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PubMed2006

Optimal standards for fetal biometry: to each measurement its fitting model.

OBJECTIVE: To determine the best mathematical model to construct charts of fetal abdominal circumference (AC) and femur length (FL). METHODS: Ultrasound measurements were made on 1,336 normal fetuses in one center. Four mathematical models were compared (a linear-quadratic model, a linear-cubic model, the Rossavik model and a new two-phase model, which has been found to best fit fetal head data). RESULTS: The best fitting of AC and FL data was obtained with the linear-quadratic model without separate computing for gender. Centile charts have been computed. CONCLUSION: Fetal growth of AC and FL is much simpler than that of the head. Therefore, a unique mathematical model should not be used to fit all measurements.

Abdomen↗
PubMed1989

Improved biometry of the anterior eye segment.

In this paper, a method is presented to evaluate the true values of several optical parameters of the anterior eye segment. These are: the thicknesses of the cornea and lens, the depth of the anterior chamber and the anterior and posterior curvatures of the cornea and lens. First, a photo is taken of each patient's eye with a Topcon SL-45 Scheimpflug camera. There are two effects distorting the photo. As the film plane and the object plane are perpendicular to each other, the imaging scale is not constant over the photo, a phenomenon which is called the camera distortion. As the light passes through different refractive media on its way from the inner structures of the eye to the camera, the rays of light are refracted, which is called the refractive distortion of the eye. Following these distortions, the proportions on the photo do not correspond to those in the human eye. The intention of this paper is to calculate the true optical parameters of the anterior eye segment. The seeming optical parameters are taken from the photo and the path of light from a point in the film plane through the camera and the refracting surfaces into the eye is constructed by ray tracing. A set of representative points calculated according to ray tracing provides a basis to evaluate the true optical parameters. This work is done using a Basic program, that accepts the seeming parameters from the photo as input values and provides the true values as output. The adjectives seeming and true added to the optical parameters indicate a value correlating with a distorted photo and a value that was corrected by the theory. The two terms were chosen by mnemonic reasons, although another pair of adjectives such as distorted and corrected might have been of higher precision. For an average adult human eye the optical parameters from the photo were compared with the calculated ones. A phantom eye with well-known optical parameters was constructed and photos were taken from this eye to verify the calculations.

Anterior Eye Segment↗
PubMed1995

The use of Scheimpflug photography in the documentation of clinical states and in the biometry of the anterior eye segment.

From the start of our collaboration with the Institut für Experimentelle Ophthalmologie in the early 1980s, the scientist Otto Hockwin has always taken the greatest interest in the clinical use of Scheimpflug photography. I became a student of Hockwin's through my work on the effects of Verapramil. The straightforwardness and purposeful approach with which Hockwin persued any subject, once he had taken it up, served me as example and thereby helped me repeatedly to regain courage and patience in my own work. The Scheimpflug apparatus developed by Hockwin's team has proven its superiority over the conventional slit lamp photography through its excellent depth of focus. Further to the clinical applications of the Scheimpflug photography worked out by us and summed up once again in this paper, it also presents a widening of the scope hence available within ophthalmological teaching methods, which we can hardly do without these days. The students benefit from the far superior spatial image conveyed by the optical section through the anterior eye segment, compared to that obtained by the conventional slit lamp photography alone. The precision of the reproducible image of the anterior segment furthermore represents a vital supplementary aid in the solution of pre- and postoperative, as well as specialist diagnostic problems.

Adult↗
PubMed1995

Anterior chamber angle biometry: a comparison of Scheimpflug photography and ultrasound biomicroscopy.

Scheimpflug photography and ultrasound biomicroscopy allow measurement of anterior chamber angle width. To analyze the value of both diagnostic tools, measurements of the same subjects were correlated. Anterior chamber angle width in both eyes of 20 volunteers without any ophthalmological case history was measured in eight meridians. Scheimpflug photographs were recorded on Kodak T-max 400 black-and-white film using a Topcon SL-45 camera. Measurement of chamber angle was done with the aid of a self-programmed PC software. Ultrasound biomicroscopic measurements were obtained using a Humphrey UBM 840 system with a 50-MHz transducer. The chamber angle was measured as described by Pavlin et al. The data of both methods were correlated and analysed for statistically significant differences using a paired t test (level of significance p < or = 0.05). Both methods showed similar changes in chamber angle width and were able to document a variation in angle width with regard to location. The correlation averaged at 0.64. In 4 meridians significant differences were found between the two methods. Scheimpflug photography, however, is unable to visualize directly the angle itself. Both methods are limited by the fact that the angle is defined by curvilinear structures, i.e. posterior corneal surface and anterior iris surface. Scheimpflug photography is able to document changes in angle configuration. Ultrasound biomicroscopy, however, is a more precise method, because it allows direct documentation of all structures involved in chamber angle configuration.

Anterior Chamber↗
PubMed1993

Prediction of high birthweight from maternal characteristics, symphysis fundal height and ultrasound biometry.

The possibility to predict a large infant during pregnancy was assessed using data from a prospective cohort study of 537 singleton pregnancies with term deliveries. Maternal characteristics, symphysis fundal height and ultrasound measurements were used in multivariate analyses for the prediction of an infant with a birthweight of > or = 4,500 or > or = 4,000 g. The positive predictive value was 55% for a birthweight > or = 4,000 g when only maternal characteristics were used, and increased slightly when symphysis fundal height was added. The corresponding value for a single ultrasound measurement at 37 gestational weeks was 52%. Using all available clinical data, positive predictive values of 45 and 80% could be achieved for birthweights of > or = 4,500 and > or = 4,000 g, respectively.

Adult↗
PubMed2005

Biometry of face and brain in fetuses with trisomy 21.

The aim of this study was to specify the early setting of the particular craniofacial morphology in Down syndrome during the fetal period from data based on postmortem examinations. The study included 1277 fetuses at 15-38 gestational weeks (GW): 922 control fetuses and 355 fetuses with trisomy 21, selected from fetopathology units in Paris. Body weight (BW) and nine dimensions of the face, skull, and brain were recorded: the outer and inner canthal distances (OCD, ICD), biparietal diameter (BPD), head circumference (HC), brain weight (BrW), occipitofrontal diameters of left and right hemispheres (lOFD, rOFD), weight of the infratentorial part of the brain (IBW), and maximal transversal diameter of the cerebellum (CTD). Four ratios were computed: BPD/HC, OCD/BPD, BrW/BW, IBW/BrW. Differences between trisomic fetuses and control fetuses were tested by age interval. Results showed that BW, rOFD, and lOFD were lower in trisomic fetuses as early as 15 GW. Cerebellar hypoplasia included lower IBW and CTD in trisomic fetuses. The IBW/BrW ratio was higher in trisomic fetuses, showing that growth restriction affected the infratentorial part of the brain less than the supratentorial part. Early brachycephaly was found in trisomic fetuses, with higher values of BPD and BPD/HC from 15 GW. ICD and OCD were not significantly different in the two groups, but OCD/DBP ratio was lower in trisomic fetuses. These results confirm the early phenotypical expression of trisomy 21 on craniofacial morphology, associated with a marked restriction of brain growth, especially in the supratentorial part.

Biometry↗
PubMed1992

Prediction of birthweight by fetal ultrasound biometry.

A total of 104 women with singleton pregnancies who were delivered between 37 and 42 weeks gestation had ultrasound scans during the fortnight before delivery. The biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL) were measured in all cases. Estimation of fetal weight (EFW) was done by four different methods: using AC alone, AC/BPD, AC/FL and AC/BPD/FL. Results were compared with values of actual birthweights at delivery. There was no significant difference between the mean birthweights of the 47 boy and 57 girl fetuses studied. The EFW(Shepard) method showed the least bias overall: mean percentage error 1.7%, standard deviation (SD) 10.6%. The other three methods significantly underestimated birthweights on average: EFW(Deter), mean error 2.2%, SD 9.3%, p < 0.02; EFW(Campbell), mean error 5.4%, SD 9.5%, p < 0.001; EFW(Hadlock), mean error 5.6%, SD 9.3%, p < 0.001. The percentage error in each group was significantly negatively correlated (p < 0.001) with the scan-delivery interval. Two new equations were generated which gave more accurate predictions for the cases under study using AC, BPD and FL as a combination and also in addition to scan-delivery interval (SDI) in days.

Abdomen↗
PubMed1999

[Analysis of productivity, quality and cost of first grade laboratories: blood biometry].

OBJECTIVE: Assessment of productivity, quality and production costs and determination of the efficiency of top grade clinical laboratories in Mexico. METHODS: Ten laboratories were selected from among the total number (52) existing in Mexico City, and the Donabedian model of structure, process and results were applied. Blood count was selected as a tracer. RESULTS: The principal problems found were: inadequate distribution of trained human resources, poor glass material, inadequate analytic process and low productivity. These factors are reflected in the unit costs, which exceed reference laboratory costs by 200%. Only 50% of the laboratories analyzed generate reliable results. Only 20% of the laboratories studied operate efficiently. CONCLUSIONS: To solve the problems identified requires integral strategies at different levels. A specific recomendation for the improvement of quality and productivity is an assessment of the cost/benefit of creating a central laboratory and using the remaining sites exclusively for the collection of samples.

Biometry↗
PubMed2003

Larval biometry of Simulium rubrithorax (Diptera: Simuliidae) and size comparison between populations in the states of Minas Gerais and Roraima, Brazil.

The number of larval instars of Simulium (Hemicnetha) rubrithorax Lutz (Diptera: Nematocera) was determined using the lateral length of the head capsule. In this study 1,035 larvae, of different sizes, were measured (639 from the state of Roraima and 396 from the state of Minas Gerais). A frequency distribution analysis was carried out on the measurements of the lateral length of the head capsule to determine the number of larval instars. The limits of each instar were defined by the lower frequency of the measurements falling in a range of values, by the presence of the "egg burster" that characterizes the first larval instar, and by the developmental stage of the gill histoblast. The determination of the instar number was tested using a Student's t-test (p < 0.05), the Dyar rule and the Crosby growth rule. The results indicate the existence of 7 larval instars for this species, although this result was not in accordance to the Crosby rule. Last-instar larvae from two widely separated geographical populations (Roraima and Minas Gerais), collected in habitats with different water temperature were compared and no differences (p > 0.05) were observed between them.

Animals↗
PubMed1983

Prediction of fetal growth deviation by ultrasonic biometry. II. Clinical application.

A previously developed mathematical formula for prediction of fetal growth deviation at birth by means of ultrasonic fetometry was applied to 505 unselected singleton pregnancies. The gestational age was assessed by measuring the fetal biparietal diameter (BPD) in the 17th week of pregnancy. In the 33rd and 38th week of pregnancy, BPD and the abdominal diameters (AD) were measured. In detecting fetuses small-for-gestational age (SGA) in the 33rd week, the ultrasonic diagnostic test had a nosological sensitivity of 77% and a nosological specificity of 78%. The nosological sensitivity and specificity for detecting fetuses large-for-gestational age (LGA) were 75% and 82%, respectively. The result was not improved significantly when the formula was applied to the total group in the 38th week. At the 33rd week examination risk groups with high prevalence of SGA and LGA fetuses were identified. When these groups were submitted to an additional examination in the 38th week, the prevalence of SGA and LGA fetuses in the new risk groups increased to 50%. At the 33rd week examination the predictive value of a negative test for SGA and LGA was 98%. Thus, the procedure described is well suited for general screening of pregnant women with ultrasound, and, combined with other biochemical and biophysical tests, makes possible a close clinical surveillance of the fetus at risk.

Biometry↗
PubMed1987

Longitudinal ultrasonic biometry of various parameters in fetuses with abnormal growth rate.

The growth rate of various organs and parameters was evaluated by ultrasound examination in one group of small-for-gestational age (SGA) and another group of large-for-gestational age (LGA) fetuses. Three different patterns of growth were selected in the SGA group and two different types of growth acceleration were observed in the LGA group. On the basis of these results, it has been concluded that the type of intra-uterine growth retardation or acceleration is dependent more on the time at which the insult which brings it on, appears, and less on the specific etiological factor.

Biometry↗
PubMed2006

Scheimpflug biometry of the anterior segment after implantation of foldable iris-fixated lenses.

PURPOSE: To evaluate intraocular dimensions of the anterior segment of myopic phakic eyes after implantation of foldable iris-fixated lenses. METHODS: Seventeen myopic eyes that received a foldable iris-fixated phakic intraocular lens (PIOL) were assessed. Distances between the cornea and the IOL-optic edge and between the IOL optic and the crystalline lens were evaluated using Scheimpflug photography 3 months postoperatively. RESULTS: The average postoperative distance between the central corneal endothelium and the anterior surface of the IOL was 2.01 +/- 0.26 mm. The distance between the corneal endothelium and the peripheral edge of the IOL averaged 1.32 +/- 0.18 mm at the 12 o'clock position and 1.34 +/- 0.21 mm at the 6 o'clock position. The distance between the crystalline lens and the posterior surface of the IOL averaged 0.73 +/- 0.09 mm. CONCLUSIONS: The high quality of the three-dimensional Scheimpflug images allowed measurements of intraocular distances in PIOL implanted eyes. Distances between the foldable iris-fixated IOL and crucial surrounding tissues could be determined 3 months postoperatively.

Adult↗
PubMed1998

[Ultrasonographic fetal biometry charts in Niger].

Ultrasound scanning to confirm fetal growth is an essential part of prenatal screening and depends on comparison with biometric reference charts. Charts for ultrasound scanning in Niger were established at the Poudriere Hospital in Niamey between 1994 and 1997. A total of 5,197 measurements were made on 736 fetuses to obtain 50 values for biparietal diameter, transverse abdominal diameter, and femoral length between the 14th and 41st weeks from the last menses. Each parameter was presented with dispersion and compared with similar findings from other series to establish reference charts for the population of Niger. Transverse abdominal fetal diameter in Niger appeared to be below normal. These charts establish a local reference at a given time but will require revision in the future.

Biometry↗
PubMed1999

[Study of the posterior cruciate ligament using a 3D computer model: ligament biometry during flexion, application to surgical replacement of the ligament].

We have developed a 3D computed model of the knee joint, constructed from MRI acquisitions in a living individual. We have used this model to perform an anatomic and biometric study of the posterior cruciate ligament (PCL) during flexion, and an assessment of the optimal location for an intraarticular graft. The method used a 3D computed model constructed from MRI acquisitions during knee flexion (0 to 75 degrees). The range of motion was limited by a positioning device. We took 13 acquisitions from 0 to 75 degrees of flexion. Each acquisition consisted of 21 sagittal cross sections of 3 mm slice thickness. We used the Delaunay reconstruction to obtain a 3D geometric model. A matching process to fix one part of the articulation during the movement, allows for the kinematic analysis of the tibia relative to the fixed femur. This model allows to follow the displacement of a bone point during knee flexion. Knowing the relative displacement of the bone insertions of the ligament, it may be possible to determine the length of the PCL and its bands, to evaluate the length variation during movement, and to determine the optimal location for the insertion of an intraarticular graft, that would lead to the least stretch during flexion. It was found that the mean length of the PCL was 30.2 mm, with the posterior band being 30% longer than the anterior band. During flexion the posterior band increases its length by 10% at 50 degrees flexion, and by 20% at 75 degrees flexion. The anterior band stretches more, to reach 40% elongation at 75 degrees flexion. The best position for insertion of a graft seems to be in the posterolateral portion of the anatomic tibial insertion, and posterior to the anatomic femoral insertion. This method confirms the data in the literature, states precisely the length of the different bands of the PCL, and specifies the points of insertion for a graft, which lead to the least variation in length during flexion.

Biometry↗