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Biomedical subjects

R C Hawkes

Publications and source records attributed to R C Hawkes.

At least 19 recordsLinked to original sources
PubMed2006

Development of a combined microPET-MR system.

As evidenced by the success of PET-CT, there are many benefits from combining imaging modalities into a single scanner. The combination of PET and MR offers potential advantages over PET-CT, including improved soft tissue contrast, access to the multiplicity of contrast mechanisms available to MR, simultaneous imaging and fast MR sequences for motion correction. In addition, PET-MR is more suitable than PET-CT for cancer screening due to the elimination of the radiation dose from CT. A key issue associated with combining PET and MR is the fact that the performance of the photomultiplier tubes (PMTs) used in conventional PET detectors is degraded in the magnetic field required for MR. Two approaches have been adopted to circumvent that issue: retention of conventional, magnetic field-sensitive PMT-based PET detectors by modification of other features of the MR or PET system, or the use of new, magnetic field-insensitive devices in the PET detectors including avalanche photo-diodes (APDs) and silicon photomultipliers (SiPMs). Taking the former approach, we are assembling a modified microPET Focus 120 within a gap in a novel, 1T superconducting magnet. The PMTs are located in a low magnetic field (approximately 30mT) through a combination of magnet design and the use of fiber optic 'bundles'. Two main features of the modified PET system have been tested, namely the effect of using long fiber optic bundles in the PET detector, and the impact of magnetic field upon the performance of the position sensitive PMTs. The design of a modified microPET-MR system for small animal imaging is completed, and assembly and testing is underway.

Animals↗
PubMed1987

Rapid Fourier imaging using steady-state free precession.

Reversal of the read gradient in a SSFP imaging experiment allows a full spin echo to be collected in the interval tau between successive rf pulses. Orthogonal gradient pulses are used to dephase and subsequently rephase the transverse magnetization each tau enabling 2D or 3D Fourier techniques. The minimum data collection time per slice in the 3D technique is 3.1 s (128 X 256). For a 2D data collection, an oscillating bipolar sawtooth gradient is used to select the slice. Each phase-encode value must be averaged over an equivalent portion of the oscillating slice-selection gradient and this condition gives a minimum of 25 s for 2D data collection. Excellent slice selection is achieved with less than 5% of the signal lying outside the slice profile central lobe. Images at 0.14 T show tissue contrast may be manipulated by changing the rf pulse angle, an example of which is the presence or absence of gray/white matter contrast at rf pulse angles of 30 and 90 degrees, respectively. The pulse angle theta dependence of five samples with different values of T2/T1 was measured and numerically calculated with good agreement between theory and experiment for theta less than or equal to 90 degrees.

Brain↗
PubMed1987

Fast imaging of CSF flow/motion patterns using steady-state free precession (SSFP).

Using a rapid Fourier SSFP imaging technique, which is sensitive to slow flow (approximately 1 mm/sec) in the plane of the image, we obtained 135 brain MRI examinations. The CSF flow/motion patterns were mapped by two images with orthogonal in plane flow sensitivity directions. Analysis showed significant deviations from the "normal" pattern in ventricular enlargements because of obstruction (no evidence of CSF flow/motion) or in normal pressure hydrocephalus (complex, intensive flow pattern in lateral ventricles) suggesting a diagnostic potential for this fast imaging technique.

Brain↗
PubMed1986

The application of steady-state free precession to the study of very slow fluid flow.

An NMR imaging technique sensitive to slow flow (approximately 1 mm/s) using a conventional imaging gradient strength (0.025 mT/cm) is described. Two projections with different spatial magnetic periodicity (determined by the SSFP pulse interval), and thus with different flow sensitivities, are subtracted to give signal from flows in a velocity window.

Animals↗
PubMed1986

Mapping of normal and abnormal cerebrospinal fluid flow/motion patterns using steady state free precession imaging.

In a comparative study more than 35 brain magnetic resonance imaging examinations were analyzed by mapping the CSF flow/motion pattern using the steady state free precession technique with two different flow sensitivity directions. Significant deviations from the normal pattern were seen in ventricular enlargements due to obstruction with no evidence of CSF flow/motion and in normal pressure hydrocephalus with complex flow pattern in lateral ventricles, suggesting a diagnostic potential for this fast imaging technique with sensitivity to very slow flow.

Cerebrospinal Fluid↗
PubMed1984

Imaging the pregnant human uterus with nuclear magnetic resonance.

Nuclear magnetic resonance (NMR) techniques have been used to produce images of the pregnant and nonpregnant human uterus. A series of pictures is presented showing the normal nonpregnant uterus and pelvic organs, the uterus and its contents in pregnancy at 17, 30, and 40 weeks' gestation, and the pelvic organs in the early puerperium. In early pregnancy the uterus and placenta are clearly seen and the dimensions and configuration of the pelvis can be readily assessed. Because of the relatively long scan time of 2 minutes, better images of the fetus were obtained in the third trimester when movement is more restricted. The potential value of this technique in obstetrics is discussed.

Female↗
PubMed1984

Imaging ovarian tumours by nuclear magnetic resonance.

The application of nuclear magnetic resonance imaging to the diagnosis of ovarian tumours has been studied in a group of seven patients with ovarian masses and several healthy volunteers who provided examples of normal pelvic anatomy. In three patients, benign unilocular ovarian cysts were demonstrated and in three patients, recurrent ovarian tumours were identified and the extent of the tumours defined. One patient with bilateral ovarian endometriomas was imaged. Endometrial cysts, like masses in other systems which contain blood or lipid-rich material, show high-density images whereas malignant tumours show tissue densities closer to those of normal tissues. The potential value of this technique in the assessment of pelvic disease is discussed.

Endometriosis↗
PubMed1984

The use of nuclear magnetic resonance in the diagnosis of lateral canal entrapment.

The use of nuclear magnetic resonance (NMR) in the diagnosis of radicular pain due to lateral canal stenosis in 21 patients is reported. NMR was able to distinguish normal intervertebral discs from degenerate discs, and NMR evidence of reduction of epidural fat was more reliable than radiculography in identifying lateral root entrapment. NMR is an important advance in the investigation of lumbar radiculopathies.

Adult↗
PubMed1983

Nuclear magnetic resonance imaging of the knee: examples of normal anatomy and pathology.

Nuclear magnetic resonance images of the knee were obtained from three normal volunteers and from two patients. The pathology included an osteosarcoma of the distal femur and a fracture of the tibia. Steady State Free Precession (SSFP) techniques were used with a 0.15 Tesla resistive type magnet. Normal anatomy was well displayed and the size of the osteosarcoma was accurately predicted. Using SSFP techniques, the blood in the knee joint was not visualised, but the underlying tibial fracture was clearly outlined.

Adolescent↗
PubMed1980

Nuclear magnetic resonance tomography of the brain.

Nuclear magnetic resonance (NMR) has long promised to provide a risk-free alternative method for both structural and functional tomography of the human body, since the original small scale demonstration of its principles by Lauterbur. The considerable technical problems involved in scaling up a successful 8 cm diameter line-scan NMR imaging apparatus have been overcome, and 128 x 128 element NMR tomograms of electronically definable planes less than 1 cm thick through the living brain can be produced routinely in total time of less than 2.5 min. The method used is briefly described, and it is compared with radionuclide emission tomography, which it most resembles. The contrast mechanism in the images and the hazard are also briefly discussed.

Brain↗
PubMed1980

Nuclear magnetic resonance (NMR) tomography of the brain: coronal and sagittal sections.

Directly produced nuclear magnetic resonance (NMR) coronal and sagittal tomograms of the human brain are shown. These are presented together with axial transverse images of the same two volunteer subjects. The reasons for the ease of producing sections in any orientation by NMR are explained. The images are interpreted in terms of contrast mechanisms and anatomical detail.

Computers↗
PubMed1980

Nuclear magnetic resonance (NMR) tomography of the brain: a preliminary clinical assessment with demonstration of pathology.

A preliminary clinical evaluation of the nuclear magnetic resonance scans of patients with a variety of intracranial abnormalities is presented. We compare this noninvasive technique, which uses no ionizing radiation, against information obtained from conventional neuroradiological procedures and X-ray computed tomography of the same patients. The ability to produce coronal and sagittal as well as axial transverse images directly is shown to have important implications for precise lesion assessment.

Adult↗
PubMedDate not supplied

The application of NMR imaging to the evaluation of pituitary and juxtasellar tumors.

Nuclear magnetic resonance (NMR) imaging was used to evaluate pituitary and juxtasellar tumors in 37 patients representing a wide range of pathology. The value of the multiplanar facility of NMR is emphasized in providing accurate volumetric information and establishing the topographical relation of tumors to adjacent structures. Current limitations of the method and possible future developments to improve diagnostic precision are discussed.

Acromegaly↗