Choroidal melanomas: correlation of NMR spectroscopy and MR imaging

Six freshly enucleated, unfixed human eyes with choroidal melanomas were imaged on a 1.4-T superconducting magnetic resonance (MR) imaging system. Immediately thereafter the eyes were sectioned, and tumor samples were removed for study on a variable-field (0.19-1.4 T) nuclear MR spectroscopy unit. Shorter T1 and T2 relaxation times were observed in those tumors with the greater concentrations of melanin. This is believed to result from the paramagnetic effect of radicals known to exist in melanin. High magnetic field MR imaging can enable one to distinguish between pigmented melanomas; proteinaceous effusions; fresh and subacute hematomas; and nonmelanotic tumors, including amelanotic melanomas; but may not enable melanotic melanoma to be distinguished from fat or amelanotic melanoma from other nonpigmented tumors.     

Cardiac and vascular imaging with an MR snapshot technique

Real-time vascular and cardiac magnetic resonance (MR) imaging has been reported only with echo-planar imaging. In this study, the fast low-angle shot (FLASH) MR imaging sequence was reduced to repetition times of 3 msec and echo times of less than 1.3 msec with use of an improved MR imaging system. The resulting 200-msec MR images (64 X 128 pixels) are called snapshot FLASH images. They allow measurements from dynamic series of MR images depicting processes such as relaxation behavior and the cardiac cycle in the absence of motion and flow artifacts. In animal studies (at 4.7 T) and in studies of human volunteers (at 2.0 T), vascular and cardiac snapshot FLASH images were obtained as a single shot, as reconstructed motion, and as real-time movies. The arbitrary and fast T1 contrast of these images and the reduction of motion artifacts result in favorable applications for the depiction of myocardial and great-vessel anatomy. These clinical applications can be performed on conventional MR imagers with minor technical modifications.     

MR imaging of nitrosyl-iron complexes: experimental study in rats

PURPOSE: To assess the influence of several nitrosyl-iron complexes on proton nuclear spin relaxation rates to establish a magnetic resonance (MR) imaging technique for nitric oxide. MATERIALS AND METHODS: The influence of aqueous phantom solutions of nitrosyl-iron complexes on proton relaxation rates was analyzed for signal enhancement at conventional 1.5-T MR imaging. To induce formation of nitrosyl-iron complexes in a biologic tissue, isolated rat liver was perfused with a saline solution of the NO donor sodium nitroprusside (SNP), and the MR signal intensity was examined thereafter. RESULTS: All investigated nitrosyl-iron complexes shortened the longitudinal, or T1, and transverse, or T2, relaxation times in a concentration-dependent fashion. Relaxivities were highest with a dinitrosyl-iron complex bound to albumin and with a water-soluble mononitrosyl-iron dithiocarbamate complex. The contrast properties of 240 micromol/L of a paramagnetic nitrosyl-iron complex were sufficient to substantially enhance the signal intensity of SNP-perfused rat livers at hydrogen 1 MR imaging. CONCLUSION: Nitrosyl-iron complexes exhibit a contrast effect at MR imaging that can be exploited for NO imaging in living animals and patients with conventional (1)H MR imaging techniques.     

Pitfall in MR imaging of lymphadenopathy after lymphangiography

In two patients examined with magnetic resonance (MR) imaging after lymphangiography, opacified pelvic lymph nodes could not be distinguished from subcutaneous or retroperitoneal fat because of the short T1 and long T2 relaxation times of lymphangiographic contrast media. Opacified nodes removed from one patient had relaxation times similar to those of fat. Thus, assessment of lymphadenopathy with MR imaging should be performed before lymphangiography to obviate this potential pitfall.     

Bone marrow: ultrasmall superparamagnetic iron oxide for MR imaging

An ultrasmall superparamagnetic iron oxide (USPIO) preparation was evaluated as a potential intravenous contrast agent for magnetic resonance (MR) imaging of bone marrow. One hour after administration of USPIO (40, 80, and 160 mumols of iron per kilogram body weight) in rats and rabbits, T1 and T2 relaxation times were, respectively, approximately 30%, 50%, and 65% lower than precontrast relaxation times. Maximum decrease in relaxation times of marrow occurred within 1-24 hours after intravenous administration; thereafter, relaxation times slowly returned to normal within 7 days. In vivo MR imaging of rabbits and rats confirmed that USPIO decreases signal intensity of red and yellow marrow. The decrease was most marked with gradient echo pulse sequences. An animal model of intramedullary tumor demonstrated the potential of USPIO to enable differentiation between tumor and normal red marrow. USPIO-enhanced MR imaging improves detection of smaller tumors and allows differentiation of tumor deposits from islands of hyperplastic or normal red marrow.     

Magnetic resonance imaging findings of angiosarcoma of the scalp

OBJECTIVE: The purpose of this study was to investigate the magnetic resonance (MR) imaging findings of angiosarcoma of the scalp retrospectively. METHODS: Eight patients with angiosarcoma of the scalp were included in this study. All patients were examined with 1.5-T MR imaging units and commercially available head coils. RESULTS: In all 8 patients, MR images revealed thickened scalp or tumors with prolonged T1 and T2 relaxation times. They were well enhanced. T2-weighted MR imaging with fat saturation and contrast-enhanced T1-weighted MR imaging with fat saturation clearly showed tumors invading the subcutaneous fat tissue and muscles. In 4 patients, the tumors were larger on MR images than on inspection. CONCLUSIONS: Magnetic resonance imaging was useful in determining the extent of angiosarcoma of the scalp because it visualized the tumor invasion into surrounding structures that could not be seen on physical inspection.     

Low field (0.02 T) nuclear magnetic resonance imaging of the brain

Many technical and instrumental alternatives are available to obtain good spatial and contrast resolution in magnetic resonance (MR) imaging. Optimum field strength remains a controversial question. In spite of its inherent low signal-to-noise ratio, low field imaging exhibits some advantages. It is well established that the relaxation times are dependent on the magnetic field strength. In low fields the relaxation times, especially T1, are shorter and the relative differences of T1 between different tissues are larger. Other benefits are the ease of installation of the device, its cost effectiveness, and the obvious avoidance of hazards caused by the magnetic field. In this report we describe six cases of cerebral lesions studied with an MR imager operating at a field strength of 0.02 T (200 G). This is the lowest field strength reported in clinical MR imaging. The information obtained was equal to that of the CT studies performed on the same patients.     

Sodium and proton MR properties of cartilage during compression

Proton and sodium MR relaxation times of bovine articular cartilage specimens were measured as a function of proteoglycan (PG) depletion and as a function of mechanical compression. Proton and sodium relaxation times of normal cartilage were compared with relaxation times of PG-depleted cartilage to evaluate the significance of PG depletion-induced changes in MR relaxation parameters. These comparisons were conducted for both uncompressed and mechanically compressed states. The mechanical compressions were performed with an MR-compatible pressure cell and evaluated dynamically via interleaved one-dimensional proton and sodium MR projection imaging. The comparisons indicate that sodium relaxation parameters are sensitive to PG depletion when cartilage is in a mechanically compressed state or an uncompressed state. In contrast, proton relaxation parameters do not change significantly with PG depletion when cartilage is in an uncompressed state. However, during mechanical compression, proton T2 becomes sensitive to PG depletion. These results support the potential of sodium magnetic resonance imaging (MRI) as a possible modality for obtaining imaging contrast related to PG depletion. The results also indicate the potential of proton MRI to provide such contrast if the image acquisition is conducted in conjunction with a mechanical compression via physical exercise.J. Magn. Reson Imaging 10:961-967, 1999.     

Prolonged T1 relaxation of the hemopoietic bone marrow in patients with chronic leukemia

Eleven patients with chronic leukemia (7 with chronic lymphocytic leukemia and 4 with chronic myeloid leukemia) were evaluated with magnetic resonance (MR) imaging and T1 relaxation time measurements by use of a 1.5 tesla whole body MR scanner. Bone marrow biopsies were obtained from the posterior iliac crest (within 72 hours of the MR examination) in order to provide data on bone marrow cellularity and differential counts. The patients with chronic leukemia all showed a significant prolongation of the T1 relaxation times compared with the normal range for hemopoietic bone marrow.     

Cardiac transplantations in dogs: evaluation with MR

To assess the potential of magnetic resonance (MR) imaging as an early predictor of cardiac transplant rejection, electrocardiogram-gated (ECG-gated) MR imaging was performed in 12 dogs with heterotopic cardiac transplants. Twenty-two examinations were performed in vivo, and ten postmortem examinations were performed immediately after the dogs were killed. Examinations were performed from 3 days to 14 weeks after transplantation. A 0.35-T superconducting magnet was used with the spin-echo pulse sequence. There was a significant increase (P less than .02 to P less than .001) in T2 relaxation times and intensity values for the transplanted hearts compared with native hearts at all time intervals after transplantation. T1 relaxation times of native and transplanted hearts showed no significant difference on the in vivo ECG-gated studies. However, T1 values calculated on post-mortem studies were significantly longer (P less than .005) in the transplanted compared with the native hearts. With longer pulse repetition and echo delay times, there was an increase in the contrast between the rejecting transplanted heart and the native heart. Thus, ECG-gated MR imaging using the spin-echo technique displays cardiac allograft rejection in vivo. The rejected myocardium in vivo is characterized by a prolonged T2 relaxation time.     

T2 mapping of human femorotibial cartilage with turbo mixed MR imaging at 1.5 T: feasibility

The feasibility of a high-spatial-resolution technique for mapping T1 and T2 in articular cartilage in the human knee was evaluated. The technique, turbo mixed magnetic resonance (MR) imaging, is based on a pulse sequence in which inversion-recovery and spin-echo measurements are interleaved. The sequence was first validated in a phantom experiment in which T1 and T2 values obtained with an accepted spectroscopic technique were correlated with those obtained by using a clinical magnetic resonance imager with the turbo mixed technique. T2 maps were obtained with turbo mixed imaging in 25 volunteers (17 men, eight women; mean age, 30.8 years; range, 23-45 years). A high correlation (r = 0.99) was found between T1 and T2 values obtained at spectroscopy and those obtained at turbo mixed imaging. Relative differences in the range of cartilage relaxation times between the two techniques were less than 20%. Turbo mixed imaging in human volunteers showed T2 cartilage relaxation times that corresponded with previously published data. Turbo mixed imaging, thus, is feasible for T2 mapping of cartilage.     

MR imaging of Hallervorden-Spatz disease

Hallervorden-Spatz disease (HSD) is a movement disorder with neuropathology including abnormal iron storage, disordered myelination, and loss of brain substance. Cranial magnetic resonance (MR) imaging of two patients with HSD provided good quality imaging of these patients' atrophic brain stems and cerebella, regions partially degraded by beam-hardening artifact on X-ray CT. Magnetic resonance also demonstrated signal aberrations in the lentiform nuclei and surrounding white matter consistent with iron storage or disordered myelination. However, quantification of relaxation times of these lesions was not specific for either process. The diagnosis of HSD remains one of exclusion, with MR providing helpful but not definitive information.     

Magnetic resonance imaging of experimental renal hemorrhage

Experimental renal hemorrhage was induced by injecting autologous blood into the left kidney of 13 rats. To investigate the magnetic resonance (MR) characteristics of acute renal hemorrhage and subsequent stages of resolution, repetitive MR images were obtained using a 0.35 Tesla imager during a period of 21 days postinduction. A dual spin-echo imaging (TR 500 and 2,000 msec, TE 28 and 56 msec) was used to calculate the relaxation times and record the intensities in the renal medulla and cortex. Histologic examination (n = 9) indicated that blood was dispersed intrarenally, and no encapsulated hematoma developed. The signal intensity on the T1- and T2-weighted images, as well as the relaxation times in the hemorrhagic renal parenchyma were unchanged during 21 days when compared with intact kidney values. Subcapsular fresh blood had a high signal intensity on T2-weighted images. A marked overlap of the relaxation parameters between intact kidney parenchyma and diffuse intrarenal hemorrhage was observed. Detection of dispersed intrarenal blood using spin echo MR imaging may be difficult.     

Proton MR chemical shift imaging using double and triple phase contrast acquisition methods

Conventional chemical shift magnetic resonance (MR) imaging with the phase contrast technique has a number of limitations with respect to quantitative accuracy. The hypothesis of this study is that the accuracy of phase contrast chemical shift MR may be improved by increasing the number of basis images from two to three. Water and fat images were obtained from phantoms and volunteers with a 1.5 T MR system using double and triple acquisition phase contrast chemical shift methods. Longitudinal relaxation time and relative water and fat content were calculated from these basis images. The T1 relaxation times of the aqueous component of composite phantoms were determined more accurately using the triple acquisition method than with the double acquisition method. In vivo studies demonstrate that the triple acquisition method separated fat and water signals more accurately and showed less field inhomogeneity dependence than the modified double acquisition method. The new method also provided a map of static field magnetic inhomogeneity and tissue magnetic susceptibility. The triple acquisition phase contrast chemical shift imaging technique should improve the prospect for quantitative tissue characterization in clinical MR.     

Improved MR imaging of the orbit at 1.5 T with surface coils

A method for obtaining localized high-resolution magnetic resonance (MR) images of the eye and orbit is demonstrated. The method uses modified surface receiver coils placed immediately adjacent to the anatomy to detect the MR signal. Surface coils provide enhanced sensitivity for imaging voxels close to the surface of the body while limiting the received patient-generated noise. The resulting improvement in signal-to-noise ratio allows for a reduction in the imaging voxel size to about 0.5 X 0.5 X 5 mm in scan times of 3.4-5 min. At this level of resolution, anatomic detail in the orbital region previously unobservable in MR images is seen.     

Longitudinal relaxation times of 129Xe in rat tissue homogenates at 9.4 T.

Longitudinal relaxation times of 129Xe were measured in homogenates of rat brain, kidney, liver, and lung at varying oxygenation levels as a means to assess the feasibility of magnetic resonance (MR) imaging of tissue using laser-polarized (LP) 129Xe as the signal source. The measured relaxation times ranged from 4.4 +/- 0.4 sec in deoxygenated lung homogenate to 22 +/- 2 sec in deoxygenated brain homogenate. When the LP gas is introduced to the subject via inhalation, these relaxation times are long enough to allow accumulation and subsequent MR imaging of LP 129Xe in tissues. Imaging of dissolved LP 129Xe will yield an intrinsic signal-to-noise ratio (SNR) that is approximately 3% of the proton intrinsic SNR. This relatively low intrinsic SNR is expected to be adequate for some tracer applications. T1 of 129Xe was found to depend on the oxygenation level of the tissue, and the effect of oxygenation is likely dependent on the amount of hemoglobin in the tissue homogenate.     

Rectal carcinoma: high-spatial-resolution MR imaging and T2 quantification in rectal cancer specimens

PURPOSE: To prospectively compare high-spatial-resolution T1-weighted, T2-weighted, and intermediate-weighted spectral fat-saturated magnetic resonance (MR) imaging for the differentiation of tumor from fibrosis and for delineation of rectal wall layers in rectal cancer specimens. MATERIALS AND METHODS: The local ethics committee approved the protocol, and written informed consent was obtained from each patient. Thin-section high-spatial-resolution MR imaging was performed in specimens obtained from 23 patients (16 men, seven women; median age, 64 years; age range, 39-84 years) immediately after resection. Seven patients underwent neoadjuvant treatment. T1-weighted spin-echo, T2-weighted fast spin-echo, and intermediate-weighted spectral fat-saturated MR images were obtained in the transverse plane. Differences in signal intensity between tumor and fibrosis and between tumor and rectal wall layers were evaluated by using visual scoring and measurements of T2 relaxation time. Statistical differences were evaluated by using the Wilcoxon signed rank test and a mixed-model regression analysis. All images were compared with whole-mount histopathologic slices (n = 86). RESULTS: T2-weighted MR images provided the best differentiation between tumor and fibrosis (P < .001). Mean visual signal intensity scores were -1.8 for T2-weighted MR images, -1.4 for intermediate-weighted spectral fat-saturated MR images, and -0.2 for T1-weighted MR images. T2 relaxation times were 97 msec +/- 4.6 for tumor and 70 msec +/- 3.8 for fibrosis (P < .001). Substantial overlap was noted between the tumor and the circular layer of the muscularis propria (97 msec +/- 2.1), and less overlap was noted between the tumor and the longitudinal layer of the muscularis propria (88 msec +/- 1.6). CONCLUSION: T2-weighted MR imaging provides superior delineation of rectal wall layers and better differentiation of tumor from fibrosis in rectal cancer specimens compared with T1-weighted MR imaging and intermediate-weighted spectral fat-saturated MR imaging by using thin-section high-spatial-resolution sequences.     

Indicator dilution time-activity curves demonstrated by rapid magnetic resonance imaging techniques and paramagnetic contrast agent

Indicator dilution time-activity curves are demonstrated using magnetic resonance imaging (MRI) as the detector and a paramagnetic contrast agent as the indicator. Manganese chloride was injected into a flow phantom. The nuclear magnetic resonance (MR) intensity was measured downstream. Several flow rates were used. The observed MR intensity decreased as the paramagnetic indicator passed through the imaging plane. The qualitative changes of the MR intensity decrease varied in accordance with indicator dilution theory. The equations for gradient refocused echoes, paramagnetic compound relaxation changes, and the indicator dilution analysis were combined and evaluated. Quantitative analysis demonstrates several problems in its implementation.     

Experimental acute pancreatitis: MR relaxation time studies using gadolinium-DTPA

Spin-lattice (T1) and spin-spin (T2) relaxation times of normal and sodium taurocholate-induced pancreatitis (38 rats) were determined in vitro using a 10.7-MHz magnetic resonance (MR) spectrometer. The increase in pancreatic T1 time in acute hemorrhagic pancreatitis correlated well with the elevated water content of the organ. Gadolinium-DTPA did not affect significantly the relaxation times of normal pancreas in vitro during 1 t 20 min postinjection, but it decreased the elevated T1 times of inflamed pancreas almost to baseline values. MR imaging studies of rat pancreas in vivo (8 rats, 0.35-T resistive magnet) indicated that the swollen pancreas and associated edema were depicted using a T2-weighted SE sequence. Fifteen minutes postinjection of gadolinium-DTPA a homogeneous enhancement of inflamed pancreas was detected. The differentiation of pancreatic necrotic foci from surrounding viable tissue and edema could not be detected on Gd-DTPA-enhanced MR images after 15 min postinjection although microscopical workup indicated these different tissue constituents in the pancreas.     

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.