Minisymposium on technical aspects of magnetic resonance imaging.
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Brain↗
Biomedical subjects
M Bergström
Publications and source records attributed to M Bergström.
Cerebrospinal fluid flow studied with gated magnetic resonance imaging during the various parts of the cardiac cycle.
The pulsatile movement of cerebrospinal fluid (CSF) through the Sylvian aqueduct has been studied in two normal volunteers. A standard magnetic resonance scanner was used as well as a routine spin echo sequence. Series of ECG-gated axial images were obtained perpendicular to the long axis of the Sylvian aqueduct. Previously it has been demonstrated by flow phantom experiments that the phase information can be used to obtain a linear relation between phase and flow velocity. By multiplying the CSF flow velocity by the cross-sectional area of the aqueduct of Sylvius obtained in each image, the CSF flow variation during the cardiac cycle could be demonstrated and measured.
Cerebrospinal Fluid↗
Performance study of the PC-384 positron camera system for emission tomography of the brain.
A positron camera system PC-384 has been designed and built for quantitative positron emission computed tomography of the brain. This head scanner consists of 384 bismuth germanate oxide scintillation detectors with a crystal packing fraction of 80%. The entire detector assembly rotates around a small circle (wobble) to achieve the necessary ray sampling. Seven simultaneous images are produced with four detector rings. Performances of the system are discussed and clarified based on experimental data.
Brain↗
Correction for scattered radiation in a ring detector positron camera by integral transformation of the projections.
A "deconvolution" algorithm for the determination of the scatter contribution in positron emission tomography is described. The projected distributions of scattered radiation measured with a line source at different positions in water phantoms are described analytically. It is shown that an integral transformation of the observed projections with a slightly modified analytical function gives an adequate description of the scattered radiation. The scatter distribution from any composite object can thus be calculated and subsequently subtracted. The algorithm is tested on different objects. The result shows that the level of scattered radiation can be reduced from 25 to 1% of the total count rate in the center of the projection from a homogeneous phantom.
Models, Theoretical↗
Effect of dexamethasone treatment on volume and contrast enhancement of intracranial neoplasms.
In a prospective study the effect of dexamethasone treatment on tumor volume and contrast enhancement was evaluated by computed tomography (CT) in 15 patients with intracranial lesions. Histological diagnoses were confirmed in 13 patients who had undergone surgical intervention. A CT study of the head, with and without contrast medium, was performed prior to the dexamethasone treatment and at various intervals during the treatment for 8-19 days. The volume, attenuation, and contrast enhancement of the tumor were measured and related to the time after the start of the treatment. In six meningiomas there was no change in the volume and enhancement of the tumors. Out of four gliomas, there was an increase in volume of two tumors, whereas the other two cases showed a decrease in the tumor volume. In one glioma a distinct decrease in enhancement was observed. In three cases of metastasis a decrease in enhancement and tumor volume was noted. An acoustic neurinoma and an unverified lesion, considered radiologically to be a glioma, also showed a decrease in tumor volume and contrast enhancement. In tumors that responded to the treatment, a decrease both in volume of the tumor and peritumoral brain edema as well as a decrease in contrast enhancement of the tumor were observed.
Adult↗
Discrepancies in brain tumor extent as shown by computed tomography and positron emission tomography using [68Ga]EDTA, [11C]glucose, and [11C]methionine.
A patient with an anaplastic (malignant) astrocytoma was examined with computed tomography (CT) and with positron emission tomography (PET), in the latter case using [68Ga]EDTA, [11C]glucose, and [11C]methionine. The CT examination as well as the [68Ga]EDTA study showed a small tumor located in the region of the head of the left caudate nucleus. The [11C]glucose examination showed increased uptake on the same region, as did the [11C]methionine examination, but the latter also showed a considerable uptake in the entire left thalamic region. The patient died 15 days after the [11C]methionine study and a histologic evaluation of thin sections obtained at autopsy showed excellent agreement between tumor extent and activity distribution after [11C]methionine administration. The tumor tissue seen only with [11C]methionine was histologically different from that part of the tumor observed with the other tracers. Although cytologically similar, the latter showed large necrotic areas and an ability to induce marked endothelial proliferation, whereas in the former neither necroses nor notable endothelial proliferation was seen. In this case more than 50% of the tumor would have remained radiologically imperceptible without the [11C]methionine PET examination.
Astrocytoma↗
C-11-labeled glucose and its utilization in positron-emission tomography.
Carbon-11-labeled glucose was prepared photosynthetically using the green alga Scenedesmus obtusiusculus Chod. The carbohydrates were extracted from the cells with dilute HCI and the glucose was isolated and purified using high-performance liquid chromatography. The manipulations in the hot cell are described. Analysis of the material (gas liquid chromatography and HPLC) showed that the glucose obtained was radiochemically pure. The total incorporation of the 11CO2 added to the algae was 60-80%. The radiochemical yield of pure carrier-added glucose was approximately 25%, at 40 min after E.O.B. including the HPLC purification and sterile filtration. The C-11 glucose uptake in rat brain was compared with that of commercial D[U-14C]glucose, and preliminary PET studies with D-[11C]glucose in a patient with a brain infarct are presented.
Animals↗
Positron emission tomography with 68Ga-EDTA in the diagnosis and localization of csf fistulas.
Five patients with cerebrospinal fluid (CSF) rhinorrhea were investigated with computed tomography (CT) and positron emission tomography (PET) to localize the site of a CSF fistula. After intrathecal injection of 10 MBq of 68Ga-EDTA, radioactivity was demonstrated in the basal cisterns. In three cases, the site of the fistula was visualized with PET. It is not always possible to demonstrate a CSF leakage with CT cisternography (CTC) using metrizamide, particularly in cases with minute fistulas or intermittent CSF rhinorrhea. With further experience and improved PET techniques, it may be possible to detect even very small fistulas.
Cerebrospinal Fluid Rhinorrhea↗
Determination of object contour from projections for attenuation correction in cranial positron emission tomography.
A contour-finding algorithm is described by which the object periphery is outlined in positron emission tomography (PET) scans. The positions of maximum slopes are determined in the projections. These positions are shown to correspond well to the borders of the activity region. By backprojecting these points in the projections into the image plane, the size and shape of the region of activity must be outlined. Cord lengths across this region are then determined for attenuation correction. The accuracy of the algorithm has been tested on 10 patients with both PET and computed tomography (CT) examinations. Points on the periphery of the skull, as determined with the contour-finding algorithm in PET, coincided with those determined by CT, with a standard deviation of 1.5 mm and a maximum deviation of 3.5 mm. In testing the influence of the skull bone on the PET values, it was found that ignoring the higher attenuation coefficient of bone, 5 mm thick, in the attenuation correction caused an error in the determination of activity of 11% peripherally and 6% centrally in the object. These errors could be reduced to less than 1% by increasing the assumed attenuating region by 4.5 mm.
Brain↗
Effect of dexamethasone treatment on peritumoral brain edema: evaluation by computed tomography.
In a prospective study, the effect of dexamethasone treatment on brain edema was evaluated by computed tomography (CT) in 14 patients with intracranial neoplasm. A CT study was made immediately prior to the beginning of the treatment and at various intervals for 8 to 19 days thereafter. The volume and attenuation of the edema were measured and related to the time after the start of treatment. In five cases of meningioma, only minor changes were shown; the edema volume either decreased or increased slightly or did not change at all. In four gliomas, a substantial decrease was noted in the edema volume in two cases and a smaller decrease was observed in two cases. In three metastases, a linear decrease in edema volume was noted during the entire follow-up, reducing it to one-fourth of the initial volume after 2 weeks of treatment. In one case of acoustic neuroma and in one undiagnosed lesion, a marked decrease in edema volume was also noted. The attenuation of the remaining edema was constant during the entire treatment time.
Adult↗
Head fixation device for reproducible position alignment in transmission CT and positron emission tomography.
A head-positioning device allowing accurate position transference between computed tomography and positron emission tomography is described. A base plate is fixed to the patient's head through either an individual mold or screws into the calvarium. This base plate fits onto the headholders of the two devices, thus ensuring that scans are taken at the same level. Using the regular software, the coordinates of an anatomic structure may be determined and transferred between the two images.
Humans↗
Positron emission tomography with 68Ga-EDTA compared with transmission computed tomography in the evaluation of brain infarcts.
The diagnostic value of positron emission tomography (PET) was evaluated in 41 examinations of 40 patients. 68Ga-EDTA was used as a positron source. The findings were correlated with those of conventional of CT scanning. A clearly pathologic accumulation of 68Ga-EDTA was detected in 29 of 41 PET scans. The precontrast CT scans were negative in 11 and non-conclusive in one patient. CT after administration of contrast medium was performed in 29 patients. Of these, 21 had a clearly pathologic PET scan and 14 had visible contrast enhancement on CT examination. The injury of the blood-brain barrier thus was better demonstrated with PET than with CT. The topologic diagnosis was, however, better demonstrated at CT. It seems that CT and PET are supplementary examinations and that PET is superior to CT in the detection of injury of or absence of the blood-brain barrier.
Adult↗
CT findings and glucocorticoid receptors in intracranial lesions with edema.
Glucocorticoid receptors were measured in the surgical specimens of 19 intracranial tumors and one brain confusion. None of the patients had received any steroid treatment prior to the operation. Preoperative computed tomography (CT) scans of these patients were evaluated with respect to attenuation values, contrast enhancement, volume of the tumor and edema, and the other characteristics. These various findings were plotted against the amount of glucocorticoid receptors. There was some correlation between the amount of receptor and attenuation as well as contrast enhancement of the tumor. No definite correlation between the volume of edema and/or size of the tumor and the amount of receptor was found in the material taken in its entirety. However, in two tumor groups, namely meningiomas with marked edema and circumscribed, discrete gliomas, a tendency toward a high amount of glucocorticoid receptors was observed. The positive correlation with contrast enhancement, reinforced by reports in the literature that contrast enhancement is affected by steroids, corroborates the theory that the steroid-receptor interaction plays an important role in the vascular permeability of tumors.
Adolescent↗
Attenuation profiles of the petrous bone with acoustic neuroma.
Attenuation profiles across the petrous bone covering the whole internal auditory meatus (IAM) were constructed from the printouts obtained by computed tomography (CT) with narrow collimation performed on 12 patients with 13 acoustic neuromas. In healthy patients the attenuation profiles of right and left petrous bone were very similar in shape. The attenuation values of the individual pixels in the pixel columns of the printout located at the site of the porus and the IAM reflected the demineralization of the petrous bone and the widening of the porus and the IAM caused by the acoustic neuroma. A widening deep in the meatus was demonstrated in a patient with an intracanalicular tumor, and therefore it seems possible to make this diagnosis by CT scanning combined with the construction of attenuation profiles across the petrous bone. In the presence of unilateral acoustic neuroma there was a significant and characteristic difference in shape between the attenuation profiles of the two sides with generally lower attenuation values on the tumor side together with signs of widening of the porus and the IAM. In cases of bilateral acoustic neuroma comparison of the attenuation profiles can be made with mean attenuation curves obtained from scanning normal petrous bones. The prevailing physical limitations for demonstrating a narrow bony canal like the IAM with CT was experimentally analyzed using bone-simulating plastic material.
Humans↗
Head fixation system for integration of radiodiagnostic and therapeutic procedures.
A head fixation system is described enabling exact transfer of positions between neuroradiological and therapeutic procedures. The key item of the system is a base plate that is rigidly attached to the patient's head, either by a plastic mould or screws onto the calvarium. The base plate may easily and accurately be attached to diagnostic or therapeutic units. Coordinates of target points in the various units are directly related through the exact application of the base plate. Procedures for the exact comparison of spatial information have been worked out. The system has been used for diagnostic procedures such as plain skull radiography, cerebral angiography, CT scanning, position emission tomography, and gamma camera examinations, as well as for therapeutic procedures such as stereotaxic biopsy and radiation treatment.
Head↗
A critical evaluation of two methods of head fixation.
Two head-fixation systems, one using Thermoplast and the other Lightcast were tested as to reproducibility by comparing stereotactic coordinates before and after CT scan and after removal and reapplication of the helmets. Helmets constructed of Lightcast were more consistently stable than those constructed of Thermoplast probably due in part to the dental fixation used with the former. With Lightcast the change in position of coordinates was consistently less than 3 mm, i.e. 2 pixels, which is within the tolerance of the system as a whole.
Bandages↗
An approach to stereotaxic radiography.
A simple approach to stereotaxic radiography, including a new method for determination of target coordinates, is described. The proposed technique may be used in combination with conventional equipment for roentgen examinations available in X-ray departments and operating rooms; the only additional outfit needed is a coordinate frame that can be attached to the patient's head. Determination of the coordinates is easily made graphically, or from a simple equation using a pocket calculator or a mini-computer.
Brain↗
Positron emission tomography in the evaluation of subdural hematomas.
Fifteen patients with 21 subdural effusions were investigated both with transmission computer assisted tomography (CAT) and positron emission tomography (PET). The tracer in the emission studies was 68Ga-EDTA. Twelve lesions were visualized both with CAT and PET. Five lesions that were negative or doubtful on CAT were visualized with PET, whereas four lesions negative or doubtful on PET were demonstrated by CAT. The two methods complement each other due to the fact that they are based on different mechanisms: CAT mainly on attenuation of the fluid collection. PET on isotope accumulation, particularly in the hematoma membranes.
Adolescent↗