Magnetic resonance imaging of hepatic focal lesions: dynamic contrastographic evaluation with gadolinium versus reticulo-endothelial hepato-specific contrast media

PURPOSE: To compare the potentials of AMI-25 (Endoren) to those of Gadolinium with the dynamic contrast-enhanced technique in the differential diagnosis of focal liver lesions. MATERIAL AND METHODS: Forty patients with at least one focal liver lesion diagnosed at US underwent MRI. We used a 1.5 T unit and employed single-shot half-Fourier T2-weighted FSE and spoiled gradient-echo T1-weighted sequences before and after Gadolinium injection. Multiple acquisitions were obtained during the arterial, portal and delayed phases. Twenty-four to 48 hours later T2*-weighted GRE and SPGR/90 degrees sequences were obtained after AMI-25 administration. In the characterization of solid lesions the gold standard was biopsy performed with a shearing needle; for the diagnosis of angiomas and of 11 metastatic lesions we considered follow-up and clinical data as important diagnostic elements. RESULTS: We found 12 hepatocarcinomas, 14 metastases, 4 cases of focal nodular hyperplasia (FNH), 4 adenomas and 6 angiomas. The diagnosis was correct and confirmed by the conventional examination in all cases but 2 adenomatous lesions and 2 angiomas. Precontrast studies showed slight hyperintensity in 2 of 4 cases of FNH, while the other 2 lesions appeared isointense and were therefore detected only on postcontrast images, where there was contrast agent uptake during the arterial phase and rapid washout. We found only one central scar hyperintense on T2- and hypointense on T1-weighted images. After AMI-25 administration all lesions appeared isointense to surrounding parenchyma on T2* GRE sequences. Adenomas were isointense in the precontrast phase and postcontrast 3 of them showed strong Gadolinium uptake and rapid washout. After AMI-25 two of the 4 lesions were hyperintense while the other two were isointense to the parenchyma. Four of 6 angiomas exhibited a typical pattern characterized by signal hyperintensity on T2-weighted sequences and on AMI-25-enhanced T1- and T2-weighted sequences. Two angiomas were supposed to be of malignant nature but histology showed the presence of a strong fibrotic component. Hepatocarcinomas could be detected on precontrast images. After Gadolinium administration 10 lesions appeared hyperintense in the arterial phase and 2 were hypointense. After AMI-25 all lesions exhibited homogeneous signal hyperintensity and appeared slightly bigger than on Gadolinium-enhanced images. The metastases were only partly demonstrated by MRI. Postgadolinium studies showed 13 lesions with hyperintense signal in the portal phase. AMI-25 administration detected 14 lesions that appeared slightly bigger than on Gadolinium-enhanced images. CONCLUSIONS: AMI-25 can help also in characterizing primary lesions with an atypical signal pattern after contrast agent administration thanks to its intrinsic capability of accumulating in benign lesions. However it remains difficult to characterize well differentiated hepatocarcinomas and adenomas. Finally, AMI-25 improves MR capabilities in detecting secondary lesions and possible satellite nodules.     

Monitoring radiation-induced changes in bone marrow histopathology with ultra-small superparamagnetic iron oxide (USPIO)-enhanced MRI.

The purpose of this study was to monitor radiation-induced alterations of the blood-bone marrow barrier (BMB) and the reticuloendothelial system (RES) with AMI-227-enhanced magnetic resonance imaging (MRI). Twenty New Zealand white rabbits (n = 10 following total body irradiation and n = 10 controls) underwent AMI-227-enhanced MRI. Pulse sequences included dynamic fast low-angle shot (FLASH; TR/TE 50/4 msec, flip angle 60 degrees) MRI and static T1- and T2-weighted spin-echo (SE) and turbo-SE sequences of the lumbar spine and sacrum. Bone marrow enhancement was quantified as delta signal intensity (SI) (%) =|[(SIpost - SIpre)/SIpre] x 100%| and compared with histopathology, including iron stains and electron microscopy. Dynamic bone marrow deltaSI (%) data steadily increased up to 10-15 minutes after AMI-227 administration, while blood deltaSI (%) data stayed nearly constant, histologically corresponding to iron oxide leakage into the bone marrow interstitium. This bone marrow contrast enhancement increased significantly following irradiation, corresponding to alterations of the endothelial lining of the bone marrow sinusoids. Late postcontrast images exhibited a significant positive T1 enhancement and negative T2 enhancement of the normal bone marrow, which further increased with irradiation due to increased RES activity. Irradiation-induced changes in bone marrow physiology could be reliably assessed with AMI-227-enhanced MRI.     

Clinical application of superparamagnetic iron oxide to MR imaging of tissue perfusion in vascular liver tumors

Previous studies of AMI-25, a particulate iron oxide magnetic resonance contrast agent, imaged liver tumors 1 or more hours after injection, in the retention phase after complete clearance of AMI-25 from the circulation. In the present study, imaging was performed in the distribution phase, during the first 12 minutes after injection while contrast agent remain in circulation, and these images were compared with those obtained in the retention phase. Nineteen patients with cancer were studied, including 15 imaged during the distribution phase. T2-weighted distribution phase images demonstrated 90% of the lesions detected by means of T2-weighted retention phase images, showed a 3.5-fold increase in contrast-to-noise ratio over images obtained before administration of AMI-25, and increased diagnostic confidence by reducing signal from small intrahepatic blood vessels. Distribution phase images showed little contrast agent uptake by cancer tissue. Both distribution and retention phase images demonstrated greater contrast agent uptake by hemangiomas than by malignant neoplasms (P less than .01). The use of both distribution phase and retention phase AMI-25-enhanced images offers improved diagnostic accuracy in the detection and characterization of focal liver lesions.     

Enhancement of phase-contrast MR angiography with superparamagnetic iron oxide

The effect of superparamagnetic iron oxide particles (AMI-227) was assessed in three-dimensional (3D) phase-contrast (PC) MR angiography (MRA), with various scanning parameters for rats at 1.5 T. The blood T1 and T2 before and after 20 μmol Fe/kg of AMI-227 injection were measured sequentially at .47 T. The visualization of abdominal aorta, renal artery, inferior vena cava, and portal vein was respectively evaluated before and after AMI-227 injection qualitatively by the four confidence levels and quantitatively by analysis of signal-to-noise ratio (SNR) of vessels. The blood T1 and T2 were sufficiently shortened for at least 1 hour after AMI-227 injection. The visualization of each vessel was improved by AMI-227 at various velocity encoding (VENC) value, suggesting the extended application of PC-MRA in various conditions. The optimal flip angle was increased from 20° to 30° in higher VENC after AMI-227 injection, resulting in higher signal from blood flow. Quantitative analyses showed that the optimal flip angle to achieve the maximum SNR seemed to be 20° in unenhanced images, but the optimal flip angle of the high speed flow was increased by contrast enhancement. The postcontrast PC-MRA provides the increased sensitivity of slow flow components, even with a high VENC gradient. AMI-227 can significantly improve SNR to blood vessels during 3D-PC-MRA with various scanning parameters.     

Detection of focal hepatic lesions: comparison of unenhanced and SHU 555 A-enhanced MR imaging versus biphasic helical CTAP

The purpose of this study was to compare the diagnostic sensitivity of unenhanced magnetic resonance (MR) imaging, and MR imaging with a new superparamagnetic iron oxide (SPIO)-enhanced contrast agent (SHU 555 A) with biphasic helical computed tomography during arterial portography (CTAP) in patients with focal liver lesions. Eighteen patients with a total of 91 (78 malignant, 13 benign) proven liver lesions underwent unenhanced short tau inversion recovery (STIR), T2-weighted (T2-w) TSE, and SHU 555 A-enhanced T2-w turbo spin-echo (TSE) MR imaging and biphasic helical CTAP. The standard of reference was histopathologic analysis of resected specimens in 59 lesions, intraoperative ultrasound with biopsy in 20 lesions, and CT-guided biopsy and follow-up in 12 lesions. Diagnostic performance of the imaging modalities was compared quantitatively and qualitatively by assessing lesion involvement in liver segments. There were 68 lesions detected on unenhanced T2-w TSE, which resulted in a sensitivity of 75%. With the STIR sequence, 76 lesions were detected, for a sensitivity of 84%, and with SHU 555 A-enhanced MRI, 84 lesions were detected, for a sensitivity of 92%. CTAP detected 88 lesions, for a sensitivity of 97%. The accuracy for unenhanced T2-w TSE was 98%, for STIR 99%, for enhanced-MRI 100%, and for CTAP 95%. The specificity was 100% for SHU 555 A-enhanced MRI and 95% for CTAP. SHU 555 A-enhanced MRI was superior to nonenhanced MRI (P < 0.05) and equivalent to CTAP in terms of sensitivity. Due to the absence of false-positive results on SHU 555 A-enhanced MRI, the specificity and accuracy of enhanced MRI were higher than those of CTAP, but the difference was not statistically significant (P = 0.134).     

Superparamagnetic iron oxide contrast agents: physicochemical characteristics and applications in MR imaging

Superparamagnetic iron oxide MR imaging contrast agents have been the subjects of extensive research over the past decade. The iron oxide particle size of these contrast agents varies widely, and influences their physicochemical and pharmacokinetic properties, and thus clinical application. Superparamagnetic agents enhance both T1 and T2/T2* relaxation. In most situations it is their significant capacity to reduce the T2/T2* relaxation time to be utilized. The T1 relaxivity can be improved (and the T2/T2* effect can be reduced) using small particles and T1-weighted imaging sequences. Large iron oxide particles are used for bowel contrast [AMI-121 (i.e. Lumirem and Gastromark) and OMP (i.e. Abdoscan), mean diameter no less than 300 nm] and liver/spleen imaging [AMI-25 (i.e. Endorem and Feridex IV, diameter 80-150 nm); SHU 555A (i.e. Resovist, mean diameter 60 nm)]. Smaller iron oxide particles are selected for lymph node imaging [AMI-227 (i.e. Sinerem and Combidex, diameter 20-40 nm)], bone marrow imaging (AMI-227), perfusion imaging [NC100150 (i.e. Clariscan, mean diameter 20 nm)] and MR angiography (NC100150). Even smaller monocrystalline iron oxide nanoparticles are under research for receptor-directed MR imaging and magnetically labeled cell probe MR imaging. Iron oxide particles for bowel contrast are coated with insoluble material, and all iron oxide particles for intravenous injection are biodegradable. Superparamagnetic agents open up an important field for research in MR imaging.     

Superparamagnetic iron oxide: Detection of focal liver lesions at high-field-strength MR imaging

AMI-25 was evaluated at 1.5 T as a superparamagnetic iron oxide contrast agent for the liver. Sixteen patients with up to five suspected focal liver lesions were examined with T1-, proton-density—, and T2-weighted spin-echo sequences before and after intravenous administration of AMI-25 (15 μmol/kg iron). The contrast-to-noise ratio (C/N) increased from 1.8 to 3.5 on 600/15 (TR msec/TE msec) images and from 1.7 to 7.9 on 2,500/15 images after AMI-25 administration (P <.01). C/N did not change significantly on 2,500/90 images. Two blinded readers counted the number of lesions visible on unenhanced and contrast-enhanced images, with the 32 sets of images of the 16 patients presented in random order. Both readers identified more lesions on AMI-25–enhanced images, but the difference was not statistically significant (P >.05). Two patients reported minor side effects (flushing, sensation of heat, lower back pain). On the basis of the results obtained in a limited number of patients, the authors conclude that at 1.5 T, AMI-25 does not significantly improve the detection of focal liver lesions on conventional spin-echo images.     

Comparison of ultrasmall particles of iron oxide (USPIO)-enhanced T2-weighted, conventional T2-weighted, and gadolinium-enhanced T1-weighted MR images in rats with experimental autoimmune encephalomyelitis

BACKGROUND AND PURPOSE: Ultrasmall particles of iron oxide (USPIO) constitute a contrast agent that accumulates in cells from the mononuclear phagocytic system. In the CNS they may accumulate in phagocytic cells such as macrophages. The goal of this study was to compare USPIO-enhanced MR images with conventional T2-weighted images and gadolinium-enhanced T1-weighted images in a model of experimental autoimmune encephalomyelitis (EAE). METHODS: Nine rats with EAE and four control rats were imaged at 4.7 T and 1.5 T with conventional T1- and T2-weighted sequences, gadolinium-enhanced T1-weighted sequences, and T2-weighted sequences obtained 24 hours after intravenous injection of a USPIO contrast agent, AMI-227. Histologic examination was performed with hematoxylin-eosin stain, Perls' stain for iron, and ED1 immunohistochemistry for macrophages. RESULTS: USPIO-enhanced images showed a high sensitivity (8/9) for detecting EAE lesions, whereas poor sensitivity was obtained with T2-weighted images (1/9) and gadolinium-enhanced T1-weighted images (0/9). All the MR findings in the control rats were negative. Histologic examination revealed the presence of macrophages at the site where abnormalities were seen on USPIO-enhanced images. CONCLUSION: The high sensitivity of USPIO for macrophage activity relative to other imaging techniques is explained by the histologic findings of numerous perivascular cell infiltrates, including macrophages, in EAE. This work supports the possibility of intracellular USPIO transport to the CNS by monocytes/macrophages, which may have future implications for imaging of human inflammatory diseases.     

Diffusion- and magnetisation transfer-weighted MRI in childhood moya-moya

Abstract MRI in two children with moya-moya demonstrated low signal on T2-weighted images in the acute and subacute phases of ischaemia. Gradient-echo sequences, more sensitive to magnetic susceptibility, demonstrated these abnormalities better. Signal loss, due to temporary accumulation of iron, decreases progressively and disappears in the chronic stage of the disease. Diffusion-weighted MRI allows early detection of ischaemic lesions and can be used to monitor progressive spreading of the lesions. Magnetisation transfer maps provide sharp contrast, useful for demonstrating cortical atrophy. Received: 14 August 1997 Accepted: 22 September 1997     

MR lymphangiography using ultrasmall superparamagnetic iron oxide in patients with primary abdominal and pelvic malignancies: radiographic-pathologic correlation

OBJECTIVE: The purpose of this study was to administer ultrasmall superparamagnetic iron oxide (USPIO) and compare changes in signal intensity of lymph nodes in patients with primary abdominal and pelvic malignancies. Also, we correlated radiographic with pathologic findings. SUBJECTS AND METHODS: Nineteen patients with proven primary abdominal or pelvic cancer (prostatic [n = 10]; colonic [n = 5]; endometrial [n = 1]; Merkel cell tumor [n = 1]; lymphoma [n = 1]; seminoma [n = 1]) were enrolled as part of our phase II and phase III clinical trials. In these patients, 49 lymph nodes (mean size, 1.4 cm) revealed on CT or MR imaging were evaluated on T1-weighted spin-echo, T2-weighted fast spin-echo, and T2*-weighted gradient-echo MR imaging at 1.5 T 24-36 hr after IV administration of USPIO. Quantitative analyses used measurements of unenhanced and enhanced region-of-interest values in lymph nodes. Qualitative assessment used subjective evaluation and classification of changes in signal intensity. All patients underwent lymph node biopsy or surgical dissection followed by histopathologic correlation. RESULTS: Of the 49 lymph nodes that were evaluated, 20 were benign and 29 were malignant. A decrease in nodal signal intensity on enhanced T2-weighted and T2*-weighted gradient-echo images was seen in 20 benign lymph nodes and two malignant lymph nodes. No appreciable signal change was noted in 27 of the 29 malignant lymph nodes. The mean signal intensity on fast spin-echo T2-weighted images for benign lymph nodes changed from 186.48 (unenhanced) to 73.66 (enhanced). Conversely, mean signal intensity for malignant lymph nodes was relatively unchanged from 191.17 (unenhanced) to 183.18 (enhanced). CONCLUSION: USPIO appears to be a useful MR contrast agent for characterizing benign and malignant lymph nodes based on the enhancement criteria evaluated in our study.     

Atypical MRI features of Wilson's disease: high signal in globus pallidus on T1-weighted images

Most reports of MRI in Wilson's disease have been of abnormal low-signal lesions on T1-weighted images and high signal intensity on T2-weighted images. In contrast, we report three patients who had high-signal lesions in the globus pallidus on T1-weighted images, a finding seen in patients with portal-systemic encephalopathy. The possible causes include the paramagnetic effect of copper or iron and accumulation of Alzheimer type II glial cells. Received: 26 January 1996 Accepted: 1 April 1996     

Iron-oxide-enhanced MR imaging of bone marrow in patients with non-Hodgkin's lymphoma: differentiation between tumor infiltration and hypercellular bone marrow

The aim of this study was to differentiate normal, hypercellular, and neoplastic bone marrow based on its MR enhancement after intravenous administration of superparamagnetic iron oxides in patients with cancer of the hematopoietic system. Eighteen patients with cancer of the hematopoietic system underwent MRI of the spine before and after infusion of ferumoxides ( n=9) and ferumoxtran ( n=9) using T1- and T2-weighted turbo spin-echo (TSE) and short tau inversion recovery sequences (STIR). In all patients diffuse or multifocal bone marrow infiltration was suspected, based on iliac crest biopsy and imaging such as conventional radiographs, MRI, and positron emission tomography. In addition, all patients had a therapy-induced normocellular ( n=7) or hypercellular ( n=11) reconversion of the normal non-neoplastic bone marrow. The MRI data were analyzed by measuring pre- and post-contrast signal intensities (SI) of hematopoietic and neoplastic marrow and by calculating the enhancement as deltaSI(%) data and the tumor-to-bone-marrow contrast as contrast-to-noise ratios (CNR). Changes in bone marrow signal intensity after iron oxide administration were more pronounced on STIR images as compared with T1- and T2-weighted TSE images. The STIR images showed a strong signal decline of normal and hypercellular marrow 45-60 min after iron oxide infusion, but no or only a minor signal decline of neoplastic bone marrow lesions; thus, deltaSI% data were significantly higher in normal and hypercellular reconverted marrow compared with neoplastic bone marrow lesions ( p<0.05). Additionally, the contrast between focal or multifocal neoplastic bone marrow infiltration and normal bone marrow, quantified by CNR data, increased significantly on post-contrast STIR images compared with precontrast images ( p<0.05). Superparamagnetic iron oxides are taken up by normal and hypercellular reconverted bone marrow, but not by neoplastic bone marrow lesions, thereby providing significantly different enhancement patterns on T2-weighted MR images; thus, superparamagnetic iron oxides are useful to differentiate normal and neoplastic bone marrow and to increase the bone marrow-to-tumor contrast.     

Dynamic MR imaging of liver lesions with superparamagnetic iron oxide (SH-U-555A)

Dynamic MRI with SH-U-555 (SPIO) was evaluated. Dynamic MRI was performed for 17 patients with 22 lesions. Dynamic study with T2*-weighted imaging (T2* dynamic) and T1-weighted imaging (T1 dynamic) were performed in 8 cases (10 lesions) and 9 cases (12 lesions), respectively. T2* dynamic MR images were obtained before and 30, 90, 180, 270, 360, and 450 seconds and 31 minutes after the intravenous injection of SPIO, and T1 dynamic MR images were obtained before and 0, 40, 80, 120, 180, 240, 300, 360, 420, and 480 seconds and 28 minutes after the injection of SPIO. The signal intensity of each lesion was measured before and after the injection of SPIO. The enhancement ratio of the lesions was calculated and evaluated. The enhancement ratio of hypervascular lesions decreased rapidly in the first phase of T2* dynamic MRI, while that of hypovascular lesions decreased gradually. The enhancement ratio of hypervascular lesions increased in the first phase of T1 dynamic MRI and decreased gradually, while that of hypovascular lesions lacked the increase in the first phase, in contrast to hypervascular lesions. However, the changing of signal intensity could not be recognized on images with T2* dynamic and T1 dynamic study. In conclusion, quantitative analysis using the enhancement ratio made it possible to anticipate lesion vascularity.     

RES-specific imaging of the liver and spleen with iron oxide particles designed for blood pool MR-angiography.

The purpose of this study was to determine the dependency of liver- and spleen-enhancement on particle size and dose of bolus-injectable iron oxides designed for blood-pool MR-angiography (MRA). The superparamagnetic iron oxide SHU 555 A [particle size 65 nm (group 1)] and three derivatives designed for blood-pool MRA (groups 2-4) with smaller hydrodynamic diameters (46/33/21 nm) were i.v. injected in New Zealand White rabbits at doses of 10, 20, or 40 micromol Fe/kg bw. MRI was performed before, 2, and 24 hours after contrast application using T1-weighted SE and T2-weighted TSE sequences. In addition splenic tissue was harvested post mortem and scanned ex vivo. All iron oxides significantly decreased the SI of liver and spleen in T1- and T2-weighted images at 2 and 24 hours after application of contrast media (P < 0.01). The signal intensity was inversely related to the dose applied. Decreasing particle size resulted in a lower signal enhancement in liver and spleen. However, ultra-small superparamagnetic iron oxides suited for blood-pool MRA (USPIOs, group 4) still revealed a significant signal enhancement in the liver and spleen even 24 hours after contrast application (< - 60%, 40 micromol Fe/kg bw). They might thus be used for comprehensive abdominal studies including contrast enhanced MR-angiography and RES-specific imaging.     

MRI in chronic toluene abuse: low signal in the cerebral cortex on T2-weighted images

Abstract MRI may be helpful in showing brain toxicity associated with chronic toluene inhalation. We report clinical and MRI findings over 3 years in a man with gradual neurologic decline secondary to toluene abuse. Cerebral atrophy most prominently involved the corpus callosum and cerebellar vermis. On T2-weighted images, loss of gray-white matter contrast, diffuse supratentorial white matter high-signal lesions, and low signal in the basal ganglia and midbrain were seen. In addition, MRI showed abnormal labor cortical low signal on T2-weighted images, most prominent in the primary motor and visual cortex. This cortical T2 shortening, not previously described in this condition, may reflect iron deposition. Received: 14 October 1997 Accepted: 18 December 1997     

Superparamegnetic iron oxides for MRI

Pharmaceutical iron oxide preparations have been used as MRI contrast agents for a variety of purposes. These agents predominantly decrease T2 relaxation times and therefore cause a decrease in signal intensity of tissues that contain the agent. After intravenous adminstration, dextran-coated iron oxides typically accumulate in phagocytic cells in liver and spleen. Clinical trials have shown that iron oxide increases lesion/liver and lesion/spleen contrast, that more lesions can be depicted than on plain MRI or CT, and that the size threshold for lesion detection decreases. Decreased uptake of iron oxides in liver has been observed in hepatitis and cirrhosis, potentially allowing the assessment of organ function. More recently a variety of novel, target-specific monocrydtalline iron oxides compounds have been used for receptor and immunospecific images. Future development of targeted MRI contrast agents is critical for organ- or tissue-specific quantitative and functional MRI. Correspondence to: R. Weissleder     

Patterns of lesion development in multiple sclerosis: longitudinal observations with T1-weighted spin-echo and magnetization transfer MR.

PURPOSEWe evaluated the appearance of enhancing multiple sclerosis (MS) lesions on unenhanced T1-weighted MR images and the natural course of enhancing MS lesions on serial unenhanced T1-weighted and magnetization transfer (MT) MR images.METHODSOne hundred twenty-six enhancing lesions were followed up monthly for 6 to 12 months to determine their signal intensity on unenhanced T1-weighted and MT MR images. At the time of initial enhancement, the size of the lesion and the contrast ratio of enhancement were calculated for each enhancing lesion. During follow-up, the contrast ratio on the corresponding unenhanced T1-weighted image was measured, and an MT ratio (MTR) was calculated.RESULTSTwenty-five enhancing lesions (20%) appeared isointense and 101 lesions (80%) appeared hypointense relative to normal-appearing white matter on unenhanced T1-weighted images. During 6 months of follow-up, four MR patterns of active lesions were detected: initially isointense lesions remained isointense (15%); initially isointense lesions became hypointense (5%, most of which reenhanced); initially hypointense lesions became isointense (44%); and initially hypointense lesions remained hypointense (36%). MTR was significantly lower for hypointense lesions as compared with isointense lesions at the time of initial enhancement. For lesions that changed from hypointense to isointense, MTR increased significantly during 6 months of follow-up. Multiple regression analysis showed that strongly decreased MTR at the time of initial enhancement and enhancement duration of more than one scan were predictive of a hypointense appearance on unenhanced T1-weighted images at 6 months'' follow-up. Ring enhancement was found to be the only (weak) predictor of persistently hypointense signal intensity.CONCLUSIONMost enhancing lesions appear slightly to significantly hypointense on unenhanced T1-weighted images. Although most hypointensities are reversible, only those lesions that fail to recover on unenhanced T1-weighted and MT images may have considerable irreversible structural changes.     

Diagnosis of adrenal adenoma: value of central spot of high-intensity hyperintense rim sign and homogeneous isointensity to liver on gadolinium-enhanced fat-suppressed spin-echo MR images

Eighty-nine patients with 108 adrenal masses, either adenomas (n = 88) or malignant lesions (n = 20), underwent magnetic resonance imaging (MRI) of the abdomen at 0.5 T for the purpose of determining whether adrenal adenomas could be differentiated from malignant lesions on gadolinium-enhanced fat-suppressed T1-weighted spin-echo (SE) images (Gd-E FS T1WI) and on T2-weighted SE images. The imaging protocol included conventional unenhanced SE T1- and T2-weighted sequences and Gd-E FS T1WI. Three observers independently evaluated signal intensity on unenhanced and enhanced images and also the presence of structures of high signal intensity in the outer margin [hyperintense rim sign (HRS)] or in the center [hyperintense central spot (HCS)] of the adrenal masses. Forty-one (46.5%) of 88 adenomas were homogeneously isointense to liver in unenhanced and enhanced T1-weighted sequences and in T2WI. HCS and HRS were observed in 33/88 (37.5%) and 15/88 (17%) adenomas, respectively, on Gd-E FS T1WI; in contrast, these signs were never revealed in any case of malignant lesions. Sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy in classifying lesions as suggestive of adenoma were 93%, 90%, 98%, 75%, and 93%, respectively. Visual evaluation of details of tumor structures on Gd-E FS T1WI allows good characterization of adrenal masses. HCS, HRS, and homogeneous isointensity to liver are characteristic signs of adrenal adenomas.     

MRI evaluation of pigmented skin tumors. Preliminary study

Magnetic resonance imaging (MRI) was performed in 16 patients with pigmented skin lesions, seven with nodular melanomas, two with superficial spreading melanomas, two with subcutaneous melanoma metastases, and five with different benign pigmented nodular skin lesions. The results of MRI were compared with the histologic diagnoses. Signal intensities of the lesions were compared with subcutaneous fat, revealing a lower signal intensity of all lesions on T1-weighted images. Intensity measurements showed a significant (P less than .01) difference between benign and malignant lesions on T2-weighted images.     

Ferumoxides-enhanced double-echo T2-weighted MR imaging in differentiating metastases from nonsolid benign lesions of the liver

PURPOSE: To investigate whether ferumoxides-enhanced double-echo T2-weighted magnetic resonance (MR) imaging alone can allow differentiation of metastases from benign lesions in the noncirrhotic liver. MATERIALS AND METHODS: At retrospective review of files and images, 60 lesions (22 metastases, 20 hemangiomas, and 18 cysts) were identified in 42 patients. All fast spin-echo T2-weighted MR images obtained before and after administration of ferumoxides with short (80-90 msec) and long (180-250 msec) echo times (TEs) were acquired with a 1.5-T system. Differences in lesion-to-liver signal intensity ratio between images obtained with long and short TEs were calculated. Data from all 60 lesions were entered into a receiver operating characteristic analysis. Three independent readers scored their observations of each lesion with a confidence level of 1-5. The diagnostic accuracy of each analysis method was determined by calculating the area under each reader-specific receiver operating characteristic curve. Interobserver agreement was calculated with the use of chance-corrected kappa statistics. Relative sensitivity, specificity, and accuracy of characterizing benign lesions with each method were calculated. RESULTS: Markedly low signal intensity and lesion-to-liver ratio on ferumoxides-enhanced images were observed with hemangioma. The difference of lesion-to-liver ratio between long and short TEs on ferumoxides-enhanced images was significantly different from that of unenhanced images and that of metastases or cysts. Interobserver agreement was good to excellent. Ferumoxides-enhanced images (with short and long TEs) showed significantly higher diagnostic accuracy than that of unenhanced images (with short or short and long TEs). Ferumoxides-enhanced images showed similar sensitivity, specificity, and accuracy when all images were reviewed together. CONCLUSION: Ferumoxides-enhanced T2-weighted MR images appear useful in differentiating metastases from benign (nonsolid) lesions in the liver.