Magnetic Resonance Signal Intensity Changes Research Articles

Analysis of magnetic resonance signal intensity changes in the sacrococcygeal region of patients with uterine fibroids treated with high intensity focused ultrasound ablation

Objective To evaluate the magnetic resonance (MR) signal intensity changes in the sacrococcygeal region of patients with uterine fibroids treated with high intensity focused ultrasound (HIFU). Materials and Methods Two hundred and sixty-seven patients with uterine fibroids treated with HIFU between January and December 2016 were retrospectively reviewed. All patients underwent enhanced pre- and post-HIFU MRI. Multivariate analysis was used to assess the relationship between the factors and the signal intensity changes in the sacrum and the soft tissue adjacent to the sacrum. Results Among the 267 patients, 122 (46%) had MR signal intensity changes in the sacrum and/or the soft tissue adjacent to the sacrum after HIFU. Multivariate analysis showed that the position of the uterus, the distance from the dorsal side of the fibroid to the sacrum, and the ablation efficiency were significantly correlated with MR signal intensity changes in the sacrum and the soft tissue adjacent to the sacrum. Further analysis showed a significant relationship between the location of the MR signal intensity changes and uterine size, the enhancement degree of the uterus. Leg pain was only seen in patients with MR signal intensity changes both in the sacrum and the soft tissue adjacent to the sacrum. Conclusions The location of the uterus, the distance between the dorsal side of the fibroids to the sacrum, and ablation efficiency have a significant relationship with the MR signal intensity changes. The size of the uterus and the degree of enhancement are related to the locations of MR signal changes.

Gadolinium-Based Contrast Agent-Related Toxicities.

In recent years, gadolinium-based contrast agents have been associated with different types of toxicity. In particular, nephrogenic systemic fibrosis, a progressive sclerotic-myxedematous systemic disease of unknown etiology, is related to gadolinium-based contrast agent administration in patients with kidney dysfunction. More recently, evidence of magnetic resonance signal intensity changes on pre-contrast T1-weighted images after multiple gadolinium-based contrast agent administrations resulted in the hypothesis of gadolinium brain accumulation in patients with normal renal function, subsequently confirmed in pathological samples. However, there is limited current data and further investigations are necessary before drawing definite conclusions on the clinical consequences of gadolinium-based contrast agent accumulation in human tissues and particularly in the brain. Gadolinium-based contrast agent-related toxicity appears connected to molecular stability, which varies together with the pharmacokinetic properties of the compound and depends on the individual characteristics of the subject. During a lifetime, the physiological changes occurring in the human body may influence its interaction with gadolinium-based contrast agents: the integrity and developmental stage of the organs has an effect on the dynamics of gadolinium-based contrast agent distribution and excretion, thus leading to different possible mechanisms of deposition and toxicity. Therefore, the aim of this work is to discuss the pharmacokinetics and pharmacodynamics of gadolinium-based contrast agents, with a special focus on the brain, and to explore potential predominant gadolinium-based contrast agent-related toxicity in two cornerstone periods of the human life cycle: fetal/neonatal and adulthood/aged.

Spatial geometric and magnetic resonance signal intensity changes with advancing stages of nucleus pulposus degeneration

BackgroundWith advancing stages of degeneration, denaturation and degradation of proteoglycans in the nucleus pulposus (NP) lead to tissue dehydration and signal intensity loss on T2-weighted MR images. Pfirrmann grading is widely used for grading degeneration of intervertebral discs (IVDs). The criterion to differentiate IVDs of Pfirrmann Grade I from the other grades is NP homogeneity. Pfirrmann grading is qualitative and its assessment may be subjective. Therefore, assessment of quantitative objective measures correlating with early disc degeneration may complement the grading. This study aimed to evaluate the applicability of the distance between the center weighted by signal intensity (weighted center) and the geometric center as a parameter of NP homogeneity. Other phenomena related to advancing stages of degeneration were also investigated.MethodsMR images of 65 asymptomatic volunteers with a total of 288 lumbar IVDs with clearly identifiable nucleus pulposus boundary (Pfirrmann Grade I, II and III) were included in this study. A custom-written program was developed to determine the IVD longitudinal axis, define the NP boundary, and to locate the coordinates of geometric and weighted NP centers on the mid-sagittal image of each studied IVD. The distances between the weighted and geometric centers on the longitudinal axis and the perpendicular axis of each IVD were calculated.ResultsThe weighted center located posterior to the geometric center, which indicated the signal intensity was lower at the anterior portion of the NP, in 85.8% of studied IVDs. The distance between the weighted and geometric center on the longitudinal axis was significantly shorter in homogeneous (Pfirrmann Grade I) than in inhomogeneous (Grade II) IVDs. The distance on the perpendicular axis in Grade III IVDs was significantly larger than that in Grade I and Grade II IVDs.ConclusionThe relationship between the weighted and geometric centers can serve as an indicator for NP homogeneity. The distance between both centers through advancing stages of degeneration demonstrated decrease of signal intensity progressing along the longitudinal axis initially and then along the cranio-caudal direction at later stages. These findings could provide insights of initiation and subsequent progression of degenerative changes in IVDs.

Intracranial Gadolinium Deposition after Contrast-enhanced MR Imaging.

To determine if repeated intravenous exposures to gadolinium-based contrast agents (GBCAs) are associated with neuronal tissue deposition. In this institutional review board-approved single-center study, signal intensities from T1-weighted magnetic resonance (MR) images and postmortem neuronal tissue samples from 13 patients who underwent at least four GBCA-enhanced brain MR examinations between 2000 and 2014 (contrast group) were compared with those from 10 patients who did not receive GBCA (control group). Antemortem consent was obtained from all study participants. Neuronal tissues from the dentate nuclei, pons, globus pallidus, and thalamus of these 23 deceased patients were harvested and analyzed with inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy, and light microscopy to quantify, localize, and assess the effects of gadolinium deposition. Associations between cumulative gadolinium dose, changes in T1-weighted MR signal intensity, and ICP-MS-derived tissue gadolinium concentrations were examined by using the Spearman rank correlation coefficient (ρ). Compared with neuronal tissues of control patients, all of which demonstrated undetectable levels of gadolinium, neuronal tissues of patients from the contrast group contained 0.1-58.8 μg gadolinium per gram of tissue, in a significant dose-dependent relationship that correlated with signal intensity changes on precontrast T1-weighted MR images (ρ = 0.49-0.93). All patients in the contrast group had relatively normal renal function at the time of MR examination. Gadolinium deposition in the capillary endothelium and neural interstitium was observed only in the contrast group. Intravenous GBCA exposure is associated with neuronal tissue deposition in the setting of relatively normal renal function. Additional studies are needed to investigate the clinical significance of these findings and the generalizability to other GBCAs. Online supplemental material is available for this article.

Injury repairing and magnetic resonance tracing of transplanted bone marrow stromal cells in rat liver with hepatic fibrosis

To explore the recurring patterns of migration and distribution of transplanted bone marrow stromal cells (BMSCs) in rat model with hepatic fibrosis and the feasibility of magnetic resonance (MR) tracing. BMSCs labeled with 5-bromodeoxyuridine (Brdu) and super para-magnetic iron oxide (SPIO) were transplanted into rat model with hepatic fibrosis via portal vein. MR scan was performed at Hour 2, Day 3, Day 7 and Week 2 post-transplantation to analyze the hepatic features of MR signal intensity and pathohistology of BMSCs. Multiple hypo-intense lesions appeared in hepatic hilar region at Hour 2 and became smaller with the elapsing time. Hemosiderin and Brdu immunohistochemical stains showed that positive cells were found in portal vein of hepatic porta at Hour 2, small branches of portal vein, sinus hepaticus and around central veins of hepatic lobules at Day 3 and liver parenchyma (esp. in area of lesion) at Day 7 and Week 2. Some of transplanted BMSCs were tightly connected with liver cell to form liver cell cord. The signal intensity changes of MRI corresponded to histological findings at different timepoints. The transplanted BMSCs are gradually scattered in whole liver (esp. in lesion area) so that it may help to repair hepatic lesions. And the recurring patterns of MR signal intensity changes reflected the condition of distribution, immigration and differentiation of transplanted cells.

Toward Detection of Transient Changes in Magnetic-Resonance Signal Intensity Arising From Neuronal Electrical Activities

Detection of weak magnetic fields arising from neuronal electrical activities using magnetic-resonance imaging (MRI) is a potentially effective method for functional imaging of the brain. The purpose of this study is to theoretically and experimentally assess the influence of neuronal magnetic fields on magnetic-resonance signals. The neuronal magnetic field was modeled by using a current dipole formula, and the resulting magnetic-resonance signals were calculated for a voxel located close to the dipole. A current dipole strength of 12 nAmiddotm resulted in the maximum signal drop of 0.6%. In the experiments, magnetic-resonance images of the rat brain were obtained by using a 4.7-T MRI system. A pair of electrodes was attached to the left sciatic nerve for electric stimulation. Images were obtained at ten time points of 0, 30, 60, ..., and 270 ms after the electric stimulation. In the right somatosensory cortex, a transient decrease in the signal intensity was found at 0-30 ms after the stimulation, which was attributed to the effects of neuronal magnetic fields. A neuronal activation map was generated by a comparison of signal intensities between the images obtained at 30-60 ms and 60-90 ms. The right somatosensory cortex exhibited a statistically significant difference in these two groups of images.

Model-Based Analysis of Gd-BOPTA-Induced MR Signal Intensity Changes in Cirrhotic Rat Livers

To quantify the hepatic transport of the hepatobiliary contrast agent gadobenate dimeglumine (Gd-BOPTA) in rats with biliary cirrhosis of various severity degrees from magnetic resonance (MR) signal intensities using a population pharmacokinetic approach. MR signal intensity was recorded during the Gd-BOPTA perfusion of normal and cirrhotic isolated rat livers. Similar experiments were conducted with Gd-labeled Gd-BOPTA to quantify Gd-BOPTA content in liver, bile, and perfusate. All experimental data were analyzed together according to a population pharmacokinetic approach. A 6-compartment model developed from the radioactivity data adequately fit all MRI data when 4 image parameters were added to describe the relationship between the amount of contrast agent and the signal intensity. The model showed that entry of Gd-BOPTA into hepatocytes was decreased in cirrhotic livers when compared to normal livers. Although the MR signal intensity is similar in normal and cirrhotic livers, the population pharmacokinetic approach developed in this study shows a decreased entry of Gd-BOPTA into cirrhotic hepatocytes.

Evaluation of Patients with Paramyotonia at23Na MR Imaging during Cold-induced Weakness

To prospectively examine whether sodium 23 (23Na) magnetic resonance (MR) imaging can be used to visualize acute intracellular Na+ accumulation and the effects of specific therapy in patients with paramyotonia congenita (PC). Ethics committee approval and informed consent were obtained. Sixteen patients (four women, 12 men; mean age, 46.7 years +/- 16.7 [standard deviation]) with confirmed PC and 10 healthy volunteers (three women, seven men; mean age, 26.6 years +/- 3) were examined by using a 1.5-T MR system with a 16.8-MHz surface coil. 23Na MR imaging was performed before and after local cooling of the nondominant lower leg and exercising, with experimentally induced weakness scored by a neurologist. The 23Na MR examination was repeated in 13 patients and all volunteers after 3 days and, additionally, in seven patients after 4 days of oral administration of mexiletine, which blocks Na+ channels. The 23Na MR protocol comprised two-dimensional (2D) fast low-angle shot (FLASH), 2D radial, and free induction decay (FID) sequences. The FID data were fitted to a biexponential decay curve to evaluate the slow and fast components of the T2 relaxation time. Fast and slow components were assigned to intra- and extracellular Na+ concentrations, respectively. Radial and FLASH MR images were evaluated by means of a region-of-interest analysis by using 0.3% saline solution for reference. T1- and T2-weighted MR imaging were also performed. Data were analyzed by using a parametric t test. After exercising, all patients developed considerable weakness exclusively in the cooled lower leg; no weakness was observed in volunteers. In patients, all 23Na MR images showed a significant increase in 23Na signal intensity in the cooled lower leg (P < .001) in comparison with nonsignificant findings in volunteers. After treatment with mexiletine, cooling and exercise induced almost no muscle weakness and no changes in 23Na MR signal intensity in patients. 23Na MR imaging enables visualization of muscular Na+ accumulation associated with muscle weakness in patients with PC, and effects of specific therapy can be detected.

Impact of lung volume on MR signal intensity changes of the lung parenchyma

To test the hypothesis that, in magnetic resonance (MR) imaging of healthy individuals, equal relative changes in lung volume cause equal relative changes in MR signal intensity of the lung parenchyma. In two experimental runs, 10 volunteers underwent spirometrically monitored MR imaging of the lungs, with MR images acquired at 10 incremental lung volumes ranging from total lung capacity to 10% above residual volume. Average signal intensity, signal variability, and signal intensity integrals were calculated for each volunteer and for each lung volume. The effect of lung volume on signal intensity was quantified using linear regression analysis complemented by the runs test. Slopes and intercepts of regression lines were compared with an analysis of covariance. Slopes of the lines of best fit for lung volumes and signal intensities from the two runs were compared to the slope of the line of identity. Comparisons between the two runs were visualized using Bland and Altman plots. The slopes of the 10 individual regression lines yielded no significant differences (F = 1.703, P = 0.101; F = 1.321, P = 0.239). The common slopes were -0.556 +/- 0.027 (P = 0.0001) for the first and -0.597 +/- 0.0031 (P = 0.0001) for the second experimental run. Both slopes displayed no significant nonlinearity (P = 0.419 and P = 0.067). There was a strong association between changes in lung volumes (rs = 0.991, P = 0.0001) and changes in signal intensity (rs = 0.889, P = 0.0001) in the two experimental runs. Lines of best fit for lung volume and signal intensities were not significantly different from the slope of the line of identity (P = 0.321 and P = 0.212, respectively). Equal changes in lung volume cause equal changes in MR signal intensity of the lung parenchyma. This linear and reproducible phenomenon could be helpful in comparing pulmonary MR signal intensity between individuals.

Magnetic resonance behavior of lipiodol--an experimental study

To describe the characteristics of magnetic resonance (MR) signals generated by lipiodol and to assess the influence on MR imaging of hepatoma nodule. Pure lipiodol and lipiodol emulsions mixed with 76% urografin in different ratio were imaged by both CT and MR; quantitative T(1) and T(2) measurements of lipiodol were performed. Fourty-one SD rats with transplanted walker-256 sarcoma in liver were randomly divided into six groups: 0.4-0.6 ml lipiodol emulsion was infused via hepatic artery in experimental groups by means of laparotomy under celiac anesthesia. The changes in MRI signal of hepatoma nodule were observed. In vitro, iodized oil demonstrated high signal on T(1)-weighted images when performed at 37 degree, but all could be suppressed by the fat saturation sequence, and showed very low signal on T(2)-weighted images. The characteristic of MR signal with ultra fluid lipiodol was different from that of iodized oil (P<0.01), showing short T(1) and long T(2) signal; the high signal on T(1)-weighted images was only partially suppressed by the fat saturation sequence. With descending ratio of lipiodol in emulsion, the signal behavior was gradually similar to urografin (r -0.958, P<0.01). When rats were transarterially infused with emulsion, the intensity of the signal on MRI was nearly the same as that in the control rats, but when lipiodol was injected out of the hepatic artery and accumulated in lymphadenopathy, it demonstrated a signal similar to fat; the high intensity signal was maintained on T(1)-weighted images and T(2)-weighted images. There are little changes in MR signal intensity when the lipiodol is accumulated in the tumor nodules. MR behavior of lipiodol is determined by its deposit area.

Analysis of brain activity during clenching by fMRI.

It has been considered difficult to obtain satisfactory functional magnetic resonance images (fMRI) during jaw movements because the head motion during jaw movements makes artefacts on the images. To avoid these artefacts, we chose clenching task and larger pixels to allow some head motion of the subjects. Further the study discarded all data from subjects whom the head was evaluated to move more than 0.3 mm. The study examined 10 healthy right-handed volunteers with echo-planar magnetic resonance (MR) imaging and functional MR signal intensity changes could be obtained in all subjects. However, in the analysis of each pixel of individuals, three different types of pixels were established. It was determined that the pixels that synchronized positively with the task on/off and where signal intensity increase was below 10% expressed the real brain activity. Pixels showing the real brain activity were found in the sensory, motor and pre-motor cortexes in both hemispheres in all subjects, and also in the insula region of two subjects. No pixels were found in the striatum and supplementary motor areas. From the above careful consideration and individual analysis of each pixel, it was concluded that brain activity during the clenching task could be obtained by fMRI.

Radiation-induced changes in MR signal intensity and contrast enhancement of lumbosacral vertebrae: do changes occur only inside the radiation therapy field?

To evaluate temporal changes in signal intensity (SI) and degree of contrast enhancement (CE) of bone marrow in lumbosacral vertebrae inside and outside the radiation therapy (RT) field. Twenty-three patients with advanced uterine cervical cancer who were treated with RT were prospectively evaluated. Each patient underwent four dynamic magnetic resonance (MR) studies: before RT, 2 and 4 weeks after initiation of RT, and 4 weeks after completion of RT. SI and CE were calculated in all four studies of each patient. Bone marrow inside the RT field showed steady and marked increase in precontrast SI and early and transient increase in CE at 2 weeks after initiation of RT followed by progressive and marked decrease in CE at 4 weeks after initiation of RT and 4 weeks after completion of RT. Bone marrow outside the RT field showed slight increase in precontrast SI and steady and moderate decrease in CE to a lesser degree without early increase as seen in bone marrow inside the RT field. RT causes an increase in precontrast SI predominantly in bone marrow inside the RT field. However, a decrease in CE is seen in bone marrow not only inside but also outside the RT field.

Orientation-dependent changes in MR signal intensity of articular cartilage: a manifestation of the "magic angle" effect.

To study magnetic resonance (MR) imaging pattern of normal hyaline articular cartilage in the knee joint with regard to the contribution of the "magic angle" effect to the MR signal. Thirty-two healthy volunteers were imaged in a standard supine position in a 1.5-T unit using spin echo and gradient echo sequences. Nine volunteers were reimaged with the knee flexed. The signal behavior of the hyaline cartilage of the femoral condyles was evaluated qualitatively and quantitatively. The extended and flexed positions of the nine volunteers were compared. A superficial and a deep hyperintense layer and a hypointense middle cartilage layer were observed. Segments of increased signal intensity were visible along the condyles; a magic angle effect on signal intensity was evident in the hypointense middle layer with both gradient echo and spin echo images. The MR signal behavior of hyaline cartilage is influenced by the alignment of the collagen fibers within the cartilage in relation to the magnetic field. Failure to recognize this effect may lead to inaccurate diagnosis.

MR imaging of the liver after microwave coagulation therapy for hepatocellular carcinoma

Intraoperative microwave tissue coagulation (MTC) therapy was applied to 9 hepatocellular carcinoma (HCC) lesions in 5 patients. Magnetic resonance (MR) imaging was used to evaluate changes before and at two and four weeks after treatment. Two weeks after treatment, all coagulated lesions had mildly hyper-intensity with a hypo-intensity rim on T1-WI and mixed signal intensity with a hyper-intensity rim on T2-WI. Enhanced T1-WI displayed an enhanced rim corresponding to hypo-intensity rim on T1-WI (and a hyper-intensity rim on T2-WI). Four weeks after treatment, the MR image characteristics of these coagulated lesions had not changed noticeably compared with those two weeks after treatment. Histologic changes correlated well with changes in MR signal intensity. These findings suggested that MR imaging was useful for evaluation of changes after MTC therapy for HCC.

Phenylketonuria: MR imaging of the brain with clinical correlation.

Fifteen patients with biochemically documented phenylketonuria (PKU) were studied with use of magnetic resonance (MR) imaging with spin-echo T2-weighted pulse sequences. The resulting images demonstrated varying degrees of symmetric high signal intensity of the white matter within the posterior cerebral hemispheres. Involvement of the anterior hemispheres was seen only in cases with severe signal intensity changes. There was no involvement of the cerebral cortex, brain stem, or cerebellum. Moreover, no anatomic structural abnormalities were observed. Mild cortical atrophy was observed in eight of the 15 patients. There was no significant correlation between the patients' IQ scores and the level of MR signal intensity changes. Although MR imaging routinely shows relatively distinct abnormalities in patients with PKU, the clinical severity of the disease does not parallel its imaging severity.

Intervertebral disk: normal age-related changes in MR signal intensity.

The effect of age on the signal intensity of normal lumbar intervertebral disks was studied. Twenty-seven cadavers ranging in age from newborn to 79 years were studied with use of a 1.5-T magnetic resonance (MR) imager within 48 hours of death. The signal intensity in the central area of the disk was measured on a sagittal image obtained with a long repetition time (TR) and a long echo time (TE) and correlated to the age. A significant correlation between the decrease in signal intensity and age was found, although signal intensity changed less than 6% in 80 years. The decrease in signal intensity is concomitant with decreases in water and glycosaminoglycans and increases in collagen in the disk.

Magnetic Resonance Imaging of the Ischemic Femoral Head in Pigs

The magnetic resonance (MR) signal behavior of freshly excised pig femoral heads undergoing ischemic necrosis in vitro was evaluated. Ten femoral heads removed from skeletally immature pigs were stored at 37 degrees in a sealed, sterile container during the observation period. Imaging was initially performed 40 minutes after excision (base-line) and repeated at six, 12, 24, 48, and 72 hours. Changes in MR signal intensity were measured, and the T1 and T2 relaxation times were calculated for selected epiphyseal and metaphyseal areas. Signal intensities decreased during the first 24 hours and returned to baseline by 72 hours. T1 relaxation time increased most significantly between baseline and 24 hours and then decreased to near baseline level between 48 and 72 hours. T2 changes over time were not statistically significant. The type of localized, distinctive decreases in MR signal intensity occurring in clinical cases of early nontraumatic femoral head osteonecrosis was not observed in pigs. Such changes appear to require the presence of an intact and vigorous repair response within adjacent viable bone. However, the transient decrease in signal intensity and prolongation of T1 relaxation time at 12, 24, and 48 hours after traumatic vascular insult may be indicators of early femoral head ischemia.