Biomedical subjects

I R Johnson

Publications and source records attributed to I R Johnson.

At least 19 recordsLinked to original sources

PubMed2007

The interobserver reliability of off-line antral follicle counts made from stored three-dimensional ultrasound data: a comparative study of different measurement techniques.

OBJECTIVE: To assess the interobserver reliability of antral follicle counts (AFCs) made from stored three-dimensional (3D) ultrasound data using conventional two-dimensional (2D) images, 3D multiplanar view and 3D-rendered 'inversion mode'. METHODS: 3D transvaginal ultrasound was performed in the early follicular phase (days 2-5) of the menstrual cycle in 41 subjects aged < 40 years, undergoing investigation for subfertility. From the stored 3D ultrasound datasets, the number of antral follicles of 2-10 mm in diameter in each ovary was independently measured, using all three methods by three investigators, each with a different level of experience. The image quality of each dataset was subjectively categorized into one of three groups, based on the proportion of the ovarian contour that could be seen clearly. RESULTS: There was no significant difference in the mean AFC between the observers for any of the three different techniques. The intraclass correlation coefficient (ICC) for the 2D-equivalent mode, the 3D multiplanar mode, and the 3D-rendered inversion mode were indicative of good interobserver reliability for each method. The interobserver reliability for the 3D-rendered inversion mode was better with Grade 1 image quality than with Grade 3 image quality. There were no equivalent differences, however, between the three different grades of image quality with the 2D-equivalent and 3D multiplanar modes. The time taken for AFC measurement using 3D-rendered inversion mode was significantly longer than with the 2D equivalent and 3D multiplanar methods. CONCLUSIONS: 3D image displays and rendering techniques do not appear to offer any advantage over a conventional 2D display in terms of AFC measurement reliability. AFC measurement using the 3D-rendered inversion mode has an adequate interobserver reproducibility but is dependent on image quality.

Adolescent↗

PubMed2004

Endometrial and subendometrial perfusion are impaired in women with unexplained subfertility.

BACKGROUND: We used three-dimensional power Doppler angiography (3D-PDA) to examine the periodic changes in endometrial development and subendometrial vascularity during the normal menstrual cycle in 29 women with unexplained subfertility and 19 controls. METHODS: 3D-PDA was performed on alternate days from day 3 of the cycle until ovulation and then every 4 days until menses. VOCAL (Virtual Organ Computer-aided AnaLysis) and shell-imaging were used to define and to quantify the power Doppler signal within the endometrial and subendometrial regions producing indices of their relative vascularity. RESULTS: Women with unexplained subfertility demonstrated significant changes with time (P<0.001) in the indices of vascularity within the endometrium and subendometrium during the menstrual cycle characterized by a pre-ovulatory peak and post-ovulatory fall. These changes mirrored those observed in the control group but were significantly reduced in the endometrium and subendometrium during the mid-late follicular phase and early luteal phase. There were no differences in endometrial thickness or volume between the groups or in the plasma concentrations of estradiol or progesterone. CONCLUSIONS: Endometrial and subendometrial vascularity are significantly reduced in women with unexplained subfertility during the mid-late follicular phase irrespective of estradiol or progesterone concentrations and endometrial morphometry.

Adult↗

PubMed2004

The interobserver reliability of three-dimensional power Doppler data acquisition within the female pelvis.

OBJECTIVES: To examine the interobserver reliability of three-dimensional (3D) power Doppler data acquisition from the uterus and ovary. METHODS: 3D power Doppler angiography was used to acquire endometrial data from 20 patients and ovarian data from a further 20 different patients at various stages of in vitro fertilization. Two different observers each acquired two datasets from all 40 patients resulting in 80 endometrial and 80 ovarian datasets in total. Virtual Organ Computer-aided AnaLysis was used to define the object of interest and semiquantify the power Doppler signal within it. The reliability of measurements of volume and vascularity was assessed by calculating interclass correlation coefficients (ICCs) and limits of agreement between the two observers. RESULTS: Whilst volumetric data proved more reliably acquirable than power Doppler data, the interobserver reliability of data acquisition was high overall for both the endometrium and ovary with all measurements obtaining a lower ICC of above 0.9. Limits of agreement revealed minimal disagreement between the two observers for measurements of volume and vascularity within both the ovary and endometrium. The 'indices of vascularity' within the endometrium were less than those derived from the ovary and subendometrium, which were comparable. CONCLUSIONS: 3D ultrasound can be reliably used between observers to acquire power Doppler information from the ovary and endometrium thus supporting the current use and further development of this technique in clinical practice.

Data Collection↗

PubMed2004

Functional magnetic resonance imaging (magnetization transfer) and stereological analysis of human placentae in normal pregnancy and in pre-eclampsia and intrauterine growth restriction.

Magnetic resonance imaging provides a non-invasive method for investigating functional changes in the human placenta in vivo. In this study, we combine a magnetic resonance imaging technique called magnetization transfer with established stereological methods in order to analyse and compare placentae from normal (16-36 weeks of gestation) and complicated (pre-eclampsia, intrauterine growth restriction) pregnancies. Magnetization transfer provided an in vivo measure of the ratio of bound protons:total protons and stereological analysis of histological sections was used to estimate a residual:total volume ratio (the ratio of non-vascular volume to total placental volume). Statistical comparisons were drawn using tests for related samples (longitudinal data) or one-way analysis of variance (cross-sectional data). We found no significant differences in magnetization transfer between gestational age groups or between uncomplicated pregnancies and pregnancies complicated by pre-eclampsia or intrauterine growth restriction. In comparable groups of different subjects, stereological analyses also failed to demonstrate significant differences in residual:total volume ratios. We conclude that [a] the ratio of non-vascular volume:total placental volume does not alter between 16 and 36 weeks of normal gestation, and [b] this integrated response is also conserved in pre-eclampsia and intrauterine growth restriction.

Birth Weight↗

PubMed2004

Quantifying the changes in endometrial vascularity throughout the normal menstrual cycle with three-dimensional power Doppler angiography.

BACKGROUND: We used three-dimensional power Doppler angiography (3D-PDA) to examine the periodic changes in endometrial and subendometrial vascularity during the normal menstrual cycle in 27 women without obvious menstrual dysfunction or subfertility. METHODS: 3D-PDA was performed on alternate days from day 3 of the cycle until ovulation and then every 4 days until menses. Virtual organ computer-aided analysis and shell-imaging were used to define and to quantify the power Doppler signal within the endometrial and subendometrial regions producing indices of their relative vascularity. RESULTS: Both the endometrial and subendometrial vascularization index (VI) and vascularization flow index (VFI) increased during the proliferative phase, peaking approximately 3 days prior to ovulation (P < 0.001) before decreasing to a nadir 5 days post-ovulation (P < 0.001). Thereafter, both vascular indices gradually increased during the transition from early to mid-secretory phase. The flow index (FI) showed a similar pattern but with a longer nadir post-ovulation. Smoking was associated with a significantly lower VI and VFI. The FI was significantly lower in women aged > or = 31 years and significantly higher in parous patients. CONCLUSIONS: Endometrial vascularity, as assessed by 3D-PDA, varies significantly during the menstrual cycle and is characterized by a pre-ovulatory peak and post-ovulatory nadir during the peri-implantation window.

Adult↗

PubMed2003

The interobserver reliability and validity of volume calculation from three-dimensional ultrasound datasets in the in vitro setting.

OBJECTIVES: The primary aim of this validation study was to determine the interobserver reliability and validity of measurements of phantom objects of known volume using conventional and rotational techniques of volume calculation according to measurement technique. METHODS: Two observers each acquired a single three-dimensional ultrasound dataset of three water-filled objects of different size and shape. The same two observers measured all six datasets using both the conventional technique and the newer rotational technique (Virtual Organ Computer-aided AnaLysis, VOCAL( trade mark )) of volume calculation. Reliability was assessed by calculating intraclass correlation coefficients (ICC) and validity by examining the percentage difference from the 'true' volume, as determined by a water displacement technique, by the limits of agreement method. RESULTS: All of the techniques were highly reliable (ICC: 0.9962-0.9997) and valid to within 4% of the 'true' volumes. There were no significant differences in reliability according to measurement plane or between observers. Measurements made with the 6 degrees rotation step were significantly more reliable than those made by all other techniques with the exception of the 9 degrees rotation step (P < 0.05) and significantly more valid than those made with the 30 degrees rotation step or conventional technique (P < 0.05). CONCLUSIONS: Volume calculation in the in vitro setting is both reliable and valid but is dependent upon the technique applied, with rotational measurements of volume proving superior to conventional techniques.

Female↗

PubMed2003

The reliability of virtual organ computer-aided analysis (VOCAL) for the semiquantification of ovarian, endometrial and subendometrial perfusion.

OBJECTIVES: Three-dimensional power Doppler angiography (3D-PDA) has been largely used for the subjective assessment of vascular patterns but semiquantification of the power Doppler signal is now possible. We examined the intraobserver and interobserver reliability of the semiquantification of ovarian, endometrial and subendometrial blood flow using 3D-PDA, virtual organ computer-aided analysis (VOCAL) and shell-imaging. METHODS: 3D-PDA was used to acquire 20 ovarian and 20 endometrial volumes from 40 different patients at various stages of in vitro fertilization treatment. VOCAL was then used to delineate the 3D areas of interest and the 'histogram facility' employed to generate three indices of vascularity: the vascular index, the flow index and the vascularization flow index. Intraobserver and interobserver reliability was assessed by two-way, mixed, intraclass correlation coefficients (ICCs) and general linear modeling was used to examine for differences in the mean values between each observer. RESULTS: The intraobserver reliability for both observers was extremely high and there were no differences in reliability between the observers for measurements of both volume and vascularity within the ovary or endometrium and its shells. With the exception of the outside subendometrial shell volumes, there were no significant differences between the two observers in the mean values obtained for either endometrial or ovarian volume and vascularity measurements. The interobserver reliability of measurements was equally high throughout with all measurements obtaining a mean ICC of above 0.985. CONCLUSIONS: 3D-PDA and shell-imaging offer a reliable, practical and non-invasive method for the assessment of ovarian, endometrial and subendometrial blood flow. Future work should concentrate upon confirming the reliability of data acquisition and the validity of the technique before its predictive value can be truly tested in prospective clinical studies.

Endometrium↗

PubMed2003

The interobserver reliability of ovarian volume measurement is improved with three-dimensional ultrasound, but dependent upon technique.

The effect of measurement technique on the interobserver reliability of ovarian volume calculation from three-dimensional (3-D) ultrasound (US) data was investigated. Ovarian volume was calculated in 20 patients by two observers using both the "prolate ellipsoid formula" and a new 3-D rotational technique (VOCAL). There was a significant difference between observers in mean ovarian volume calculated by the prolate ellipsoid formula (31.54 mL vs. 26.54 mL: p < 0.05), which proved to be a significantly less reliable technique than 3-D rotational volume calculation with VOCAL. Image quality was significantly better (p < 0.001) and measurements were significantly more reliable (p < 0.05) in the B-plane than in the C- plane of the multiplanar display. Rotational measurement of ovarian volume from 3-D US data is significantly more reliable between observers than volume estimation from 2-D parameters using the prolate ellipsoid formula, but is dependent upon image quality, which is significantly better in the B-plane than in the C-plane.

Adult↗

PubMed2000

In vivo intravoxel incoherent motion measurements in the human placenta using echo-planar imaging at 0.5 T.

This paper presents the first in vivo measurements of intravoxel incoherent motion in the human placenta, obtained using the pulsed gradient spin echo (PGSE) sequence. The aims of this study were two-fold. The first was to provide an initial estimate of the values of the IVIM parameters in this organ, which are currently unknown. The second aim was then to use these results to optimize the sequence timings for future studies. The moving blood fraction (f), diffusion coefficient (D), and pseudo-diffusion coefficient (D*) were measured. The average value of f was 26 +/- 6 % (mean +/- SD), D was 1.7 +/- 0.5 x 10(-3) mm2/sec, and D* was 57 +/- 41 x 10(-3) mm2/sec. For the optimized values of b, the expected percentage uncertainty in the fitted values of f, D, and D* for the placenta were sigmaf/f = 14.9%, sigmaD/D = 14.3%, sigmaD*/D* = 44.9%, for an image signal-to-noise of 20:1, and a total imaging time of 800 sec.

Analysis of Variance↗

PubMed2000

The effects of vascular endothelial growth factor on endothelial cells: a potential role in preeclampsia.

OBJECTIVES: Preeclampsia is primarily a disorder of the maternal endothelium. An as yet unidentified circulating factor causes widespread alteration in endothelial function, and levels of vascular endothelial growth factor are elevated in preeclampsia. We hypothesized that vascular endothelial growth factor is involved in the alteration of endothelial function and set out to find further evidence for this contention. STUDY DESIGN: Bovine microvascular endothelial cells (B-88) were cultured in vitro. These cultured cells were then stimulated with vascular endothelial growth factor and with plasma from women with preeclampsia in the presence and absence of anti-vascular endothelial growth factor antibody. Prostacyclin, nitric oxide, and lactate dehydrogenase levels were measured. RESULTS: Vascular endothelial growth factor induced a significant concentration-dependent increase in prostacyclin production but not nitric oxide production. Cells stimulated with plasma from women with preeclampsia showed increases in production of both prostacyclin and nitric oxide. Vascular endothelial growth factor concentration in plasma was correlated with prostacyclin production by stimulated cells. The increase in prostacyclin production that usually followed the addition of plasma did not occur when anti-vascular endothelial growth factor antibody was present. CONCLUSIONS: Vascular endothelial growth factor has the ability to alter endothelial cell function in a manner analogous to that of plasma from women with preeclampsia.

Animals↗

PubMed2000

In utero perfusing fraction maps in normal and growth restricted pregnancy measured using IVIM echo-planar MRI.

The aim of this study was to measure and portray blood movement in the placenta in vivo in normal and growth restricted pregnancies, using Intra Voxel Incoherent Motion (IVIM) magnetic resonance imaging. Thirteen patients with apparently normal healthy pregnancies were scanned at 31+/-7 (mean+/-s.d.) weeks gestation and seven patients with intrauterine growth restriction (IUGR) were scanned at 31+/-4 weeks. A region of interest (ROI) was defined encompassing the placenta between the decidual and chorionic plates. The volume of moving blood within each imaging voxel of the ROI was then calculated as a percentage of the total voxel volume (f per cent). This information was colour coded to produce maps of moving blood volume. The placenta was segmented length ways into two zones of approximately equal area, termed inner and outer, the latter being adjacent to the uterine wall. f was fitted for the average in the outer zone (f(out)) and inner zone (f(in)). The parameter (f(out)-f(in)) was then calculated for each subject. This was positive in 12/13 of the normal cases and zero for one case (+10 per cent+10, mean+/-s.d.). For pregnancy affected by IUGR this value was negative in all cases (-4 per cent+/-3). Perfusion fraction mapping identified differences in function within the normal placenta in vivo, and between the placentae of normal and IUGR pregnancies. The technique has potential applications in managing, and investigating the aetiology of, pregnancy compromise.

Blood Volume↗

PubMed2000

Effect of fetal magnetic resonance imaging on fetal heart rate patterns.

OBJECTIVE: Our aim was to record the fetal heart rate before and during magnetic resonance imaging to observe the effects of the magnetic resonance imaging process on fetal heart rate parameters during imaging. STUDY DESIGN: Fetal heart rate recordings were obtained in 10 pregnant volunteers at the time of magnetic resonance imaging. All the pregnant women were at term (37-41 weeks) with singleton fetuses in the cephalic presentation. The scanning was performed on a 0.5-T purpose-built superconductive magnet by use of echo-planar imaging. The fetal heart recordings were obtained with a modified Sonicaid Meridian 800 (Oxford) Doppler ultrasound monitor. Recordings of the fetal heart were made for a period of at least 15 minutes outside the magnet and then for at least 15 minutes inside the magnet. RESULTS: There were no significant changes in any fetal heart rate parameters before and during the magnetic resonance imaging, as determined by the Wilcoxon matched-pairs signed-ranks test (P >.3). CONCLUSION: This is the first report of fetal heart rate recording during magnetic resonance imaging of the fetus. Magnetic resonance imaging does not produce demonstrable effects on fetal heart rate patterns.

Cardiotocography↗

PubMed2000

Infants exposed to MRI in utero have a normal paediatric assessment at 9 months of age.

Any differences in detailed paediatric assessment at 9 months of age in infants exposed to echo planar MRI in utero from 20 weeks gestation to term were investigated by performing a case controlled prospective observational study of 20 infants. They had all had serial echo planar MRI in the antenatal period and were compared with a control group born at the same time who had not. Statistical analysis employed likelihood ratios, odds ratios and 95% confidence intervals. The mothers of the control infants had a significantly higher standard of educational attainment (p = 0.005). A small but significant decrease in length (p = 0.047), and an increase in gross motor function (p = 0.023) of the fetuses exposed to echo planar imaging were demonstrated. No other significant developmental or social differences were seen between the two groups. Infants at 9 months of age did not demonstrate any gross abnormality likely to be related to exposure to echo planar MRI in utero.

Body Height↗

PubMed1999

Relationship between myometrial resistance artery behavior and circulating lipid composition.

OBJECTIVES: The study investigated whether an inducible alteration in endothelium-dependent relaxation in myometrial vessels could be correlated with plasma lipid composition. STUDY DESIGN: Myometrial resistance vessels were obtained from 10 women with normal pregnancy undergoing elective cesarean delivery. Paired vessels were incubated with plasma samples from patients with preeclampsia or from women with normal pregnancy and mounted on a wire myograph. After contraction with vasopressin, the degree of relaxation in response to bradykinin was observed. Plasma samples were assayed for cholesterol, triglycerides, apolipoprotein A1, and apolipoprotein B. RESULTS: A significant reduction in endothelium-dependent relaxation with respect to control values was observed in vessels incubated in plasma samples from patients with preeclampsia (P =.0001). Although no significant difference was noted between the lipid profiles of the 2 subgroups, a significant correlation was found between the vessel relaxation and the plasma content of apolipoprotein A1 (R2 = 0.36, P = .025). CONCLUSION: Plasma samples from women with pregnancies complicated by preeclampsia are capable of altering endothelium-dependent myometrial vessel relaxation. A significant relationship between the apolipoprotein A1 concentration and endothelial behavior supports the suggestion that aberrant lipid metabolism may be involved in the endothelial dysfunction characteristic of preeclampsia.

Adult↗

PubMed1999

The changes in magnetic resonance properties of the fetal lungs: a first result and a potential tool for the non-invasive in utero demonstration of fetal lung maturation.

OBJECTIVE: To measure magnetic resonance parameters T1 and T2 of the fetal lungs and investigate the relationship of these parameters to changes in volume and gestation. DESIGN: Prospective cross-sectional study. SETTING: Large teaching hospital in Nottingham and the Magnetic Resonance Centre at the University of Nottingham. POPULATION: Normal pregnancies from 20 weeks to term. METHODS: T1, T2, and lung volume were measured in the fetus using echo-planar magnetic resonance imaging. MAIN OUTCOME MEASURES: The relationship of T1 and T2 to gestational age and lung volume. RESULTS: Linear regression demonstrated a significant relationship (P < 0.001) between gestational age and lung volume, T1 and T2. There was also a significant relationship between lung volume and T1 and T2 (P < 0-001). CONCLUSIONS: Relaxation time measurements give additional information to lung volume estimation in the assessment of lung physiology in utero. We have demonstrated the progressive changes which take place in the fetal lungs between 20 weeks and term. The physiological changes which can be demonstrated with this non-invasive technique may have an important application in the demonstration of fetal lung maturity in a prospective non-invasive manner.

Cross-Sectional Studies↗

PubMed1999

Assessment of fetal lung growth in utero with echo-planar MR imaging.

PURPOSE: To measure changes in normal fetal lung volume with increasing gestation by using echo-planar magnetic resonance (MR) imaging. MATERIALS AND METHODS: Fifty-six singleton fetuses were examined longitudinally with respect to lung volume by using echo-planar MR imaging between 19 weeks gestation and term. RESULTS: Lung volume increased exponentially with gestation from 8 to 125 mL. Volume was related to gestation by using the equation, volume = 0.8375e0.1249g (R2 = 0.77), where g = gestation. Lung volume had a direct relationship to fetal volume with increasing gestation (R2 = 0.75). There was no significant relationship between amniotic fluid volume and lung volume (R2 = 0.11). CONCLUSION: Variation in lung volumes can be assessed by using echo-planar MR imaging, regardless of variations in amniotic fluid volume. These measurements are less than those obtained from postmortem and neonatal studies but are similar to those obtained by using three-dimensional ultrasonography. Lung volume estimations obtained by using echo-planar imaging may have important clinical and research applications when noninvassive assessment of lung volume is required.

Adult↗

PubMed1999

Mechanisms of endothelium-dependent relaxation in myometrial resistance vessels and their alteration in preeclampsia.

OBJECTIVE: To investigate the importance of prostacyclin and nitric oxide synthesis in endothelium-dependent relaxation in myometrial resistance vessels, and to test the hypothesis that a deficiency in nitric oxide synthesis contributes to the known alterations in endothelial function in preeclampsia. METHODS: Thirty-six women with normal pregnancies and 14 with preeclampsia had the myometrium biopsied at cesarean section. Resistance arteries were dissected and mounted on a wire myograph. After preconstriction with vasopressin, vessels were treated cumulatively with bradykinin. The process was repeated in the presence of indomethacin and then indomethacin and NG-monomethyl-L-arginine (L-NMMA). RESULTS: The vessels from women with normal pregnancies showed endothelium-dependent relaxation to bradykinin which was not significantly altered by the presence of indomethacin. The addition of L-NMMA significantly, but only partially, reduced the relaxation to bradykinin in the presence of indomethacin (p = 0.03). The vessels from women with preeclampsia showed markedly reduced relaxation to bradykinin (p < 0.0001), as compared to vessels from normal pregnant women. Relaxation of vessels from women with preeclampsia was increased by the addition of indomethacin (p = 0.03) but was virtually eradicated by the presence of L-NMMA. CONCLUSIONS: Eicosanoid synthesis plays little part in the relaxation of normal pregnant myometrial vessels to bradykinin. Nitric oxide synthesis mediates part but not all of the endothelium-dependent relaxation. In preeclampsia, relaxation to bradykinin is reduced; inhibition of eicosanoid synthesis allows increased relaxation, and nitric oxide synthesis appears to mediate a greater proportion of the relaxation than in normal pregnant women.

Adult↗

PubMed1998

Non-invasive mapping of placental perfusion.

BACKGROUND: We aim to develop a clinical technique for the non-invasive measurement of placental perfusion, to enable early detection of intrauterine growth restriction (IUGR). Pregnancies with this complication are characterised by low placental perfusion. METHODS: We measured placental perfusion by means of perfusion-sensitive echoplanar imaging (EPI); a rapid method of making magnetic resonance images. Perfusion measurements were done on six healthy volunteers with normal pregnancies and nine with pregnancies complicated by IUGR. Perfusion maps were created to assess the relation between placental perfusion and fetal size at birth. FINDINGS: Pregnancies complicated by IUGR differed significantly from normal pregnancies in patterns of perfusion within the placenta (p<0.0001, ANOVA). Subsequent analysis showed that the proportion of placentas with low perfusion rates was higher in the IUGR group than in the normal group. A significant correlation between areas of reduced placental perfusion and fetal size was demonstrated (p=0.041, Spearman's rank correlation). INTERPRETATION: Non-invasive imaging of placental perfusion by means of EPI has potential as a clinical tool in assessing the dynamics of placental perfusion.

Echo-Planar Imaging↗