Biomedical subjects

B Nordell

Publications and source records attributed to B Nordell.

27 records · Page 2Linked to original sources

PubMed1977

Determination of some parameters for pion radiobiology studies.

An experimental investigation of the central axis depth-dose and stopping rate distribution of the SIN biomedical pion beam is reported. The pion stopping rate in a thin disc of tissue-equivalent plastic was determined using a counter telescope. The dose rate at the position of this dic 'target' was measured using a specially designed parallel-plate tissue-equivalent ionization chamber. Both dose rate and pion stopping rate are given as a function of depth for beams of two different momenta spread. The energy deposition required per pion stop to fit the measured dose rate curves was calculated and found to be between 37 and 40 MeV. From the stopping rate measurements the depth-dose distribution of pion interaction dose (star-dose) and the dose due to the pion slowing down have been evaluated. The maximum star-dose is found at a depth of about 2 g cm-2 beyound the maximum of the ionization dose.

Elementary Particles↗

PubMedDate not supplied

Cardiac-gated MR angiography of pulsatile flow: k-space strategies.

Signal strength in time-of-flight magnetic resonance (MR) angiography of pulsatile flow is modulated by the time-varying intraluminal magnetization strength. The specific appearance of MR angiographic images therefore depends on the relationship of different phase-encoding steps to the pulsatile flow waveform. Cardiac-phase gating can be applied with phase-encoding reordering to acquire different regions of k-space during the desired phases of the cardiac cycle. The authors have developed a simulation program for evaluating the merits of different encoding strategies for pulsatile flow. The model was validated with phantom studies. High signal intensity relative to that in conventional MR angiographic studies can be attained with strategies that impose relatively small penalties in total acquisition time.

Artifacts↗

PubMedDate not supplied

A dynamic phantom for generation of contrast bolus curves for the evaluation of digital subtraction angiography systems.

A solid dynamic phantom has been constructed, which allows quantitative measurements of the signal-to-noise ratios in processed images from digital subtraction angiography (DSA) units. Profiles of silicone rubber placed in concentric circles on a plate which is rotated in the image plane generates bolus curves with five different transit times in each examination. The phantom is suited for measurement on DSA units working with matched or recursive filtering.

Angiography, Digital Subtraction↗

PubMedDate not supplied

A rotating phantom for the study of flow effects in MR imaging.

A common type of phantom used for the study of flow effects in MR imaging is the tube phantom, where a liquid passes through a set of tubes placed in the main magnetic field of an MR scanner. Among the disadvantages with this type of phantom are that a distribution of velocities is present in each tube, and that quantifications of flow effects using tube phantoms may be very time-consuming. In this work, we describe the design and the properties of a rotating wheel flow phantom used for quantification of the effects of flow through the imaging plane as well as in the imaging plane. The proposed phantom is constructed as a rotating gel-filled wheel, surrounded by static volumes filled with the same gel, and the evaluation of the information from rotating and static parts is made with a specially designed computer program. The phantom can be used as a plug flow phantom covering simultaneously an interchangeable velocity interval, which at present has the range -52 mm/s, +52 mm/s. It is shown that the phantom gives adequate information on the dependence of pixel content on first-order motion in MR modulus and phase images. Among the fields of application are rapid calibration of MR imaging units for flow determination using phase information, as well as testing of pulse sequence characteristics and verification of theoretical predictions concerning the flow dependence in MR images.

Electron Spin Resonance Spectroscopy↗

PubMedDate not supplied

A method for MR quantification of flow velocities in blood and CSF using interleaved gradient-echo pulse sequences.

The aim of this study was to establish a rapid method for in vivo quantification of a large range of flow velocities using phase information. A basic gradient-echo sequence was constructed, in which flow was encoded along the slice selection direction by variation of the amplitude of a bipolar gradient without changes in sequence timings. The influence of field inhomogeneities and eddy currents was studied in a 1.5 T interleaved sequences for calibration and in vivo flow determination were constructed, and flow information was obtained by pairwise subtraction of velocity-encoded from velocity non-encoded phase images. Calibration was performed in a nongated mode using flow phantoms, and the results were compared with theoretically calculated encoding efficiencies. In vivo flow was studied in healthy volunteers in three different areas using cardiac gating; central blood flow in the great thoracic vessels, peripheral blood flow in the popliteal vessels, and flow of cerebrospinal fluid (CSF) in the cerebral aqueduct. The results show good agreement with results obtained with other techniques. The proposed method for flow determination was shown to be rapid and flexible, and we thus conclude that it seems well suited for routine clinical MR examinations.

Aorta↗

PubMedDate not supplied

Cardiac gated MR imaging of cerebrospinal fluid flow.

This is a preliminary investigation of the cerebrospinal fluid (CSF) spaces using cardiac gated magnetic resonance imaging. A variation of intensity of the signal from the cerebral aqueduct is demonstrated during the cardiac cycle. The pattern of this variation suggests pulsatile CSF flow. Calculations that have been verified by phantom measurements show that CSF flow rates less than 1 mm/s may be detectable. Magnetic resonance may therefore offer a new method for the demonstration and measurement of CSF flow.

Cerebral Aqueduct↗

PubMedDate not supplied

Quantitative study of flow dependence in NMR images at low flow velocities.

A basic theoretical model that describes the effects of flow in and out of the imaging plane in nuclear magnetic resonance (NMR) images, obtained with the standard pulse sequences single spin echo, multiple spin echo, and inversion recovery, is presented. Theoretically calculated signal values are compared with experimental results obtained from single-slice images of a flow phantom for variable flow velocity v as well as for variable echo time and inversion time at flow velocities less than 10 mm/s, corresponding to those found in cerebrospinal fluid, in capillary systems, and in smaller veins. The quantitative correspondence between theory and experiment is good in the range of velocities studied and for the imaging parameters used, but discrepancies occur when higher velocities are studied. In addition, flow in a capillary model is demonstrated qualitatively for very low linear flow velocities, less than 1 mm/s. It is concluded that the model describes the essentials of the inflow-outflow effect and that this effect can predict the flow dependence of the NMR signal for low flow velocities. Observed differences between model and experiment may be due to effects of flow-induced phase alterations and due to uncertainty in measurements of the relaxation times T1 and T2. The model described here can be extended to suit other types of pulse sequences and to suit multislice imaging. It can also be extended to incorporate flow-induced phase effects.

Blood Flow Velocity↗

PubMedDate not supplied

Changes in energy metabolism following roentgen irradiation of in vivo growing Ehrlich ascites tumour cells studied by 31P magnetic resonance spectroscopy.

The energy metabolism in Ehrlich ascites tumour cells following in vivo irradiation of a dose of 5.0 Gy was studied in vitro in their ascites fluid up to 48 hours using 31P magnetic resonance spectroscopy measuring ATP, ADP and inorganic phosphate (Pi). The results are also related to radiation induced changes in cell cycle composition. ATP was reduced by more than 50 per cent 20 to 24 hours after irradiation but normalized at 48 hours. ADP was reduced to about half the normal level 24 to 48 hours after irradiation. When the ATP and ADP had reduced levels, the inorganic phosphate increased correspondingly. Addition of glucose to the ascites cell suspension at the time of minimum ATP level immediately raised the ATP:Pi ratio. Since the glucose concentrations in blood and in ascites fluid following irradiation were also reduced, lack of glucose for energy production might have been a major contributing factor for the reduced ATP production.

Adenine Nucleotides↗

PubMedDate not supplied

Stereotaxic angiography in gamma knife radiosurgery of intracranial arteriovenous malformations.

Gamma knife radiosurgery is an effective alternative to embolization or microsurgical removal of small arteriovenous malformations, particularly in eloquent areas of brain tissue. Stereotaxic angiography is a useful diagnostic and targeting adjunct to gamma knife radiosurgery, and the authors present their experience (1,100 patients) with methods and technique, and show how the nidus of the arteriovenous malformation can be defined angiographically. Dose planning employing digitization of the subtraction image enables determination of the spatial coordinates of the lesion by means of an interactive computer program.

Cerebral Angiography↗