现为快速上升,然后为缓慢上升的平台,而正常肝实质则呈现持续缓慢上升的态势.PCTAP扫描表现:肿瘤在30 s的时间内,密度变化几乎呈直线,无增强表现.结论 肝动脉是肝转移瘤的主要血液供应来源,门静脉几乎不参与肝转移瘤血液供应.     

Characterization of focal liver lesions with a new ultrasound contrast agent using continuous low acoustic power imaging: comparison with contrast enhanced spiral CT

PURPOSE: To evaluate the concordance of the enhancement patterns of a new ultrasound contrast agent (SonoVue) with those obtained with dual-phase contrast-enhanced spiral CT (CE-CT) in the characterization of focal liver lesions (FLLs). MATERIALS AND METHODS: Sixty-two patients with focal liver lesions discovered at ultrasound and also studied with CECT underwent contrast-enhanced ultrasound using continuous low acoustic power imaging after receiving a 2.4 ml bolus of the new US contrast agent SonoVue, consisting of a dispersion of sulphur hexafluoride microbubbles. The examinations were made using ATL HDI-5000, Acuson SEQUOIA and Aloka 5500 Prosound ultrasound systems with 5.2 MHz curved-array probes. The concordance between US and CE-CT images was evaluated on site by two radiologists blinded to CT RESULTS: The FLLs were assessed in the arterial (20 s after CM injection), portal (after 45-60 s) and late (after 120 s) phases for: 1) presence/absence of enhancement 2) distribution of enhancement (homogenous or target distribution, centripetal or centrifugal flow, and other), 3) qualitative enhancement pattern (hyperechoic, hypoechoic, or isoechoic) versus normal liver parenchyma. RESULTS: The concordance between SonoVue-enhanced US and CE-CT was 85%. Moreover during portal venous phase with CEUS it was possible to differentiate between malignancy or benignity of 91% of lesions. CONCLUSIONS: The preliminary data obtained in this study suggest that continuous low acoustic power imaging and contrast-enhanced US show similar results to CT in contrast distribution and contrast enhancement patterns.     

Total-liver-volume perfusion CT using 3-D image fusion to improve detection and characterization of liver metastases

The purpose of this study was to evaluate the feasibility of a total-liver-volume perfusion CT (CTP) technique for the detection and characterization of liver metastases. Twenty patients underwent helical CT of the total liver volume before and 11 times after intravenous contrast-material injection. To decrease distortion artifacts, all phases were co-registered using 3-D image fusion before creating blood-flow maps. Lesion-based sensitivity and specificity for liver metastases of first the conventional four phases (unenhanced, arterial, portal venous, and equilibrium) and later all 12 phases including blood-flow maps were determined as compared to intraoperative ultrasound and surgical exploration. Arterial and portal venous perfusion was calculated for normal-appearing and metastatic liver tissue. Total-liver-volume perfusion values were comparable to studies using single-level CTP. Compared to four-phase CT, total -liver-volume CTP increased sensitivity to 89.2 from 78.4% (P = 0.046) and specificity to 82.6 from 78.3% (P = 0.074). Total -liver-volume CTP is a noninvasive, quantitative, and feasible technique. Preliminary results suggest an improved detection of liver metastases for CTP compared to four-phase CT.     

Hepatic focal lesions: role of color Doppler ultrasonography with contrast media

INTRODUCTION: The differential diagnosis of focal hepatic lesions is still studied by diagnostic imaging operators. A big step forward in the field of ultrasound (US) has come from the color Doppler mode permitting accurate studies of the vascularization of focal hepatic lesions. Echocontrast agents have further improved color Doppler sensitivity to slow flows and have permitted to visualize intralesional vascular signals which were missed at B-mode US. New data have thus been acquired which can be integrated with flowmetric findings to help make the correct differential diagnosis with a fair safety margin. We studied the pathognomonic US pattern for each type of lesion. MATERIAL AND METHODS: We examined 55 patients with single hepatic lesions which had already been typified: they were 10 hepatic angiomas, 3 focal nodular hyperplasias (FNH), 2 hepatic adenomas, 20 hepatocarcinomas and 20 hepatic metastases. Color Doppler investigations were performed on each patient before and after the intravenous (i.v.) administration of an echocontrast agent (Levovist, Schering AG, Berlin, Germany). For each lesion we studied the morphological characteristics, the resistance index (RI) of intralesional arterial vessels, the hepatic perfusion index and the maximum speed in intralesional vessels. RESULTS: Contrast-enhanced US showed no intralesional signals or afferent branches in 8 hepatic angiomas, which however exhibited some peripheral vascularization; weak intralesional vascular signals were demonstrated in 2 cavernous angiomas. Intralesional signals, as well as peripheral vascularization, were detected in the 3 FNH cases, which also exhibited a centripetal afferent branch; the hepatic perfusion index in these lesions never exceeded .25. The two hepatic adenomas had similar color flowmetry to FNH also after i.v. contrast agent administration, except for the contripetal afferent vessel which was not seen. In the 20 hepatocarcinomas, contrast-enhanced images showed numerous intralesional signals and afferent branches which, with the peripheral vascularization, resulted in a basket-like pattern. Flowmetry of intralesional arterial vessels showed an irregular systodiastolic range, with RI = .32 +/- .5 in 12 lesions and high in the remaining 8 lesions (RI = .82 +/- 10). The hepatic perfusion index was .65 +/- 10 in all patients. In 14 of the 20 hepatic metastases, B-mode US showed no intralesional signals except for 6 metastases from colorectal carcinoma, and contrast-enhanced findings were about the same. The hepatic perfusion index at flowmetry ranged .30 to .45 in all patients.     

Liver metastases from colorectal cancers: detection with CT during arterial portography

A total of 45 metastases to the liver from colorectal cancer were resected in 22 patients. The detectability of these lesions with the following modalities was determined: real-time ultrasound (US), computed tomography (CT), selective celiac arteriography (SCA), infusion hepatic angiography (IHA), CT during arterial portography (CTAP), and CT following intraarterial injection of iodized poppyseed oil (Lipiodol). The total detection rate (sensitivity) was 58% for US, 63% for CT, 27% for SCA, 50% for IHA, 84% for CTAP, and 38% for CT with iodized oil. Ten of 18 lesions less than 15 mm in largest diameter were demonstrated preoperatively by CTAP only. CTAP is useful in clarifying the locations of the lesions in the liver and should always be performed before liver metastases from colorectal cancer are resected.     

低机械指数实时超声造影评价恶性肿瘤治疗后肝内复发转移的临床研究

目的:探讨低机械指数超声造影成像技术定性诊断恶性肿瘤治疗后肝内可疑复发转移病灶的价值。材料和方法:78个肝脏局灶性病变,同期行实时超声造影、CT增强检查,最终诊断经穿刺活检病理证实62个结节,另13个局部治疗后坏死结节及3个增生结节经综合影像及12~34个月随访证实。结果:超声造影诊断的敏感性96.2%,特异性92.3%,准确性94.9%,阳性预测值92.3%,阴性预测值96.2%。70个结节同期CT增强诊断,结果与最终诊断及超声造影诊断的一致性比较无统计学差别。结论:实时超声造影是定性诊断肝局灶性病变的有效方法,尤其对经肝动脉栓塞后碘油沉积病灶残存血流灌注的评判较CT具有优势。     

Ultrasound contrast agents: an overview

With the introduction of microbubble contrast agents, diagnostic ultrasound has entered a new era that allows the dynamic detection of tissue flow of both the macro and microvasculature. Underpinning this development is the fact that gases are compressible, and thus the microbubbles expand and contract in the alternating pressure waves of the ultrasound beam, while tissue is almost incompressible. Special software using multiple pulse sequences separates these signals from those of tissue and displays them as an overlay or on a split screen. This can be done at low acoustic pressures (MI < 0.3) so that the microbubbles are not destroyed and scanning can continue in real time. The clinical roles of contrast enhanced ultrasound scanning are expanding rapidly. They are established in echocardiography to improve endocardial border detection and are being developed for myocardial perfusion. In radiology, the most important application is the liver, especially for focal disease. The approach parallels that of dynamic CT or MRI but ultrasound has the advantages of high spatial and temporal resolution. Thus, small lesions that can be indeterminate on CT can often be studied with ultrasound, and situations where the flow is very rapid (e.g., focal nodular hyperplasia where the first few seconds of arterial perfusion may be critical to making the diagnosis) are readily studied. Microbubbles linger in the extensive sinusoidal space of normal liver for several minutes whereas they wash out rapidly from metastases, which have a low vascular volume and thus appear as filling defects. The method has been shown to be as sensitive as three-phase CT. Microbubbles have clinical uses in many other applications where knowledge of the microcirculation is important (the macrocirculation can usually be assessed adequately using conventional Doppler though there are a few important situations where the signal boost given by microbubbles is useful, e.g., transcranial Doppler for evaluating vasospasm after subarachnoid haemorrhage). An important situation where demonstrating tissue devitalisation is important is in interstitial ablation of focal liver lesions: using microbubble contrast agents at the end of a procedure allows immediate evaluation of the adequacy of the ablation which can be extended if needed; this is much more convenient and cost-saving than moving the patient to CT and perhaps needing an additional ablation session at a later date. Similar considerations suggest that contrast-enhanced ultrasound might have a role in abdominal trauma: injury to the liver, spleen and kidneys can be assessed rapidly and repeatedly if necessary. Its role here alongside dynamic CT remains to be evaluated. Infarcts or ischaemia and regions of abnormal vascularity, especially in malignancies, in the kidneys and spleen seem to be useful and improved detection of the neovascularisation of ovarian carcinomas is promising. Similar benefits in the head-and-neck and in the skin while the demonstration of the neovascularisation of atheromatous plaques and of aggressive joint inflammation offer interesting potentials.     

Assessment of irradiated brain metastases by means of arterial spin-labeling and dynamic susceptibility-weighted contrast-enhanced perfusion MRI: initial results

RATIONALE AND OBJECTIVES: To assess if preradiation and early follow-up measurements of relative regional cerebral blood flow (rrCBF) can predict treatment outcome in patients with cerebral metastases and to evaluate rrCBF changes in tumor and normal tissue after stereotactic radiosurgery using arterial spin-labeling (ASL) and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion MRI. METHODS: In 25 patients with a total of 28 brain metastases, DSC MRI and ASL perfusion MRI using the Q2TIPS sequence were performed with a 1.5-T unit. Measurements were performed prior to and at 6 weeks, 12 weeks, and 24 weeks after stereotactic radiosurgery. Follow-up examinations were completely available in 25 patients for Q2TIPS and 17 patients with 18 metastases for DSC MRI. The rrCBF of the metastases and the normal brain tissue was determined by a region-of-interest analysis. rrCBF values were correlated with the treatment outcome that was classified according to tumor volume changes at 6 months. RESULTS: The alteration of the rrCBF at the 6-week follow-up was highly predictive for treatment outcome. A decrease of the rrCBF value predicted tumor response correctly in all metastases for Q2TIPS and in 13 of 16 metastases for DSC MRI. The pretherapeutic rrCBF was not able to predict treatment outcome. The rrCBF values in normal brain tissue affected by radiation doses less than 0.5 Gy remained unchanged after therapy. CONCLUSION: These preliminary results suggest that ASL and DSC MRI techniques determining rrCBF changes in brain metastases after stereotactic radiosurgery allow the prediction of treatment outcome.     

CT and MR imaging of advanced Zollinger-Ellison syndrome

The CT and magnetic resonance (MR) findings in 13 patients with advanced Zollinger-Ellison syndrome are described. In eight patients (62%) one or more primary tumors were found with both methods. All patients with proven liver metastases (n = 7) were identified by MR. Computed tomography was positive in six of these patients. Three patients with lymph node metastases were identified on CT and MR and one patient had bone metastases. Computed tomography and MR were inferior to selective arteriography in the detection of multiple lesions of the pancreas in a patient with multiple endocrine neoplasia-I syndrome. On the T1-weighted MR images, the primary tumors demonstrated no consistency with regard to their signal intensity relative to the adjacent pancreatic parenchyma. All gastrinomas had an increased relative signal intensity on the T2-weighted images with the exception of a calcified tumor. Liver and lymph node metastases had a low signal intensity on the T1-weighted images and an increased signal intensity on the T2-weighted images. The signal intensity of primary tumors and metastases was independent of size. In conclusion, MR was able to detect abnormalities based on its outstanding lesion/normal tissue contrast, whereas CT diagnosis was based mostly on contour distortion. For the current technique, MR is considered at least equal to CT.     

菲立磁增强MRI检测肝脏占位病变与三期动态增强CT扫描的比较研究

目的　比较菲立磁增强MRI和增强CT扫描在肝脏实性占位病变检测中的应用价值。方法　对 18例肝内局灶性占位患者行MR平扫及菲立磁增强扫描。观察肝脏与病灶信号强度变化 ,形态及数目 ,比较增强前后T2 WI病灶及肝脏的信噪比 (SNR)及对比噪声比 (CNR) ,做出MRI定性诊断 ,并与增强CT扫描诊断进行比较。其中肝细胞肝癌 4例 ,复发性肝癌 4例 ,转移瘤 4例 ,肝血管瘤 6例。结果　菲立磁增强明显降低正常肝组织信号强度 ,而恶性肿瘤的信号强度无强化 ,病灶—肝脏信噪比增加可清晰显示病变 ,并发现新病灶。肝血管瘤的血池效应与增强CT扫描比较有鉴别诊断意义。结论　做为增强CT扫描和Gd -DTPAMR增强的补充方法 ,SPIO增强MRI对肝脏占位病变的显示 ,小病灶发现和定性诊断中有重要的临床意义     

实时超声造影在肝脏局灶性病变诊断中的应用

目的:评价实时超声造影技术在肝脏局灶性病变诊断中的作用及意义.方法:采用实时超声造影技术,对我院269例肝脏局灶性病变进行超声造影检查.结果:92.4%恶性病变动脉相呈现回声增强.病灶动脉相呈现高增强或等增强、延迟相消退为低增强或无增强,在良性病变中占13.8%(19/138),恶性病变中为94.7%(124/131);实时超声造影诊断肝脏局限性病灶的敏感度89.6%,特异度97.5%,诊断符合率93.2%.结论:实时超声造影可显示肝局灶性病变的血流灌注特点,对肝局灶性病变的分类诊断有重要的应用价值.     

Arterial perfusion abnormalities of the liver after hepatic arterial infusion chemotherapy and their correlation with changes in the metastases: evaluation with CT and angiography

We studied the progress of hepatic arterial perfusion abnormalities in 50 patients receiving long-term arterial infusion chemotherapy for palliative treatment of liver metastases from colorectal cancers and correlated the findings with changes in the metastases. Intraarterially and IV enhanced CT scans and digital subtraction angiograms of the liver were made in all patients before chemotherapy and at 3-month intervals during chemotherapy for 1 year. Before the chemotherapy, all patients had normal hepatic arterial perfusion. Arterial perfusion abnormalities were detected in 30 patients (60%) after 6 months of chemotherapy and in 41 patients (82%) after chemotherapy for 1 year. After 6 months of chemotherapy, 36% of the regressive and 39% of the progressive metastases were located in areas with arterial perfusion abnormalities. After 1 year of chemotherapy, 54% of the regressive and 60% of the progressive metastases were situated in portions of the liver with perfusion abnormalities. Hepatic arterial perfusion abnormalities were found to be progressive during intraarterial infusion chemotherapy. No relationship between arterial perfusion abnormalities and tumor response to chemotherapy could be detected.     

Hepatic metastases: the value of quantitative assessment of contrast enhancement on computed tomography

Objective: Occult and overt hepatic metastases have been the target of research in an effort to improve detection and characterisation of cancer spread and, consequently, guidance of treatment. This paper aims to illustrate the value of two quantitative techniques for assessing contrast enhancement during CT in the detection of hepatic metastases. It outlines the applications to which they can be put, and the ease of incorporation into current protocols. Methods and material: The first technique, perfusion CT, uses a single location dynamic CT sequence to obtain time–attenuation data whilst a short, high concentration IV bolus of contrast passes through the abdominal vasculature. Quantitative hepatic arterial and portal values are calculated, along with a perfusion image map. The second technique uses densitometric analysis during a modified contrast enhanced dual-phase liver CT examination. Semi-quantitative values are calculated from the images obtained at the 25 and 40 s times. Results: Both perfusion CT and densitometric analysis have been to shown to differentiate between normal and tumour-bearing liver as defined by structural CT. Hepatic metastases are associated with increased arterial perfusion and arterial phase enhancement. Increased arterial phase enhancement on densitometric analysis in the absence of overt lesions heralds the onset of visible metastases in the liver in the ensuing 18 months. Perfusion CT has also demonstrated a correlation between high arterial perfusion around a visible metastasis and increased survival. Conclusion: Both techniques can provide more information than is available from conventional enhanced CT scans alone. An algorithm for the clinical application of perfusion CT is proposed. The ease with which these quantitative techniques can be performed and the extra information they provide could lead to improved staging of cancer and more appropriate patient management.     

Morphologic and functional changes in nontumorous liver tissue after radiofrequency ablation in an in vivo model: comparison of 18F-FDG PET/CT, MRI, ultrasound, and CT.

Rimlike contrast enhancement on morphologic imaging and increased tracer uptake on (18)F-FDG PET in the periphery of the necrosis can hamper differentiation of residual tumor from regenerative tissue after radiofrequency ablation of liver lesions. This study used MRI, CT, ultrasound, and (18)F-FDG PET/CT to assess the typical appearance of lesions in nontumorous animal liver tissue after radiofrequency ablation. METHODS: Lesions were created by radiofrequency ablation of normal liver parenchyma in 21 minipigs. Follow-up was performed by 3 contrast-enhanced morphologic modalities-MRI, CT, and ultrasound-and by (18)F-FDG PET/CT immediately, 3 and 10 d, and 1, 2, 3, and 6 mo after radiofrequency ablation. Images were evaluated qualitatively for areas of increased enhancement and regions of elevated tracer uptake. Furthermore, all images were assessed quantitatively by determination of ratios comparing enhancement/tracer uptake in the periphery of the necrosis with enhancement/tracer uptake in normal liver parenchyma. Imaging findings were compared with histopathology findings. RESULTS: Immediately after radiofrequency ablation, no increase in (18)F-FDG uptake was visible, whereas elevated enhancement was noticed in the periphery of the necrosis on all morphologic imaging procedures. At further follow-up, an area of rimlike increase in (18)F-FDG uptake surrounding the necrosis was detected on PET/CT. The rimlike pattern of increased enhancement in the arterial phase was present for all liver lesions on CT, MRI, and ultrasound, especially between day 3 and month 1 after the radiofrequency ablation. Both elevated glucose metabolism and enhancement persisted for 6 mo postinterventionally. Histologic examination showed a hemorrhagic border converting into a regeneration capsule. CONCLUSION: If performed immediately after radiofrequency ablation, (18)F-FDG PET/CT probably has benefits over those of morphologic imaging procedures when assessing liver tissue for residual tumor. Later follow-up may be hampered by visualization of peripheral hyperperfusion and tissue regeneration. Further studies on a patient population are essential.     

Hepatic MRI with SPIO: detection and characterization of focal liver lesions

A variety of parenterally administered iron oxides have been developed for contrast-enhanced MRI of the liver. Two different classes of iron oxides are currently clinically approved or in phase 3 trials: superparamagnetic iron oxides (SPIO) with a high R2/R1 relaxivity ratio and short blood half-life (AMI-25 and SH U 555 A), and ultrasmall paramagnetic iron oxides (USPIO) with a lower R2/R1 relaxivity ratio and longer blood half-life (AMI-227). All iron oxides significantly increase tumor-to-liver contrast and allow detection of more lesions than unenhanced MRI on T2-weighted images at a field strength of 0.2–1.5 T. Malignant lesions without phagocytic cells exhibit constant signal on T2-weighted accumulation phase images with all three iron oxides. All iron oxides cause a signal decrease of benign lesions with either phagocytic cells or a significant blood pool on T2-weighted accumulation phase images. The signal decrease of benign lesions is proportional to the Kupffer cell activity or tumor vascularity and is useful for lesion characterization. Another enhancement feature for the differentiation of benign from malignant lesions is ring enhancement of malignant lesions (metastases) on T1-weighted enhanced images either during the perfusion phase with SH U 555 A or during the accumulation phase with AMI-227, which is attributed to the blood pool effects of the compounds. Differentiation of lesions and vessels is easier on enhanced images with angiographic effects than on unenhanced images. Iron oxides improve the quality of two-dimensional MR angiography techniques of the portal venous system by decreasing background signal (liver tissue with all iron oxides) and increasing intravascular signal (AMI-227). The use of iron oxides for hepatic MRI provides an alternative to the existing multistep diagnosis with CT, CT portography, MRI and biopsy. Received: 24 September 1997; Revision received: 12 November 1997; Accepted: 14 November 1997     

CT during arterial portography: diagnostic pitfalls.

Computed tomography (CT) during arterial portography (CTAP) is an important technique for evaluating the liver before hepatic tumor resection. With this technique, most tumors are of low attenuation compared with that of enhancing parenchyma. At times, low-attenuation lesions are encountered that represent perfusion abnormalities rather than tumor deposits. These perfusion abnormalities can be categorized as (a) those resulting from improper technique; (b) those extending from hilum to capsule (straight-line sign), with or without an obstructing mass; (c) perihilar and periligamentous abnormalities; (d) subcapsular defects (linear or wedge shaped); and (e) those seen with cirrhosis or regenerating nodules. Adjuvant use of delayed CT, magnetic resonance imaging, and intraoperative ultrasound aids in characterization of these nontumorous defects, thereby improving specificity. The authors conclude that when potential candidates are evaluated for hepatic tumor resection, knowledge of the existence of the various diagnostic pitfalls of CTAP and their imaging characteristics is imperative to avoid inadvertent false results.