Regions Of Low Signal Intensity Research Articles

Patterns of Signal Intensity in CISS MRI of the Inner Ear and Eye.

Constructive interference in steady state (CISS) is a gradient echo magnetic resonance imaging (MRI) pulse sequence that provides excellent contrast between cerebrospinal fluid and adjacent structures but is prone to banding artifacts due to magnetic field inhomogeneities. We aimed to characterize artifacts in the inner ear and eye. In 30 patients (60 ears/eyes) undergoing CISS sequence MRI, nine low-signal intensity regions were identified in the inner ear and compared to temporal bone histopathology. The number and angle of bands across the eye were examined. In the cochlea, all ears had regions of low signal corresponding to anatomy (modiolus (all), spiral lamina (n = 59, 98.3%), and interscalar septa (n = 50, 83.3%)). In the labyrinth, the lateral semicircular canal crista (n = 42, 70%) and utricular macula (n = 47, 78.3%) were seen. Areas of low signal in the vestibule seen in all ears may represent the walls of the membranous utricle. Zero to three banding artifacts were seen in both eyes (right: 96.7%, mean 1.5; left: 93.3%, mean 1.3). Low signal regions in the inner ear on CISS sequences are common and have consistent patterns; most in the inner ear represent anatomy, appearing blurred due to partial volume averaging. Banding artifacts in the eye are more variable.

In vivo magnetic resonance imaging of iron oxide-labeled, intravenous-injected mesenchymal stem cells in kidneys of rabbits with acute ischemic kidney injury: detection and monitoring at 1.5 T

Background: Acute kidney injury (AKI) is one of the most important causes of mortality and morbidity worldwide. Mesenchymal stem cells (MSCs) can be used for stem cell-based therapy containing AKI. Magnetic resonance imaging (MRI) is an ideal mean for stem cells tracking by labeling with superparamagnetic iron oxide (SPIO). Therefore, using the iron oxide-labeled mesenchymal stem cells (MSC) to treat the AKI and evaluating migration, distribution, and homing of cells by MRI is an ideal method for cell therapy and cell tracking in vivo. Methods: In vitro, the MSCs were labeled with 25 μg/mL for 24 h, and test the labeled efficiency and cells viability. In vitro experiments, magnetic resonance imaging (MRI) measurement of non-labeled and SPIO-labeled MSCs (SPIO-MSCs) was performed in correlation to detectable cells concentrations and detectable time windows. In vivo experiments, MRI evaluation was performed before and after ischemic/reperfusion AKI (N = 14) and intravenous injection of 5 × 105 SPIO-MSCs (N = 10), PBS (N = 6) up to 8 days using a clinical 1.5 T scanner. Signal intensity of kidneys were measured and tested for statistical significance (unpaired Student’s t-test, p < 0.05) in comparison histology (hematoxylin and eosin [H&E], Prussian blue). Results: In vitro, MSCs can be labeled with the SPIO without affecting the viability and labeling efficiency. SPIO-MSCs showed a reduction of signal intensity at T2WI and T2*WI, 5 × 104 cells/mL, SPIO-MSCs were the minimum imaging cells concentration using a 1.5 T MR in vitro. In vivo, SPIO-MSCs administration resulted in a T2*WI signal intensity decrease in renal medulla caused by SPIO-MSCs accumulation in contrast to control groups (p < 0.05) up to day 3 after transplantation, but T2*WI low signal intensity region of the renal medulla revealed an decrease at day 5, and no significant differences between SPIO-MSCs and control animals at day 8. Conclusion: Our data demonstrate that in vitro and in vivo, cell-tracking and monitoring of kidney distribution of intravenous injected SPIO-MSCs after AKI is feasible in MRI at 1.5 T.

Detection of hemorrhagic hypointense foci in radiation injury region using susceptibility-weighted imaging

Susceptibility-weighted imaging (SWI), a novel, highly sensitive 3D gradient echo MR imaging technique, is used to detect hemorrhage. To evaluate SWI at 3.0T for detection and visualization of hemorrhage at radiation injury region after radiotherapy for brain glioma. In 16 patients who had radiation injury in the vicinity of the previously resected and irradiated high-grade brain glioma, SWI examinations were performed on a 3T MR scanner. The presence of intralesional hypointense foci on SWI was evaluated by two neuroradiologists. Frequency of these foci on SWI was assessed and the number of these foci was counted. Diagnosis of radiation injury was assigned by means of histopathology or follow-up MR image. In all 16 cases with cerebral radiation injury, nine were verified by means of histopathologic examination, seven by follow-up image. While in one patient quality of SWI was poor, in all remaining patients diagnostic-quality SWI was obtained. The intralesional hypointense foci were detected in 12 of 15 patients. These hypointense foci were nodular, angular, or tubular regions of low signal intensity on SWI. The distribution of these foci was diffusive (n=5) or scattered (n=7). Number of these foci per cm(2) on SWI was 7.25 ± 3.67. SWI is a novel and promising technique for evaluation of hemorrhage at radiation injury regions in the vicinity of the previously treated gliomas.

073 T2-weighted MRI has high diagnostic accuracy for myocardial haemorrhage in myocardial infarction: a preclinical validation study in swine

Background Myocardial haemorrhage after myocardial infarction (MI) frequently goes undetected. Since the paramagnetic effects of oxidised iron may result in signal loss on T2* and T2-weighted MRI, we investigated the diagnostic accuracy of T2-weighted MRI in experimental MI. Methods Acute MI was created in swine (43±9.5 kg) by occluding the left anterior descending coronary artery (n=10) or circumflex (n=5) for 90 min followed by reperfusion for ≤3 days (n=2), 10 days (n=7) or 60 days (n=6). Cardiac MRI was performed at 1.5 T using T2-prepared steady-state free-precession (T2P-SSFP) and gadolinium enhanced (CE) MRI. Left ventricular (LV) sections were visually inspected, photographed and stained for histology. Gross images and histology were scored for myocardial haemorrhage by an experienced cardiac pathologist blinded to all other data. Regions of low signal intensity on T2-weighted and CE-MRI were independently determined by three cardiologists blinded to the pathology results. Results Eighty ventricular slices of pathology were matched with MRI (n=68 for first pass CE-CMR). All sections exhibited hyperintense zones consistent with oedema on T2-weighted, scar on CE-MRI and pathologic evidence of MI. Myocardial haemorrhage occurred in 49 LV sections (61%) and corresponded with signal voids on 48 T2-weighted (98%) and 26 CE-MRI (53%). Alternatively, signal voids occurred in the absence of haemorrhage in three T2-weighted (90% specificity) and five CE-MRI (84% specificity). On first pass CE-MRI, 27/43 perfusion defects corresponded with haemorrhage (63% sensitivity) while 5/25 defects occurred in the absence of haemorrhage (80% specificity). The positive and negative predictive values for pathological evidence of haemorrhage were 94% & 96% for T2-weighted, 84% & 53% for CE-MRI, and 84% & 56% for first pass perfusion. Conclusions T2-weighted MRI has high diagnostic accuracy for myocardial haemorrhage. Heterogeneity of signal intensity associated with acute MI on T2-weighted MRI is partially due to intramyocardial haemorrhage.

Differentiation of Glioma and Radiation Injury in Rats Using In Vitro Produce Magnetically Labeled Cytotoxic T-Cells and MRI

BackgroundA limitation with current imaging strategies of recurrent glioma undergoing radiotherapy is that tumor and radiation injury cannot be differentiated with post contrast CT or MRI, or with PET or other more complex parametric analyses of MRI data. We propose to address the imaging limitation building on emerging evidence indicating that effective therapy for recurrent glioma can be attained by sensitized T-cells following vaccination of primed dendritic cells (DCs). The purpose of this study was to determine whether cord blood T-cells can be sensitized against glioma cells (U-251) and if these sensitized cytotoxic T-cells (CTLs) can be used as cellular magnetic resonance imaging probes to identify and differentiate glioma from radiation necrosis in rodent models.Methodology/Principal FindingsCord blood T and CD14+ cells were collected. Isolated CD14+ cells were then converted to dendritic cells (DCs), primed with glioma cell lysate and used to sensitize T-cells. Phenotypical expression of the generated DCs were analyzed to determine the expression level of CD14, CD86, CD83 and HLA-DR. Cells positive for CD25, CD4, CD8 were determined in generated CTLs. Specificity of cytotoxicity of the generated CTLs was also determined by lactate dehydrogenase (LDH) release assay. Secondary proliferation capacity of magnetically labeled and unlabeled CTLs was also determined. Generated CTLs were magnetically labeled and intravenously injected into glioma bearing animals that underwent MRI on days 3 and 7 post- injection. CTLs were also administered to animals with focal radiation injury to determine whether these CTLs accumulated non-specifically to the injury sites. Multi-echo T2- and T2*-weighted images were acquired and R2 and R2* maps created. Our method produced functional, sensitized CTLs that specifically induced U251 cell death in vitro. Both labeled and unlabeled CTLs proliferated equally after the secondary stimulation. There were significantly higher CD25 positive cells (p = <0.006) in CTLs. In addition, T2- and T2*-weighted MR images showed increased low signal intensity areas in animals that received labeled CTLs as compared to the images from animals that received control cells. Histological analysis confirmed the presence of iron positive cells in sites corresponding to MRI low signal intensity regions. Significant differences (p = <0.001) in tumor R2 and R2* values were observed among the groups of animals. Animals with radiation injury exhibited neither MRI hypointense areas nor presence of iron positive cells.ConclusionOur results indicate that T-cells can be effectively sensitized by in vitro methods and used as cellular probes to identify and differentiate glioma from radiation necrosis.

An automatic geometrical and statistical method to detect acoustic shadows in intraoperative ultrasound brain images

In ultrasound images, acoustic shadows appear as regions of low signal intensity linked to boundaries with very high acoustic impedance differences. Acoustic shadows can be viewed either as informative features to detect lesions or calcifications, or as damageable artifacts for image processing tasks such as segmentation, registration or 3D reconstruction. In both cases, the detection of these acoustic shadows is useful. This paper proposes a new method to detect these shadows that combines a geometrical approach to estimate the B-scans shape, followed by a statistical test based on a dedicated modeling of ultrasound image statistics. Results demonstrate that the combined geometrical-statistical technique is more robust and yields better results than the previous statistical technique. Integration of regularization over time further improves robustness. Application of the procedure results in (1) improved 3D reconstructions with fewer artifacts, and (2) reduced mean registration error of tracked intraoperative brain ultrasound images.

Distortion correction for a double inversion-recovery sequence with an echo-planar imaging readout

A double inversion-recovery (DIR) sequence with an echo-planar imaging (EPI) readout can be used to image selectively the grey matter of the brain, and this has previously been applied to improve the sensitivity of the statistical analysis of functional magnetic resonance imaging (fMRI) data. If a procedure were to be implemented to remove the distortions that are inherent in the EPI-based fMRI data set, then a similar technique would have to be applied to the DIR-EPI image also to ensure that it matches the geometry of the functional data. A comparison of candidate methodologies for correcting distortions in DIR-EPI images, based on the reversed-gradient method, is presented. A corrected image could be calculated from two DIR-EPI images acquired with k-space traversal in opposite directions, but that method was not able to cope with the large regions of low signal intensity corresponding to the nulled white matter. It was found that the optimal procedure to apply the reversed-gradient method to DIR-EPI images was to acquire two additional EPI images (without the two inversion pulses) with opposite-direction k-space traversal; the distortion-correction information calculated from those EPI images was then applied to the DIR-EPI data.

Magnetic resonance imaging of para-acetabular insufficiency fractures in patients with malignancy

To describe the characteristic magnetic resonance imaging (MRI) findings of para-acetabular insufficiency fractures in patients with malignancy, and compare the MRI appearance of these fractures with that of metastatic bone disease. MRI examinations were reviewed in 16 patients with a known malignant tumour and severe hip pain that raised the possibility of local recurrence or metastatic disease. Six patients had received pelvic irradiation, and three patients were receiving steroid medication. The total number of fractures detected was 21: a solitary fracture was present in 11 patients and five patients had bilateral para-acetabular fractures. Two patients had associated sacral insufficiency fractures, and one of them had stress fractures involving both acetabular columns. Conventional radiography allowed the diagnosis of 14 (67%) fractures; six (28%) radiographic examinations were negative; and one (5%) examination was equivocal for fracture. Available scintigraphic and computed tomography (CT) studies revealed typical findings of fracture. Using MRI, insufficiency fractures appeared as linear regions of low signal intensity on T1- and T2-weighted images. Marked marrow oedema was evident in all cases. Fractures characteristically were parallel to the superior acetabulum in a curvilinear fashion in 18 (86%) instances, and were oblique in three (14%) instances. The fractures demonstrated considerable enhancement after intravenous gadolinium administration. No associated soft tissue masses were documented. Para-acetabular insufficiency fractures are a cause of hip pain, which may mimic skeletal metastasis in the patient with malignancy and pelvic irradiation. Recognition of the characteristic MRI findings of these fractures can preclude misdiagnosis and unnecessary bone biopsy.

Comparison of 1.5 and 8 Tesla High-Resolution Magnetic Resonance Imaging of Lacunar Infarcts

We present a case report comparing 1.5 fast spin-echo (FSE) and high-resolution 8 Tesla (T) gradient echo (GE) MRI of a patient with multiple lacunar infarcts. A 51-year-old man with a history of previous lacunar infarctions was studied with two-dimensional Fourier transform axial 8 T GE MRI using the following parameters: 3 mm thick slices skip 3 mm, flip-angle approximately 20 degrees, TR 800 milliseconds, TE 12 milliseconds, 1024 x 1024 matrix, field of view (FOV) 20 cm, and bandwidth 50 kHz. These images were then compared with routine clinical 1.5 T T2-weighted FSE images with 5 mm thick sections, 256 x 256, FOV 20, TR 5650, TE 102, and 16 echo train length. The majority of the infarctions were seen as areas of high signal intensity on both the 1.5 and 8 T images. They were seen in the corona radiata or the basal ganglia. More lesions were seen on the 8 T images. Low intensity signal was best demonstrated on the 8 T images at segments of the periphery of a few of the larger infarcts. There were a few small punctate low signal intensity regions localized at the termination of some of the microvessels on the 8 T images only. The foci of decreased signal intensity in regions of chronic hemorrhage appeared larger on the 8 T images compared with the 1.5 T images. The 8 T images demonstrated direct visualization of many small vessels, primarily in the deep white matter, which were not visible on the 1.5 T images. On the 8 T images, some of the infarcts appeared to be located between the medullary veins of the deep white matter. This case report indicates that GE 8 T images demonstrate more infarctions compared with the FSE 1.5 T images. It is possible to simultaneously identify the microvessels of the brain, small foci of hemorrhage, and lacunar infarctions using 8 T MRI.

Malignant Peripheral Nerve Sheath Tumors of Intrathoracic Vagus Nerve

The authors report two cases of malignant peripheral nerve sheath tumors arising from the vagus nerve in the mediastinum in patients who had no stigmata of neurofibromatosis (von Recklinghausen's disease). Computed tomography showed homogeneous soft tissue masses, with minimal calcification seen in one patient. T2-weighted magnetic resonance images showed regions of low signal intensity caused by a dense cellular population.

Appearance of anterior cruciate ligament autografts in their tibial bone tunnels on oblique axial MRI

The objective of this study was to observe the changing appearance of human anterior cruciate ligament (ACL) grafts in their tibial bone tunnels by MRI using oblique axial images. One-hundred and eight knees in 75 patients were studied by MRI at 1–33 months after arthroscopic ACL reconstructions using double-looped, autogenous semitendinosus and/or gracilis tendons. Knees with poor stability were excluded from this study. The examinations were performed at 0.2T with spin echo proton density and T 2-weighted oblique axial images. Appearances of grafts were mainly described on spin echo proton density images based upon time after surgery. The grafts appeared as homogeneous, low signal intensity areas in the bone tunnels at 1 month after the surgery. Ring-shaped low signal intensity areas were observed along the wall of the bone tunnels in the 2- to 3-month group. In many grafts from this group, each tendinous bundle appeared as a low signal area separated by a high signal intensity area. In all cases in the 4- to 6-month group, the thickness of the ring-shaped low signal intensity area had increased, whereas the thickness of the high signal intensity area had decreased. In almost all of the cases, the interior of the bone tunnel gradually became a homologous low signal intensity region by 7 to 12 months after the surgery. According to these results, it is suggested that the maturation of the tendon-bone interface was completed from 6 to 12 months after the ACL reconstruction.

Peripheral focal low signal intensity areas in the degenerated annulus fibrosus on T2-weighted fast spin echo MR images: correlation with macroscopic and microscopic findings in elderly cadavers.

To correlate the peripheral focal low signal intensity areas in the degenerated annulus fibrosus on T2-weighted fast spin echo MR images with the macroscopic and microscopic findings in cadavers derived from elderly subjects. Twenty-eight intervertebral disks (16 lumbar and 12 cervical) derived from four nonembalmed cadavers were examined with T1-weighted spin echo and proton density-weighted and T2-weighted fast spin echo MR imaging. The signal intensities of the annulus fibrosus were evaluated on sagittal MR images and correlated with the findings on corresponding sagittal anatomic sections. The MR imaging-histologic correlation was then studied. Peripheral focal low signal intensity areas and adjacent regions of high signal intensity were found in five lumbar intervertebral disks. Peripheral focal low signal intensity regions consisted of disorganized compact annular fibers, tiny fissures, and dense fibrosis. The high signal intensity regions, adjacent to the areas of low signal intensity, consisted of mucoid degeneration, tiny fissures, and chondroid metaplasia. Awareness of the histologic findings in regions that reveal peripheral focal low signal intensity with adjacent regions of high signal intensity in the degenerated annulus fibrosus on T2-weighted images may facilitate effective interpretation of clinical MR images of the spine.

Magnetic resonance imaging and spectroscopy of combretastatin A4 prodrug-induced disruption of tumour perfusion and energetic status.

The effects of combretastatin A4 prodrug on perfusion and the levels of 31P metabolites in an implanted murine tumour were investigated for 3 h after drug treatment using nuclear magnetic resonance imaging (MRI) and spectroscopy (MRS). The area of regions of low signal intensity in spin-echo images of tumours increased slightly after treatment with the drug. These regions of low signal intensity corresponded to necrosis seen in histological sections, whereas the expanding regions surrounding them corresponded to haemorrhage. Tumour perfusion was assessed before and 160 min after drug treatment using dynamic MRI measurements of gadolinium diethylenetriaminepentaacetate (GdDTPA) uptake and washout. Perfusion decreased significantly in central regions of the tumour after treatment. This was attributed to disruption of the vasculature and was consistent with the haemorrhage seen in histological sections. The mean apparent diffusion coefficient of water within the tumour did not change, indicating that there was no expansion of necrotic regions during the 3 h after drug treatment. Localized 31P-MRS showed that there was decline in cellular energy status in the tumour after treatment with the drug. The concentrations of nucleoside triphosphates within the tumour fell, the inorganic phosphate concentration increased and there was a significant decrease in tumour pH for 80 min after drug treatment. The rapid, selective and extensive damage caused to these tumours by combretastatin A4 prodrug has highlighted the potential of the agent as a novel cancer chemotherapeutic agent. We have shown that the response of tumours to treatment with the drug may be monitored non-invasively using MRI and MRS experiments that are appropriate for use in a clinical setting.

Atypical demyelinating lesions in patients with multiple sclerosis

We describe an atypical MRI appearance of multiple sclerosis (MS). Lesions characterized on T2-weighted images by a well-defined rim of increased signal intensity and a concentric region of higher signal intensity were seen in 6 of 132 patients with MS. On T1-weighted images these lesions were evident as regions of low signal intensity, often with a rim of contrast enhancement or increased signal intensity. These appearances tended to be shown by new, evolving lesions.

Studies on bromobenzene-induced hepatotoxicity using in vivo MR microscopy with surgically implanted RF coils.

Using surgically implanted RF coils at 300 MHz, three-dimensional microscopic MR images of rat liver were obtained in vivo to follow the development of pathology induced by bromobenzene exposure. Formalin fixed specimens of liver from these animals were also imaged using in vitro MR microscopy, followed by conventional optical microscopy. All MR images were acquired using a spin-warp pulse sequence with TR = 950 ms and TE = 23 ms. The in vivo images were reconstructed as 256(2) x 32 arrays with a voxel size of (50 microns)2 x 219 microns, while the in vitro images were reconstructed as 256(2) x 128 arrays, giving an isotropic resolution at (39 microns)3. Based on results from six animals, we have found in all animals exposed to bromobenzene, image intensity decreased in specific hepatic tissue regions. These regions were well correlated to low signal intensity areas observed in in vitro MR images at higher resolution. Conventional optical microscopy indicated that the low signal intensity regions corresponded to areas of necrosis. The decrease in signal intensity is consistent with increased local diffusion coefficients as a result of necrosis. This study demonstrates that MR microscopy with implanted RF coils can be successfully used to follow tissue pathological changes in living tissues.

し骨洞嚢胞例

Magnetic resonance imaging (MRI) was useful in diagnosing primary ethmoid mucocele, which appeared as a high signal intensity with a distinct border in T2-weighted images and a low signal intensity region in T1-weighted images. The mucocele was treated by intranasal ethmoidectomy.

Lymph nodes: microstructural anatomy at MR imaging.

High-resolution microscopic magnetic resonance (MR) images of rodent lymph nodes were directly correlated with sections obtained for histologic study to determine the microstructural anatomy of lymph nodes seen at MR imaging and to evaluate signal intensity changes induced by a novel intravenous lymphotropic MR contrast agent (ultrasmall superparamagnetic iron oxide [USPIO]). High-resolution T2-weighted images of unenhanced lymph nodes demonstrated medullary sinus as regions of low signal intensity and follicles as high-intensity structures. After a single intravenous administration of USPIO (160 mumol/kg), both T1-weighted and T2-weighted images showed areas of focal signal intensity loss in medullary sinuses corresponding to the distribution of uptake by macrophages. Lymph follicles appeared unchanged in signal intensity, as they are largely devoid of macrophages. This model of microscopic MR imaging should provide the basis for (a) understanding differences between patterns of contrast-enhanced normal lymph nodes and those of diseased ones and (b) guiding the development of targeting strategies for novel pharmaceuticals at the cellular level.

Differentiation of proliferating from resting cartilage in human fetal nasal septum by magnetic resonance imaging

Magnetic Resonance Imaging (MRI) has been used for the characterization of human fetal nasal septa. The images were made from fixed fetal heads from spontaneous abortions of different gestational age. The "in-plane" resolution of the images (at a pixel size of 312 x 312 microns2) allowed a detailed anatomical analysis of the midfacial structures of the fetal heads. In T2-weighted midsagittal sections a low signal intensity region of the septal cartilage could be seen. This part was shown to consist of immature proliferating cartilage by histochemical methods and contrasted to mature resting tissue at the rim of the septum. Direct comparison of the MR images with histological sections demonstrated the potential of MRI in pre- and postoperative evaluation of patients requiring surgical reconstruction of either traumatic or congenital defects of the face.

Occult intraosseous fracture: detection with MR imaging.

Magnetic resonance (MR) images were retrospectively evaluated in eight patients who had recent, symptomatic knee injuries and in whom plain radiographs showed no fractures. T2-weighted images revealed irregular, intraosseous areas of high signal intensity; T1-weighted and proton density images revealed speckled or linear regions of low signal intensity in corresponding areas. In the seven patients whose injuries did not result from direct contusion, abnormalities occurred in subchondral locations. Two patients underwent bone scintigraphy, which showed increased activity in locations corresponding to areas of abnormality noted on MR images. Two patients underwent follow-up MR imaging at 6 weeks and 3 months, which showed complete resolution of the abnormalities. The authors speculate that the MR imaging findings represent microscopic compression fracture of trabecular bone and discuss the related entity, stress fracture.

In vivo imaging of the rat anatomy with nuclear magnetic resonance.

Live rats were imaged by nuclear magnetic resonance (NMR). These images demonstrated fine detail and high object contrast. Motion artifacts are not apparent in 4-minute images, and major blood vessels are demonstrated as regions of low signal intensity because of blood flow. Selective contrast enhancement is possible by varying NMR imager accumulation parameters.