The effects of the method of death and lapsed time on proton relaxation time T1 in autopsied muscle samples.

RATIONALE AND OBJECTIVES: The variation of measured magnetic resonance T1 relaxation times of autopsied human muscle samples is confusing. Hence, the authors studied rats' muscles to evaluate the effect of fiber type, the relative area of nonmyofiber space, fat and water content, cell death, and the mechanism of death on proton T1. METHODS: Rats were studied on a 0.1 T magnetic resonance device. We studied how death by cervical dislocation, pentobarbital injection, or a combination of these methods, as well as the amount of time lapsed after death, variably affected T1. RESULTS: Death itself did not affect T1, but the mechanism of death did: rats killed by cervical dislocation after ether anesthesia had longer T1 than those killed with an overdose of pentobarbital. T1 was significantly shorter 1 day after death than at 4 hours after and returned to baseline levels within 4 days after death. Repeated warming caused variation in T1 and obscured other possible changes. CONCLUSIONS: Investigation methods should be strictly controlled and standardized before measurements of the relaxation time, T1, of muscle tissue will provide consistent results.

Medial tibial pain: a dynamic contrast-enhanced MRI study.

The purpose of this study was to compare the sensitivity of different magnetic resonance imaging (MRI) sequences to depict periosteal edema in patients with medial tibial pain. Additionally, we evaluated the ability of dynamic contrast-enhanced imaging (DCES) to depict possible temporal alterations in muscular perfusion within compartments of the leg. Fifteen patients with medial tibial pain were examined with MRI. T1-, T2-weighted, proton density axial images and dynamic and static phase post-contrast images were compared in ability to depict periosteal edema. STIR was used in seven cases to depict bone marrow edema. Images were analyzed to detect signs of compartment edema. Region-of-interest measurements in compartments were performed during DCES and compared with controls. In detecting periosteal edema, post-contrast T1-weighted images were better than spin echo T2-weighted and proton density images or STIR images, but STIR depicted the bone marrow edema best. DCES best demonstrated the gradually enhancing periostitis. Four subjects with severe periosteal edema had visually detectable pathologic enhancement during DCES in the deep posterior compartment of the leg. Percentage enhancement in the deep posterior compartment of the leg was greater in patients than in controls. The fast enhancement phase in the deep posterior compartment began slightly slower in patients than in controls, but it continued longer. We believe that periosteal edema in bone stress reaction can cause impairment of venous flow in the deep posterior compartment. MRI can depict both these conditions. In patients with medial tibial pain, MR imaging protocol should include axial STIR images (to depict bone pathology) with T1-weighted axial pre and post-contrast images, and dynamic contrast enhanced imaging to show periosteal edema and abnormal contrast enhancement within a compartment.

T1rho dispersion of rat tissues in vitro.

The purpose of this study was to demonstrate T1rho dispersion in different rat tissues (liver, brain, spleen, kidney, heart, and skeletal muscle), and to compare the 1/T1rho data to previous 1/T1 data and magnetization transfer of rat tissues at low (0.1 T) B0 field. The 1/T1rho dispersion showed a fairly similar pattern in all tissues. The highest 1/T1rho relaxation rates were seen in liver and muscle followed by heart, whereas the values for spleen, kidney, and brain were quite similar. Compared to 1/T2 relaxation rate, the greatest difference was seen in liver and muscle. The rank order 1/T1rho value at each locking field B1 was the same as the transfer rate of magnetization from the water to the macromolecular pool (Rwm) for liver, muscle, heart, and brain. The potential value T1rho imaging is to combine high T1 contrast of low field imaging with the high signal to noise ratio of high static field imaging. When the T1rho value for a given tissue is known, the contrast between different tissues can be optimized by adjusting the locking time TL. Further studies are encouraged to fully exploit this. Targets for more detailed research include brain infarct, brain and liver tumors.

Temporal lobe pathology in epilepsy: proton magnetic resonance spectroscopy and positron emission tomography study.

Hippocampal atrophy characterized by neuronal loss is a common feature in intractable temporal lobe epilepsy in adults. In proton magnetic resonance spectroscopy, a reduction in N-acetylaspartate or in its ratio to other metabolites is considered a sensitive method for detecting neuronal loss. This noninvasive approach was used to study the temporal lobes, especially the hippocampal regions of children with partial epilepsy. In all cases, 2-[18F]fluoro-2-deoxy-D-glucose scans were studied to verify the extension of the hypometabolic area. Five children manifested temporal lobe epilepsy; in 2 of them, epilepsy was intractable. Both manifested temporal hypometabolism on positron emission tomography, hippocampal atrophy on magnetic resonance imaging, and significant reductions in the metabolite ratios on spectroscopy ipsilateral to the seizure focus, as verified by EEG. Three children with temporal lobe epilepsy had infrequent seizures. One of them had a reduction in metabolite ratios in the hippocampus and hippocampal atrophy on magnetic resonance imaging ipsilateral to the seizure focus. The results show that the value of proton spectroscopy lies not only in lateralizing hippocampal atrophy but also in detecting bilaterality and the extent of neuronal loss outside hippocampi. This noninvasive preoperative diagnostic method can be considered an additional technique to be used in conjunction with other imaging techniques for clinical assessment of children with intractable temporal lobe epilepsy.

Proton spectroscopy in children with epilepsy and febrile convulsions.

An association between complex febrile convulsions and the development of hippocampal atrophy, which is characterized by neuron loss and gliosis, has been suggested but is still controversial. In proton magnetic resonance spectroscopy (1H-MRS) a reduction in N-acetylaspartate (NAA), a neuron marker, or in its ratio to other metabolites, that is, creatine and phospocreatine (Cr) and choline-containing compounds (Cho), is considered a sensitive method for detecting neuron loss. We performed 1H-MRS of mesial temporal regions, including hippocampi, in two different groups of children with epilepsy: in children with a history of complex febrile convulsions (CFCs) (n = 7; mean age 7.1 years) and in children without any history of CFCs, referred to herein as the non-CFC group (n = 6; mean age 7.6 years). Changes in the metabolite ratios were detected in 57% of children in the CFC group and in 67% of children in the non-CFC group. In both groups, NAA/(Cho + Cr), NAA/Cho, and NAA/Cr were significantly decreased ipsilaterally to the seizure focus when compared with the control group, but no significant differences were detected between the CFC and non-CFC groups. Also on the contralateral side, NAA/(Cho + Cr) and NAA/Cr were significantly decreased in both patient groups, but the differences were not significant between the CFC and non-CFC groups. Metabolite abnormalities in the mesial temporal region were detected in children with intractable epilepsy and in children whose epilepsy is well controlled by antiepileptic medication. The noninvasive 1H-MRS can be considered an additional diagnostic method to promote early detection of mesial temporal abnormalities that, in the light of this study, seem to be underdiagnosed in children with either temporal lobe epilepsy or other seizure types.

Kinematic magnetic resonance imaging of the upper cervical spine using a novel positioning device.

STUDY DESIGN: The development of a novel positioning device for magnetic resonance imaging of the upper cervical spine and an evaluation of motion patterns of the craniovertebral junction in asymptomatic volunteers as a part of the whole cervical spine motion. OBJECTIVES: To design and construct a positioning device that enables magnetic resonance imaging of the cervical spine in rotation, lateral bending, flexion, and extension in a horizontally open magnetic resonance scanner, and to define reference values for movements of the occiput (C0), the atlas (C1), and the axis (C2) in asymptomatic volunteers. SUMMARY OF BACKGROUND DATA: In previously used devices, the direction of motion is limited usually to flexion-extension, or the position of the head and neck are adjusted without a positioning device using semihard wedges or pillows. METHODS: Magnetic resonance imaging of the upper cervical spine in 20 asymptomatic individuals (10 men and 10 women) was performed in a horizontally open 0.23-T magnetic resonance imager in progressive steps during rotation, lateral bending, and flexion-extension using axial, coronal, and sagittal imaging planes, respectively. The positions of C0, C1, and C2 were measured, and pattern of motions between segments analyzed. Lateral displacement of the atlas during lateral bending and cranial migration distance during flexion-extension were assessed. RESULTS: The nonferromagnetic positioning device was designed and constructed. The motion patterns of the craniovertebral junction during rotation did not differ between the men and women, but in lateral bending there was a small difference between genders at C1-C2. In men, the position of C1 during flexion-extension was consistently more extended in relation to C0 and C2 than in women. CONCLUSIONS: The new positioning device allows magnetic resonance imaging of the upper cervical spine during flexion, extension, rotation, and lateral bending. To assess the relationship between C0-C1 and C1-C2 in flexion and extension, separate reference values for men and women are recommended.

The relationship between cardiac and liver iron evaluated by MR imaging in haematological malignancies and chronic liver disease.

Although iron overload is clinically significant, only limited data have been published on iron overload in haematological diseases. We investigated cardiac and liver iron accumulation by magnetic resonance imaging (MRI) in a cohort of 87 subjects who did not receive chelation, including 59 haematological patients. M-HIC (MRI-based hepatic iron concentration, normal values <36 µmol/g) is a non-invasive, liver biopsy-calibrated method to analyse iron concentration. This method, calibrated to R2 (transverse relaxation rate), was used as a reference standard (M-HIC(R2)). Transfusions and ferritin were evaluated. Mean M-HIC(R2) and cardiac R(*) of all patients were 142 µmol/g (95% CI, 114-170) and 36.4 1/s (95% CI, 34.2-38.5), respectively. M-HIC(R2) was higher in haematological patients than in patients with chronic liver disease or normal controls (P<0.001). Clearly elevated cardiac R2(*) was found in two myelodysplastic syndrome (MDS) patients with severe liver iron overload. A poor correlation was found between liver and cardiac iron (n=82, r=0.322, P=0.003), in contrast to a stronger correlation in MDS (n=7, r=0.905, P=0.005). In addition to transfusions, MDS seemed to be an independent factor in iron accumulation. In conclusion, the risk for cardiac iron overload in haematological diseases other than MDS is very low, despite the frequently found liver iron overload.

Iron overload: accuracy of in-phase and out-of-phase MRI as a quick method to evaluate liver iron load in haematological malignancies and chronic liver disease.

OBJECTIVES: The purpose of this prospective study was to evaluate the accuracy of in-phase and out-of-phase imaging to assess hepatic iron concentration in patients with haematological malignancies and chronic liver disease. METHODS: MRI-based hepatic iron concentration (M-HIC, µmol g(-1)) was used as a reference standard. 42 patients suspected of having iron overload and 12 control subjects underwent 1.5 T in- and out-of-phase and M-HIC liver imaging. Two methods, semi-quantitative visual grading made by two independent readers and quantitative relative signal intensity (rSI) grading from the signal intensity differences of in-phase and out-of-phase images, were used. Statistical analyses were performed using the Spearman and Kruskal-Wallis tests, receiver operator curves and κ coefficients. RESULTS: The correlations between M-HIC and visual gradings of Reader 1 (r = 0.9534, p < 0.0001) and Reader 2 (r = 0.9456, p < 0.0001) were higher than the correlations of the rSI method (r = 0.7719, p < 0.0001). There was excellent agreement between the readers (weighted κ = 0.9619). Both visual grading and rSI were similar in detecting liver iron overload: rSI had 84.85% sensitivity and 100% specificity; visual grading had 85% sensitivity and 100% specificity. The differences between the grades of visual grading were significant (p < 0.0001) and the method was able to distinguish different degrees of iron overload at the threshold of 151 µmol g(-1) with 100% positive predictive value and negative predictive value. CONCLUSION: Detection and grading of liver iron can be performed reliably with in-phase and out-of-phase imaging. Liver fat is a potential pitfall, which limits the use of rSI.

Low-field strength magnetization transfer contrast imaging of the patellar cartilage.

The time-dependent saturation transfer (TDST) method was applied at 0.1 T in order to evaluate the magnetization transfer contrast (MTC) of the patellar cartilage in vivo. Nine knees were examined. The MTC image of the knee is also demonstrated. The MTC of 63% of the patellar cartilage was attained. Magnetization transfer MR imaging may be of additional help in the evaluation of cartilage disorders at low-field MR imaging.

Tissue specificity of low-field-strength magnetization transfer contrast imaging.

The time-dependent saturation transfer technique was used to measure the transfer of magnetization in several rat tissues at 0.1 T. The length of the saturation pulse was varied from 0 to 510 msec. The magnetization transfer contrast effect was characteristic for each type of tissue. A substantial reduction of image intensity was obtained in skeletal muscle (74%), heart (71%), spleen (64%), brain (65%), pancreas (64%), liver (64%), kidneys (62%), and lungs (56%) with the longest saturation pulse available. Much smaller declines occurred in stagnant blood and peritoneal fat. The potential of this imaging technique for clinical conditions is discussed.

Orthopedic and interventional applications at low field MRI with horizontally open configuration. A review.

The recently introduced horizontally open configuration imagers allow imaging of knee, hip or shoulder during whole range of motion, which is not possible in conventional MR imagers. Special joint motion devices can be used to provide accurate and reproducible studies. In cervical spine, functional MR imaging may be useful in evaluating alarligament stability in patients with late sequelae of a whiplash injury, and in patients with rheumatoid arthritis who are clinically suspected of having a cervical myelopathy or superior migration of the odontoid process. In shoulder, full range of motion abduction study may be helpful in assessing the supraspinatus tendon impingement. To evaluate patellofemoral malalignment, quadriceps loading is recommended since associated contracting muscles and related soft tissue structures can be evaluated. The position of the femoral head relative to the acetabulum during different positions can be assessed. Open-configuration scanners provide an access to patients during scanning procedure, and therefore permit interventional procedures to be monitored with MRI. Such interventions include aspiration cytology/biopsy and different drainage procedures.

Magnetization transfer and spin lock MR imaging of patellar cartilage degeneration at 0.1 T.

PURPOSE: To investigate magnetization transfer (MT) parameters and rotating frame relaxation time T1 rho in patellar cartilage at different levels of degeneration. MATERIAL AND METHODS: Thirty cadaveric patellae were examined at 0.1 T using the time-dependent saturation-transfer MT technique and the spin lock (SL) technique. In an SL experiment, nuclear spins are locked with a radiofrequency (RF) field, and the locked nuclear magnetization relaxes along the magnetic component of the locking RF field. The specimens were divided into three groups according to the level of cartilage degeneration. MT parameters and T1 rho were measured. RESULTS: The MT effect was greater in degenerated cartilage than in normal cartilage. T1 rho was longer in advanced cartilage degeneration than in intermediate cartilage degeneration. CONCLUSION: The results suggest that more studies are needed to fully establish the value of SL imaging in cartilage degeneration.

Cerebrospinal fluid flow in children with normal and dilated ventricles studied by MR imaging.

PURPOSE: . To quantify the cerebrospinal fluid (CSF) dynamics in the aqueduct of children with normal and dilated ventricles using MR phase-contrast technique. MATERIAL AND METHODS: Eighteen patients (6 months to 17 years of age) with various neurological symptoms underwent routine brain MR imaging and CSF flow measurement in the aqueduct. Nine patients had normal ventricles, 5 had dilated ventricles and 4 had a ventriculoperitoneal shunt. RESULTS: The CSF velocity and flow rates in the aqueduct in patients with normal and dilated ventricles showed marked inter-individual variation and clear overlap. In a patient with tight aqueductal stenosis and increased ventricular pressure, pronounced CSF flow in the aqueduct was measured. Absence of flow in another patient with aqueductal stenosis was detected. Measurable although low flow in the aqueduct in 4 patients with a ventriculoperitoneal shunt was found. CONCLUSION: Quantitative phase MR flow measurement in the aqueduct demonstrated aqueductal stenosis; these patients had either pronounced flow or no flow in the aqueduct.

Ultrasound, computed tomography and magnetic resonance imaging in myopathies: correlations with electromyography and histopathology.

Imaging of examinations by ultrasound (US), computerized tomography (CT) and low field magnetic resonance imaging (MRI) were compared with EMG and muscle biopsy findings in the same muscles of 33 patients with different neuromuscular diseases. None of the imaging methods revealed specific diagnostic details, but gave valuable information on the extent and distribution of muscle involvement. In myopathies all imaging modalities corresponded well with the EMG and histopathology findings, but in the neuropathies with minimal tissue destruction EMG was, understandably, more sensitive. The imaging characteristics of MR were as good as those of CT, but MRI has the advantage of not requiring ionizing radiation. US is the most economical method and it was found to be, despite its lower resolution, very informative in the hands of an experienced examiner, especially for the detection of fibrosis. The good agreement of histopathology with pathologic imaging and EMG findings implies that the accuracy of muscle biopsy increases, if its site is selected on the basis of imaging and/or EMG examination.

Exercise-induced changes in magnetization transfer contrast of muscles.

Magnetization transfer contrast (MTC) technique provides a new type of contrast in MR imaging. The MTC method is based on the interaction between the spins of free protons and those with restricted motion. Exercise-induced changes in signal intensity and MTC were measured in the forearm muscles of 10 volunteers at 0.1 T. There was 26% increase in signal intensity of active flexor muscles after exercise when imaged with ordinary gradient echo sequence. Despite this marked intensity increase, the postexercise values of MTC did not differ from the preexercise ones.

Cerebrospinal fluid flow in patients with dilated ventricles studied with MR imaging.

The purpose of this study was to measure the cerebrospinal fluid (CSF) velocity and flow in the aqueduct in patients with wide ventricles with or without signs of normal pressure hydrocephalus (NPH) before and after shunt surgery. We studied 18 patients with wide ventricles with MRI and measured the CSF velocity values in the aqueducts. Twelve patients with the clinical triad of NPH were examined. Six patients were studied only before shunt surgery and 6 patients were studied both before and after shunt surgery. Three patients with wide ventricles without clinical triad of NPH, and 3 patients with hydrocephalus following subarachnoid hemorrhage were also examined. Seven NPH patients with hyperdynamic CSF flow and three NPH patients with normal CSF velocity and flow values showed a positive clinical response to shunt surgery. Two of the three patients with hydrocephalus and hyperdynamic CSF flow values in the aqueduct secondary to subarachnoid bleeding responded to shunt surgery. One patient with same disease and low CSF velocity and flow values did not respond. No change was detected in the CSF flow values of the aqueduct when measurements before and after shunt surgery were compared. Ventriculoperitoneal shunting does not change the CSF dynamics in the aqueduct.

Age-related MRI changes at 0.1 T in cervical discs in asymptomatic subjects.

The age-dependent occurrence of cervical degenerative changes was studied using 0.1 T MRI in 89 asymptomatic volunteers aged 9 to 63 years. The degree of DD (disc darkening on T2*-weighted images), disc protrusions and prolapses, narrowing of disc spaces, dorsal osteophytes and spinal canal stenosis were assessed. Abnormalities were commoner in older subjects, 62% of being seen in those over 40 years old. In subjects aged less than 30 years there were virtually no abnormalities. DD was the most common abnormality, seen in 10% of discs; 57% DD was in subjects aged over 40. DD at the C5/6 level was the most common finding. No differences in abnormal findings between males and females was observed, nor any statistically significant association between DD and other abnormalities. Thus, DD begins later age in the cervical spine than in the lumbar region. Asymptomatic degenerative changes are common on MRI in the cervical spine after 30 years of age.

Dynamic contrast-enhanced MR imaging and MR-guided bone biopsy on a 0.23 T open imager.

OBJECTIVE: To assess the feasibility of MR (magnetic resonance)-guided bone biopsies. DESIGN AND PATIENTS: Thirty-six consecutive patients with known or suspected benign or malignant bone lesions underwent comprehensive MR imaging. A dynamic contrast-enhanced sequence followed by stationary T1-weighted sequences were obtained and MR-guided bone biopsy of the tumor at the site with fastest enhancement was performed using an open 0.23 T MR imager. RESULTS: All MR-guided bone biopsies samples were estimated to be sufficient by the pathologists. The biopsy specimens were diagnostic in 34 of 36 cases. CONCLUSION: MR-guided bone biopsies combined with dynamic contrast-enhanced imaging are feasible and safe for the diagnostic investigation of equivocal bone lesions.

MR-guided core biopsies of soft tissue tumours on an open 0.23 T imager.

PURPOSE: To assess the feasibility of MR-guided soft tissue core biopsies on an open 0.23 T magnet. MATERIAL AND METHODS: Twenty-nine consecutive patients with known or suspected benign or malignant soft tissue tumours underwent MR imaging. A one-slice dynamic enhancement sequence was used to obtain an enhancement curve of the tumour. MR-guided core biopsy of the tumour was performed in the same session. RESULTS: All biopsies could be performed on an open 0.23 T magnet. Standard MR images and dynamic enhancement curves were used in deciding biopsy route and target. The MR-guided core biopsy specimens were sufficient for histopathological diagnosis in 27 of 29 cases. CONCLUSION: Open magnet configuration allows easy access to the patient and near real-time imaging guidance of soft tissue tumours. Minimally invasive MR-guided core biopsies of soft tissue tumours are feasible and help to avoid open surgical biopsies.