Biomedical subjects

D C Crawford

Publications and source records attributed to D C Crawford.

At least 37 records · Page 2Linked to original sources

PubMed1992

Visual impact of adaptive speckle reduction on US B-mode images.

Adaptive speckle reduction, which is designed to improve image contrast, dramatically alters the familiar appearance of the ultrasonographic B-mode scan. The acceptability to radiologists of this alternative method of display was assessed. Four experienced radiologists selected B-mode scans from 83 liver and 71 breast examinations and graded the change in diagnostically important features after adaptive speckle reduction. There was no loss of important anatomic detail in the smoothed images and a net reduction in image artifacts. Removal of speckle noise improved definition of lesion margins in 38.3% of cases and enhanced visibility of metastases in 35.4% of liver studies and 7.7% of breast lesions. In 42.1% of cases, the textural information in the image was judged to be enhanced. Image information in general was said to be better seen in 49.5% of cases. The preliminary radiologic experience with speckle-reduced B-mode echograms is favorable and does not indicate generation of any substantial image artifacts.

Breast Neoplasms↗

PubMed1991

Grain boundary character distributions in Ni-16Cr-9Fe using selected area channeling patterns: methodology and results.

Selected area channeling patterns imaged on an SEM are digitized and displayed on the screen of a Macintosh computer, on which the user selects channeling bands that are measured to determine orientation. Grain boundary misorientations are found using the orientation information for pairs of grains adjacent at grain boundaries, and the boundaries are classified as low angle boundaries (LABs), coincident site lattice boundaries (CSLBs), or general boundaries (GHABs) based on the misorientation information. The technique was implemented to analyze the grain boundary character distributions (GBCDs) in Ni-16Cr-9Fe. The GBCDs of solution annealed material were similar to those expected in an aggregate of randomly oriented polycrystals. However, sequential thermomechanical treatments (5% tensile strain + 945 degrees C:75 min + 2% tensile strain + 890 degrees C:15 h + 3% tensile strain + 890 degrees C:20 h or 9% compressive strain + 890 degrees C:20 h + 9% compressive strain + 890 degrees C:20 h + 3% compressive strain + 890 degrees C:15 h) applied after the solution anneal lowered the proportions of GHABs in the GBCDs from 76-79% to 47-64%. The CSL-enhanced GBCDs of both the tensile-deformed samples and the compression-deformed sample appear to have evolved mainly through impingement of twin and twin-related boundaries during recrystallization; the CSL-enhanced GBCD of a compression-deformed sample appears to have been influenced by grain rotation processes to a greater degree than were the tensile-deformed samples The CSL boundaries in the CSL-enhanced GBCDs were, in general, closer to the exact CSL misorientations than were those in the near-random GBCDs of the solution annealed material. An analysis of the distribution of misorientation axes did not indicate any correlation between grain misorientation texture and GBCD evolution.

Alloys↗

PubMed1991

What might echography learn from image science?

We review the current state of knowledge of the processes by which the information content of ultrasonic pulse-echo images is transferred to an observer, to the point of contributing to diagnostic judgments. As systematic knowledge in this specific field is rather sparse, we present relevant information and techniques derived from other areas of image science, both medical and otherwise. Quantitative measures both of the information content of ultrasonic and other images and of their characteristic noise content are first considered. An account is then given of the relevant aspects of human visual psychophysics, with particular reference to perception of contrast and detail, image texture, movement and colour, again with emphasis on documenting quantitative aspects of such behaviour. Against this background, we consider the efficiency, in current practice, of image information transfer to a human observer, how and to what extent this could be improved by changes in practice and, in particular, in what situations substantial innovations in machine processing of image data would be expected to improve human performance. It is suggested that several problems in the field may provide a worthwhile and challenging scope for future research.

Humans↗

PubMed1990

Structural cardiac abnormalities in the fetus: reliability of prenatal diagnosis and outcome.

The outcomes of 129 pregnancies in which the fetus was found to have a structural cardiac abnormality are reviewed. Over a 30-month period from January 1985 to June 1987, 1924 patients were referred to the British Heart Foundation Research Centre for Perinatal Cardiology at Guy's Hospital for fetal cardiac scanning. A total of 129 structural cardiac abnormalities was diagnosed; 53% of these patients were referred because of an abnormal 'four-chamber view' on ultrasound at the referring hospital; 47 of the pregnancies (69% of the 68 patients referred before 28 weeks) were terminated, and in the remaining 82 pregnancies outcome was poor with only 20 infants (16%) surviving longer than 11 months. The prenatal diagnosis was fully or partly correct in 96% of the 111 cases where it was possible to verify the diagnosis by post-mortem or postnatal diagnosis. In the 82 pregnancies not terminated, 13 of the 22 cases given a moderate or good prognosis survived more than 11 months (59% survival), but only seven of the 60 (12% survival) given a fatal, poor or uncertain prognosis. The benefits of a multidisciplinary approach are discussed.

Chromosome Aberrations↗

PubMed1989

The accuracy of fetal echocardiography in the diagnosis of congenital heart disease.

The accuracy of the echocardiographic diagnosis of fetal heart disease in an experienced centre was evaluated by analysing the results achieved during 1987 at the Perinatal Cardiology Unit, Guy's Hospital. In this one year, 978 high-risk patients were referred for fetal echocardiography. Of these, 74 cases were found to have cardiac malformation, 69 of which were predicted from the prenatal study. Of the 69, the autopsy specimen was available for correlative purposes in 41 cases. A postnatal echocardiogram was performed by us in a further 15 cases. The result of autopsy or of a postnatal echocardiogram was obtained from another hospital in 7 cases. Postmortem was refused in 5 cases, while one further case remains alive but has not had a postnatal echocardiogram. Close correlation was achieved between the predicted echocardiographic diagnosis and the anatomical results. Some minor errors in the complete interpretation of a defect were found, particularly in those fetuses in whom image quality was poor, due to early (less than 20 weeks) or late (greater than 34 weeks) gestation or to maternal obesity. Difficulty in echocardiographic interpretation was also experienced in unusual defects. There was one false positive prediction of coarctation of the aorta. One major (total anomalous pulmonary venous drainage) and 5 minor abnormalities (two atrial and three ventricular septal defects) detected after birth were overlooked on the fetal study. Although the echocardiogram in prenatal life is not as accurate as it can be postnatally, with suitable experience a high degree of precision can now be achieved.

Autopsy↗

PubMed1989

Fetal diaphragmatic hernia: the value of fetal echocardiography in the prediction of postnatal outcome.

Nineteen pregnancies complicated by fetal congenital diaphragmatic hernia (CDH) referred for fetal echocardiography have been reviewed. Congenital heart disease was diagnosed prenatally in three fetuses; in one of these the pregnancy was terminated, the two other infants died in the neonatal period. The presence of the fetal stomach within the thorax or a hernia/heart area ratio greater than 1.7 was associated with a large diaphragmatic defect. Polyhydramnios was not associated with a poor postnatal outcome. Evidence of cardiac ventricular disproportion before 24 weeks gestation in isolated CDH was associated with 100% mortality. Development of ventricular disproportion during the third trimester was associated with a survival rate of 75%. In three fetuses, all of whom survived, no ventricular disproportion was detected during the third trimester examination.

Echocardiography↗

PubMed1988

Obstetric importance, diagnosis, and management of fetal tachycardias.

During 1980-7, 23 pregnancies of 22-38 weeks' duration were investigated for fetal tachycardia. Twelve were cases of supraventricular tachycardia, eight of atrial flutter, and three cases in which the rhythm varied between supraventricular tachycardia and atrial flutter. In 11 cases the fetus had developed non-immune fetal hydrops before referral; 12 cases were non-hydropic at referral but one of this group of fetuses became hydropic during treatment. No relation was found between the rate or type of arrhythmia and the presence or absence of intrauterine heart failure. One non-hydropic infant was delivered electively prematurely. Maternal antiarrhythmic treatment was instituted in the remaining 22 cases. Conversion of the arrhythmia was achieved with digoxin alone in five cases and with a combination of digoxin and verapamil in nine. Control of the arrhythmia was achieved in seven of the 10 non-hydropic fetuses, and all were delivered at term with no deaths. Of the 12 hydropic fetuses, control was achieved in seven. Only three of the hydropic fetuses were delivered close to term. There were two deaths, both in the hydropic group. Of the whole group, five neonates suffered severe complications of prematurity. In this series the main benefit of treatment appeared to be in prolonging gestation of those hydropic fetuses in which conversion was achieved.

Delivery, Obstetric↗

PubMed1988

Prenatal detection of congenital heart disease: factors affecting obstetric management and survival.

Our recent experience in the diagnosis and management of fetal congenital heart disease is presented. During an 18-month period from January 1985 to June 1986, 1757 fetal echocardiograms were performed on a total of 989 antenatal patients. Cardiac anomalies were accurately predicted in 74 cases, 34 of which were associated with extracardiac or chromosomal anomalies. Twenty-three pregnancies were electively terminated. Currently the survival rate for ongoing pregnancies is 17%. A false negative diagnosis was made in 16 cases, the majority involving minor anomalies with a good prognosis and a survival rate of 81%. Prenatal detection of congenital heart disease places the fetus at high risk for chromosomal and extracardiac anomalies. Congenital heart disease detectable during pregnancy is usually severe and associated with a poor long-term prognosis. Termination of the pregnancy may be a reasonable option if a severe anomaly is detected early in pregnancy.

Echocardiography↗

PubMed1988

Atrioventricular septal defect in prenatal life.

In a series of more than 3500 pregnancies referred for fetal echocardiography, 29 cases of atrioventricular septal defect were detected in the fetus. There was a chromosomal anomaly in 14 of these cases, left atrial isomerism in 12, and right atrial isomerism in two. Complete heart block was found in 11 of the cases with left atrial isomerism. Many associated cardiac abnormalities were found, particularly in the fetuses with atrial isomerism; the most common were double outlet right ventricle or aortic arch anomalies. The prognosis was poor in all patients with atrioventricular septal defect detected prenatally. Fifteen pregnancies went to term but there are only four survivors. Two of those have trisomy 21, a further patient has inoperable defects, and only one remains well and is awaiting corrective surgery for a partial atrioventricular septal defect.

Abnormalities, Multiple↗

PubMed1988

Coarctation of the aorta in prenatal life: an echocardiographic, anatomical, and functional study.

In a prospective echocardiographic study of over 2000 pregnancies, 24 fetuses were found to have dilatation of the right ventricle and pulmonary artery when these structures were compared with those of the left heart. In 18 of these cases the diagnosis of coarctation or interruption of the aorta was correctly inferred from these findings. On direct echocardiographic examination of the aortic arch, arch hypoplasia or interruption of the aortic arch was recognisable prenatally in 10 of these 18 cases, most readily between 20-30 weeks' gestation. In 11 of 12 cases of aortic arch anomaly studied by Doppler echocardiography, a reduction in blood flow in the ascending aorta was demonstrated. The intracardiac appearances were suggestive of coarctation but the Doppler findings were within normal limits in two further cases which later proved to be normal. A diaphragmatic hernia was found in four fetuses and the intracardiac echocardiography and Doppler findings were the same as those found in fetuses with aortic coarctation. Five cases of coarctation were overlooked on the prenatal echocardiogram but these were found at follow up of the infants. Thus coarctation of the aorta can be diagnosed prenatally, although the condition may be missed or incorrectly predicted by the criteria examined in the present study. Reduced aortic blood flow is a demonstrable feature of aortic arch abnormalities but it is found in other conditions that are not associated with coarctation.

Aorta↗

PubMed1988

Measurements of the dimensions of the aortic and pulmonary pathways in the human fetus: a correlative echocardiographic and morphometric study.

Thirty normal hearts from fetuses aborted at 10-33 weeks' gestation were measured directly and the results were compared with echocardiographic measurements in 20 normal live fetuses of 23-27 weeks' gestation. The diameters of the aorta, aortic isthmus, pulmonary arteries, and arterial duct were measured at standard levels and expressed as a ratio of the diameter of the ascending aorta. The ratios for the isthmus, the duct, and the right pulmonary artery were: 0.63 (0.11), 0.51 (0.13), 0.56 (0.10) respectively for the direct measurement and 0.73 (0.07), 0.7 (0.08), 0.62 (0.06) respectively at echocardiography. These results show that in mid-gestation the isthmus of the human fetus is not as small as that reported in animal models. This indicates that the distribution of the fetal circulation may not be the same either.

Aorta↗

PubMed1987

Inactivation of human immunodeficiency virus by Betadine.

Human immunodeficiency virus (HIV), the etiological agent of the acquired immunodeficiency syndrome (AIDS), was treated with either Betadine (povidone-iodine) Solution or Betadine Surgical Scrub. HIV inactivation was analyzed using the viral reverse transcriptase assay or by observing the cytopathic effect produced in HIV-infected, H-9, T-cell cultures. The minimum effective Betadine dose was 0.25% for complete inactivation of HIV that was treated for various time intervals (immediate vortex to ten minutes). The titer of HIV stocks used in these experiments (10(5) TCID50 per mL) was greater than amounts generally detected in clinical specimens. Our results provide a rationale for the use of povidone-iodine as a topical antiseptic against HIV in the clinic or laboratory.

Cytopathogenic Effect, Viral↗

PubMed1987

Effects of alfentanil on the pressor and catecholamine responses to tracheal intubation.

The effects of alfentanil (given during induction of anaesthesia) on the haemodynamic and catecholamine responses to tracheal intubation were studied in 44 adult patients who received alfentanil 10 micrograms kg-1 or 40 micrograms kg-1, or saline placebo. Alfentanil 10 micrograms kg-1 and 40 micrograms kg-1 prevented any increase in heart rate and arterial pressure after tracheal intubation. Alfentanil 40 micrograms kg-1 produced profound hypotension and bradycardia. The use of alfentanil in both doses was associated with a decrease in plasma adrenaline concentrations after tracheal intubation.

Aged↗

PubMed1987

Doppler assessment of umbilical artery blood flow for the prediction of outcome in fetal cardiac abnormality.

In a series of 244 pregnancies referred for fetal echocardiography, the umbilical artery waveform was also studied by pulsed Doppler ultrasound. In 152 normal pregnancies diastolic flow in the umbilical artery was always detectable after 20 weeks gestation. In 4 of 58 normal patients examined before 20 weeks, diastolic flow was absent in some part of the recording. In 34 fetuses with congenital heart disease detected at between 18 and 37 weeks gestation, 10 were found consistently to have associated absent diastolic flow. Five of these fetuses died in utero between 5 and 21 days after the recording; three were aborted and the remaining two died in the neonatal period at 4 and 7 days after the examination. Fetal congenital heart disease with normal umbilical blood flow also had a poor prognosis in general, but the adverse outcome was much less immediate than in fetuses with absent diastolic flow. No correlation was found between the type of congenital heart disease and the characteristics of the umbilical artery waveform. Absent diastolic flow in the umbilical artery indicates a poor short-term prognosis for fetuses with congenital heart disease, particularly after 20 weeks, when fetal death is predictable.

Diastole↗

PubMed1987

Doppler echocardiographic evaluation of the normal human fetal heart.

Pulsed wave Doppler estimates of blood flow velocity were made across the mitral, tricuspid, aortic, and pulmonary valves in a series of 120 normal fetuses (gestational age 16-36 weeks). In 36 of these the data were obtained in all four sites. The maximum and mean velocities were calculated for each valve and these values were plotted against gestational age. There was little change in these values throughout pregnancy. The orifice dimensions of the valves were measured by cross sectional echocardiography. At all ages the tricuspid orifice was larger than the mitral and the pulmonary orifice was larger than the aortic. The blood flow values for each valve were derived from the product of the mean velocity and the valve orifice dimensions. The output of the right ventricle was usually, but not always, greater than that of the left ventricle. Combined ventricular output increased from approximately 50 ml/min at 18 weeks to 1200 ml/min at term. Despite limitations in the accuracy of the technique these results form a useful basis for the analysis of blood flow in the normal fetus and for the interpretation of abnormal Doppler findings in prenatal life.

Aortic Valve↗

PubMed1987

Free radical production in amniotic fluid and blood plasma by medical ultrasound.

Evidence is reported that continuous wave and long pulse ultrasonic systems can induce relatively large amounts of free radicals in biological fluids in vitro under conditions similar to those currently in use for therapeutic applications. The operating conditions and approximate threshold intensities under which these instruments can produce free radicals are described.

Amniotic Fluid↗

PubMed1986

Familial recurrence of congenital heart disease in a prospective series of mothers referred for fetal echocardiography.

Fetal echocardiography can ascertain, at an early stage in pregnancy, recurrences of congenital heart disease (CHD) in mothers with a family history of CHD. In 1,021 mothers referred for this reason, 20 recurrences were found; 17 occurred when there had been 1 previously affected child, and 3 when there had been 2 previously affected children. No recurrences were found in the 41 cases in which a parent had CHD. The overall recurrence rate was 1 in 52 with a previously affected child and 1 in 10 with 2 previously affected children. However, certain forms of CHD recurred much more frequently than others. Aortic valve atresia was associated with a recurrence rate of 1 in 28, coarctation of the aorta at a rate of 1 in 15, complex CHD at a rate of 1 in 11 and truncus arteriosus at 1 in 13. These findings are inconsistent with previous family studies; this may be due to more complete ascertainment, particularly of major lesions, possibly overlooked by postnatal family studies because of fetal loss. Alternatively, the availability of prenatal diagnosis may be producing an increase in family size after major CHD. The results support current doubts on the polygenic theory of inheritance for all forms of CHD.

Aortic Coarctation↗

PubMed1986

Prenatal screening for congenital heart disease.

Routine ultrasound examination of the fetus is already established in most obstetric units in Britain. A simple method was devised to evaluate one section of the fetal heart systematically. Examination of this section, the four chamber view, may readily be incorporated into routine obstetric screening. Severe cardiac abnormalities detectable in this view occur in two per 1000 pregnancies. For six years the department of paediatric cardiology at Guy's Hospital, London, served as a referral centre for fetal echocardiography. As teaching became more widespread an increasing proportion of cases of cardiac anomaly were referred because the obstetrician suspected abnormality on examination of the four chamber view. Currently 80% of detected abnormalities are referred for this reason. Further extension and organisation of teaching might result in most severe cardiac malformations being detected in early prenatal life.

Female↗