Fast spin echo imaging with suspended respiration: gadolinium enhanced MR imaging of liver tumors

Magnetic resonance (MR) imaging of 43 patients with hepatic tumor was performed during suspended respiration using a fast scan spin echo (SE) technique (SE 200/40) with a single excitation. The resulting images were superior in terms of image quality to conventional ones. Due to the lack of soft tissue contrast, 38 patients received Gd-diethylenetriaminepentaacetic acid (DTPA) at 0.05 mmol/kg and serial scanning (CE-MR) was repeated. Twelve of 14 hepatomas showed isointensity or slightly reduced intensity compared with the liver in unenhanced MR. All metastases (nine patients) showed low signal intensity that was statistically significant (p less than 0.001) in differentiating between hepatomas and metastatic liver tumors. With contrast enhanced MR, both hepatomas and metastases showed changes that cannot be further classified until more cases have been examined. In all 12 cavernous hemangioma cases, Gd-DTPA pooling was observed with extremely high contrast, which was a pathognomonic sign. In fact, four cavernous hemangiomas in two patients with a diameter of 1.0 cm were successfully imaged.     

Evaluation of fast MR imaging with suspended respiration in hepatic tumors

The purpose of this study is to evaluate the possibility of qualitative diagnosis in hepatic tumors by fast magnetic resonance (MR) imaging with suspended respiration using partial flip angle and gradient echo technique at 0.5 T. Fast MR imaging does not replace conventional spin-echo procedures, but is complementary to it. For the analysis of contrast as a function of flip angle, 32 hepatocellular carcinomas (HCCs) of nodular type and 11 hemangiomas were examined with flip angles of 20, 40 and 60 degrees on sagittal images. In general, the lesions showed relatively high and low intensities on the images with flip angles of 20 and 60 degrees, respectively. On the images with flip angle of 40 degrees, signal-to-noise (S/N) ratio was higher, but contrast between tumor and liver was lesser than with that of other angles. The change of contrast-to-noise (C/N) ratio between the flip angles of 20 and 60 degrees in hemangiomas was larger than that in HCCs, significantly. It was useful for evaluation of lesions to observe the change of C/N ratio, and it was necessary for detection of lesions to obtain the images with at least three flip angles. For dynamic MR imaging, 18 HCCs including 5 cases after transcatheter chemoembolization (TCE) and 5 hemangiomas were examined with flip angle of 40 degrees. With employment of Gd-DTPA, S/N ratio and contrast were improved in many cases, and hemodynamics of tumors was able to be observed. It was suggested that dynamic MR imaging was useful especially in evaluation of efficacy of TCE using lipiodol.     

Multisection T1-weighted hybrid-rare: A pulse sequence for MR imaging of the entire liver during suspended respiration

It is shown that the maximum average-data-collection-speed (ADCS) of multisection 2D hybrid-RARE sequences is independent of TR and TE_eff, and a monotonically increasing function of echo-train-length (ETL). This result was used in the design of an optimized T₁-weighted hybrid-RARE sequence that produces 20 images of the abdomen in 31 s divided into four breath-hold periods. The resulting ADCS is 58 lines in k-space per second. Twenty-four subjects (2 healthy volunteers and 22 patients) were imaged with a protocol that also included: (a) breath-hold T₁-weighted FLASH which acquires data at 34 lines in k-space per second (49 s scan time), and (b) T₁-weighted conventional spin-echo (9:44 minutes scan time) with respiratory compensation. The experiments show that this T₁-weighted-hybrid-RARE sequence has: (1) a level of T₁ weighting that is comparable with the conventional sequences, (2) very low vulnerability to susceptibility artifacts, (3) high data acquisition efficiency, and (4) higher SNR than T₁-weighted-FLASH. In conclusion, the T₁-weighted-hybrid-RARE sequence described herein is an efficacious and reproducible technique for rapid imaging of the upper abdomen during suspended respiration.     

Receptor imaging: application to MR imaging of liver cancer

A new contrast agent for magnetic resonance (MR) imaging, directed to asialoglycoprotein (ASG) receptors on hepatocytes, was used for detection of liver cancer in rats. Ultrasmall superparamagnetic (mean size, 12 nm) particles of iron oxide (USPIOs) were targeted to ASG receptors by coating particles with arabinogalactan (AG). Liver T2 relaxation times decreased more effectively after a single intravenous administration of AG-USPIO than after an equal dose of a conventional superparamagnetic liver MR contrast agent (AMI-25; mean size, 72 nm). Receptor affinity studies demonstrated that receptor-mediated attachment and subsequent cellular endocytosis do not occur in primary malignant (hepatocellular carcinoma) or metastatic (adenocarcinoma) tumors, because the surface ASG receptors are lost during malignant dedifferentiation. In vitro relaxation and in vivo MR imaging experiments of liver tumors show that targeting USPIO to hepatocytes rather than to the mononuclear phagocytic system allows a considerable dose reduction, increases tumor-liver contrast, and potentially allows distinction of ASG-positive (benign hepatocellular) and ASG-negative (malignant hepatocellular) tumors.     

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.     

Superparamagnetic iron oxide: clinical application as a contrast agent for MR imaging of the liver

Superparamagnetic iron oxide (ferrite) particles were evaluated as a contrast agent for magnetic resonance (MR) imaging. In this pilot study, doses ranging from 10 to 50 mumol/kg were administered intravenously to 15 patients. Ferrite-enhanced images of the liver obtained with standard pulse sequence techniques significantly increased the number of hepatic lesions detected (P less than .01) and reduced the threshold size for detection to 3 mm (P less than .01). The improved clinical performance of ferrite-enhanced images correlated with significant increases in measured contrast-to-noise ratios (P less than .01). Degradation of superparamagnetic activity and/or clearance of ferrite from the liver was demonstrated as early as 12 hours after injection, suggesting that the lack of chronic toxicity observed in animal studies may be reproduced in humans. These initial clinical results appear to confirm extensive preclinical data indicating that ferrite administered at a dose of 20 mumol/kg has the potential to significantly improve the performance of abdominal MR imaging.     

Focal liver lesions: MR imaging with Mn-DPDP--initial clinical results in 40 patients.

Manganese (II) N,N'-dipyridoxylethylenediamine-N,N'-diacetate-5,5'-bis(phosphate) (DPDP) was evaluated as a contrast agent for magnetic resonance (MR) imaging (1.5 T) of focal liver lesions in 40 patients. Doses of 5 and 10 mumol/kg were administered intravenously. Mn-DPDP-enhanced T1-weighted images were compared quantitatively and subjectively with standard T1- and T2-weighted nonenhanced images. Use of Mn-DPDP resulted in a statistically significant increase in signal intensity of liver parenchyma in T1-weighted images at both doses. No enhancement was seen in metastases, cholangiocarcinomas, or lymphomas, while all hepatocellular carcinomas were enhanced. Enhancement was seen in focal nodular hyperplasia and in regenerative nodules. The lesion-to-liver contrast in Mn-DPDP-enhanced gradient-recalled-echo images was superior to that of all precontrast images (P less than .01). The number of nonenhancing malignant liver lesions detected in spin-echo (SE) images was increased (272 in T2-weighted SE images vs 390 in T1-weighted Mn-DPDP-enhanced SE images). Image interpretation (eg, visualization and demarcation of the lesions) was markedly better in Mn-DPDP-enhanced images than in all precontrast images (P less than .001).     

Fat-suppression MR imaging in neuroradiology: techniques and clinical application.

Fat-suppression techniques are useful in MR imaging to eliminate strong signals from fatty tissues that interfere with signals from adjacent areas. Various methods of fat suppression have been devised, but when suppression of fat is used in combination with contrast enhancement employing paramagnetic agents (e.g., gadopentetate dimeglumine), the definition of normal anatomic structures is significantly improved, enhancing lesions become more conspicuous, and lesional margins are better defined in regions of the body with large amounts of fat, whose signal is suppressed. Contrast-enhanced fat-suppressed T1-weighted images provide more information than do conventional MR images. In this review, several types of fat-suppression techniques and their clinical applications in neuroradiology are described. Gadopentetate dimeglumine-enhanced, fat-suppressed T1-weighted images appear to have significant advantages over conventional T1-weighted contrast-enhanced images and should replace them in imaging regions of the body where large amounts of fat are present.     

Contrast agents for MR imaging of the liver: a clinical overview

Different contrast agents have been clinically used in MR imaging of the liver including extracellular gadolinium chelates, contrast agents targeted to the macrophage-monocytic phagocytic system (MMPS), hepatobiliary contrast agents, and blood-pool contrast agents. Extracellular gadolinium chelates are optimally used for characterization of focal hepatic lesions, whereas hepatobiliary and MMPS-targeted contrast agents are optimally used for detection and preoperative evaluation. The present review portrays these contrast agents and discusses their advantages and shortcomings. Received 14 June 1996; Revision received 14 August 1996; Accepted 16 August 1996     

MR全肝灌注成像在原发性肝细胞癌的初步研究

 目的 探讨全肝MR灌注成像(MR perfusion imaging,MRPI)对肝硬化基础上小肝癌的显示和定量评价的价值.方法 肝硬化病史、AFP升高、原发性肝细胞癌(hepatocellular carcinoma, HCC)患者7例,经常规MR扫描图像上共发现7个待观察病灶,使用全肝MRPI观察待测病灶的特征.绘制时间-信号强度曲线.观察肿瘤与左、右半肝的肝实质达峰时间(time to peak, TTP)、最大上升斜率(maximum slope of increase, MSI)、最大下降斜率(maximum slope of decrease,MSD).观察强化曲线的类型.结果 7个病灶均经病理证实为HCC,肿瘤与左、右半肝肝实质的TTP、MSI、MSD分别为(25.536, 40.834, 44.456) S、(19.0318, 11.2481, 15.8437) S-1及(14.9591, 6.9082, 8.9218) S-1,肿瘤与肝实质之间差异有统计学意义(P<0.05).7个病灶时间-信号强度曲线均表现为早期迅速升高,之后明显下降.结论 全肝MRPI有助于肝硬化基础上小肝癌的早期诊断与定量分析.     

Rapid three-dimensional angiography with undersampled MR imaging

Techniques for subtraction angiography with magnetic resonance imaging have been extended from two to three dimensions, and a novel method that reduces the expected data acquisition time by at least an order of magnitude is presented. Electrocardiogram-gated three-dimensional (3D) images are acquired by Fourier transform technique, and flow contrast is obtained by subtracting pairs of images acquired at different points in the cardiac cycle. The vascular tree is shown in 3D perspective by means of a surface detection and a 3D display program. Isotropic 3D angiography requires determining the disposition of the blood vessels in a matrix of cubical voxels. Using orthodox Fourier transform technique, for an image matrix with 256 voxels to the edge, a data acquisition with 256 X 256 = 65 K phase-encodings would be needed. If gated, this would require approximately 1 day. In this study we abbreviate the data acquisition by doing only 1/64 of the usual set of phase-encoding gradient pulses. Spatial resolution is undiminished, but aliasing or "wraparound" results in each of the two phase-encoded coordinates of the 3D image. This aliasing is rectified in a two stage process. First, 64 copies of the undersampled 3D arteriogram are juxtaposed in a two-dimensional grid pattern. This assembles many copies of the complete vascular tree. Because they occupy only a small fraction of ambient volume, these copies are unlikely to overlap or collide with one another. Second, a single copy of the vascular tree is isolated by a surface detection program that takes advantage of the fact that the vascular tree is topologically connected. Studies of the abdominal aorta are presented.     

Brain in eclampsia: MR imaging with clinical correlation

Cranial magnetic resonance (MR) imaging was performed on eight consecutive patients with generalized tonic-clonic seizures caused by eclampsia. Each patient underwent serial neurologic examinations until all symptoms resolved. Six of those eight patients underwent follow-up MR imaging. These patients were compared with those in previous case reports of MR imaging abnormalities of the brain in eclampsia. MR imaging typically demonstrates bilateral hyperintense lesions on T2-weighted images and iso- to hypointense lesions on T1-weighted images. MR imaging abnormalities are most commonly located in the distribution of the posterior cerebral circulation and are associated with visual disturbances. Basal ganglia and deep white matter lesions are less common and are associated with mental status changes. Most lesions seen at MR imaging in patients with eclampsia are reversible.     

CT和MR肝脏灌注成像技术及其临床应用

近年来随着CT、MR功能成像研究的发展,国内外有不少学者尝试使用CT、MR肝脏灌注成像评价肝脏功能及肝脏病变的血液动力学特征。综述了近来国内外CT、MR灌注成像在肝脏评价中的应用现状,重点是图像分析方法及临床应用。     

颅脑磁共振弥散张量成像应用进展

磁共振弥散张量成像技术是利用水分子的弥散运动各向异性进行成像,是目前唯一反映人体活体组织空间组成信息及病理状态下各组织成分之间水分子交换功能状况的检查方法,可以从细胞及分子水平来研究疾病状况。本文回顾DTI的原理和潜在的临床应用,如脑缺血性疾病、脑发育、脑肿瘤、外伤性脑损伤和癫痫、多发性硬化、代谢性疾病等。     

MR imaging of the liver

MR imaging is establishing a role as a primary diagnostic technique, with increasing evidence showing MR imaging to have advantages over CT regarding diagnostic sensitivity and specificity for many pathologies of solid organs, bile and pancreatic ducts, bowel, peritoneum, and retroperitoneum. In addition, there are increasing concerns regarding the risks of radiation and iodinated contrast associated with CT imaging of the abdomen. The incidence of contrast-induced nephropathy associated with iodinated contrast used for CT scanning is difficult to ascertain because reporting is spurious and variable in interpretation.     

Amebic liver abscess: MR imaging

Hepatic magnetic resonance (MR) imaging was performed in 12 patients with 13 amebic liver abscesses. While no specific image or intensity pattern was noted, most lesions were round or oval with smooth, well-defined margins; had decreased signal intensity compared with that of liver parenchyma on T1-weighted images and increased signal intensity on T2-weighted images; and had prominent, often multiple rims of variable signal intensity. Signal homogeneity within the abscess was present more often on T1- than on T2-weighted images. Diaphragmatic disruption was seen in two cases on coronal MR images. An amebic empyema was differentiable from sympathetic pleural effusions by its hyperintensity on both T1- and T2-weighted images. In patients who also underwent computed tomography (CT) or ultrasonography (US), no lesion was missed with any modality, and except for shape, no consistent features were found among images obtained with the different modalities. The data suggest that CT, US, and MR imaging are comparably effective in the detection of amebic abscess.     

T2-weighted MR imaging of the liver: Qualitative and quantitative comparison of SPACE MR imaging with turbo spin-echo MR imaging

Objective

To qualitatively and quantitatively compare T2-weighted MR imaging of the liver using volumetric spin-echo with sampling perfection with application-optimized contrast using different flip angle evolutions (SPACE) with conventional turbo spin-echo (TSE) sequence for fat-suppressed T2-weighted MR imaging of the liver.

Materials and methods

Thirty-three patients with suspected focal liver lesions had SPACE MR imaging and conventional fat-suppressed TSE MR imaging. Images were analyzed quantitatively by measuring the lesion-to-liver contrast-to-noise ratio (CNR), and the signal-to-noise ratio (SNR) of main focal hepatic lesions, hepatic and splenic parenchyma and qualitatively by evaluating the presence of vascular, respiratory motion and cardiac artifacts. Wilcoxon signed rank test was used to search for differences between the two sequences.

Results

SPACE MR imaging showed significantly greater CNR for focal liver lesions (median = 22.82) than TSE MR imaging (median = 14.15) (P < .001). No differences were found for SNR of hepatic parenchyma (P = .097), main focal hepatic lesions (P = .35), and splenic parenchyma (P = .25). SPACE sequence showed less artifacts than TSE sequence (vascular, P < .001; respiratory motion, P < .001; cardiac, P < .001) but needed a longer acquisition time (228.4 vs. 162.1 s; P < .001).

Conclusion

SPACE MR imaging provides a significantly increased CNR for focal liver lesions and less artifacts by comparison with the conventional TSE sequence. These results should stimulate further clinical studies with a surgical standard of reference to compare the two techniques in terms of sensitivity for malignant lesions.     

Phenylketonuria: MR imaging of the brain with clinical correlation

Fifteen patients with biochemically documented phenylketonuria (PKU) were studied with use of magnetic resonance (MR) imaging with spin-echo T2-weighted pulse sequences. The resulting images demonstrated varying degrees of symmetric high signal intensity of the white matter within the posterior cerebral hemispheres. Involvement of the anterior hemispheres was seen only in cases with severe signal intensity changes. There was no involvement of the cerebral cortex, brain stem, or cerebellum. Moreover, no anatomic structural abnormalities were observed. Mild cortical atrophy was observed in eight of the 15 patients. There was no significant correlation between the patients' IQ scores and the level of MR signal intensity changes. Although MR imaging routinely shows relatively distinct abnormalities in patients with PKU, the clinical severity of the disease does not parallel its imaging severity.