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PubMed1983

Nuclear magnetic resonance: a gray scale model for head images.

The gray scale of nuclear magnetic resonance (NMR) head images is explained in terms of tissue and machine parameters. Tissue parameters considered here include the spin-lattice relaxation time, the spin-spin relaxation time, and the proton density. Machine parameters include the pulse sequence (saturation recovery, inversion recovery, or spin echo), the repetition time, and the delay time. The ability of the operator to alter the NMR gray scale predictably is examined by computer simulation. The simulation computes NMR pixel values for a selected combination of tissue and machine parameters. The computed values are compared with those extracted from clinical NMR images. The agreement between simulation and clinical pixel values implies that the operator can use the machine parameters to alter the NMR gray scale, and thereby control contrast, appropriate to the diagnostic requirements. The extent to which the NMR gray scale can be predictably controlled is illustrated through graphs, simulated contrast displays, and representative NMR images.

Brain Chemistry↗

PubMed1984

Magnetic resonance imaging of brain tumors: measurement of T1. Work in progress.

Longitudinal relaxation times (T1) of 20 brain tumors were calculated in vivo using a whole-body magnetic resonance unit with a 0.15-T resistive magnet. Images employing standard inversion recovery pulse sequences with different intervals between the 180 degrees pulse and selective excitation pulses were compared on every point of the 256 X 256 pixel matrix. Tumor, white matter, and gray matter were sampled from each patient from the computed T1 image for T1 measurement. Astrocytomas, neurinomas, and metastatic tumors showed longer T1 values than did meningiomas. Lipomas had the shortest T1s. It is concluded that it is difficult to predict histological types of brain tumors by the measurement of T1 alone because of the wide variation in relaxation times, but measurement of T1 can be helpful in differentiating brain tumors when additional information about the patient's condition is known.

Adolescent↗

PubMed1984

Magnetic resonance imaging of the neck. Part I: Normal anatomy.

Magnetic resonance (MR) images of the neck were obtained in 24 patients using a specially designed radio-frequency coil, standard and high-resolution imaging techniques, and a variety of spin echo and inversion recovery pulse sequences. Cervical vascular structures were more easily identified with MR than with CT because of the inherent contrast of flowing blood. The laryngeal skeleton, paralaryngeal tissues, trachea, thyroid, esophagus, and muscles were identified in all cases by MR using morphologic criteria comparable with CT criteria. The spatial resolution of high-resolution MR was slightly inferior to high-resolution CT. However, streak artifacts due to motion and x-ray beam hardening often limited CT, but did not affect MR. Anatomic resolution was best using high-resolution spin echo images obtained with TR = 2.0 seconds and TE = 28 msec because this imaging technique offered excellent contrast between normal tissues and had the highest signal-to-noise ratio. With further improvements in spatial resolution MR is likely to become an important technique for imaging the neck.

Adolescent↗

PubMed1985

Multispectral analysis of magnetic resonance images.

Magnetic resonance (MR) imaging systems produce spatial distribution estimates of proton density, relaxation time, and flow, in a two dimensional matrix form that is analogous to that of the image data obtained from multispectral imaging satellites. Advanced NASA satellite image processing offers sophisticated multispectral analysis of MR images. Spin echo and inversion recovery pulse sequence images were entered in a digital format compatible with satellite images and accurately registered pixel by pixel. Signatures of each tissue class were automatically determined using both supervised and unsupervised classification. Overall tissue classification was obtained in the form of a theme map. In MR images of the brain, for example, the classes included CSF, gray matter, white matter, subcutaneous fat, muscle, and bone. These methods provide an efficient means of identifying subtle relationships in a multi-image MR study.

Basal Ganglia Diseases↗

PubMed1993

Denervated human skeletal muscle: MR imaging evaluation.

Because determination of neurologic integrity after severe limb trauma is crucial in patient care, the authors assessed magnetic resonance (MR) imaging as a tool to map denervated motor units of skeletal muscle in patients with traumatic peripheral neuropathy. Denervation was confirmed in 22 patients with use of electromyography, surgery, or both. MR imaging was performed with moderately T1- and T2-weighted spin-echo and short-tau inversion-recovery (STIR) sequences. MR imaging was unreliable in depicting acute denervation. Muscles of patients with subacute denervation had prolonged T1 and T2, which contributed to conspicuous hyperintensity on STIR images. Chronically denervated muscles showed marked atrophy, variable changes on STIR images, and conspicuous fatty infiltration on T1-weighted images. Normal variants in motor unit anatomy were seen in denervated muscle volumes outside the expected distribution of the injured nerve. MR imaging is promising for the noninvasive mapping and monitoring of denervated muscle in subacute and chronic phases of peripheral neuropathy.

Extremities↗

PubMed1994

Age-related changes in marrow distribution in the shoulder: MR imaging findings.

PURPOSE: To define age-specific patterns of distribution of red and yellow marrow about the shoulder. MATERIALS AND METHODS: Red and yellow marrow distribution was reviewed on magnetic resonance images of 189 subjects aged 15-69 years. Double-echo and fast spin-echo, gradient, and short inversion time inversion recovery pulse sequences were used. The acromion, glenoid, and proximal humeral epiphysis, metaphysis, and diaphysis in each shoulder were graded semiquantitatively and qualitatively. RESULTS: There was a wide variation in the normal pattern of red-yellow marrow distribution both among subjects and among locations. All five anatomic locations showed an orderly progression from greater to lesser amounts of red marrow with increasing age. Many of the subjects had focal subchondral red marrow in the epiphysis, which was associated with patient age (P = .0001) and gender (P = .04). CONCLUSION: Knowledge of normal patterns of marrow distribution can prevent their being misinterpreted as marrow-based disease.

Acromion↗

PubMed1995

MR imaging in evaluation of suspected hip fracture: frequency of unsuspected bone and soft-tissue injury.

PURPOSE: To determine the frequency of unsuspected pelvic fracture and soft-tissue injury in patients referred for magnetic resonance (MR) imaging for possible radiographically occult hip fracture. MATERIALS AND METHODS: Seventy patients with symptoms of possible hip fracture but negative plain radiographs were evaluated with MR imaging. Large-field-of-view T1-weighted coronal images were obtained, and additional T2-weighted or short inversion time inversion recovery (STIR) sequences were used. The number of soft-tissue and bone injuries identified was recorded. RESULTS: Eighty percent of patients had bone or soft-tissue abnormalities. Occult femoral and pelvic fractures were demonstrated in 37% and 23% of patients, respectively. Soft-tissue abnormalities were noted in 74% of patients. When a proximal femoral fracture was not present, MR imaging revealed a 27% frequency of occult pelvic fracture and a 50% frequency of bone or soft-tissue abnormality. CONCLUSION: A high prevalence of occult pelvic fracture and soft-tissue injury may be identified with MR studies designed to evaluate occult hip fracture when large-field-of-view T1-weighted coronal sequences are combined with T2-weighted or STIR sequences.

Adult↗

PubMed1996

Does altered biomechanics cause marrow edema?

PURPOSE: To determine if altered weight bearing causes the appearance of marrow edema on magnetic resonance (MR) images. MATERIALS AND METHODS: Twelve volunteers underwent MR imaging with a short inversion time inversion-recovery (STIR) sequence at 1.5 T. The hips, knees, ankles, and feet were evaluated before and 2 weeks after altered weight bearing achieved with overpronation of one foot. Three volunteers underwent imaging a third time, 2 weeks after overpronation was stopped. Two observers assessed the images for evidence of marrow edema. RESULTS: Changes were seen on images in 11 volunteers; the overpronated side only was affected in 10. Most changes occurred in the foot followed by the tibia and the femur. Most changes were a diffuse increase in marrow edema. In two volunteers, the changes resembled those of stress fractures. CONCLUSION: Altered weight bearing should be added to the list of causes of increased medullary signal intensity (ie, marrow edema) on MR images.

Adult↗

PubMed1996

Mesial temporal sclerosis: diagnosis with fluid-attenuated inversion-recovery versus spin-echo MR imaging.

PURPOSE: To compare the accuracy of a fluid-attenuated inversion-recovery (FLAIR) sequence with that of a conventional double spin-echo (SE) sequence in the identification of increased signal intensity of the hippocampus in mesial temporal sclerosis (MTS). MATERIALS AND METHODS: Three blinded reviewers independently graded the FLAIR and SE images in 36 patients with intractable complex partial seizures. Reproducibility was tested. At histopathologic examination, the criterion standard, 32 patients had MTS. RESULTS: The accuracy of FLAIR images was 97% versus 91% for SE images (P<.02). The radiologists preferred the contrast properties of FLAIR to those of SE images by a significant margin (P<.0001). Surgical to nonsurgical hippocampal contrast-to-noise ratio (C/N) measurements were better for the second echo of the SE sequence than for FLAIR (P<.002). Hippocampus-to-background tissue C/N was superior with FLAIR (P<.0001). CONCLUSION: FLAIR provides images with T2-weighted contrast and complete suppression of high signal intensity of CSF. Incorporation of a FLAIR sequence into the routine MR evaluation of patients with epilepsy is recommended.

Adult↗

PubMed1997

Radiographically occult scaphoid fractures: value of MR imaging in detection.

PURPOSE: To evaluate the diagnostic value of magnetic resonance (MR) imaging in patients with clinical suspicion of scaphoid fractures and normal initial plain radiographs. MATERIALS AND METHODS: MR imaging was performed within 7 days after trauma in 42 patients with clinical suspicion of scaphoid fractures and normal plain radiographs. T1-weighted spin-echo, T2*-weighted gradient-echo, and short inversion time inversion-recovery (STIR) sequences were performed. MR images were evaluated independently by two radiologists. Six-week follow-up radiographs were used as a standard to diagnose fractures. RESULTS: MR imaging depicted occult fractures of the scaphoid bone in 14 patients (33%), the capitate bone in four (10%), the trapezium in one (2%), and the distal radius in two (5%). All wrist fractures were detected with a combination of STIR and T1-weighted spin-echo sequences. The sensitivity and specificity for detection of radiographically occult fractures of the wrist were 100% each for the first and 95% and 100%, respectively, for the second radiologist with an almost perfect interobserver agreement (K = 0.953). CONCLUSION: MR imaging has a high sensitivity for detection of fractures of the scaphoid bone and wrist not evident on plain radiographs and may enable early diagnosis and treatment.

Adolescent↗

PubMed1999

Yield of fluid-attenuated inversion recovery in drug-resistant focal epilepsy with noninformative conventional magnetic resonance imaging.

PURPOSE: To determine the role in presurgical assessment and evaluate the yield of fast fluid-attenuated inversion recovery (FLAIR) sequences for patients with intractable partial epilepsy for whom conventional magnetic resonance imaging (MRI) was normal. MATERIAL AND METHODS: Forty patients were selected. Conventional MRI including spin echo T1-weighted sagittal images and fast spin echo T2-weighted axial images was normal in 33 patients and showed noninformative lesions in 7. Fast FLAIR and T2-weighted sequences were performed perpendicularly to the hippocampal long axis. RESULTS: Additional abnormalities were found in 40%. They were correlated with electroclinical data in 13 patients (32.5%) and not correlated or doubtful in 3 (7.5%). CONCLUSION: Fast FLAIR sequences brought congruent additional information in 32.5% cases and seemed useful in presurgical evaluation.

Adolescent↗

PubMed2004

Extent and distribution of white matter hyperintensities in stroke patients: the Sydney Stroke Study.

BACKGROUND AND PURPOSE: White matter hyperintensities (WMHs) on T2-weighted MRI are common in stroke patients and healthy elderly individuals. The detailed anatomical distribution of these lesions in stroke patients has not been examined. METHODS: A total of 112 stroke or transient ischemic attack patients and 87 matched control subjects from the Sydney Stroke Study underwent MRI scans that included a T2-weighted fluid-attenuated inversion recovery (FLAIR) sequence. WMHs were delineated from each FLAIR MRI by an automated method. Region of interest and voxel-wise statistical parametric mapping approaches were applied to examine the volume, distribution, and severity of WMHs of the patient and control groups, and subgroups with large or lacunar infarcts. RESULTS: Stroke subjects had significantly more WMHs than controls in all brain regions except the occipital lobe and in all arterial territories except the anterior callosal and anterior medial lenticulostriate. In the frontotemporal regions, average WMH volumes in patients were >3.5x those in controls. The total number of discrete WMHs was not different in the 2 groups, but stroke patients had more large (>20 mm) and high-intensity lesions. Subjects with lacunar infarcts had more WMHs than those with large infarcts, who, in turn, had more WMHs than control subjects. Lacunar infarction subjects had more WMHs than subjects with large thromboembolic or cardioembolic strokes. Those with anterior arterial territory infarction had more WMHs in the frontal regions. Subjects with single or multiple lacunes did not differ in volumes of WMHs. CONCLUSIONS: Stroke patients have significantly more WMHs in nearly every brain region than healthy controls. Those with lacunar infarcts are particularly affected. WMHs represent a significant proportion of the ischemic lesion burden in stroke and transient ischemic attack patients.

Aged↗

PubMed1996

Fluid-attenuated inversion recovery (FLAIR) for assessment of cerebral infarction. Initial clinical experience in 50 patients.

BACKGROUND AND PURPOSE: Our aim was to evaluate fluid-attenuated inversion recovery (FLAIR) sequence in the diagnosis of cerebral infarction with MRI. METHODS: A retrospective review was undertaken of 50 consecutive MRI studies ordered for suspected cerebrovascular accident. All studies included FLAIR and rapid acquisition with relaxation enhancement (RARE) T2-weighted spin-echo sequences. The two sequences were compared independently by four observers at two different institutions. Detectability of lesions and image quality were scored. RESULTS: Overall, FLAIR sequences proved superior in 10 patients, detecting acute cortical infarcts missed with RARE spin-echo technique in five patients. In five additional patients, improved characterization of chronic infarction and improved detection of microangiopathic deep hemispheric changes were observed. One brain stem infarct was missed with the FLAIR sequence. CONCLUSIONS: FLAIR offers advantages in detection of acute infarcts affecting the cortical ribbon, is a useful, rapid adjunct to conventional T2-weighted spin-echo sequences, and has the potential to replace these in the future.

Artifacts↗

PubMed2004

Cerebral blood volume in T2-weighted white matter hyperintensities using exogenous contrast based perfusion MRI.

We used perfusion weighted magnetic resonance imaging (MRI) to determine relative regional cerebral blood volume (rCBV) in regions of white matter hyperintensity (WMH) in 28 elderly stroke patients and 27 healthy comparison subjects, using T2-weighted fluid-attenuated inversion recovery (FLAIR) sequence MRI for anatomical localization and bolus gadolinium-DTPA tracking for perfusion weighted imaging. We found that WMHs had significantly lower rCBV than contralateral normal WMH, irrespective of size or group membership, and rCBV was significantly related to the size of the WMH. For the larger WMHs, there was a significant increase in rCBV from inner core to outer ring. The findings suggest hemodynamic perturbation in the microvasculature of hyperintense regions, which becomes greater as the size of the WMH increases. This is equally applicable to stroke patients and healthy older individuals.

Aged↗

PubMed2005

Expansion of HIV-specific CD4+ and CD8+ T cells by dendritic cells transfected with mRNA encoding cytoplasm- or lysosome-targeted Nef.

Transfection with synthetic mRNA is a safe and efficient method of delivering antigens to dendritic cells for immunotherapy. Targeting antigens to the lysosome can sometimes enhance the CD4+ T-cell response. We transfected antigen-presenting cells (APCs) with mRNA encoding Gag-p24 and cytoplasmic, lysosomal, and secreted forms of Nef. Antigen-specific cytotoxic T cells were able to lyse the majority of transfected targets, indicating that transfection was efficient. Transfection of APCs with a Nef construct bearing lysosomal targeting signals produced rapid and prolonged antigen presentation to CD4+ and CD8+ T cells. Polyclonal CD4+ and CD8+ T-cell lines recognizing multiple distinct epitopes were expanded by coculture of transfected dendritic cells with peripheral blood mononuclear cells from viremic and aviremic HIV-infected subjects. Importantly, lysosome-targeted antigen drove a significantly greater expansion of Nef-specific CD4+ T cells than cytoplasmic antigen. The frequency of recognition of CD8 but not CD4 epitopes by mRNA-expanded T cells was inversely proportional to sequence entropy and was similar to ex vivo responses from a large chronic cohort. Thus human dendritic cells transfected with mRNA encoding lysosome-targeted HIV antigen can expand a broad, polyclonal repertoire of antiviral T cells, offering a promising approach to HIV immunotherapy.

CD4-Positive T-Lymphocytes↗

PubMed1994

Magnetic resonance imaging signal changes in denervated muscles after peripheral nerve injury.

The evaluation of peripheral nerve disorders has traditionally relied on a clinical history, physical examination, and electrodiagnostic studies. Recent studies have used magnetic resonance imaging (MRI) to evaluate a variety of both nerve and muscle disorders. In this article, we describe the use of MRI, using short-tau inversion recovery (STIR) sequences, to evaluate muscle signal characteristics in a variety of peripheral nerve disorders. A total of 32 patients were studied, and 12 representative cases are discussed in detail. Increased STIR signal in muscle was seen in cases of severe axonotmetic injuries involving the transection of axons producing severe denervation changes on electromyography. The increased STIR signal in denervated muscles was seen as early as 4 days after the onset of clinical symptoms, which is significantly earlier than changes detected on electromyography. The MRI signal changes were reversible when the recovery of motor function occurred as a result of further muscle innervation. In cases of neurapraxic nerve injuries, characterized by conduction block without axonal loss, the STIR signal in muscle was normal. These findings show that MRI using STIR sequences provides a panoramic visual representation of denervated muscles useful in localizing and grading the severity of peripheral nerve injury secondary to either disease or trauma. MRI using STIR sequences may therefore play an important role in the prediction of clinical outcome and the formulation of appropriate therapy early after peripheral nerve injury.

Adolescent↗

PubMed2000

Chronic cerebrospinal fluid leak into skull base causing intramedullary osteolysis.

We present the rare case of a 74-year-old woman with extensive intramedullary osteolysis of the petroclival skull base straddling both sides of the basi-occiput and basi-sphenoid. She presented with clinical features of recurrent spontaneous cerebrospinal fluid (CSF) otorrhoea despite three previous attempts at repair of the CSF leak. Recent advances in imaging techniques enable accurate radiological diagnosis of skull base lesions. We performed T1- and T2-weighted magnetic resonance (MR) images, a fluid attenuated inversion recovery (FLAIR) sequence MR, and a diffusion scan to study the characteristics of the skull base pathology. This revealed extensive osteolysis, with cystic spaces within the clivus and the petrous pyramid extending also to the basi-occiput. The leak was sealed using the technique of subtotal petrosectomy with obliteration of the eustachian tube and blind pit closure of the ear canal. The patient has been followed up for six months with no recurrence of symptoms.

Aged↗

PubMed1992

[Prediction for effectiveness of steroid pulse therapy by MRI in Graves' ophthalmopathy].

Fifteen patients with Graves' ophthalmopathy (GO) were treated with intravenous methylprednisolone (steroid pulse therapy, 1g daily for 3 days a week, 2-4 times) and followed up by ophthalmological assessment and magnetic resonance imaging (MRI). The signal intensity of enlarged eye muscle and retrobulbar fat was examined with MRI at 0.5T with short inversion time inversion recovery (STIR) sequences. The signal intensity of eye muscle and retrobulbar fat tissue in STIR was evaluated as the ratio to cerebral substantia alba (signal intensity ratio). The thickness of enlarged eye muscle was measured by T1-weighted coronal images. The signal intensity ratios of enlarged eye muscle of GO patients were significantly higher than those of eight normal subjects. Although the signal intensity ratios of muscle and retrobulbar fat before therapy were not related to the severity of clinical findings of GO assessed by ophthalmopathy index, the initial signal intensity ratios of eye muscle and retrobulbar fat of ten patients with improved clinical findings of GO after steroid pulse therapy tended to be higher than those of five patients without improvement by the therapy. After the therapy the signal intensity ratios of muscle and retrobulbar fat were significantly decreased in ten patients with favorable response. Our data suggested that high signal intensity in STIR may reflect edema caused by acute inflammation associated with GO. In conclusion, MRI may be a useful tool for determining the indication and prognosis of steroid pulse therapy. We strongly recommend measuring the signal intensity of eye muscle as well as muscle thickness in MRI to evaluate the activity of GO.

Adipose Tissue↗