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.     

Computed tomographic enhancement of the liver, liver abscesses, spleen, and major vessels with perfluorooctylbromide emulsion. Influence of dosage and injection velocity in an animal model.

RATIONALE AND OBJECTIVES. Computed tomographic (CT) enhancement of the liver, liver abscess, spleen, and major vessels was investigated between 2 and 48 hours after intravenous administration of perfluorooctylbromide (PFOB emulsion) in an animal model of 63 rabbits. METHODS. Twenty-one animals received 3 g/kg PFOB as a fast bolus injection. Using a slow infusion rate, the same number of animals received either the same dose (3 g/kg) or half the dose (1.5 g/kg). RESULTS. Vascular enhancement was best after bolus injection of 3 g/kg emulsion. The density peak occurred after 2 hours. A continuous enhancement of approximately 100 Hounsfield units (HU) was observed up to 24 hours in the animals receiving 3 g/kg, independent of the injection velocity. A density peak of 70 HU was found 2 hours after the infusion of 1.5 g/kg. The density peak of the liver, the spleen, and the abscess wall was observed 48 hours after emulsion administration in all groups receiving 3 g/kg. The peak was approximately 150 HU for the liver, 400 HU for the spleen, and 150 HU for the abscess wall. In animals receiving only 1.5 g/kg perflubron, the peak density of the abscess wall was 132 HU after 12 hours, approximately 80 HU for the liver between 2 and 48 hours, and approximately 280 HU after 48 hours for the spleen. CONCLUSIONS. PFOB emulsion produces the highest vascular enhancement within the first 2 hours after the bolus injection of 3 g/kg. For spleen and abscess wall imaging, even the relatively low dose of 1.5 g/kg produced a satisfactory enhancement level for a significant length of time, whereas liver enhancement was best after administration of the higher dose.     

超顺磁性氧化铁（SPIO）对比剂肝脾MR成像的比较研究

目的 比较两种超顺磁性氧化铁（superparamagnetic iron oxide,SPIO)对比剂,Ferumoxides及SHU－555A在肝脾MR成像中的效应。材料与方法 36例已知为肝转移癌患者于SPIO造影前后进行T2WI快速自旋回波成像（T2WI TSE）及T1WI梯度回波快去速相位成像（T1WI FLASH）。扫描伪为1．0T MR机。18例患者行Ferumoxides增强后90分钟进行MR成像;另18例行SHU－55A快速团柱增强,注药后即刻、30秒及480秒行T1WI FLASH成像,10分钟行T2WI TSE成像。测量肝脾、肝转移癌SPIO增强前后的信号强度（signal intensity,SI),计算两种SPIO对比剂在肝脾、肝转移癌增强前后SI变化的百分比（percentage signal intensity change,PSIC)及病灶肝脏对比噪声比（lesion-to-liver contrast-to-noise ratio,CNR)及其变化（ΔCNR）。结果 在T2WI TSE图像上,两种SPIO对比剂造成的肝实质SI下降无显著性差异（P＞0．05）。Ferumoxides引的脾信号下降显著大于SHU－555A（P＜0．05）。两种SPIO对比剂均导致肝实转移癌SNR显著增高。T1WI FLASH图像上,两种对比剂均可导致延迟像上肝脏SI的轻度下降及肝转移癌CNR下降,两者肝脏SIC之间无显著性差异。T1WI上两种对比剂均可导致脾脏SI显著升高,两者脾脏PSIC之间无显著性差异（P＞0．05）。结论 两种SPIO在肝脏的TI及T2增强效应相似,而脾脏的T2增强效应,Ferumoxides强于SHU－555A。     

Gadolinium-DTPA in the assessment of liver tumours by magnetic resonance imaging

The effect of gadolinium-DTPA (Gd-DTPA, Schering AG) as a magnetic resonance imaging (MRI) contrast agent was studied in 15 patients with liver tumours. A dose of 0.1 mmol/kg was used. An analysis of the time-course of enhancement, a comparison of four different pulse sequences, and a dose-comparison study were carried out with monitoring of haematological and biochemical parameters before and after injection of Gd-DTPA. Maximum enhancement, that is, increase in signal intensity, was noted on IR1400/400/13 between 10 and 20 min after injection while on SE580/40 and SE580/80 maximum enhancement was noted 30 min after injection. In some cases enhancement was noted up to 120 minutes after injection. SR1000/13f sequences showed very little enhancement. On comparison with contrast-enhanced X-ray computed tomography (CT), enhancement was greater on MRI in seven cases, equal in six and less in two, as assessed subjectively. Additional lesions were shown in one case using Gd-DTPA compared to precontrast enhanced MRI scans. However, no additional lesions were seen on contrast-enhanced MRI scans compared to contrast-enhanced CT scans. Gd-DTPA is capable of enhancing liver tumours on MRI and may have a place in the assessment of the operability of such lesions.     

Computed tomographic enhancement of liver and spleen in the dog with iodipamide ethyl ester particulate suspensions

Particulate suspensions have been developed for use as contrast agents to aid in the detection of hepatic lesions by CT. In several previous rodent studies, the toxicity and tissue concentrations of iodipamide ethyl ester (IDE) particles have been evaluated. The purpose of this study was to determine the pharmacokinetics of IDE in three dogs by evaluation of CT enhancement. Serum chemistry and hematologic parameters after intravenous administration were also followed. A dose of 75 mgI/kg IDE caused an increase of 40-60 Hounsfield units (HU) in liver attenuation, which persisted from 5 minutes to ten hours postinfusion. No enhancement of tissues other than liver and spleen was observed. IDE was completely eliminated from the liver within seven days. A mild transient elevation of liver enzymes may be attributable to the use of barbiturates rather than IDE. A transient depression of the white blood count was the only biochemical or hematologic change that was clearly in response to the infusion of IDE particulates.     

Bolus versus continuous infusion of microbubble contrast agent for liver US: initial experience

Institutional review board approval and informed consent were obtained. To prospectively assess if continuous infusion of galactose-palmitic acid can prolong the duration of hepatic enhancement at ultrasonography over bolus injection, 11 patients received two injections--one bolus injection (2 mL/sec) and one continuous infusion (1.5 mL/min)--with the same dose of galactose-palmitic acid (4 g, 300 mg/dL). Two unenhanced baseline sweep scans (mechanical index of 0.7 and 1.3) of the relevant liver lobe were acquired followed by contrast-enhanced sweeps after bolus injection and continuous infusion. Each sweep was saved as cine loops and analyzed with a personal computer. Duration of enhancement more than 3 dB was prolonged by continuous infusion from 4.3 minutes +/- 2.4 (+/-standard deviation) at bolus injection to 10.1 minutes +/- 3.0 (P < .005). Maximal parenchymal enhancement was 11.0 dB +/- 3.2 (bolus injection) and 9.2 dB +/- 3.8 (infusion, P < .05). Peak liver-to-lesion contrast was 14.2 dB +/- 6.3 (bolus injection) and 13.2 dB +/- 7.1 (infusion, not significant). Continuous infusion of galactose-palmitic acid markedly prolongs but slightly diminishes hepatic enhancement; liver-to-lesion contrast remains unchanged.     

Phase II double-blind, dose-ranging clinical evaluation of gadobenate dimeglumine in focal liver lesions: with analysis of liver and kidney signal change on early and delayed imaging

To evaluate the effect of contrast dose using gadobenate dimeglumine, 30 patients with focal liver lesions documented by computed tomography or ultrasound were studied by magnetic resonance imaging at 1.5 T. Patients received one of four doses of gadobenate dimeglumine (0.025, 0.05, 0.1, or 0.2 mmol/kg) or saline. The order of dosage was randomized, with both the physician and patient blinded to the administered dose. Scans were obtained before, immediately following injection, and after 80 minutes of delay. Enhancement effects were quantified by region of interest measurements. Films were also reviewed in a randomized prospective fashion by an abdominal radiologist blinded to contrast dose and diagnosis. Higher doses led to a statistically significant improvement in enhancement of normal liver, both on immediate (P = 0.01 for the comparison of 0.1 and 0.2 mmol/kg immediately post-contrast) and delayed scans (P = 0.003 for the same comparison). Liver-lesion contrast-to-noise ratio also increased with dose, although results for most comparisons by dose were not statistically significant. Scans following gadobenate dimeglumine injection were judged to provide additional diagnostic confidence sufficient to affect patient management in 10 of 24 cases. In seven cases this information was provided by dynamic scans, in one case by delayed scans, and in two cases by both dynamic and delayed scans. In 2 of the 10 cases the dose was 0.025 mmol/kg, in 2 cases 0.05 mmol/kg, in 3 cases 0.1 mmol/kg, and in 3 cases 0.2 mmol/kg. Gadobenate dimeglumine is effective for imaging of focal liver lesions at a range of doses, with trends toward improved diagnostic information at higher doses.     

Improved tissue characterization of focal liver lesions with ferumoxide-enhanced T1 and T2-weighted MR imaging

The purpose of our study was to evaluate the potential value of ferumoxide-enhanced T1-weighted magnetic resonance (MR) imaging for tissue characterization of focal liver lesions when combined with T2-weighted sequences. Images were acquired within 30 minutes after the end of ferumoxide administration, when ferrite particles were not totally cleared from the intravascular compartment. Thirty-eight patients with 47 focal liver lesions underwent T1-weighted gradient-echo (TR/TE 150/4.1 msec) and T2-weighted fast spin-echo (3180-8638/90 msec) MR imaging at 1.5 T before and after intravenous administration of ferumoxides (10 micromol/kg body weight). A qualitative and quantitative analysis was performed. During the early phase after infusion of ferumoxide, blood vessels showed hypersignal intensity on T1-weighted fast low-angle shot (FLASH) images, while liver signal decreased. Hemangiomas showed both homogeneous and inhomogeneous enhancement patterns, and liver metastasis most typically showed ring enhancement. Hypervascular tumors (hepatocellular carcinomas and focal nodular hyperplasias) showed a slight degree of homogeneous enhancement. Quantitatively, the degree of enhancement and lesion-to-liver contrast on ferumoxide-enhanced images were significantly different among these tumors. Our results demonstrate that distinct enhancement patterns obtained on ferumoxide-enhanced T1-weighted MR imaging improve tissue characterization of focal liver lesions when combined with T2-weighted images.     

Differential patterns of contrast enhancement in different focal liver lesions after injection of the microbubble US contrast agent SonoVue

PURPOSE: To identify differential contrast enhancement patterns in different focal hepatic lesions after injection of the microbubble contrast agent SonoVue using high or low acoustic power imaging. MATERIAL AND METHODS: Forty-seven focal hepatic lesions (1-8 cm) were detected in 45 patients at unenhanced gray-scale ultrasound (US) and evaluated by color Doppler (CD) US with spectral analysis of tumoral vessels. Lesions were subsequently evaluated by US contrast specific modes after IV bolus administration of 2,4-4,8 ml of SonoVue, by intermittent high acoustic power (18 patients) or by continous low acoustic power imaging (27 patients), during arterial, portal and late phase. Subjective evaluation of lesions appearance before and after SonoVue injection was performed. For final diagnosis multiphasic helical CT (21 patients) and/or fine needle US guided biopsy (24 patients) were considered as the reference procedures. RESULTS: Final diagnoses comprised 22 hepatocellular carcinomas (HCCs; 1,5-6 cm), 2 macroregenerative nodules (RNNs; 1-2 cm), 10 metastasis (2-3,5 cm), 10 hemangiomas (2-6 cm) and 3 focal nodular hyperplasias (FNHs; 1-3 cm). On CD evaluation HCCs revealed peripheral basket shaped (12/22) or intranodular (10/22) arterial pattern while, after SonoVue injection HCCs revealed diffuse contrast enhancement during arterial phase with contrast washout during portal and late phase. Metastases did not reveal flow signals on CD or contrast enhancement after SonoVue injection, except for 2 metastases which revealed peripheral and central vessels on CD and a diffuse contrast enhancement during arterial phase, appearing hypoechoic to the adjacent liver during portal and late phase. RNNs revealed dotted contrast-enhancement during portal and late phase with isoechoic appearance to the adjacent liver. Hemangiomas revealed some peripheral venous flows on CD and a peripheral nodular contrast enhancement during arterial phase with a centripetal fill-in during portal and late phase. FNHs revealed low resistance peripheral or central arterial vessels and a diffuse contrast enhancement during arterial phase, preceded or not by central spoke wheel shaped contrast enhancement, and a persistent iso-hyperechogenicity during portal and late phase. CONCLUSIONS: SonoVue injection has showed to identify differential contrast enhancement patterns in different focal hepatic lesions.     

Effective contrast use in CT angiography and dual-phase hepatic CT performed with a subsecond scanner

OBJECTIVE: To deduce an optimal injection protocol for CT angiography and fast dual-phase hepatic CT. METHODS: Fifty-two patients underwent fast dual-phase hepatic CT using one of three different injection protocols: A (0.9 g/sec iodine injection rate, 36 g dose); B (1.35 g/sec, 30 g); C (1.6 g/sec, 40 g). Aortic attenuation time curves as well as aorta-to-liver contrast and hepatic enhancement time curves obtained by region of interest measurements along the helical axis were analyzed. RESULTS: Protocol C revealed a significantly higher peak in aortic attenuation and hepatic enhancement than the other protocols. Approximately 50 seconds after the bolus injection, hepatic enhancement declined to a plateau similar to that seen with the other protocols. In terms of the areas under the curves of the aorta-to-liver contrast and hepatic enhancement dynamics, protocol C was significantly superior to the other protocols. CONCLUSIONS: A high iodine injection rate realized by a high iodine concentration in conjunction with fast dual-phase scanning (total scan time < 50 seconds) promises to enhance CT angiography and contrast of liver lesions.     

Radio-frequency ablation of hepatic metastases: postprocedural assessment with a US microbubble contrast agent--early experience.

PURPOSE: To evaluate contrast agent-enhanced ultrasonography (US) in the detection of untreated tumor after radio-frequency (RF) ablation of hepatic metastases. MATERIALS AND METHODS: Twenty patients with solitary colorectal liver metastases underwent percutaneous RF tumor ablation. Pre- and postablation imaging was performed with nonenhanced and enhanced color and power Doppler US and contrast-enhanced helical computed tomography (CT). Initial follow-up CT and US were performed 24 hours after ablation. The findings at US and CT were compared. RESULTS: Nonenhanced US demonstrated intratumoral signal in 15 of 20 metastases before ablation. This signal increased after contrast agent administration. Contrast-enhanced US performed 24 hours after ablation demonstrated residual foci of enhancement in three tumors, whereas no US signals were seen in any tumor on nonenhanced scans. CT demonstrated small (< 3-mm) persistent foci of residual enhancement in these three tumors and in three additional lesions that were not seen at US (US sensitivity, 50%; specificity, 100%; diagnostic agreement with CT, 85%). All six patients with evidence of residual tumor underwent repeat RF ablation. CONCLUSION: Contrast-enhanced US may depict residual tumor after RF application and thereby enable additional directed therapy. The potential reduction in treatment sessions and/or ancillary imaging procedures might increase the ease and practicality of percutaneous ablation of focal hepatic metastases.     

Gadobenate dimeglumine-enhanced liver MR imaging: value of dynamic and delayed imaging for the characterization and detection of focal liver lesions

The aim of this study was to determine the value of delayed-phase imaging (DPI) of gadobenate dimeglumine (Gd-BOPTA)-enhanced MR imaging for the evaluation of focal hepatic tumors compared with precontrast imaging and early dynamic phase imaging. The MR images were obtained in 48 patients with 98 focal hepatic tumors. Three-dimensional gradient-echo (GRE) imaging obtained before and 30, 60, and 1 h after administration of 0.1 mmol/kg of gadobenate dimeglumine. Each image set was analyzed qualitatively (lesion detection, conspicuity, delineation, and enhancement pattern on DPI) and quantitatively [signal-to-noise ratio (SNR), tumor–liver contrast-to-noise ratio (CNR)]. Improved lesion-to-liver contrast during the dynamic phase imaging was observed compared with precontrast images. The DPI showed a homogeneous enhancement of liver parenchyma and distinctive enhancement features of focal liver lesions: metastases (85%) showed a target shaped enhancement, and hepatocellular carcinomas (HCCs) showed an inhomogeneous (58%) or homogeneous enhancement (21%). The DPI showed better performance for the detection of metastases than other images by increasing lesion delineation (p<0.05). The absolute CNR of metastasis measured from periphery of the tumors on DPI was greater than precontrast and arterial phase imaging (p<0.05). The Gd-BOPTA during both dynamic and delayed phases provides valuable information for the characterization of focal liver lesions, and furthermore, Gd-BOPTA-enhanced DPI contributed to the improved detection of liver metastasis compared to precontrast and early dynamic imaging.     

Hepatic x-ray computed tomography. Value of delayed (6 hours) scanning in patients with normal biliary function

Delayed hepatic CT (DH-CT) was studied in 250 patients without any major bile duct pathology. One hundred thirty-five of these patients had liver metastases. All patients were administrated 76 grams of iodine. Tolerance of the examination was good. Six hours after injection, average contrast enhancement in the normal liver was 24 HU (greater than 1.3 g/kg iodine), 22 HU (1 to 1.3 g/kg) and 14 HU (1 g/kg). Comparison of scans taken before, immediately after, and 6 hours post-injection revealed the frequent superiority of postinjection scans for diagnosis of liver metastases. Focal steatosis is the only benign pathology to benefit from DH-CT, because of the parallelism in the difference in density between the normal and steatotic tissue regardless of the time of scanning. Aside from isolated tumors requiring exploration by conventional CT (pre- and post-contrast studies), the workup of liver metastases can be optimized by postcontrast and DH-CT scans.     

Pulse inversion ultrasonography with ultrasonography contrast media (levovist) in the evaluation of hepatic metastasis

PURPOSE: To evaluate if Pulse Inversion Harmonic Imaging with contrast agent injection (Levovist) is able to determine an increase of echogenicity in normal hepatic parenchyma, and to compare its capability to detect metastatic focal lesions with that of standard US and spiral CT. To define and standardize the technical and methodological aspects of this new technique. MATERIAL AND METHODS: A selected group of 72 patients (42 males and 30 females) with clinical and instrumental suspect of hepatic metastatic lesions was included in the prospective study. Each patient was examined by conventional ultrasound (US), Pulse Inversion Harmonic Imaging (PI) and spiral-CT (spCT). US examination was performed using an HDI 5000 (ATL, Bothell, USA) equipped with a broadband probe (5.0-2.0 MHz). 2.5 g Levovist (Schering AG-Berlin) was administered intravenously, at concentration of 300 mg/ml and a flow rate of 7 ml/min. Video clips obtained with the acquired images before and after contrast medium administration were transferred to a magnet optic disk unit. Examinations were evaluated by an experienced radiologist blindly on a workstation that allowed a qualitative-quantitative analysis. SpCT images were evaluated separately by another experienced radiologist. US images were evaluated qualitatively (number of lesions, site of lesion, diameter of the smallest lesion detectable) and quantitatively (increase in parenchymal echogenicity 20", 40", 60" and 5' after the injection of contrast agent). RESULTS: In all cases examined, the echogenicity of normal hepatic parenchyma increased after contrast agent administration, reaching a peak of about 250% (1DS) at 60 s and a decreasing gradually in 5 minutes. Conventional US detected 195 focal lesions, CT 231, and US with pulse inversion technique and contrast agent (US-PI) 287. Mean differences among the number of lesions detected by the different techniques per each patient were also calculated. Wilcoxon Signed Rank Test showed a statistically significant difference between US-PI and US (p < .0001), CT and US (p = .0052) and US-PI and CT (p = .0121). US-PI detected the smallest lesions, which went undetected by the CT and conventional US examinations. DISCUSSION AND CONCLUSIONS: In 10 cases (14.3%) contrast enhanced US-PI demonstrated the presence of a number of lesions greater than 5 (diffuse metastatization and inoperability) in comparison to that detected by spCT). The greater echogenicity of normal hepatic parenchyma using pulse inversion technique after Levovist infusion allowed to better demonstrate hepatic metastases. This technique showed a higher identification rate of small lesions in comparison to basal examination and to spiral CT. Contrast enhanced US-PI demonstrated a remarkable increase in echogenicity of hepatic parenchyma in portal phase. The technique significantly improves the detection of focal lesions allowing visualization of smaller lesions compared to CT and US. These results indicate that the technique could be used in the staging of liver metastasis. However, large multicentric trials are required to validate US-PI and better define its role in the work-up of patients with neoplastic disorder.     

High-dose gadoteridol in MR imaging of intracranial neoplasms.

Twelve patients with a high suspicion of brain metastases by previous clinical or radiologic examinations were studied in a phase III investigation with magnetic resonance (MR) imaging at 1.5 T after a bolus intravenous injection of 0.1 mmol/kg gadoteridol followed at 30 minutes by a second bolus injection of 0.2 mmol/kg gadoteridol. All lesions were best demonstrated (showed greatest enhancement) at the 0.3-mmol/kg (cumulative) dose, with image analysis confirming signal intensity enhancement in the majority of cases after the second gadoteridol injection. More lesions were detected with the 0.3-mmol/kg dose than with the 0.1-mmol/kg dose, and more lesions were detected with the 0.1-mmol/kg dose than on precontrast images. In this limited clinical trial, high-dose gadoteridol injection (0.3-mmol/kg cumulative dose) provided improved lesion detection on MR images specifically in intracranial metastatic disease.     

The real capabilities of contrast-enhanced ultrasound in the characterization of solid focal liver lesions

Contrast-enhanced US (CEUS) using intravenous agents is a rapidly evolving field even though the main clinically recognized application is the characterization of focal liver lesions. Several reports have described the improvement provided by CEUS in the characterization of focal liver lesions in comparison to unenhanced US. CEUS with low transmit power insonation allows the real-time assessment of focal liver lesion contrast enhancement and vascularity during the different dynamic phases after injection of an intravenous contrast agent. CEUS allows the accurate characterization of focal liver lesions as benign or malignant based on the lesion contrast enhancement pattern during the arterial phase and lesion vascularity during portal--late phase in comparison to the adjacent liver parenchyma. During the portal--late phase, benign lesions present prevalently a sustained contrast enhancement with hyper or isovascular appearance to the adjacent liver while malignant lesions present prevalently microbubble washout with hypovascular appearance. On the other hand, the histology of focal liver lesions can only be confidently predicted in selected cases by CEUS, as in liver haemangiomas presenting typical nodular peripheral enhancement with subsequent centripetal fill-in and focal nodular hyperplasia with central spoke wheel-shaped contrast enhancement.     

Ultrasonographic detection of focal liver lesions: increased sensitivity and specificity with microbubble contrast agents

Ultrasonography (US) is the first choice for screening patients with suspected liver lesions. However, due to a lack of contrast agents, US used to be less sensitive and specific compared with computed tomography (CT) and magnet resonance imaging (MRI). The advent of microbubble contrast agents increased both sensitivity and specificity dramatically. Rapid developments of the contrast agents as well as of special imaging techniques were made in recent years. Today numerous different US imaging methods exist which based either on Doppler or on harmonic imaging. They are using the particular behaviour of microbubbles in a sound field which varies depending on the energy of insonation (low/high mechanical index, MI) as well as on the properties of the agent themselves. Apart from just blood pool enhancement some agents have a hepatosplenic specific late phase. US imaging during this late phase using relatively high MI in phase inversion mode (harmonic imaging) or stimulated acoustic emission (SAE; Doppler method) markedly improves the detection of focal liver lesions and is also very helpful for lesion characterisation. With regards to detection, contrast enhanced US performs similarly to CT as shown by recent studies. Early results of studies using low MI imaging and the newer perfluor agents are also showing promising results for lesion detection. Low MI imaging with these agents has the advantage of real time imaging and is particularly helpful for characterisation of focal lesions based on their dynamic contrast behaviour. Apart from the techniques which based on the morphology of liver lesions there were some attempts for the detection of occult metastases or micrometastases by means of liver blood flow changes. Also in this field the use of US contrast agents appears to have advantages over formerly used non contrast-enhanced methods although no conclusive results are available yet.     

Gadolinium-ethoxybenzyl-DTPA, a new liver-specific magnetic resonance contrast agent. Kinetic and enhancement patterns in normal and cholestatic rats.

OBJECTIVES. Gadolinium-ethoxybenzyl-DTPA (Gd-EOB-DTPA) is a new hepatobiliary magnetic resonance imaging (MRI) contrast agent with a dual elimination: 70% via the liver and bile and 30% via the kidney in normal rats. The abdominal enhancement patterns of this new compound and the uptake mechanism by the liver were studied in rats using tissue relaxometry and MRI. METHODS. Twelve normal rats, 33 rats treated with agents designed to inhibit biliary excretion of the agent, and 6 rats with surgically ligated common bile ducts received Gd-EOB-DTPA intravenously. Distribution and excretion were measured by MR relaxometry. MR signal intensity was measured over time for liver, kidney, and bowel. RESULTS. In normal animals, 0.1 mmol/kg Gd-EOB-DTPA induced a significantly greater (200%) and more prolonged liver signal enhancement (100% at 30 minutes) than Gd-DTPA at the same dose. Either hyperbilirubinemia, induced by common bile duct ligation, or bromosulfophtalein (BSP) infusion inhibited liver uptake of Gd-EOB-DTPA, resulting in a preferential elimination via the kidney. Taurocholate (TC), an inhibitor of the bile acid transporter, was unable to block the liver uptake of Gd-EOB-DTPA. Blood half-lives of Gd-EOB-DTPA in rats were 2.4 minutes for the first component and 8.2 minutes for the second. CONCLUSIONS. Data indicate that transport of Gd-EOB-DTPA through the liver into bile is driven by the organic anion transporter. The relation between enhancement of liver and kidney may be diagnostically useful to indirectly evaluate liver excretory function. Yet, persistent enhancement of liver, even in the presence of severe hyperbilirubinemia, should be sufficient to identify focal mass lesions.     

国产Gd-DTPA大剂量增强MRI探查脑转移瘤的临床研究

目的探讨国产Gd-DTPA三倍量（0.3mmol/kg）增强MRI检查脑转移瘤时病灶体积与病灶检出的关系。方法用国产Gd-DTPA大剂量增强MRI检查70例脑转移瘤患者。先行平扫,然后静脉注射常规量(0.1mmol/kg)国产Gd-DTPA。注射后即刻行T1WI扫描、20min后行延迟扫描。距第一次注射30min后,再注射0.2mmol/kg的Gd-DTPA,从而达到累积剂量0.3mmol/kg。第二次注射后即刻及20min后分别行T1WI扫描。对MR扫描所见进行定性、定量分析。结果三倍量增强比常规量增强扫描发现了更多的转移病灶（86→363,P＜0.01）。对于直径大于10mm的转移瘤病灶,三倍量增强的检出率和其它扫描序列之间没有显著性差异。而对于直径小于10mm的转移瘤病灶,三倍量增强的检出率和其它扫描序列之间有显著性差异（P＜0.05）。尤其对于直径小于5mm的病灶,三倍量增强扫描可以检出89.8%～97.8%的病灶,而常规量增强扫描仅能检出0.4%～0.9%的病灶（P＜0.01）。结论国产Gd-DTPA三倍量(0.3mmol/kg)增强可提高脑转移瘤病灶的检出率,尤其对于直径小于5mm的病灶效果更好。     

Dynamic MR imaging of the liver with Gd-DTPA: initial clinical results

Gd-DTPA was evaluated as a hepatic contrast agent for MR imaging. Twenty-six consecutive patients referred for suspected masses in the liver were studied at 1.5 T. Fourteen patients had hepatic metastases and one patient each had cholangiocarcinoma and multicentric hepatocellular carcinoma. Four patients had cavernous hemangiomas and the remainder had other benign lesions. Diagnoses were proved by biopsy, sonography, or radionuclide scintigraphy in 23 cases and by autopsy in one case. Precontrast scans were obtained by using standard pulse sequences. In addition, breath-hold scans were obtained before and after bolus administration of 0.1 mmol/kg Gd-DTPA by using a multislice T1-weighted gradient-echo pulse sequence with an ultrashort echo time. Mean lesion-liver signal difference/noise increased by 50% (p less than .01) in the immediate postcontrast phase. In two of 26 cases, multiple additional lesions as small as 3 mm were detected after contrast administration that were not seen before contrast administration. In no case was lesion-liver contrast worsened on scans obtained immediately after administration of contrast material. However, on delayed scans, detection of lesions worsened in some cases because of equilibration of contrast material between liver and lesion. These initial clinical results suggest that enhancement with Gd-DTPA is a practical method for improving lesion-liver contrast and has the potential to improve the accuracy of MR imaging in the liver. However, optimized fast imaging techniques are required for best results.