Biomedical subjects
Publications and source records attributed to D J Beacock.
Patent foramen ovale (PFO) and atrial septal aneurysm have been cited as potential risk factors for cryptogenic stroke. We present two cases which we propose to directly illustrate paradoxical embolisation as a mechanism of cerebrovascular accident. The diagnosis of PFO is discussed and the literature reviewed.
A real-time magnetic resonance imaging (MRI) acquisition sequence was evaluated for the assessment of left ventricular wall motion (WM) and wall thickening (WT). Ten normal volunteers and 21 patients were studied. Short-axis cine images of the left ventricle (LV) were acquired with a fast gradient echo and an ultrafast segmented echo-planar imaging (EPI) sequence. Qualitative and quantitative analysis of WM and WT was performed on a segmental basis. Qualitative scores agreed between the two methods in 691 of 724 segments (95.4%) with good reproducibility. Quantitative measurements of WM and WT were significantly lower (P < 0.001) with the real-time method (WM: mean bias, 0.49 mm; WT: mean bias, 0.61 mm). The largest differences were observed in the anterior and lateral segments and in patients with dilated ventricles. The lower resolution of the real-time sequence and artifacts was probably responsible for these differences. In conclusion, real-time cardiac MRI can be used for qualitative assessment of wall dynamics but is presently insufficient for quantitative analysis.
This study investigates the use of real-time acquisition in cardiac magnetic resonance imaging (MRI) for measurements of left ventricular dimensions in comparison with conventional gradient echo acquisition. Thirty-one subjects with a variety of left ventricular morphologies to represent a typical clinical population were studied. Short-axis data sets of the left ventricle (LV) were acquired using a conventional turbo-gradient echo and an ultrafast hybrid gradient echo/echo planar sequence with acquisition in real-time. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF) and left ventricular mass (LV mass) were measured. The agreement between the two acquisitions and interobserver, intraobserver and interstudy variabilities were determined. The bias between the two methods was 5.86 ml for EDV, 0.23 ml for ESV and 0.94% for EF. LV mass measurements were significantly lower with the real-time method (mean bias 14.38 g). This is likely to be the result of lower spatial resolution and chemical shift artefacts with the real-time method. Interobserver, intraobserver and interstudy variabilities were low for all parameters. In conclusion, real time acquisition in MRI can provide accurate and reproducible measurements of LV dimensions in subjects with normal as well as abnormal LV morphologies, but LV mass measurements were lower than with conventional gradient echo imaging.
Magnetic resonance (MR) is well suited to imaging the pericardium. High resolution images synchronized with the cardiac cycle can be obtained in any plane. The wide field of view allows additional anatomical and functional information to be obtained from adjacent structures such as the aorta, pleura, lungs and mediastinum. MR is particularly useful in cases of pericardial constriction without an associated effusion, in patients with complex or loculated pericardial effusions and in pericardial tumours. In this article we illustrate the characteristic MR features of a variety of pericardial pathologies.
Quantitative analysis of functional cardiac magnetic resonance (MR) images has been limited by the lack of well-validated, semiautomatic, methods for rapid analysis. We describe the evaluation of a DICOM-compatible PC-based parallel-processing tool, for cardiac magnetic resonance analysis (CAMRA), which supports semiautomatic image mensuration using an active contour model-based algorithm. The CAMRA software was used to analyze data from 12 patients in a multicenter acquisition and analysis trial to compare semiautomatic contour detection with manual planimetry of the left ventricular endocardium from short-axis, breath-held, cine gradient-echo images. There was excellent agreement between the manual and semiautomatic measurements of global left ventricular function, with no significant (P = 0.32) difference in the determination of ejection fraction (-0.9 +/- 3.1% [mean difference +/- 1 standard deviation]). There was no significant interobserver difference in the semiautomatically measured ejection fraction. Additionally, a single observer completed the analysis on data from 30 patients and found no significant (P = 0.05) difference in the determination of ejection fraction (-1.3 +/- 3.5% [mean difference +/- 1 standard deviation]). The CAMRA software demonstrates the capability for the reproducible evaluation of global left ventricular function in cardiac patients, with adequate interobserver reproducibility for use in multicenter trials.
18F-Fluorodeoxyglucose positron emission tomography (18FDG PET) is the recognized gold standard for the assessment of myocardial viability, but is not widely available in the UK. FDG imaging on a gamma camera with high-energy collimators (FDG SPECT) has been shown to have an accuracy comparable with that of FDG PET for the assessment of myocardial viability. This study was performed to assess the feasibility of introducing FDG SPECT for myocardial viability at a hospital a considerable distance away from a cyclotron (200 miles). Twenty-three patients, who were being actively considered for revascularization but had demonstrated fixed defects on stress/rest with nitrate tetrofosmin imaging, underwent FDG SPECT. Image quality was acceptable in all patients. Nine out of the 23 patients with defects classed as fixed on tetrofosmin imaging demonstrated viability on FDG SPECT. Six of these nine patients, reported to have some viable myocardium on FDG SPECT, underwent revascularization as a result. This study has demonstrated that FDG SPECT is feasible at a site some distance from a cyclotron.
1. We examined the effects of frequencies and patterns of electrical stimulation of the peripheral cut ends of the vagus nerves on the release of mucus glycoconjugates into feline trachea in vivo. Mucus glycoconjugates, radiolabelled biosynthetically with [35S]sulphate and [3H]glucose, were washed from a tracheal segment in situ, and dialysed before being counted and assayed chemically by the periodic acid-Schiff (PAS) method. 2. Vagal stimulation with regular pulses (10 V, 2 ms duration) at 1, 2.25, 4.5, 9 and 18 Hz produced frequency-dependent increases in the output of mucus glycoconjugates. 3. The muscarinic agonist pilocarpine (0.1-10 microM), given intrasegmentally, produced dose-dependent increases in the output of mucus glycoconjugates. 4. Pretreatment with atropine, phentolamine and propranolol reduced but did not abolish the effects of vagal stimulation. Vagus nerve stimulation still caused frequency-dependent increases in the output of mucus glycoconjugates. 5. High frequency stimulations at 22.5 and 47.5 Hz given intermittently (1 s burst then 4 s rest), whether in the absence or presence of cholinergic and adrenergic blockade, produced similar secretory responses as the same number of pulses delivered in regular trains at 4.5 and 9.5 Hz. This suggests that neither cholinergic nor non-adrenergic, non-cholinergic (NANC) nerve mechanisms in this system are potentiated by high frequency, intermittent burst stimulation. 6. In the absence of atropine, regular vagal stimulation had a greater effect on heart rate than did the same number of pulses delivered in bursts. 7. High molecular weight glycoconjugates from secretions were taken from the void volume of a Sepharose CL-2B gel filtration column and separated further by density-gradient centrifugation. Macromolecular components were observed at two densities, a typical mucin at 1.52 g ml-1, and a high density atypical component at 1.63 g ml-1. In secretions collected during vagal stimulation, either in the absence or presence of cholinergic and adrenergic blockade, the ratio of low density to high density macromolecules was higher than in unstimulated secretions. This can be explained if both cholinergic and NANC nervous vagal mechanisms stimulate the output of typical (density = 1.52 g ml-1) mucins into the feline trachea.