MR image contrast and relaxation times of solid tumors in the chest, abdomen, and pelvis

A retrospective study of 121 patients with tumors in the chest, abdomen, and pelvis was made to assess the degree of contrast between solid tumors and adjacent tissue on magnetic resonance (MR) spin echo (SE) images. Tumors examined were hepatomas (five patients), liver metastases (17), hemangiomas (seven), biliary carcinomas (eight), pancreatic carcinomas (five), renal tumors (15), adrenal tumors (eight), uterine tumors (17), bladder carcinomas (five), prostatic carcinomas (13), bone tumors (six), and lung carcinomas (15). A long repetition time (TR) and a long echo time (TE) were found the most useful to delineate tumors from liver, renal tumors from kidney, lung carcinoma from lung, pelvic tumors from muscle, and uterine tumors from the myometrium. A short TR and short TE provided the best contrast between tumors and fat and bone marrow. Therefore, for detection and staging of tumors, both a sequence with short TR and short TE and one with long TR and long TE are necessary. Pancreatic carcinomas were difficult to differentiate from liver and pancreas on all SE sequences used in the study. Contrast of adrenal tumors was independent of the sequence used. Some adrenal tumors were hypointense and some similar in intensity to the kidney. Further MR characterization of the tumors was limited.     

Combined gadolinium-enhanced and fat-saturation MR imaging of renal masses

Combined gadopentetate dimeglumine enhancement and fat-saturation (FS) spin-echo (SE) magnetic resonance (MR) imaging for the detection and characterization of renal masses was evaluated in 43 patients with a total of 71 lesions (28 solid masses and 43 cysts). SE MR sequences compared were the following: short repetition time (TR)/echo time (TE), conventional SE, short TR/TE FS SE, long TR/TE conventional SE, gadolinium-enhanced short TR/TE conventional SE, and gadolinium-enhanced short TR/TE FS SE techniques. MR findings were compared with findings of contrast-enhanced computed tomography (CT) and with pathologic findings in all patients. The sensitivities for detection of renal masses with gadolinium-enhanced FS (71 of 71 lesions) and with gadolinium-enhanced short TR/TE conventional (65 of 71 lesions) SE sequences were significantly (P less than .01) greater than with any unenhanced (short TR/TE conventional [40 of 71 lesions], or long TR/TE [39 of 71 lesions]) SE sequence. Lesion characterization was also best with the gadolinium-enhanced FS SE sequence (65 of 71 lesions correctly classified). When combined pre- and postcontrast short TR/TE FS SE images were analyzed with both qualitative (visual) and quantitative (region-of-interest measurements) assessment, lesion characterization improved even further (70 of 71 lesions were correctly characterized). All lesions detected with CT were visualized with the gadolinium-enhanced FS SE MR sequence, which in addition depicted seven cysts and two small renal cell carcinomas. In summary, the use of gadopentetate dimeglumine, especially when combined with the FS technique, was superior to unenhanced MR imaging for detection and characterization of renal lesions.     

Urinary bladder MR imaging. Part II. Neoplasm

The potential of magnetic resonance (MR) imaging for the evaluation and staging of bladder tumors was analyzed in 15 patients (11 cases of transitional cell carcinoma, two adenocarcinomas, one leiomyosarcoma, and one leiomyoma). Neoplasms were characterized by size, site, and growth pattern, and the accuracy of the staging was compared with the results of computed tomography and pathologic study. Malignancies were accurately detected and staged by MR imaging in 12 of 14 patients (85%). Tumor site and degree of bladder distention did not adversely affect detection; tumors greater than 1.5 cm were detected easily. In situ carcinoma (stage Tis) was not detected on MR images. Imaging in both sagittal and transverse planes was needed for optimal bladder evaluation. Bladder carcinoma was best displayed with a short echo delay time (TE) of 28 msec and repetition (TR) times of 1.0-2.0 sec: TR = 1.0 gave 34% contrast and TR = 2.0 gave 36% contrast between tumor and surrounding urine. Bladder-wall invasion by tumor was best evaluated with long TR (2.0 sec) and long TE (56 msec) (82% contrast). For assessing tumor extension into perivesical fat, short TR (0.5 sec) and TE (28 msec) were optimal (58% contrast). MR imaging offers an increased sensitivity for tumor detection and promises to greatly improve the staging of bladder neoplasms.     

MR imaging of the dilated biliary tract

The magnetic resonance (MR) examinations of 18 patients with dilated bile ducts were reviewed retrospectively to determine the capability of MR to demonstrate biliary dilatation, assess MR appearance of the dilated biliary tract using spin-echo techniques, and define the optimal MR imaging parameters (repetition time [TR] and echo time [TE]) for its demonstration. On images with short TR (0.5 sec) and TE (28 msec), the dilated intrahepatic and intrapancreatic bile ducts usually had lower signal intensity compared with the surrounding liver or pancreas; on images with long TR (2.0 sec) and TE (56 msec), they had higher signal intensity. Because of the observed variation in percentage of contrast between dilated bile ducts and surrounding liver and pancreas, two imaging sequences are recommended to obtain reliable demonstration of dilated intrahepatic and intrapancreatic bile ducts. The dilated common bile duct at the level of the hepatic hilus is best seen with a short TR and TE.     

Hyaline articular cartilage: relaxation times,pulse-sequence parameters and MR appearance at 1.5 T

In order to optimize the parameters for the best visualization of the internal architecture of the hyaline articular cartilage a study both ex vivo and in vivo was performed. Accurate T1 and T2 relaxation times of articular cartilage were obtained with a particular mixed sequence and then used for the creation of isocontrast intensity graphs. These graphs subsequently allowed in all pulse sequences (spin echo, SE and gradient time (TR), echo time (TE) and flip angle (FA) for optimization of signal differences between MR cartilage zones. For SE sequences maximum contrast between cartilage zones can be obtained by using a long TR (> 1,500 ms) with a short TE (< 30 ms), whereas for GRE sequences maximum contrast is obtained with th shortest TE (< 15 ms) combined with a relatively long TR (> 400 ms) and an FA greater than 40°. A trilaminar appearance was demonstrated with a superficial and deep hypointense ozne in all sequences and an intermediate zone that was moderately hyperintense on SET1-weighted images, slightly more hyperintense on proton density Rho and SE T2-weighted images and even more hyperintense on GRE images.     

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.     

Recurrent thyroid carcinoma: characteristics on MR images

Magnetic resonance (MR) imaging was used in 32 patients, including eight with benign disease, after partial or total thyroidectomy to determine sensitivity and specificity of MR imaging in the detection of tumor recurrence, to compare signal intensities of scar versus recurrent tumor qualitatively and quantitatively, and to define the extent of recurrent tumor. Findings from surgery (n = 23), needle biopsy (n = 1), or clinical follow-up (n = 8) were used for verification. Of 24 patients with primary thyroid carcinoma, 15 had recurrence and nine had a normal postsurgical thyroid bed. Diagnosis from MR images was correct in 20 cases, but false positive in three and false negative in one. Local recurrence was characterized by low to medium intensity on short repetition time (TR)/short echo time (TE) images and medium to high intensity on long TR/long TE images. Scar in the normal postsurgical thyroid bed showed low intensity on both short and long TR/TE images. Local recurrence of thyroid carcinoma and lymph node metastasis produced positive contrast compared with muscle on short TR/short TE (31 + 19%) and long TR/long TE (85 + 30%) images; fibrosis produced negative contrast, particularly on long TR/long TE (-56, -80%) images. These results indicate the capability of MR imaging in the evaluation of recurrence of thyroid tumors and in the differentiation of abnormal tissue due to tumor recurrence from postoperative fibrosis by means of signal contrast relative to a reference tissue.     

Chondrosarcomas of the skull base: MR imaging features.

The magnetic resonance (MR) images from 17 patients with chondrosarcomas of the skull base were retrospectively reviewed to characterize the size, location, signal intensity, and extension of these tumors. Eleven patients with chondrosarcomas received intravenously administered gadopentetate dimeglumine. In 16 patients, computed tomographic (CT) scans were obtained to evaluate intratumorous mineralization and bone erosion. On short repetition time (TR)/echo time (TE) MR images, chondrosarcomas generally had low to intermediate signal intensity; on long TR/TE MR images, they generally had very high signal intensity. Signal heterogeneity on long TR/TE MR images was seen in 10 of 17 tumors (59%) and was caused by matrix mineralization, fibrocartilaginous elements, or both. Matrix mineralization was demonstrated with CT in seven of the 16 chondrosarcomas. Chondrosarcomas showed marked enhancement after administration of gadopentetate dimeglumine in either a heterogeneous (n = 8) or homogeneous (n = 3) pattern. The information about the size and extent of these neoplasms was important in the choice of surgical approaches for gross total resection of tumor.     

A comparison between fast and conventional spin-echo in the detection of multiple sclerosis lesions

Long repetition time (TR) spin-echo (SE) with T₂- or proton density weighting is the sequence of choice to detect the brain lesions of multiple sclerosis (MS). Fast spin-echo (FSE) permits the generation of T₂-weighted images with similar contrast to SE but in a fraction of the time. We compared the sensitivity of FSE and SE in the detection of the brain lesions of MS. Six patients with clinically definite MS underwent brain imaging with both dual echo (long TR, long and short echo time (TE) SE and dual echo FSE. The SE and FSE images were first reviewed independently and then compared. A total of 404 lesions was detected on SE and 398 on FSE. Slightly more periventricular lesions were detected using SE than FSE (145 vs 127), whereas more posterior cranial fossa lesions were detected by FSE (77 vs 57). With both SE and FSE the short TE images revealed more lesions than the long echo. These results suggest that FSE could replace SE as the long TR sequence of choice in the investigation of MS.     

Magnetization transfer contrast MRI of musculoskeletal neoplasms

Magnetic resonance imaging (MRI) examinations were performed in 15 patients with musculoskeletal neoplasms to assess the value of magnetization transfer contrast in tumor characterization. Multiplanar gradient-recalled echo sequences (TR 500-600/TE 15-20/flip angle 20–30°) were performed first without and then with magnetization transfer contrast generated by a zero degree binomial pulse (MPGR and MTMPGR). Standard T1-weighted spin echo images (SE; TR 300-400/TE 12-20) and either T2-weighted SE (TR 2000-2900/TE 70-80) or T2-weighted fast spin echo (FSE; TR 4000-5000/TE 100-119 effective) images were also obtained. Signal intensities on MTMPGR scans were compared to those on MPGR scans for both tumors and normal tissues. Signal intensity ratios (SIR) and contrast-to-noise ratios (CNR) were also compared for all sequences. MTMPGR images provided better contrast between pathologic tissues and muscle than did standard MPGR images, increasing both conspicuity of lesions and definition of tumor/muscle interfaces. Benign and malignant tumors, with the exception of lipoma, underwent similar degrees of magnetization transfer and could not be distinguished by this technique.     

Fibrolamellar hepatocellular carcinoma: MR appearance

We report two cases of fibrolamellar hepatocellular carcinoma, each of which had lower signal intensity than normal liver on short repetition time (TR), short echo time (TE) spin-echo (SE) images and demonstrated a central scar-like area of low signal intensity which did not become hyperintense on long time TR/TE SE images.     

Capsular retraction of the liver in malignant tumor of the biliary tract MRI findings

Retraction of the liver capsule adjacent to a hepatic tumor is an unusual feature that has received little attention in radiological literature. We report two patients with pathologically proved malignant tumor of the biliary tract (one cholangiocarcinoma and one gallbladder cancer) in whom magnetic resonance imaging (MRI) showed retraction of the liver capsule to the tumors. MRI was performed at 1.0 T using a spin-echo (SE) technique, with T1 (TR/TE = 450/15 msec) and T2 (TR/TE = 2000/45 to 90 msec)-weighted images. Capsular retraction was seen on both T1- and T2-weighted SE MRI. Although capsular retraction of the liver adjacent to hepatic tumors is highly suggestive for epithelioid hemangioendothelioma, these two cases confirm that retraction of the liver capsule adjacent to hepatic tumors can be associated with other types of tumor, and especially with malignant tumors of the biliary tract.     

MR imaging of intracranial metastatic melanoma

Ten patients with intracerebral metastases from malignant melanoma were evaluated with magnetic resonance (MR) imaging performed at 1.5 T using spin-echo techniques. On the basis of histopathologic findings in three of 10 cases and CT appearances in all 10 cases, three patterns were identified on analysis of MR signal intensities in both short repetition time/echo time (TR/TE) and long TR/TE spin-echo scans. In comparison to normal cortex, nonhemorrhagic melanotic melanoma appeared markedly hyperintense on short TR/TE images and isointense, mildly hypointense on long TR/TE images. Nonhemorrhagic, amelanotic melanoma appeared isointense or mildly hypointense on short TR/TE and isointense or mildly hyperintense on long TR/TE images. Hemorrhagic melanoma varied in appearance, depending on the stage of hemorrhage. Melanotic, nonhemorrhagic melanoma can be distinguished from early and late subacute hemorrhage by its signal intensity on long TR/TE images. Spin-echo MR appears to be the method of choice for diagnosing melanotic metastases.     

Subacute intracranial hemorrhage: contribution of spin density to appearance on spin-echo MR images

The T2 and pseudodensity (proportional to proton density) of intracranial hemorrhages and normal white matter were calculated. The mean T2 (+/- standard deviation) was 120 +/- 62 for hemorrhage and 61 +/- 11 for white matter. Pseudodensity values were normalized to a white matter value of 1, and the value for hemorrhage was 1.56 +/- 0.28. These values were used to determine which components of hemorrhage-white matter contrast are due to T1, T2, and density. The results indicate that on spin-echo (SE) images obtained with a long repetition time (TR)/short echo time (TE) (2,500/0-20 [TR msec/TE msec]), the contrast is mainly due to density differences, with a modest T2 contribution on 20-msec-TE images and nearly no T1 component. At 600/0-20, the contrast continues to be largely determined by density differences, again with a modest T2 component on 20-msec-TE images. If the T1 of hemorrhage is extremely short, the T1 component of contrast on 600/0-20 SE images will be somewhat greater than the density component. Because contrast on short TR/short TE images may be largely or entirely determined by pseudodensity or T2, it is inaccurate to refer to 600/20 images as "T1-weighted". The assumption that high signal intensity at this sequence implies a "short T1" will lead to misleading conclusions.     

周围型肝内胆管细胞癌的CT与病理对照研究

目的：研究周围型肝内胆管细胞癌CT表现的病理基础。探讨与其它肝内肿瘤的鉴别点。材料和方法：对照分析22例肝内胆管细胞癌(低分化腺癌18例、中分化腺癌2例、乳头状粘液腺癌2例)手术切除标本病理所见与CT(22例)，超声(9例)，血管造影(2例)表现。结果：CT上瘤块呈均匀低密度(90%)——反映肝内胆管细胞癌瘤体很少出现出血，坏死、囊变的均质特征；瘤块边界不清(100%)与肿瘤的浸润性生长方式和缺少纤维包膜有关；增强后仅有轻度强化提示肿瘤的少血管特性；所有病例都无肝硬化的CT表现。结论：周围型肝内胆管细胞癌有着和其他肝肿瘤(特别是肝细胞癌)不同的病理特征，CT检查对此可作出较正确判断。     

Acute intracranial hemorrhage: intensity changes on sequential MR scans at 0.5 T

Thirty-seven patients underwent MR imaging at 0.5 T within 7 days of a CT-documented intracranial hemorrhage. A total of 57 hematomas were evaluated. Twelve patients underwent serial scanning and 12 patients had multiple hemorrhages into different intracranial compartments. The appearances of the hematomas on spin-echo (SE) images with a short repetition time (TR) of 500 msec and short echo time (TE) of 32 msec (SE 500/32), long TR/intermediate TE (SE 2000/60), and long TR/long TE (SE 2000/120) were carefully evaluated with specific attention to the precise time after ictus. Hematomas showed heterogeneous, complex, rapidly changing intensities. There was a significant amount of variation among patients, especially between the third and seventh days. Hematomas studied between 12 and 24 hr after hemorrhage were mildly hyperintense on short TR scans and markedly hyperintense on long TR (intermediate and long TE) scans (stage I). These findings in acute hemorrhage have received little prior attention. Over the next 1-2 days, hematomas became iso- to mildly hypointense on short TR scans and markedly hypointense on long TR scans (stage II). Hypointensity on long TR scans has previously been described at high field strengths; our communication demonstrates that this phenomenon is seen routinely at intermediate field strengths as well. Hematomas became markedly hyperintense on short TR scans beginning on approximately the fourth day postictus and redeveloped hyperintensity on long TR scans approximately 5-6 days after ictus (stage III). By the end of the first week they were hyperintense on all pulse sequences (stage IV). MR findings on the first day after intracranial hemorrhage (in particular, subtle hyperintensity on short TR scans) probably allow for a specific diagnosis, while the variable, hetergeneous, and rapidly changing intensities noted between days 2 and 7 are often less specific.     

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.     

Preliminary clinical results with low flip angle spin-echo MR imaging of the head and neck

A new approach for producing primarily T2- and proton-density-weighted MR images in less time than the conventional long TR, long TE imaging is to reduce the TR of a double spin-echo pulse sequence and to also reduce the RF excitation flip angle to minimize the resulting T1 sensitivity. In preliminary studies with a human volunteer and five patients with various diseases of the head and neck, conventional long TR, long TE and short TR, short TE images were compared with short TR, long TE images with reduced flip angles (45 degrees, 30 degrees), which required only 40% of the imaging time of the long TR images. The latter images showed a similar contrast pattern to the conventional T2-weighted image, and contrast-to-noise measurements indicated an increase in contrast between the lesion and nearby tissue when the flip angle was reduced. Furthermore, the maximum contrast/noise per unit imaging time on the short TR, long TE image was comparable to that on the long TR, long TE image. Optimization of the flip angle with short TR allows a substantial reduction in imaging time but with a reduction in multislice capability. This technique will be most useful in areas of complex anatomy where two or more orthogonal imaging planes are required, such as the head and neck.     

Painful sickle cell crisis: bone marrow patterns observed with MR imaging

Eleven patients with homozygous sickle cell anemia (SCA) undergoing painful crisis were studied with magnetic resonance (MR) imaging. The signal intensity of bone marrow was diffusely decreased in the axial and peripheral skeleton on short repetition time (TR)/echo time (TE) images and long TR/TE images, which suggested hematopoietic marrow hyperplasia and was confirmed by isotope marrow scans in five patients. Focal areas of further decrease in signal intensity were seen on short TR/TE images in 12 of the 14 (86%) painful joints and three of the five (60%) painless joints. In the painful joints, these focal areas converted to high signal intensity on long TR/TE images, presumably due to edema, which suggested acute marrow infarction. In the painless joints, these low-intensity focal areas remained as low signal on long TR/TE images, which suggested absence of edema and thus areas of old infarction or fibrosis. These results indicate that MR imaging may enable differentiation between acute and chronic marrow infarcts in patients with SCA and serve as a useful guide in monitoring and directing therapy.     

MR imaging of brain abscesses

The MR images and CT scans of 14 patients with surgically verified pyogenic cerebral abscesses were reviewed. The MR findings correlated well with those seen on CT and were believed to be sufficiently characteristic to allow early and accurate diagnosis with MR alone. These features include (1) peripheral edema producing mild hypointensity on short TR/short TE and marked hyperintensity on long TR/intermediate to long TE scans; (2) central necrosis with abscess fluid hypointense relative to white matter and hyperintense relative to CSF on short TR/short TE scans and hyperintense relative to gray matter on long TR/intermediate to long TE scans (the fluid had concentric zones of varying intensity in seven cases, a finding not previously identified in other lesions); (3) extraparenchymal spread (intraventricular or subarachnoid), which was detected more easily on MR than on CT and was manifested by increased intensity relative to normal CSF on both short TR/short TE and long TR/intermediate TE scans; and (4) visualization of the abscess capsule, which was iso- to mildly hyperintense relative to brain on short TR/short TE scans and iso- to hypointense relative to white matter on long TR/intermediate to long TE scans. On the long TR scans, the relative hypointensity of the rim allowed for visualization of the typical morphologic features of the capsule, which in turn aided in differentiation of abscesses from other lesions (as it does on CT). To investigate the cause of the capsular intensity, pathologic studies of the capsules were reviewed when available (10 cases). Fibrosis was identified in all mature abscess capsules, but the combination of the intensities seen on short TR/short TE and long TR/intermediate to long TE scans as well as the temporal changes in intensity were believed to be incompatible with fibrosis as a cause of the capsular changes. Intensity patterns were suggestive of hemorrhage, but neither acute nor chronic hemorrhage was identified on routine H and E stains, while iron stain revealed scant hemorrhage in only two of the eight patients in whom these stains were used. We believe the capsular intensity (in particular the hypointense rims on long TR scans) may reflect paramagnetic T1, and to a greater extent T2, shortening, possibly due to the presence of heterogeneously distributed free radicals that are products of the respiratory burst produced by actively phagocytosing macrophages in the capsule wall. Distinctive MR features of pyogenic abscesses should afford early and accurate diagnosis.