Biomedical subjects

R T Constable

Publications and source records attributed to R T Constable.

60 records · Page 4Linked to original sources

PubMedDate not supplied

Signal-to-noise and contrast in fast spin echo (FSE) and inversion recovery FSE imaging.

Fast spin echo (FSE) imaging has recently experienced a renewed enthusiasm in the clinical setting for its ability to provide high contrast T2-weighted images in short imaging times. This article evaluates the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) properties of the FSE sequence, inversion recovery (IR) FSE sequence, and conventional SE imaging. The results indicate that FSE imaging displays similar contrast properties to SE imaging, but that the SNR and CNR are improved secondary to the longer TRs and longer effective TEs that may be used. The SNR per unit time of the FSE sequence, and hence its efficiency, is at least a factor of 8 better than the SE sequence when 16 echoes are acquired for each excitation. The addition of a slice selective inversion pulse in IR-FSE allows rapid generation of IR images with image contrast similar to that of conventional IR sequences. When used with a multicoil array for abdominal, pelvic, and spine imaging, the IR-FSE sequence produces images that are virtually free of motion artifact from the subcutaneous fat immediately adjacent to the coils. Both FSE and IR-FSE, when compared with SE imaging, provide superior image contrast and SNR in reduced imaging time.

Brain↗

PubMedDate not supplied

Fast spin echo STIR imaging.

OBJECTIVE: Our goal was to evaluate the image quality, contrast characteristics, and possible clinical utility of STIR images obtained using a fast SE (FSE) technique. MATERIALS AND METHODS: The signal and contrast characteristics of FSE STIR images were evaluated using a lipid/water phantom and normal volunteers. Based upon these results, optimal FSE STIR imaging parameters were chosen. Conventional STIR and FSE STIR images were then obtained (while maintaining an equal number of section locations between the two sequences) in a series of 14 patients with known musculoskeletal abnormalities. These images were compared side by side by two experienced MR radiologists for image quality and lesion detection. RESULTS: There were no statistically significant differences between the FSE STIR images and conventional STIR images in lesion detection, image quality, motion artifact, or final diagnosis. CONCLUSION: STIR imaging provides optimal contrast for detection of many pathologic abnormalities. This is especially true for musculoskeletal tumors and infection. The long imaging time and reduced number of sections obtainable with conventional SE (CSE) STIR sequences limit their routine use. Our results show that FSE STIR images of the musculoskeletal system can be obtained up to seven times more rapidly than CSE STIR images without compromising lesion detection or image quality.

Adipose Tissue↗

PubMedDate not supplied

Perturbation of the temperature distribution in microwave irradiated tissue due to the presence of metallic thermometers.

To date, satisfactory thermal dosimetry during the clinical application of localized hyperthermia can only be achieved using invasive thermometry. However the presence of commonly used metallic thermometers, such as thermocouples, may lead to the distortion of the temperature field due to self-heating of the probe under microwave irradiation. A computer simulation of the effect of this self-heating on the steady-state temperature distribution in plane-microwave irradiated homogeneous tissue has been undertaken and the significance of the effect for clinical hyperthermia dosimetry is assessed. The results indicate that a distortion of the temperature field in the neighborhood of the thermometer by several degrees can occur under adverse conditions.

Body Temperature↗

PubMedDate not supplied

Minimizing the self-heating artefacts due to the microwave irradiation of thermocouples.

The self-heating of metallic thermocouples in therapeutic microwave fields has long been recognized as a source of temperature artefacts in clinical hyperthermia dosimetry. We examine several techniques by which the probe and tissue heating artefacts resulting from self-heating may be quantitatively assessed, and discuss these in the context of their applicability to clinical hyperthermia.

Hyperthermia, Induced↗

PubMedDate not supplied

The cerebellum's role in reading: a functional MR imaging study.

BACKGROUND AND PURPOSE: Long considered to have a role limited largely to motor-related functions, the cerebellum has recently been implicated as being involved in both perceptual and cognitive processes. Our purpose was to determine whether cerebellar activation occurs during cognitive tasks that differentially engage the component processes of word identification in reading. METHODS: Forty-two neurologically normal adults underwent functional MR imaging of the cerebellum with a gradient-echo echo-planar technique while performing tasks designed to study the cognitive processing used in reading. A standard levels-of-processing paradigm was used. Participants were asked to determine whether pairs of words were written in the same case (orthographic processing), whether pairs of words and non-words rhymed with each other, respectively (phonologic assembly), and whether pairs of words belonged to the same category (semantic processing). Composite maps were generated from a general linear model based on a randomization of statistical parametric maps. RESULTS: During phonologic assembly, cerebellar activation was observed in the middle and posterior aspects of the posterior superior fissure and adjacent simple lobule and semilunar lobule bilaterally and in posterior aspects of the simple lobule, superior semilunar lobule, and inferior semilunar lobule bilaterally. Semantic processing, however, resulted in activation in the deep nuclear region on the right and in the inferior vermis, in addition to posterior areas active in phonologic assembly, including the simple, superior semilunar, and inferior semilunar lobules. CONCLUSION: The cerebellum is engaged during reading and differentially activates in response to phonologic and semantic tasks. These results indicate that the cerebellum contributes to the cognitive processes integral to reading.

Adult↗

PubMedDate not supplied

Fast spin-echo MR imaging of the cervical spine: influence of echo train length and echo spacing on image contrast and quality.

PURPOSE: To examine the interaction of echo train length and interecho spacing and their effects on image quality and contrast in fast spin-echo sequences of the cervical spine. METHODS: Forty-three patients with suspected cervical disk disease were prospectively evaluated with fast spin-echo with varying echo train lengths and interecho spacing. A flow phantom was used to confirm findings related to cerebrospinal fluid pulsation. Parameters were manipulated to adjust contrast, signal-to-noise ratio, the effects of artifacts, and the speed of acquisition. RESULTS: In general, increasing echo train length increased homogeneity and high intensity of cerebrospinal fluid signal and reduced acquisition time; however, it decreased the signal-to-noise ratio of cerebrospinal fluid and cord and increased blurring, and, to a lesser extent, edge enhancement, and "truncation-type" artifact. Increasing interecho space permitted the use of longer echo times but minimally decreased contrast and signal-to-noise ratio of cord and cerebrospinal fluid. In addition, increasing echo spacing increased blurring, edge enhancement, truncation-type, magnetic susceptibility, and motion artifacts. CONCLUSIONS: For cervical spine imaging, a long echo train length and short echo spacing partially compensate for cerebrospinal fluid flow and produce the best myelographic effect but must be modulated by other constraints, such as artifact production or technical capabilities.

Cervical Vertebrae↗