Biomedical subjects

J MacFall

Publications and source records attributed to J MacFall.

13 recordsLinked to original sources

PubMed1999

Magnetic resonance assessment of cerebral perfusion in depressed cardiac patients: preliminary findings.

OBJECTIVE: The authors investigated the links between depression, cardiac disease, and microcirculatory cerebral blood flow (CBF). METHOD: A magnetic resonance imaging technique based on arterial spin tagging was used to estimate microcirculatory CBF in depressed (N = 5) and comparison (N = 14) elderly subjects with coronary artery disease. Signal intensity ratios corresponding to relative microcirculatory CBF were calculated for four regions on two axial images through the upper and lower halves of the lateral ventricles. RESULTS: On the superior image, estimates of microcirculatory CBF were statistically significantly lower on the left side in the depressed subjects than in the nondepressed group. When the ratios in the superior and inferior images were averaged, the depressed subjects had lower values for both left periventricular regions of interest and the parietal region. CONCLUSIONS: Despite the small study group and indirect estimates of blood flow, these preliminary findings suggest that a relative cerebral hypoperfusion may underlie depression in elderly cardiac patients.

Age Factors↗

PubMed1998

Overview of diffusion imaging.

Diffusion is a major advance in the continuing evolution of MR imaging. It provides contrasts and characterization between tissues at a cellular level that may imply differences in function as well as framework. With the development of echo-planar imaging (EPImh54) diffusion the quality of the data will be such that clinically relevant information can result, and thus clinical usage of EPI diffusion will increase. Many potential applications of diffusion have not yet been explored.

Brain↗

PubMed1997

Hyperthermic treatment of malignant diseases: current status and a view toward the future.

New studies in hyperthermia at the basic science, engineering, and clinical level have stimulated renewed enthusiasm for re-investigating its potential as an anticancer therapy. This article reviews the salient features of these recent results and points out areas for additional investigation. Highlighting these new results is the publication of several positive phase III trials for thermoradiotherapy compared to radiotherapy alone. Important highlights are the encouraging results using magnetic resonance imaging for noninvasive thermometry. If this technology is successfully implemented with real time power control it will revolutionize the clinical application of hyperthermia.

Animals↗

PubMed1994

MR imaging of high-grade cerebral gliomas: value of diffusion-weighted echoplanar pulse sequences.

OBJECTIVE: The purpose of this study was to evaluate the usefulness of diffusion-weighted echoplanar MR imaging in the examination of high-grade brain gliomas compared with that of conventional spin-echo (SE) or fast spin-echo (FSE) MR imaging. We hypothesize that diffusion-weighted MR imaging may enable us to differentiate various tumor components on the basis of differences in the diffusion of water. SUBJECTS AND METHODS: Conventional SE and FSE MR images were obtained in 10 patients with high-grade brain glioma. Diffusion-weighted echoplanar MR images were obtained with a head gradient coil capable of providing diffusion-weighted imaging along the cephalocaudal axis. Using SE and FSE MR images as a baseline, we evaluated the diffusion-weighted MR images for usefulness in distinguishing tumor components on the basis of differences in diffusion. RESULTS: Areas of tumor that showed significant enhancement on T1-weighted SE MR images obtained after injection of contrast material were markedly hyperintense on diffusion-weighted images and had a lower apparent diffusion coefficient (ADC) than the ADCs for nonenhancing tumor and peritumoral edema. Cystic or necrotic portions of tumor showed the most signal suppression on diffusion-weighted images and were associated with the highest ADCs. On T2-weighted FSE MR images, areas of hyperintensity observed in white matter oriented parallel to the direction of the diffusion gradient could be differentiated into two patterns on the basis of findings on diffusion-weighted images: areas that showed marked signal suppression with a higher ADC, most likely representing areas of predominantly peritumoral edema, and areas that showed a lesser degree of signal suppression with similar but slightly lower ADCs than those of edema, most likely representing areas of predominantly nonenhancing tumor. CONCLUSION: Diffusion-weighted echoplanar MR imaging is a useful technique for examining high-grade cerebral gliomas. It enabled us to differentiate various components of the tumor (e.g., enhancing, nonenhancing, cystic, or necrotic) and to distinguish areas of predominantly nonenhancing tumor from areas of predominantly peritumoral edema when the abnormality was located in the white matter aligned in the direction of the diffusion-weighted gradient. Diffusion-weighted echoplanar MR imaging appears to be a powerful tool in the characterization of brain neoplasms.

Adolescent↗

PubMed1993

Pulsatile motion artifact reduction in 3D steady-state-free-precession-echo brain imaging.

An image can be made from the echo of a steady-state-free-precession and pulse sequences for this purpose have been implemented on various commercial systems under such names as "CE-FAST" and "SSFP" (herein generically termed SSFP-Echo). Such sequences can be employed to achieve strong T2-weighting with reduced T2* effects, but are limited by their sensitivity to flow and motion which produce artifacts. Simple considerations indicate that this sensitivity is primarily related to the (implementation-dependent) moments of the imaging gradients. In this work, MR imaging of the brain using a standard implementation of the sequence with large moment "crusher" gradients on the slice select axis (to dephase the FID of the SSFP) is compared to a modified implementation with reduced moment gradient pulses and different radiofrequency (RF) phase cycling. Asymmetric echo acquisition and narrowed bandwidth was used to further reduce gradient moments. The sensitivity of this sequence to flow and motion artifacts, especially for motion perpendicular to the slice, is thus expected to be significantly reduced. The modified sequence was found to have flow and motion artifacts reduced by a factor of five in the axial plane and a factor of two in the coronal plane. These modifications can thus significantly reduce the flow and motion artifacts commonly seen in conventional images of the SSFP echo with little or no penalty in scan time or signal-to-noise ratio.

Artifacts↗

PubMed1993

Three dimensional MR gradient recalled echo imaging of the inner ear: comparison of FID and echo imaging techniques.

The detailed structures of the inner ear make this region a diagnostic challenge for radiologists. Thin section high resolution CT is the "gold standard" for studies of the fine bony detail of the inner ear. Although CT can delineate bony structures, fine soft tissue details surrounded by CSF/endolymph (such as nerves in the internal auditory canal) are not easily identified. Conventional MR spin-echo T2-weighted images provide good image contrast for such structures, but the current commercially available minimum slice thickness of approximately 2-3 mm is too thick for the inner ear. Volume gradient recalled echo (GRE) MR imaging techniques can be used to achieve thin slices (< 2 mm) while maintaining adequate contrast for detailed examination. In the work reported here a volume GRE sequence that images the echo formed in a steady-state-free-precession (termed "CE-FAST" or "SSFP" on various commercial MRI systems and called SSFP-echo in this work) was used to image inner ear structures. This technique was compared with images generated using conventional volume GRE techniques (GRASS). While small flip angle volume GRE imaging has been used for inner ear imaging previously, the low contrast typical of such density weighting makes it difficult to distinguish soft tissue structures from surrounding CSF/endolymph. In this work, contrast-to-noise ratios (CNR) between CSF/endolymph and brain parenchyma were compared between the sequences at 15 degrees, 30 degrees, 60 degrees, and 90 degrees flip angles. The SSFP-echo sequence produced higher CNR for such structures and consistently outperformed GRASS sequences at flip angles of 30 degrees, 60 degrees, and 90 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Practical choices of fast spin echo pulse sequence parameters: clinically useful proton density and T2-weighted contrasts.

With the development of fast spin echo (FSE) MRI techniques, T2-weighted images of the brain may be obtained much more quickly than when using conventional spin echo techniques (CSE), because made the individual echoes on the FSE pulse sequence are phase encoded, allowing acquisition of the same spatial information as in CSE with less excitations. The pulse sequence parameters (echo train length, bandwidth, echo spacing) are discussed. Images were obtained on four volunteers using both CSE and FSE while varying repetition time, echo time and matrix. Comparison for signal intensity gray-white differentiation, fat and CSE signal, arifacts and vascular resolution showed that FSE images comparable in quality to those of CSE can be obtained in less than half the time. A practical choice of FSE parameters is recommended for clinical use. However, artifacts, possibly related to CSF and vascular pulsation, of which the radiologist should be aware, were identified on the FSE images.

Artifacts↗

PubMed1992

Evaluation of complex cystic masses of the brain: value of steady-state free-precession MR imaging.

OBJECTIVE: This study evaluated the effectiveness of steady-state free-precession (SSFP) MR imaging of complex cystic masses of the brain compared with that of conventional T1- and T2-weighted spin-echo imaging. Our hypothesis is that SSFP MR images provide better characterization of these masses and facilitate more appropriate preoperative diagnoses and planning. SUBJECT AND METHODS: Axial T1-weighted and SSFP MR images and specimens for pathologic examination were obtained in seven consecutive patients, 9-81 years old, with cystic mass lesions of the brain and neurologic symptoms and signs directly related to the masses. Axial contrast-enhanced T1-weighted images were obtained in six patients, surgical exploration was done in five patients, and stereotaxic biopsy was done in two. After examination of the routine spin-echo and SSFP images, the usefulness of SSFP images was determined by how well they facilitated correct preoperative diagnosis. RESULTS: On SSFP MR images, the solid or inhomogeneous components of a cystic mass had extremely low signals in contrast to the high signal of surrounding fluid. On routine spin-echo images, however, the signals of these components were masked by the signal of the surrounding fluid. SSFP MR images helped markedly in diagnosis of hemorrhagic, epidermoid, and arachnoid cysts. In cases of enhancing brain tumors, SSFP MR images provided the same information that contrast-enhanced images did. Overall, when SSFP MR imaging was used, more information about the texture and constituents of the cystic mass was obtained, and a more useful diagnosis was made. CONCLUSION: Initial results show that SSFP MR imaging is a more useful technique than conventional spin-echo imaging for characterizing complex cystic masses of the brain. SSFP MR imaging (1) allows distinction of edema from tumor, (2) helps establish where biopsy has the best chance of providing tissue that will show pathologic changes, and (3) helps distinguish simple cysts from tumors, tumor-cyst, or multicompartmental cyst and may be particularly helpful in detecting the contents of hemorrhagic cysts.

Adult↗

PubMed1986

A time-of-flight method of measuring flow velocity by magnetic resonance imaging.

A new time-of-flight method for direct imaging of flow velocities by magnetic resonance is presented. The technique uses selective exciting and refocusing RF pulses to selectively affect planes oriented in orthogonal directions in space, with the region of excitation perpendicular to the flow and the refocusing region parallel to and including the flow. The positions of the sources of the resulting spin echoes are imaged, showing a displacement equal to the product of the velocity and the echo time. These images clearly show the profile of the velocity distribution, both in laminar and nonlaminar flows.

Blood Flow Velocity↗

PubMedDate not supplied

MRI of absent left pulmonary artery.

Unilateral absence of a pulmonary artery, more accurately referred to as unilateral proximal interruption of a pulmonary artery, is a rare congenital anomaly that may occur as an isolated lesion or in association with other congenital cardiovascular abnormalities. Diagnosis of associated lesions is imperative as early detection and intervention may significantly improve the patient's prognosis. We present the case of an adult patient who had come to our attention after suffering neurological decompression illness related to scuba diving. The patient's cardiopulmonary anatomy was evaluated using MRI gated spin echo, cine, and breath-held fast spoiled recalled echo sequences.

Adult↗

PubMedDate not supplied

Non-invasive thermometry using magnetic resonance diffusion imaging: potential for application in hyperthermic oncology.

The proposition to use non-invasive thermometry based on magnetic resonance diffusion imaging for applications in therapeutic hyperthermia is examined. The measurement of proton motion predominantly associated with the self-diffusion of water can be characterized by a Boltzmann temperature dependence (i.e. e-Ea/kT). The activation energy (Ea) is on the order of 0.2 eV and, for a restricted range (approximately 30 degrees) at a base temperature of approximately 300 K, the relationship between the effective diffusion coefficient and temperature is approximately linear. This response has been empirically demonstrated in water-based gel phantoms using magnetic resonance imaging (MRI). Additionally, it is feasible to have compatibility between radiofrequency (RF) heating devices and MRI equipment. An MRI-compatible heating applicator that includes a hexagonal array of coherently phased dipoles was assembled. This heating array easily fits into a standard 1.5 T head imaging coil (diameter 28 cm). The RF fields associated with heating (130 MHz) and imaging (64 MHz) were decoupled using bandpass filters providing isolation in excess of 100 dB. This isolation was sufficient to allow simultaneous imaging and RF heating without deterioration of the image signal-to-noise ratio. In this report temperature, spatial and time resolution achieved in phantom are examined in order to assess the potential for using this non-invasive temperature measurement in applications of hyperthermic oncology. Using this system and conventional multi-slice imaging techniques, 0.5 degrees C resolution in a voxel size of less than 1 cm3 has been achieved using an acquisition time of 4.15 min.

Diffusion↗

PubMedDate not supplied

Application of new technology in clinical hyperthermia.

Two areas of technical progress related to hyperthermic oncology are presented: (1) numerical modelling of absorbed power and temperature distributions; and (2) non-invasive thermometry using magnetic resonance imaging. The results represent achievements made during the past 5 years at Duke University Medical Center's Departments of Radiation Oncology and Radiology. They represent examples of progress in the technology of hyperthermia that have potential for greatly improving the delivery, monitoring and assessment of clinical hyperthermia.

Body Temperature↗

PubMedDate not supplied

Temperature dependence of canine brain tissue diffusion coefficient measured in vivo with magnetic resonance echo-planar imaging.

The intensity of conventional spin-echo diffusion-weighted magnetic resonance (MR) images is approximately linearly dependent on temperature over a restricted range using conventional diffusion-weighted spin-echo magnetic resonance imaging (MRI). However, conventional diffusion-weighted MRI is too motion sensitive for in vivo thermometry. The present work evaluated rapid diffusion-weighted echo-planar imaging (EPI), which is less sensitive to motion, for application to non-invasive thermometry in acrylamide gel materials and in vivo in canine brain tissue for applications in therapeutic hyperthermia. The rapidly switched, strong gradients needed for EPI were achieved using a 'local' z-axis gradient coil. Gel materials were heated with a small (10 cm diameter) spiral surface microwave (MW) applicator at 433 MHz, while in vivo heating was accomplished with whole body RF hyperthermia using an annular phased array (130 MHz). The MW or RF fields associated with heating and imaging (64 MHz) were decoupled using bandpass filters providing isolation in excess of 100 dB. This isolation was sufficient to allow simultaneous imaging and MW or RF heating without deterioration of the image signal-to-noise ratio. Using this system in a gel, temperature sensitivity of the diffusion coefficient was observed to be (3.04 +/- 0.03)%/degrees C which allowed temperature changes of 0.55 degrees C to be resolved for a 1.8 cm3 region in < 10 s of data acquisition. In vivo, cardiac gating of the pulse sequence was necessary to minimize motion artifacts in the brain. The temperature sensitivity of brain tissue was (1.9 +/- 0.1)%/degrees C allowing temperature changes of 0.9 degrees C to be resolved in a 0.9 cm3 volume in < 10 s of data acquisition. We conclude that with further optimization of the data acquisition conditions it will be possible to determine 0.5 degrees C temperature changes in 1 cm3 volumes in < 10 s using this technique.

Animals↗