T1-weighted Gradient-recalled Echo Research Articles

Detection of Portal Perfusion Abnormalities

To estimate the accuracy, sensitivity, and specificity of 3 ferucarbotran-enhanced magnetic resonance (MR) imaging sequences prospectively for the detection of nontumoral portal perfusion abnormalities. Thirty-nine noncirrhotic patients with liver metastases underwent computed tomography during arterial portography (CTAP) and MR imaging comprising T1-weighted gradient recalled echo (GRE), T2-weighted fast spin echo (FSE), and T2*-weighted GRE sequences with and without ferucarbotran. Magnetic resonance images were reviewed by 4 blinded observers for rating based on the confidence scale. The accuracy, sensitivity, and specificity for each sequence were measured by receiver operating characteristic analysis. Contrast-to-noise ratio (CNR) and relative signal-to-noise ratio changes were statistically compared. Thirty-nine nontumoral perfusion defects were observed in 22 patients by CTAP. Receiver operating characteristic analysis showed the accuracy was higher for T2*-weighted GRE (0.884) than for T1-weighted GRE (0.572) and T2-weighted FSE (0.597). T2*-weighted imaging achieved the highest sensitivity (81.4%) and the lowest specificity (86.6%). Postenhanced T2*-weighted imaging achieved the highest CNR (19.3 +/- 9.2). T2*-weighted imaging was the most accurate and sensitive method for detecting portal perfusion abnormalities compared with T1- or T2-weighted imaging, whereas T1- or T2-weighted imaging is superior in specificity to T2*-weighted imaging during ferucarbotran-enhanced MR imaging.

Expression of vascular endothelial growth factor in hepatocellular carcinoma and the surrounding liver: correlation with MR imaging and angiographically assisted CT

We summarize and discuss our previous research results on the correlation between findings on magnetic resonance (MR) imaging and angiographically assisted computed tomography (CT) and the intensity of vascular endothelial growth factor (VEGF) expression in hepatocellular carcinoma (HCC) and in the surrounding nontumorous liver. MR images (n = 22), CT during arterial portography (n = 20), and CT hepatic arteriography (n = 17) were retrospectively correlated quantitatively and qualitatively with VEGF expression in HCCs and in the surrounding liver assessed by western blotting. HCC-to-liver contrast-to-noise ratio correlated with VEGF expression index (VEGF(IND)) values of HCCs inversely on opposed-phase, T1-weighted, spoiled gradient recalled-echo (GRE) images, directly on T2-weighted, fast spin-echo images, and marginally and inversely on gadolinium-enhanced hepatic arterial-phase GRE images. On T2-weighted fast spin-echo images, standard deviation ratio of HCCs correlated directly with VEGF(IND) values of HCCs. By CT hepatic arteriography, the contrast-enhancement index of HCCs showed a moderate inverse correlation with VEGF(IND) values of HCCs, and the contrast-enhancement index of the liver showed marginal, moderate direct correlation with VEGF(IND) values in the liver. Heterogeneities of HCCs on images correlated directly with VEGF(IND) values of HCCs on opposed-phase T1-weighted GRE images, T2-weighted fast spin-echo images, hepatic arterial-phase GRE images, equilibrium-phase GRE images, and CT hepatic arteriogram. Our results may reflect that MR signal intensity, hepatic arterial vascularity, and heterogeneity of HCCs on CT or MR images are closely related to the intensity of VEGF expression in HCC as upregulated by hyper- or hypoxia in HCCs. Although the real effects of our results on radiologic practice are debatable at this moment, we believe that our results may help future radiologic practice in conjunction with biomolecular or genetic treatment for HCCs.

Detection of Liver Metastases from Adenocarcinoma of the Colon and Pancreas: Comparison of Mangafodipir Trisodium–Enhanced Liver MRI and Whole-Body FDG PET

The objective of our study was to assess the relative performance of mangafodipir trisodium-enhanced liver MRI and whole-body FDG PET for the detection of liver metastases from adenocarcinoma of the colon and pancreas. Imaging data of 34 patients (23 men, 11 women; age range, 44-78 years) with adenocarcinoma of the colon (n = 27) or adenocarcinoma of the pancreas (n = 7) who had undergone mangafodipir trisodium-enhanced liver MRI and whole-body FDG PET were retrospectively reviewed for the presence and number of liver metastases. Histopathology (n = 25) or follow-up imaging (n = 9) served as the standard of reference. Breath-hold T1-weighted gradient-recalled echo, respiratory-triggered T2-weighted fast spin-echo, and mangafodipir trisodium-enhanced axial fat-saturated high-spatial-resolution (256 x 512) T1-weighted gradient-recalled echo images were obtained on a 1.5-T scanner. FDG PET was performed after the injection of 15-20 mCi (555-740 MBq) of FDG. The sensitivity, positive predictive value, and accuracy were calculated for each technique. The performances of the two techniques were compared using the Fisher's exact test. Thirty patients had hepatic metastases and four had no hepatic metastases according to the standard of reference. The total number of metastases was 79, including 33 that measured less than 1 cm. Based on a per-patient analysis, MRI and FDG PET showed sensitivities of 96.6% and 93.3%, positive predictive values of 100% and 90.3%, and accuracies of 97.1% and 85.3%, respectively. According to a per-lesion analysis, MRI and FDG PET showed sensitivities of 81.4% and 67.0%, positive predictive values of 89.8% and 81.3%, and accuracies of 75.5% and 64.1%, respectively. MRI detected more hepatic metastases than FDG PET (p = 0.016). Of the 33 subcentimeter lesions confirmed on the standard of reference, all were identified on MRI, whereas only 12 were detected on FDG PET (p = 0.0001). In patients with colon and pancreatic adenocarcinoma, high-spatial-resolution mangafodipir trisodium-enhanced liver MRI and whole-body FDG PET were comparable in the detection of patients with liver metastases. FDG PET provided additional information about extrahepatic disease and was useful in initial staging. However, significantly more and smaller liver metastases were detected on MRI than on FDG PET.

MRI predictors of risk of incident Alzheimer disease

To determine if baseline entorhinal and hippocampal volumes and their rate of atrophy could predict the risk of incident Alzheimer disease (AD). The authors used proportional odds models to assess the relationship between entorhinal and hippocampal size and risk of incident AD among 58 nondemented elderly people. All participants were followed with annual clinical evaluations and structural MRI scans for up to 5 years (baseline and 5 years of follow-up). At baseline, 23 of 58 participants received a diagnosis of amnestic mild cognitive impairment (MCI) and 35 of 58 were healthy control subjects with no cognitive impairment. Structural MRI scans were acquired with a T1-weighted three-dimensional spoiled gradient-recalled echo pulse sequence in a 1.5 T scanner. Entorhinal and hippocampal volumes were derived from 1.6-mm gapless coronal images reformatted to be perpendicular to the long axis of the hippocampus and were normalized by dividing with intracranial volume. Fourteen of 58 nondemented participants developed AD during the follow-up period. Initial diagnosis of MCI was a significant predictor of incident AD. In addition, both baseline entorhinal volume and its slope of decline were independent predictors of incident AD, but initial hippocampal size and its rate of decline were not, after controlling for entorhinal volume. In nondemented individuals, entorhinal cortex atrophy is associated with risk of Alzheimer disease.

Expression of Vascular Endothelial Growth Factor in Hepatocellular Carcinoma and the Surrounding Liver and Correlation with MRI Findings

The purpose of our study was to assess the correlation between the quantitative and qualitative imaging findings on unenhanced and gadolinium-enhanced MR images and the intensity of vascular endothelial growth factor (VEGF) expression in hepatocellular carcinomas and in the surrounding nontumorous liver. The intensities of VEGF expression in hepatocellular carcinoma and in the surrounding liver by Western blot analysis were converted to VEGF expression indexes (VEGF(IND)) in 22 surgical specimens ranging in size from 14 to 126 mm (mean, 47.6 +/- 29.5 mm) that were resected in 22 patients (17 men and five women; age range, 41-85 years [mean, 64 years]) between April 2000 and October 2002. MR images were retrospectively evaluated to determine contrast-to-noise ratios (CNRs), signal intensity SD ratios, and phase-shift indexes. Signal intensity characteristics of hepatocellular carcinomas were reviewed independently by two experienced radiologists who were unaware of the pathologic diagnosis or the results of immunoblotting. CNRs, SD ratios, and phase-shift indexes were correlated with VEGF(IND) using a simple regression test, and signal intensity characteristics were correlated with VEGF(IND) using the Spearman's rank correlation test. On opposed-phase T1-weighted spoiled gradient-recalled echo (GRE) images, CNRs correlated inversely with the VEGF(IND) of hepatocellular carcinomas (r = -0.46, p = 0.038). CNRs on T2-weighted fast spin-echo images correlated directly with the VEGF(IND) of hepatocellular carcinomas (r = 0.49, p = 0.025), and on gadolinium-enhanced hepatic arterial phase GRE images marginally and inversely correlated with VEGF(IND) (r = -0.39, p = 0.081). On T2-weighted fast spin-echo images, SD ratios correlated directly with the VEGF(IND) of hepatocellular carcinomas (r = 0.44, p = 0.044). No correlation was found between phase-shift indexes and VEGF expression. The qualitatively assessed signal intensity heterogeneities of hepatocellular carcinomas correlated directly with the VEGF(IND) of hepatocellular carcinomas on opposed-phase T1-weighted GRE, T2-weighted fast spin-echo, hepatic arterial phase GRE, and equilibrium phase GRE images. Our results indicate that the signal intensity and heterogeneity of hepatocellular carcinomas on MR images correlate with the degree of VEGF expression in hepatocellular carcinomas.

Magnetic resonance imaging of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most common primary hepatic malignancy, usually develops in patients with cirrhosis, growing sequentially from low-grade dysplastic nodules to frank malignant HCC. Its recognition is critical because curative treatment and prognosis require early diagnosis. Survival in patients with HCC relates directly to the number, size, and extent of lesions at diagnosis. Imaging of HCC is complicated because the tumor has a varied imaging appearance and frequently coexists with other cirrhotic nodules. Magnetic resonance imaging (MRI), the best available diagnostic technique, offers good contrast resolution and diagnostic sensitivity ranging from 33% to 77%. The main difficulty is not in diagnosing large tumors, but rather small tumors (<2 cm), because of considerable overlap on imaging between benign (regenerative), borderline (dysplastic), and malignant nodules. Increasing degrees of histological malignancy are associated with increasing arterialization and loss of portal blood supply; therefore, recognition of HCC requires dynamic imaging with gadolinium-enhanced T1-weighted sequence. Typically, HCC is a focal lesion with high signal intensity on T2-weighted images, variable signal intensity on T1-weighted images, intense arterial phase enhancement after gadolinium injection, and isointensity or hypointensity at the portal venous phase. The sensitivity of MRI for detecting small lesions is low, and improvement is still needed. Newer contrast agents, higher field strength (3 Tesla) imaging, and perfusion and diffusion MRI techniques possibly will provide greater sensitivity and specificity for detecting small HCCs in the future.

Non-invasive assessment of hepatic iron overload: are we finally there?

Iron excess in tissues can lead to toxicity and organ disease. The liver, as the primary site of body iron deposition, is also a principal target for its toxicity. Heavy iron overload in humans is usually associated with a genetically determined disturbance of iron homeostasis (i.e. hereditary hemochromatosis, HH) or with intensive transfusion regimens associated with hereditary anemia (i.e. bthalassemia). Liver biopsy is the most accurate method for assessing hepatic iron burden and provides important information on underlying liver damage and diseases. However, it entails the risk for potential complications while accurate iron measurements may be biased by sampling variability in advanced chronic disease. Therefore, at least within a diagnostic workup, costs and benefits of liver biopsy should be carefully considered. In hereditary hemochromatosis, a positive genetic test for HFE or other hemochromatosis gene mutations (transferrin receptor 2, hemojuvelin, hepcidin) may allow to avoid liver biopsy in most symptomatic patients, whereas histology remains essential in homozygotes with abnormal transaminases, hepatomegaly or serum ferritin higher than 1000 ng/ml [1]. In recent years, the potential role of mild iron overload as factor of comorbidity in the progression of several hepatic disorders (e.g. viral hepatitis, alcoholic liver disease, nonalcoholic fatty liver disease, porphyria cutanea tarda) has been increasingly recognized. In fact, accurate evaluation of hepatic iron content is now regarded as an important clinical manoeuvre in the management of chronic non-HH liver disease. Due to safety concerns of liver biopsy, non-invasive methods to measure hepatic iron content have been, therefore, devised. Serum ferritin may be a good surrogate marker for evaluating iron stores but suffers from low specificity. High sensitivity has been reported for the superconducting quantum interference device (SQUID) that measures magnetic susceptibilities [2]. SQUID, however, is not widely available and requires experienced operators. Computed tomography shows attenuation of the liver in the presence of excess iron, but seems to suffer of low sensitivity and specificity particular at mild iron overload grades and in the presence of fat [3]. Magnetic resonance has been intensively exploited, until recently, as a sensitive and specific tool for assessing hepatic iron overload [4‐9]. Due to the paramagnetic properties of iron, its increased hepatic content decreases both the T2 relaxation time and the liver signal’s intensity (SI): this gives the typical dark liver at MRI. Gradient-recalled-echo (GRE) techniques have been shown to be more accurate in quantifying mild iron overload states than spin-echo sequences due to higher sensitivity to field inhomogeneities induced by paramagnetic substances. Most published studies agree on the fact that MRI is accurate in assessing a moderate-severe iron overload but a validated and cost effective method for taking advantage of MRI in quantifying also low grades of iron stores was still missing. In addition, an ideal method should also be simple and easy to be standardized in order to be transferred and applied to different machines. Gandon and coworkers seem to have taken a fundamental step toward this end [7]. They studied 174 patients by both percutaneous liver biopsy with biochemical assessment of hepatic iron concentration and MRI of the liver with various GRE sequences on a 1.5 T magnet. They calculated liver iron concentration by evaluating the correlation between liver to muscle (L/M) signal intensity ratio and developed an algorithm to calculate magnetic resonance hepatic iron concentration. Data obtained in a study group (nZ139) that included patients with suspected iron overload or patients managed for hepatitis C, were then applied to a validation group (nZ35). A highly

Non-invasive assessment of hepatic iron stores by MRI

MRI has been proposed for non-invasive detection and quantification of liver iron content, but has not been validated as a reproducible and sensitive method, especially in patients with mild iron overload. We aimed to assess the accuracy of a simple, rapid, and easy to implement MRI procedure to detect and quantify hepatic iron stores. Of 191 patients recruited, 17 were excluded and 174 studied, 139 in a study group and 35 in a validation group. All patients underwent both percutaneous liver biopsy with biochemical assessment of hepatic iron concentration (B-HIC) and MRI of the liver with various gradient-recalled-echo (GRE) sequences obtained with a 1.5 T magnet. Correlation between liver to muscle (L/M) signal intensity ratio and liver iron concentration was calculated. An algorithm to calculate magnetic resonance hepatic iron concentration (MR-HIC) was developed with data from the study group and then applied to the validation group. A highly T2-weighted GRE sequence was most sensitive, with 89% sensitivity and 80% specificity in the validation group, with an L/M ratio below 0.88. This threshold allowed us to detect all clinically relevant liver iron overload greater than 60 micromol/g (normal value <36 micromol/g). With other sequences, an L/M ratio less than 1 was highly specific (>87%) for raised hepatic iron concentration. With respect to B-HIC range analysed (3-375 micromol/g), mean difference and 95% CI between B-HIC and MR-HIC were quite similar for study and validation groups (0.8 micromol/g [-6.3 to 7.9] and -2.1 micromol/g [-12.9 to 8.9], respectively). MRI is a rapid, non-invasive, and cost effective technique that could limit use of liver biopsy to assess liver iron content. Our MR-HIC algorithm is designed to be used on various magnetic resonance machines.

Potential of magnetic resonance lymphography with intrapulmonary injection of gadopentetate dimeglumine for visualization of the pulmonary lymphatic basin in dogs: preliminary results.

To evaluate a new approach of magnetic resonance (MR) lymphography with intraalveolar injection of a conventional extracellular contrast agent (gadopentetate dimeglumine) for imaging lymphatic basin draining from specific portions of the lung. Three-dimensional T1-weighted spoiled gradient-recalled echo MR sequence images were acquired serially before and for 40 minutes after intraalveolar injection of gadopentetate dimeglumine in a total of 14 anesthetized beagle dogs. Six of these dogs received 1 mL undiluted and low-concentration (75%) contrast agent into the same portion of the right caudal lobe during a 7-day interval. In all dogs, including these 6 dogs, MR lymphography was repeated with injection of the low-concentration contrast agent into different lung regions at 7-day intervals to evaluate the differences of the visualized draining lymphatic station. Lymphatic enhancement was quantified by percent increases of signal intensity against precontrast. Postmortem examination of the lymphatic anatomy was performed in 7 of these animals. In all dogs, the lymphatic station draining from the injection sites was visualized within 5 minutes after contrast injection. The maximum percent increase of signal intensity of the same middle tracheobronchial lymph nodes was significantly greater with a low-concentration (75%) contrast agent than with an undiluted one in the same 6 dogs (n = 6, 247.6 +/- 30.5% vs. 204.2 +/- 33.8%; P < 0.01). Different lymphatic stations draining from the different injection sites were visualized in all dogs. In a total of 12 MR studies that showed extended nodal enhancement after injection of the low-concentration contrast agent, the enhancement peak of the most proximal nodes (n = 12) from the injection sites appeared earlier than that of their distant nodes (n = 12), with a maximum percent increase of signal intensity of 249.8 +/- 42.4%. The visualized lymph nodes were found in the appropriate locations postmortem, with significant correlation for nodal sizes (r = 0.965; P < 0.0001). MR lymphography with low-concentration gadopentetate dimeglumine can quickly and sufficiently visualize the drainage lymphatic station from specific lung portions, and may have the potential of sentinel node mapping in lung cancer.

Hepatocellular carcinoma in cirrhotic livers: double-contrast thin-section MR imaging with pathologic correlation of explanted tissue.

The aim of our study was to determine the sensitivity of double-contrast MR imaging in the detection of hepatocellular carcinomas in patients with a cirrhotic liver. Thirty-one patients underwent double-contrast MR imaging and subsequent liver transplantation. Breath-hold T1- and T2-weighted MR images were obtained before and after administration of superparamagnetic iron oxide, and three-dimensional T1-weighted gradient-recalled echo MR images were obtained 10, 40, and 120 sec after a bolus injection of gadolinium. Hypervascular lesions that failed to take up superparamagnetic iron oxide were regarded as showing typical characteristics of hepatocellular carcinoma; lesions that had only one of these two characteristics (either hypervascularity or failure to take up superparamagnetic iron oxide) were regarded as highly suspicious for hepatocellular carcinoma. Radiology reports were correlated with pathology reports for the explanted livers. Thirty-two hepatocellular carcinomas were found in 14 of the 31 patients. Combining the number of MR imaging reports citing lesions that were "typical of hepatocellular carcinoma" with the number of those citing lesions that were "highly suspicious," we found that for 25 of 32 lesions, an accurate MR imaging diagnosis of hepatocellular carcinoma was made (overall sensitivity, 78%). These lesions included 10 of the 11 lesions that were larger than 20 mm (sensitivity, 91%), 12 of the 13 lesions that were 11-20 mm (sensitivity, 92%), and three of the eight lesions that were 10 mm or less (sensitivity, 38%). Nineteen (76%) of 25 lesions had characteristics considered typical of hepatocellular carcinoma; the remaining six lesions either failed to take up superparamagnetic iron oxide and were hypovascular or were hypervascular but showed some uptake of superparamagnetic iron oxide. In patients with a cirrhotic liver, double-contrast MR imaging is highly sensitive in the diagnosis of hepatocellular carcinomas of 10 mm or larger, but success in the identification of tumors smaller than 10 mm is still limited.

MR to assess renal function in children.

Renal function evaluation in the pediatric patient is generally based on scintigraphic examinations where a baseline gamma-camera renography is used to determine single kidney function, and diuresis renography is obtained to assess urinary drainage from the pelvicalyceal system. Magnetic resonance imaging also permits the evaluation of renal functional processes using fast dynamic sequences. Principally, an agent cleared by renal excretion is intravenously injected and its cortical uptake, parenchymal transport, and eventually its urinary excretion are followed with serial images. Different approaches have been presented most of which are based on T1-weighted gradient-recalled echo sequences with short TR and TE and a low flip angle obtained after intravenous injection of Gd-DTPA or Gd-DOTA. These techniques permit renal functional assessment using different qualitative and quantitative parameters; however, most of these methods are not suitable for the evaluation of urinary tract dilatation in infants and children. For the diagnostic work-up of children with congenital urinary tract obstruction and malformation a technique was developed which permits quantitative determination of single kidney function, in addition to evaluating urinary excretion disturbances analogous to that possible with scintigraphy.

Characterization of focal hepatic lesions with ferumoxides-enhanced MR imaging: utility of T1-weighted spoiled gradient recalled echo images using different echo times.

To evaluate the different signal characteristics of focal hepatic lesions on ferumoxides-enhanced MR imaging, including T1-weighted spoiled gradient recalled echo (GRE) images using different echo times (TE) and T2- and T2*-weighted images. Ferumoxides-enhanced MR imaging was performed using a 1.5-T system in 46 patients who were referred for evaluation of known or suspected hepatic malignancies. One hundred and seven lesions (42 hepatocellular carcinomas [HCC], 40 metastases, 13 cysts, eight hemangiomas, three focal nodular hyperplasias [FNHs], and one cholangiocarcinoma) were evaluated. Postcontrast MR imaging included 1) T2-weighted FSE; 2) T2*-weighted GRE; 3) T1-weighted spoiled GRE using moderate (TE = 4.2-4.4 msec) TE; and 4) minimum (TE = 1.8-2.1 msec) TE. Signal intensities of the focal lesions were rated by two radiologists in conference as follows: hypointense, isointense or invisible, hyperintense, and markedly hyperintense. Lesion-to-liver contrast-to-noise ratio (C/N) was measured by one radiologist for a quantitative assessment. On ferumoxides-enhanced FSE images, 92% of cysts were "markedly hyperintense" and most of the other lesions were "hyperintense", and the mean C/N of cysts was significantly higher than that of other focal lesions. T2*-weighted GRE images showed most lesions with similar hyperintensities and the mean C/N was not significantly different between any two types of lesion. T1-weighted GRE images using moderate TE showed all FNHsand hemangiomas, 29 (69%) HCCs and eight (20%) metastases as "hyperintense". On T1-weighted GRE images using minimum TE, however, all HCCs and metastasis except one were iso- or hypointense, while all of the FNHs and hemangiomas were hyperintense. Ring enhancement was highly suggestive of malignant lesions, and was more commonly seen on the minimum TE images than on the moderate TE images. Addition of T1-weighted GRE images using minimum and moderate TE is helpful for characterizing focal lesions in ferumoxides-enhanced MR imaging.

Mangafodipir Trisodium (Mn-DPDP)-Enhanced MR Imaging of Hepatocellular Carcinoma: Correlation with Histopathological Findings

Materials and Methods: In 28 patients with 36 HCCs larger than 1 cm, Mn-DPDP-enhanced T1-weighted fast multiplanar spoiled gradient-recalled echo (GRE) MR images were obtained before and 15 mins after Mn-DPDP administration. Qualitative analysis focused on signal intensity (hyper-, iso-, or hypo-) relative to surrounding liver parenchyma, while the signal enhancement ratio [ER (%)] and lesion-to-liver contrast-noise ratio (CNR) were determined quantitatively. Signal intensity relative to surrounding liver parenchyma, lesion-to-liver CNR and signal ER of the lesions were correlated with their size and histopathologic grade. Results: The imaging procedure showed that relative to surrounding liver parenchyma, 74% (14/19) of HCCs 1-3 cm in size but 47% (8/17) of those larger than 3 cm were hyperintense. There was, however, no significant difference between the two groups (p>0.05). In addition, 35% (6/17) of HCCs larger than 3 cm but none of the 19 smaller lesions were hypointense, with a significant difference between the two groups (p0.05). Conclusion: At Mn-DPDP-enhanced MR imaging, HCCs 1-3 cm in size showed greater signal intensity and signal ER than HCCs larger than 3 cm. Well or moderately differentiated HCCs showed greater signal ER than those that were poorly differentiated. Lesion-to-liver CNR did not differ according to lesion size and histopathologic grade.

Adrenal hemorrhage after orthotopic liver transplantation: MR appearance.

The purpose of this paper is to describe the MR imaging findings of right adrenal hemorrhage after orthotopic liver transplantation. Twenty-seven orthotopic liver transplantation patients underwent MR studies of the liver and/or biliary system. Patients were referred to MR examination because of suspected biliary complications ( n=22) or for evaluation of mass lesions ( n=5). The standard MR protocol included T1-weighted spin-echo (SE) or gradient-recalled echo (GRE) images and T2-weighted turbo SE (TSE) images with fat suppression. In addition, cholangiography pulse sequences and/or contrast-enhanced T1-weighted images were obtained according to specific indications. In 2 patients a right adrenal mass was detected at MR imaging. Three to 4 weeks after transplantation, the lesions were markedly hyperintense on T2-weighted images and showed a hypointense capsule. Follow-up MR examinations revealed a slight decrease in size and a change in morphology. Computed tomography examinations of these 2 patients, obtained 10 weeks after transplantation, showed resolution of the hemorrhage and transformation into a cystic lesion in one case and a complete resolution of the hemorrhage and a normal right adrenal gland in the other case. Adrenal hemorrhage after liver transplantation shows typical MR features and should not be mistaken for an adrenal tumor or a postoperative abscess.

MR imaging of the wrist in rheumatoid arthritis using gadobenate dimeglumine.

To determine the dosage of gadobenate dimeglumine (Gd-BOPTA) necessary for MRI of rheumatoid arthritis of the wrist. Seven wrists inflamed with rheumatoid arthritis were imaged using a dedicated 0.2-T MR unit. Four cumulative dosages of 0.0125, 0.025, 0.05 and 0.1 mmol/kg body weight (BW) Gd-BOPTA were tested. Three-dimensional T1-weighted gradient-recalled echo sequences (GRE; TR: 100 ms, TE: 18 ms, flip angle 90 degrees , 4:55 min) were acquired prior to an intravenous injection and after each additional dosage of Gd-BOPTA. Relative enhancement, signal-difference-to-noise ratios (SDNRs) and the size of the inflamed tissue were quantified. Three radiologists independently evaluated the image quality, the size and the contrast of the enhancing tissue. The readers agreed on a dose of 0.05 mmol/kg BW as satisfactory for the evaluation of the size of the inflammatory tissue and for determination of bone involvement (kappa = 0.9, P < 0.001). Highly inflammatory pannus was depicted with adequate image contrast using 0.025 mmol/kg BW Gd-BOPTA. According to the SDNR and relative enhancement findings, a dose of 0.05 mmol/kg BW suffices for both off-center and centered regions of tissue inflammation (t-test, P < 0.05). Gadolinium-BOPTA is an alternative contrast agent for MRI of rheumatoid disease. This study shows that a dose of 0.05 mmol/kg BW suffices at low field strength.

Lateral ulnar collateral ligament of the elbow: optimization of evaluation with two-dimensional MR imaging.

To compare, in a cadaveric model, magnetic resonance (MR) imaging techniques with differing contrast and spatial resolution properties in the evaluation of disruption of the lateral ulnar collateral ligament (LUCL) at the elbow. LUCL tears were surgically created in eight of 28 cadaveric elbow specimens. All specimens underwent 1.5-T MR imaging with the following pulse sequences: T1-weighted spin echo (SE), intermediate-weighted fast SE, fat-suppressed T2-weighted fast SE, gradient-recalled echo (GRE) with high spatial resolution, intermediate-weighted fast SE with high spatial resolution, and fat-suppressed T1-weighted SE with intraarticular administration of gadopentetate dimeglumine (MR arthrography). All images were obtained in the oblique coronal plane. Two radiologists independently graded the LUCL with separate and side-by-side assessment. Areas under the receiver operating characteristic curve were as follows for readers A and B, respectively: T1-weighted SE imaging, 0.64 and 0.62; intermediate-weighted fast SE imaging, 0.87 and 0.67; T2-weighted fast SE imaging, 0.68 and 0.69; GRE imaging, 0.56 and 0.68; MR arthrography, 0.84 and 0.85; and intermediate-weighted imaging with high spatial resolution, 0.92 and 0.88. Interobserver reliability was poor with T1-weighted SE imaging (kappa = 0.13) and GRE imaging (kappa = 0.18), fair with T2-weighted fast SE imaging (kappa = 0.36), and moderate with MR arthrography (kappa = 0.46), intermediate-weighted fast SE imaging (kappa = 0.55), and intermediate-weighted imaging with high spatial resolution (kappa = 0.59). Intermediate-weighted imaging with high spatial resolution and MR arthrography showed the greatest overall ability to enable the diagnosis of LUCL tears.

Thermosensitive paramagnetic liposomes for temperature control during MR imaging-guided hyperthermia: In vitro feasibility studies

Magnetic resonance (MR) imaging-based temperature monitoring has gained interest for use in general hyperthermia treatment of tumors. Such therapy requires an accurate control of the temperature, which should range from 41 degrees to 45 degrees C. A novel type of thermosensitive MR agent is proposed: liposome-encapsulated gadolinium chelates whose temperature response is linked to the phase-transition properties of the liposome carrier. In vitro relaxometry and MR imaging were used to evaluate the thermosensitivity of the contrast properties of liposomal gadolinium diethylenetriaminepentaacetic acid bis(methylamide) (Gd-DTPA-BMA). T1 relaxivity (rl) measurements of liposomal Gd-DTPA-BMA were undertaken at 0.47 T and at temperatures of 20 degrees-48 degrees C. MR imaging was performed at 2.0 T with a gel phantom containing inserts of liposomes. Diffusion-weighted and T1-weighted gradient-recalled echo images were acquired as the phantom was heated from 22 degrees to about 65 degrees C. At ambient temperature, the r1 of liposomal Gd-DTPA-BMA was exchange limited due to slow water exchange between the liposome interior and exterior. A sharp, marked increase in r1 occurred as the temperature reached and exceeded the gel-to-liquid crystalline phase-transition temperature (Tm) of the liposomes (42 degrees C). The relaxation enhancement was mainly attributable to the marked increase in transmembrane water permeability, yielding fast exchange conditions. There was good correlation between the relaxometric and imaging results; the signal intensity on T1-weighted gradient-recalled echo images increased markedly as the temperature approached Tm. The temperature sensitivity of the diffusion-weighted technique differed from that of the liposome-based T1-weighted approach, with an apparent water diffusion coefficient increasing linearly with temperature. Since the transition from low to high signal intensity occurred in the temperature range of 38 degrees - 42 degrees C, the investigated paramagnetic liposomes have a potential role as "off-on" switches for temperature control during hyperthermia treatment.

Accurate and rapid quantitative dynamic contrast-enhanced breast MR imaging using spoiled gradient-recalled echoes and bookend T(1) measurements.

A method is presented that converts dynamic T(1)-weighted spoiled gradient-recalled echo (SGRE) image intensities into estimates of T(1) without the errors associated with imperfections in the slice profile and transmitter coil magnetic field (B(1)). The method involves T(1) measurements performed before and after a series of dynamic SGRE images. These measurements serve to calibrate and correct the SGRE signal strength equation used to estimate T(1). Simulations and phantom experiments were performed to test the method for slice-selective (two-dimensional) and slab-selective (three-dimensional) imaging, as well as for imaging performed with optimized and un-optimized B(1). For nearly all test conditions, T(1) was estimated accurately (within 10%) over a range of T(1) values expected in vivo ( approximately 1200 --> 300 msec). This method should be useful for quantifying dynamic SGRE imaging for many different applications including breast MR imaging. Magn Reson Med 42:746-753, 1999.

T-1 weighted sequences for hepatic mri: Re-evaluation using a phased array coil

The purpose of this study was to compare three T1-weighted sequences for hepatic magnetic resonance (MRI) imaging with the use of a body phased array coil. Three different T1-weighted MR sequences were compared: a conventional spin echo (CSE); half-Fourier spin echo (HFSE), and a gradient recalled echo (GRE). Three independent reviewers compared the sequences both quantitatively and qualitatively. The T1-weighted GRE sequence scored highest for overall image quality (p < 0.001), lesion conspicuity p = 0.012 , and yielded the highest contrast to noise (C/N) values. GRE T1-weighted images are the best for hepatic MRI.

Contrast enhancement and quantitative signal analysis in MR imaging of multiple myeloma: assessment of focal and diffuse growth patterns in marrow correlated with biopsies and survival rates.

This study describes infiltration patterns of multiple myeloma in spinal MR imaging and correlates the findings with biopsies, survival rates, and signal intensity measurements in unenhanced and enhanced studies. Fifty-three patients with multiple myeloma and 53 age-matched controls underwent MR imaging of the spine. Twenty-nine patients underwent sagittal T1-weighted spin-echo enhanced imaging and all patients underwent sagittal T1-weighted spin-echo unenhanced and opposed-phase gradient-recalled echo images, and signal intensity measurements were taken. MR imaging was correlated to marrow specimens (n = 40) and a clinical staging system. The probability of survival was also calculated. Finally, we performed qualitative visual evaluation (infiltration pattern, degree of tumor involvement) and a quantitative evaluation (marrow signal intensity ratios, contrast enhancement). Five infiltration patterns were found: normal-appearing marrow with low-grade interstitial infiltration (n = 5), focal (n = 18), diffuse (n = 12), focal and diffuse (n = 13), and salt-and-pepper (n = 5). Infiltration pattern correlated with clinical staging; all patients with normal-appearing and salt-and-pepper patterns were clinically stage I. Diffuse marrow infiltration was assessed by marrow ratios: low-grade infiltration, greater than 2.0; intermediate, 1.0-2.0; highgrade, less than 1.0. Contrast enhancement with a signal intensity increase greater than 40% indicated diffuse infiltration. In the control group, all of whom had no marrow disease, enhancement varied (mean +/- SD, 16% +/- 8.9%) but did not exceed 40%. Marrow involvement on MR images correlated significantly with clinical staging and survival (p < or = .001). MR imaging with opposed gradient-recalled echo sequences and contrast enhancement provided data that allowed us to classify infiltration patterns and to quantify diffuse marrow involvement in multiple myeloma, both of which correlated to clinical staging and biopsy. Also, the MR data was of prognostic value. Therefore, like laboratory parameters, biopsies, and radiographs, MR imaging can be a supporting pillar in staging and planning treatment of patients with multiple myeloma.