Leo J. Rigler lecture. MR imaging of the liver

Recent technical and clinical advances in MR of the liver are reviewed with special reference to the role of MR as a primary screening technique for detection of space-occupying lesions, especially metastases. The major current problem in upper abdominal MR imaging is physiologic motions, and this appears to have been effectively solved by newly introduced pulse-sequence and timing-parameter strategies. Short-TR/TE spin-echo sequences with extensive signal averaging and heavy T1-weighting produce images with exceptional anatomic detail and liver-cancer contrast differences. With this sequence superior sensitivity for liver-cancer detection has been shown in quantitative signal-difference to noise comparisons with other pulse sequences and in clinical comparisons with CT. MR discovered 14% more individual metastases and 3% more patients with liver cancer than CT in a blinded comparative study of 142 patients undergoing both exams. MR also showed greater specificity (98%) than CT (91%) in distinguishing patients without liver metastases. Differentiation of hemangioma from metastases was possible with greater than 90% specificity by using heavily T2-weighted sequences. Use of a fast-scan, gradient-recalled echo technique can also produce good-quality, multislice, T1-weighted studies of the liver in 20 sec--a breath-hold. MR contrast agents (such as gadolinium-DTPA and reticuloendothelial-system-specific, superparamagnetic ferrite-iron-oxide particles) offer further promise for enhanced sensitivity for liver-cancer detection. When optimal pulse sequences are employed, MR can now be appropriate as a primary screening method for detecting liver neoplasms.     

Imaging of pancreatic neoplasms: comparison of MR and CT

Thirty-two patients with pathologically proved pancreatic carcinomas or cystadenomas were evaluated with MR images obtained with T1-weighted spin echo (short TR/short TE), inversion recovery, and T2-weighted spin-echo (long TR/long TE) pulse sequences. CT was used as the reference standard to determine the ability of MR to delineate normal and abnormal pancreatic anatomy and thereby to exclude or detect pancreatic malignancy. Short TR/short TE spin-echo sequences were significantly better (p less than .05) than inversion recovery or T2-weighted spin-echo sequences in resolution of both normal and abnormal anatomy. Resolution of pancreatic anatomy correlated (r = .9) with the image signal-to-noise ratio. In seven (22%) of 32 cases, MR visualized pancreatic tumors better than CT did because it showed a signal intensity difference between the tumor and normal pancreatic tissue. Overall, the slight superiority of MR over CT for tumor visualization tended to occur in larger tumors and was not statistically significant. On T1-weighted images, 63% (20 of 32) of pancreatic tumors studied had lower signal intensities than normal pancreatic tissue, whereas on T2-weighted sequences (TE = 60, 120, and 180 msec) only 41% (13 of 32) of tumors had increased signal intensities. Currently available MR imaging techniques offer no significant advantages over CT for evaluating the pancreas for neoplasia.     

Comparison between high-field-strength MR imaging and CT for screening of hepatic metastases: a receiver operating characteristic analysis.

The diagnostic performance of high-field-strength magnetic resonance (MR) imaging (1.5 T) for detection of liver metastases was compared with that of computed tomography (CT). All patients (n = 52) underwent preoperative screening for metastases by means of MR imaging with T1-weighted, proton-density-weighted, and T2-weighted pulse sequences and CT scanning with unenhanced, incremental dynamic bolus-enhanced, and delayed contrast medium-enhanced techniques. Diagnostic performance was evaluated by means of receiver operating characteristic analysis in which 800 images (400 with and 400 without lesions) and five readers (4,000 observations) were used; images were obtained from patients (n = 39) in whom the same anatomic levels were available for all MR imaging and CT studies. Direct comparison between the best MR imaging technique (T2-weighted spin-echo imaging [repetition time, 2,000 msec; echo time, 70 msec]) and the best CT technique (incremental dynamic bolus CT) showed a strong trend of superiority of T2-weighted MR imaging over incremental dynamic bolus CT. No highly statistically significant difference (P greater than or equal to .01), however, was found between these two techniques.     

Liver metastases: detection by phase-contrast MR imaging

Forty patients with biopsy-proved metastatic liver cancers were studied by magnetic resonance (MR) imaging using one or more conventional (in-phase) pulse sequences and a corresponding phase-contrast (opposed-phase) pulse sequence. Pulse-sequence performance was quantitated by measuring signal-difference-to-noise (SD/N) ratios between cancerous tissue and liver. The SD/N performance of T2-weighted spin-echo (SE) pulse sequences improved when used with the phase-contrast technique. SE 2,000/30 opposed-phase images showed improved (P less than .001) SD/N in 72% of patients over in-phase images. The SD/N of T1-weighted SE or inversion recovery pulse sequences deteriorated when used with the phase-contrast technique. Changes in measured SD/N correlated well with image appearance and actual lesion detectability in individual cases. Phase-contrast imaging should be employed routinely when T2-weighted SE pulse sequences are relied on to detect liver cancer.     

Detection of hepatic metastases with MR imaging: spin-echo vs phase-contrast pulse sequences at 0.6 T

The purpose of this study was to compare the sensitivity of T1-weighted and T2-weighted spin-echo (SE) pulse sequences with T2-weighted phase-contrast (PC) imaging techniques for the detection of hepatic metastases. Pulse-sequences performance was evaluated in 52 consecutive patients with 88 hepatic metastases who underwent MR imaging at 0.6 T. Lesion-liver contrast-to-noise ratios (CNR) on SE 260/14 (-12.4 +/- 6.7) and PC 2350/60 (+10.8 +/- 4.2) images were significantly (p less than .05) greater than on SE 2350/60 (+ 7.8 +/- 3.9), SE 2350/120 (+8.1 +/- 4.8), SE 2350/180 (+7.9 +/- 4.5), and PC 2350/30 (+4.6 +/- 2.9) images. Sensitivity for detection of 88 individual metastases was comparable on SE 260/14 (78 of 88 patients) and PC 2350/60 (81 of 88 patients) images and was significantly (p less than .05) greater than on in-phase T2-weighted SE images (TE = 60, 70 of 88 patients; TE = 120, 69 of 88 patients; TE = 180, 65 of 88 patients). Histologic analysis of tumor-free liver showed fatty change in 11 of 13 specimens available for pathologic evaluation. In all 11 of those patients, PC images increased tumor-liver contrast in comparison with the in-phase SE images. This analysis suggests that for detection of hepatic metastases at midfield strengths, the T1-weighted, short TR/short TE (SE 260/14) and the T2-weighted, phase-contrast (PC 2350/60) pulse sequences offer comparable performance.     

Differentiation of hepatic metastases from hepatic hemangiomas and cysts by using MR imaging

T1-weighted and T2-weighted pulse sequences were employed for MR imaging of hepatic metastatic tumors (98 patients), hemangiomas (24 patients), and cysts (seven patients); a 0.6-T superconducting magnet was used. In a retrospective study, signal intensity and morphology were used to establish criteria for differentiating metastases from hemangiomas and cysts. The signal intensity of the lesion alone failed to be an etiologic discriminator because over 96% of all masses had a signal intensity less than that of liver on T1-weighted sequences, and at least 90% had a signal intensity greater than that of liver on T2-weighted sequences. Morphologic features depicted on T2-weighted images were more specific than those depicted on T1-weighted images in differential diagnosis. Amorphous, target, and halo signs and a change in morphology were present only in metastatic disease, with a frequency of 45%, 27%, 13%, and 12%, respectively. Two other morphologic patterns--doughnut and lightbulb signs--were found to have overlapping causes. Overall, at least one of the specific signs was observed in 92% of patients with metastatic disease. These data suggest that T2-weighted pulse sequences are essential for discriminating between hepatic metastases and hepatic hemangiomas and cysts. MR imaging is a promising technique for distinguishing these lesions.     

Hepatic metastases studied with MR and CT

Examinations of the liver using magnetic resonance (MR) and computed tomography (CT) were performed on 50 patients with hepatic metastases. MR and CT were comparable in their ability to detect metastases, which generally appeared hypointense compared with normal liver parenchyma on T1-weighted MR images and hyperintense on T2-weighted images. The MR imaging techniques that were most reliable in detecting metastases were inversion recovery and a relatively T2-weighted, spin-echo technique (TR = 1,500 msec, TE = 60 msec). We conclude that CT, because of its shorter imaging time, greater spatial resolution, and lower cost, should remain the preferred screening test for hepatic metastases. MR imaging should be reserved for patients with equivocal CT findings and for patients in whom there is persistent clinical suspicion of hepatic metastases despite a negative CT examination.     

Focal liver lesions: characterization with quantitative analysis of T2 relaxation time in TSE sequence with double echo time

PURPOSE: To evaluate the accuracy of calculation of T2 relaxation time with simplified algorithm in characterization of liver focal lesions with Turbo Spin Echo (TSE) T2-weighted sequences with double echo time (TE). MATERIALS AND METHODS: We carried out a retrospective analysis of 113 hyperintense hepatic focal lesions in T2-weighted sequences (52 metastases, 51 hemangiomas and 10 cysts). We have employed a single TSE T2-weighted sequence with effective TE of 83 and 165 msec and turbo factor 9. Signal intensity (IS) of each lesion was measured on different TE. Using these values, we calculated T2 relaxation time by the following simplified algorithm: T2(ms)=(TE2-TE1)/ (lnIS1-lnIS2). T2 relaxation time has been correlated with the final diagnosis, obtained by percutaneous biopsy, surgical resection or three months follow-up. RESULTS: The mean T2 relaxation time for metastases was 108,7 msec (+/-30), for hemangiomas 166,5 msec (+/- 29) and for cysts 312,4 msec (+/-19). The difference between the mean T2 relaxation time for metastases and hemangiomas was statistically significant (p<0.0001). Most metastases were best characterized between the threshold value of 130 and 140 msec. The values of specificity and sensitivity of the diagnosis of malignant hepatic lesion was respective 0,86 and 0,88. All false positive diagnoses were hemangiomas of less than one centimeter. CONCLUSIONS: Introducing double echo time TSE sequences in the protocol of liver study concurs to obtain high diagnostic accuracy in the characterization of the hepatic lesions. The quantitative analysis of T2 represents a useful additional instrument to the morphologic analysis in discrimination between hepatic lesions and can be carried out by TSE sequences with elevated reliability reducing the imaging time compared with conventional sequences. The evaluation of hepatic lesions of less than one centimeter should always include analysis of dynamic gadolinium-contrast images.     

Addition of gadolinium chelates to heavily T2-weighted MR imaging: limited role in differentiating hepatic hemangiomas from metastases

OBJECTIVE: The purpose of this study was to determine whether the addition of gadolinium-enhanced imaging to heavily T2-weighted MR imaging of the liver is valuable in differentiating hemangiomas from metastases. The T2 relaxation time was also included in our analysis. SUBJECTS AND METHODS: Fifty-one patients with 52 proven liver lesions (24 hemangiomas and 28 metastases) larger than 1 cm underwent MR imaging at 1.5 T with T2-weighted spin-echo (TR/TE, 3000/80, 160) and gadolinium chelate-enhanced dynamic T1-weighted gradient-recalled echo (80/2.6, 80) pulse sequences. Images were reviewed by observers who were unaware of the patients' clinical history; first, only T2-weighted images were reviewed and then T2-weighted plus dynamic images were reviewed together. The T2 relaxation times were calculated for each lesion. Diagnostic accuracy by each method was compared using receiver operating characteristic analysis. RESULTS: Mean T2 relaxation times were 76 +/- 26 msec for metastases and 133 +/- 25 msec for hemangiomas. The addition of dynamic scanning to the T2-weighted sequence made a statistically significant difference for only one observer (p = 0.03). However, it did not make a statistically significant contribution for either observer when compared with the T2 relaxation time. Although addition of the dynamic images resulted in correct diagnosis of six lesions, three lesions were misdiagnosed after having been correctly characterized on the T2-weighted images alone. CONCLUSION: When optimized T2-weighted images are obtained and the T2 relaxation time is calculated, routine use of gadolinium enhancement for differentiation of hemangiomas from metastases is unnecessary although dynamic scanning is valuable in selected cases.     

Hepatic tumors: differentiation by transverse relaxation time (T2) of magnetic resonance imaging

Fifty-three patients who had hepatic tumors (24 hepatomas, ten metastases, and 19 cavernous hemangiomas) underwent MR imaging using a 0.35-T superconducting imager. The transverse relaxation time (T2) was calculated from a pair of spin echo images (repetition time [TR] of 1600 msec) with echo delay times (TE) of 35 and 70 msec. The computed T2 value was obtained in a fashion similar to that used to obtain CT numbers with region-of-interest cursors. The mean T2 was 59 +/- 9 msec in hepatomas, 64 +/- 15 msec in metastases, and 100 +/- 30 msec in hemangiomas. The difference between the T2 of hemangioma and that of liver malignancies was statistically significant (P less than .001); however, differentiation between hepatoma and metastases was not possible. The T2 was shorter than 80 msec in all 24 hepatomas and in nine of ten metastases, and was longer than 80 msec in 16 of 19 hemangiomas. Forty-nine of 53 cases (92%) were correctly classified when the borderline of T2 between hemangioma and hepatic malignancies was set at 80 msec. MR with T2 calculation was valuable in differentiating between hemangioma and hepatic malignancies.     

MR imaging of the lungs: value of short TE spin-echo pulse sequences.

OBJECTIVE. An experimental short echo delay (TE = 7 msec) T1-weighted spin-echo sequence was compared with a conventional (TE = 20 msec) T1-weighted spin-echo sequence in the assessment of normal and abnormal lung parenchyma. Comparison was also made with high-resolution CT of abnormal lung parenchyma. SUBJECTS AND METHOD. At 1.5 T, an experimental short echo delay T1-weighted multislice spin-echo sequence (TR = RR interval, TE = 7 msec) was compared with an optimal conventional T1-weighted spin-echo sequence (TR = RR interval, TE = 20 msec, spatial presaturation). Ten healthy volunteers were examined with both sequences. The mean signal intensity and signal-to-noise ratios were calculated in lung parenchyma for both sequences. Two radiologists compared the visualization of normal lung parenchymal structures with the two techniques. In 24 patients with diffuse lung disease, results with both MR sequences and with high-resolution CT were compared. RESULTS. The signal intensity was significantly greater (p < .001) with the TE of 7 msec than with the TE of 20 msec, resulting in a 3.5-fold improvement in the signal-to-noise ratio. The 7-msec TE improved visualization of lung parenchymal structures, including peripheral vessels, interlobular septa or veins, and centrilobular arteries. In the patients with diffuse lung disease, pulmonary parenchymal abnormalities were better visualized on the images with TEs of 7 msec than on images with TEs of 20 msec. When compared with high-resolution CT, the sequence with a TE of 7 msec provided comparable assessment of air-space opacification and dense consolidation, but it was inferior to high-resolution CT in the anatomic assessment of lung parenchyma. CONCLUSION. This experimental spin-echo sequence with a TE of 7 msec significantly improves the signal-to-noise ratio, allowing improved visualization of normal and abnormal pulmonary parenchyma when compared with conventional spin-echo images with a TE of 20 msec. Although anatomic detail remains inferior to that seen with high-resolution CT, the improved image quality with a TE of 7 msec suggests that assessment and follow-up of parenchymal lung disease might be possible with MR, thereby avoiding ionizing radiation.     

Breast and axillary tissue MR imaging: correlation of signal intensities and relaxation times with pathologic findings

We tested a variety of inversion-recovery (IR) and spin-echo (SE) sequences by imaging the breast masses of 22 patients before surgery and 23 tissue specimens with magnetic resonance (MR) imaging at 0.6 T to determine the most effective pulse sequences to evaluate breast disease. An SE pulse sequence using a long repetition time (TR) of 1,600 msec and a long echo time (TE) of 90 msec was found to be the most sensitive in depicting carcinoma in the excised tissue specimens, with all of the carcinomas (n = 15) demonstrating irregular areas of higher signal intensity (SI) than that of the adjacent fat. However, only five of 11 breast carcinomas present in the preoperative patients produced a higher SI than that produced by fat on the same T2-weighted sequence. Five of the remaining six carcinomas in the preoperative patients appeared as localized distortions of fibroductular architecture on both T2-weighted SE and IR sequences. In axillary tissue specimens, both metastatic carcinoma and hyperplastic lymph nodes produced a high SI on T2-weighted SE sequences. However, metastatic carcinoma had a significantly longer T2 relaxation time than did hyperplastic lymph nodes.     

Short TI inversion-recovery imaging of the liver: pulse-sequence optimization and comparison with spin-echo imaging

Magnitude-reconstructed short inversion-time (TI) inversion-recovery (IR) sequences have the advantage of reducing the signal of fat while providing additive T1 and T2 contrast. A double-echo short TI IR sequence was implemented to offer different degrees of T1- and T2-dependent image contrast. In 50 consecutive patients with proved liver tumors (30 metastases, 13 hemangiomas, seven other primary liver tumors), images obtained with a double-echo IR sequence at a repetition time (TR) of 1,500 msec, echo time (TE) of 30 and 60 msec, and TI of 80 msec (TR/TE/TI = 1,500/30, 60/80) were compared with those obtained with spin-echo (SE) sequences at a TR of 275 msec and a TE of 14 msec (TR/TE = 275/14) and 2,350/60, 120, 180. Metastases-liver contrast-to-noise ratios were highest at SE 275/14, followed by IR 1,500/30/80 and SE 2,350/180. IR 1,500/30/80 and SE 275/14 sequences consistently showed higher sensitivity for the detection of metastases than T2-weighted SE sequences. Differential diagnosis of benign and malignant lesions was more reliable with T2-weighted SE sequences than T2-weighted short TI IR sequences.     

Neck neoplasms: MR imaging. Part I. Initial evaluation

Untreated neoplasms of the neck (tumors of the oropharynx, supraglottic area, carotid body, and thyroid, in addition to malignant lymphadenopathy) were evaluated in 23 patients with magnetic resonance (MR) imaging. The results were compared with computed tomographic (CT) scans in 20 patients. Contrast between tumor and fat was best on relatively T1-weighted images (500/30-35 [TR msec/TE msec]), whereas separation of tumor and muscle was best with relatively T2-weighted pulse sequences (1,500/90). Balanced images (1,500/30-35) provided best overall image quality and best demonstrated vascular anatomy. MR imaging was usually superior to CT in showing the relationship of tumor mass to muscle. MR imaging and contrast material-enhanced CT were equivalent in most patients in defining vascular anatomy, but MR imaging was superior when intravenous contrast material was not administered. However, CT was more helpful in showing bone and cartilage anatomy, and in some patients CT also was better in showing airway abnormalities. Despite these limitations, MR imaging is a promising imaging technique for studying neoplasms of the neck.     

Central nodal necrosis and extracapsular neoplastic spread in cervical lymph nodes: MR imaging versus CT.

Computed tomographic (CT) scans and magnetic resonance (MR) images obtained in 24 patients with cervical lymphadenopathy were retrospectively and blindly evaluated by two readers for the presence of central nodal necrosis (CNN) and extracapsular nodal spread (ENS). The CT studies were all enhanced, and the MR images were obtained with short repetition time (TR)/echo time (TE), long TR/double echo, and enhanced short TR/TE fat-suppressed sequences. Each MR imaging sequence was interpreted separately and then collectively. Sixty lymph nodes were identified with CT. Sensitivity for CNN was 16%-67% with the unenhanced MR pulse sequences, 50% with enhanced sequences, and 83%-100% with CT. The most accurate reading of MR images for CNN was with the unenhanced T1-weighted and T2-weighted images (86%-87%); the accuracy of CT was 91%-96%. The accuracy of MR imaging for detecting ENS was maximal with T1-weighted images (78%-90%). Gadolinium-enhanced, fat-suppressed images did not improve accuracy in evaluating CNN or ENS. CT is currently more accurate than unenhanced or enhanced MR imaging in detecting CNN or ENS.     

Differentiation between hemangiomas and metastases of the liver with ultrafast MR imaging: preliminary results with T2 calculations

We studied the efficacy of T2 measurements at high field strength in distinguishing between liver hemangiomas and hepatic metastases when an ultrafast (single-excitation) MR imaging technique is used. Fourteen patients with known liver tumors were imaged in a 2.0-T prototype ultrafast MR scanner with a spin-echo (infinite TR and TE of 30-340 msec) pulse sequence. Each image was obtained with a total data acquisition time of 20 msec. T2 calculations for hepatic metastases (n = 6) showed a mean of 79.3 +/- 13.5 msec, whereas hemangiomas (n = 8) showed a T2 of 139.8 +/- 18.8 msec (p less than .0001). T2 values of lesions had a smaller relative standard deviation than previously reported, and the range of T2 values of hemangiomas (119-181 msec) and metastases (68-103 msec) did not overlap. Our preliminary results suggest that T2 calculations with ultrafast MR imaging may be useful for differentiating hemangiomas from metastases. We hypothesize that T2 values obtained from ultrafast MR images are more reliable than those obtained from conventional MR images, primarily because of the elimination of T1 information and effects of motion on image signal intensity.     

Detection of hepatic metastases: analysis of pulse sequence performance in MR imaging

Forty-three patients with liver metastases were imaged using 14 different pulse sequences (average, 7.5 sequences per patient) to allow direct comparison of their performance. "T2-weighted" spin-echo (SE) images, "T1-weighted" inversion recovery (IR) images, and "T1-weighted" SE images were obtained using a wide range of timing parameters. Pulse sequence performance was quantitated by measuring liver signal-to-noise (S/N) ratios and cancer-liver signal difference-to-noise (SD/N) ratios. Data were standardized to reflect a constant imaging time of 9 minutes for all pulse sequences. The SE 2,000/120 (TR [repetition time]/TE [echo time]) sequence resulted in the greatest SD/N ratio of the T2-weighted SE sequences but also yielded the low S/N ratios, poor anatomic resolution, and motion artifacts common to all T2-weighted SE images. IR sequence images were also sensitive to motion artifacts because of the use of a long TR (1,500 msec). Short TR/TE T1-weighted SE sequences (SE 260/18) had the greatest SD/N ratio (P less than .05), S/N ratio, and anatomic resolution. Furthermore, extensive signal averaging appears to be a powerful solution to all types of motion artifacts in the abdomen.     

Magnetic resonance with marked T2-weighted images: improved demonstration of brain lesions, tumor, and edema

The object of this study was to determine the sensitivity of magnetic resonance (MR) for imaging intracranial lesions with heavily T2-weighted images compared with that of computed tomographic (CT) and T1-weighted images. Fifty-five patients with known intracranial pathology consisting of primary neurogenic tumors, brain infarcts, demyelinating disease, and metastases were studied by MR and CT. Patients were studied with either 0.6 or 1.5 T systems with T1- and T2-weighted radiofrequency pulse sequences. The heavily T2-weighted images were found to be superior to the T1-weighted images in terms of sensitivity, with 168 lesions found versus 86 by CT and 104 by T1-weighted imaging.     

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

PURPOSE: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION: Addition of T1-weighted GRE images using minimum and moderate TE is helpful for characterizing focal lesions in ferumoxides-enhanced MR imaging.     

Pulmonary metastases: MR imaging with surgical correlation--a prospective study.

The sensitivity of magnetic resonance (MR) imaging for detection of pulmonary metastases in 11 patients scheduled for thoracotomy and curative resection of metastases was evaluated with a prospective, controlled study. MR imaging performed at 0.5 T was compared with chest radiography, computed tomography (CT), and thoracotomy in 12 cases. (One patient had two separate occurrences of pulmonary metastases.) All images were interpreted in blinded fashion. When all MR sequences were interpreted together, MR imaging enabled correct identification of all patients with pulmonary nodules (100%). CT enabled detection of at least one nodule in all 12 cases (100%) by design; the sensitivity of chest radiography was only 64%. For individual nodules, MR imaging was at least as sensitive as CT (P2 less than .25 [two-sided value]) and significantly more sensitive than chest radiography (P2 less than .01). Among all MR sequences, short inversion time inversion-recovery sequences had the highest sensitivity for detection of individual nodules (82%).