Registration Artifacts Research Articles

Trends of Low Birth Weight (LBW): a Comparision of Two Birth Cohorts Separeted by a 15 Year Interval in Ribeirão Preto, Brazil. † 461

The incidence and some determinants of LBW were studied in two population-based cohorts of singleton live birth from families residing in Ribeirao Preto, state of Sao Paulo, southeast Brazil, the first including infants born from June 1978 to May 1979 (6750 birth-population survey) and the second including infants born from May to August 1994 (2990 birth-sample survey). The incidence of LBW was 7.2% in 1978/79 and 10.6% in 1994. After adjustment for confounding factors by multiple logistic regression, the following determinants remained significant: female gender, maternal age of 35 years and more, pre-term delivery, less than 4 prenatal visits, maternal smoking, lower maternal schooling and manual jobs/unemployment in 1978/79 and pre-term delivery, maternal smoking and cesarean section (CS) in 1994. The adjusted odds ratios comparing these two series decreased for female gender, maternal age less than 20 or 35 years and more, pre-term birth, medicare insurance, lower maternal schooling and manual workers and was increased for non-cohabiting women, primiparity, multiparity, less than four prenatal visits, CS and maternal smoking. The population attributable risk percent fell for the majority of risk factors and increased for CS delivery, pre-term birth, multiparity (≥5), primiparity and non-cohabiting women. The increase in LBW rate, comparing 1978/79 with 1994, was higher for the families with more qualified occupations, occurred only for infants delivered from 36 to 40 weeks of gestational age and weighing 1500-2499 g., who are those at risk for elective CS. The CS rate rose from 30.3% in 1978/79 to 51.1% in 1994. CS delivery had the highest increment in population attributable risk percent between 1978/79 and 1994. In 1978/79, CS increased with birth weight and gestational age (33,2% for pre-term, 32,9% for term and 33,9% for post-term birth); in 1994, the highest CS rate occurred among term birth (54,6%). The mean and median birth weight decreased for the entire newborn population and this phenomena cannot be attributable to registration artifacts. Therefore, the increase in LBW rate was probably due to iatrogenic practices associated with elective CS.

5541512 Method for the prevention of registration artifacts due to motion in magnetic resonance images

A magnetic resonance system employs a sequence of radio frequency pulses and magnetic field gradients to generate a flow-compensated image of a selected portion of a sample. Flow-compensation is performed with an oscillating readout gradient waveform which is comprised of two components. The first component is a constant amplitude gradient waveform whose amplitude is determined by the desired field-of-view and the bandwidth of the imaging system. The second component is an oscillating waveform whose amplitude, frequency and phase are chosen to obtain the desired degree of flow-compensation. The frequency of the oscillating waveform is typically chosen to match the sampling frequency of the imaging system. In effect, each acquired data point is preceded by the application of a bi-polar magnetic field gradient pulse which causes a phase shift in the acquired signal which is proportional to nuclear spin velocity. The amplitude is typically chosen to cause an incremental phase shift which when repeatedly added to the acquired MR response signal at the sampling rate causes a frequency modulation. This frequency modulation, in turn, induces a spatial displacement of signal intensity in the readout dimension which corresponds to the displacement of spin magnetization during the interval between the phase-encoding and frequency-encoding.

100 years and running: the medical imaging revolution

1995 marks the centenary of Roentgen's discovery of the X-ray. Many of the techniques in use today (eg, computed tomography, [CT]) are only a couple of decades old. Few radiologists can now keep abreast of the entire specialty, so there is increasing technique-based or system-based specialisation. Among the technique-based specialties, CT provides single-breathhold volume imaging with spiral data acquisition; the result is three dimensional and wonderfully clear. The thorax and liver can be visualised rapidly without registration artifacts, and pulmonary emboli identified directly (Radiology 1993; 188: 618). Development of very small catheters and specialised gnidewires, as described by Rees, has allowed interventional radiology techniques to probe further into the vascular system. Schenck et al showed that interventional techniques with open-MRI systems are now possible. Nuclear medicine techniques such as whitecell scintigraphy are replacing barium methods for assessment of inflammatory bowel disease. More specific isotope-receptor labelling is providing increasingly targeted information--eg, in inflammation, as shown by Jamar. Large clinical trials of positron-emission tomography (PET) are proving the ability of this technique to identify small f oc i of tumour and to differentiate recurrent malignancy from fibrosis. Crossfertilisation between PET and single-photon emission tomography (SPET) methods may make these techniques more widely available• Technical advances likewise predominate among the system-based specialties. For gastrointestinal imaging, cross-sectional techniques encroach on barium studies and endoscopy. Magnetic resonance cholangiopancreatography has improved substantially, as Laubenberger showed, and may replace purely diagnostic endoscopic retrograde cholangio-pancreatography procedures. Ultrasound can detect the increased arterial perfusion caused by colorectal hepatic metastases (Radiology 1995; 195:113). MRI and interventional techniques dominate developments in neuroradiology. Interventional procedures carry fewer complications than conventional neurosurgery for aneurysms in the posterior circulation, and some lesions previously deemed inoperable are now amenable to neuroradiological intervention (J Neurol Neurosurg Psychiatry, in press). Tumour imaging has benefited from many of the technical advances; modern CT, as shown by Vinnicombe, has provided better data about normal lymph nodes, and MRI gives new insights in breast imaging, detection of tumour recurrence, and implant complications now being established indications•

In Vivo Three-Dimensional Evaluation of the Tracheobronchial Tree

Traditionally computed axial tomography has had limitations in evaluating diseases that affect the tracheobronchial tree because of respiratory-induced artifacts, with the likelihood of missing lesions as a result of misregistration. Spiral computed tomography (CT) differs from conventional CT in that the entire thorax can be rapidly imaged in the axial plane after a single breath-hold. Five patients underwent non-contrast-enhanced volumetric CT, with emphasis on three-dimensional reconstruction, and endoscopic evaluation with pathologic confirmation. In all cases, there was complete corroboration between volumetric CT and endoscopic evaluation. The use of selective thresholds allowed the air within the tracheobronchial tree to be used as a negative contrast agent. Thus with the integration of selective windowing, detailed three-dimensional tracheobronchial anatomy may be elucidated. The absence of respiratory registration artifact due to the single breath-hold technique raises the confidence that three-dimensional and multiplanar images generated from such studies are accurate representations of the pathologic conditions at hand. By the integration of volumetric CT techniques and rapid three-dimensional display of tracheobronchial structures, volumetric CT bronchography becomes practical.

The Seasonal Variation of Suicide in Zimbabwe

In Zimbabwe, suicides were found to peak in January (possibly a registration artifact), with a subsidiary peak in November (consistent with the spring peak found in the northern hemisphere).

Measurement of the blood‐brain barrier permeability and leakage space using dynamic MR imaging. 1. Fundamental concepts

Leakage of Gd-DTPA through a defective blood-brain barrier is measured quantitatively using dynamic MRI scanning, in which repeated scans are made after a bolus injection. Image registration artifacts are minimized; a dose of 0.1 mM/kg and an IR sequence enable enhancement to be measured quantitatively. The triexponential enhancement curve is fitted to a theoretical model based on compartmental analysis. The transfer constant, or permeability surface area product per unit volume of tissue (k), and leakage space per unit volume of tissue (v1) are measured. Estimates for a quickly enhancing multiple sclerosis lesion are k = 0.050 min-1, v1 = 21%; for a slow one k = 0.013 min-1, v1 = 49%. This implies permeability in the range 4-17 x 10(-6) cm s-1, in broad agreement with other physiological methods. The method is noninvasive and can be used to make serial measurements in patients and in experimental animal models. The time course of pathological aspects of diseases with blood-brain barrier breakdown, such as multiple sclerosis, tumors, and infections (e.g., HIV) can be studied, along with their response to therapy. The measurements are of physiological variables and are therefore independent of imaging equipment and field.

THE SEASONAL VARIATION OF SUICIDE IN ZIMBABWE

In Zimbabwe, suicides were found to peak in January (possibly a registration artifact), with a subsidiary peak in November (consistent with the spring peak found in the northern hemisphere).

Computer correction of projective distortions in dental radiographs.

Distortions in radiographic images caused by changes in shape and position of the film relative to the x-ray beam can result in registration artifacts which interfere with interpretation of subtracted images. A warping transformation is described which maps known points of reference in one image into homologous points in another. The corrected image pair can then be superimposed and subtracted with significantly-reduced differences in registration to facilitate the detection of localized changes of diagnostic interest.

AN EPIDEMIOLOGICAL STUDY OF HYPOSPADIAS IN SWEDEN

ABSTRACTThe prevalence at birth of hypospadias started to increase in the beginning of the 1970s, as judged from the registration in the Swedish Register of Congenital Malformations. Further studies supported the notion that the increase was real and not due to registration artifacts. A study of the geographical distribution showed an uneven distribution in the country. Three case‐control studies with different design were performed in order to find an aeti‐ological factor which could explain the observations. None was found. No support could be obtained for a role of gestagens in the aetiology of hypospadias. A hypothesis is presented based on an observation of a possibly increased infertility—possibly male—in the couples who had a boy with hypospadias. The possible implications of this finding for aetiological studies are discussed in the light of current literature. Based on a possible male subfertility, a hypothesis is presented which could explain the noticed increase in prevalence of hypospadias in the early seventies.The hypospadiac infants were analysed from various points of view. There were signs of a generally disturbed fetal development. Thus a shorter than normal gestational age with a component of growth failure was found. There was a statistically significant association, not only with other genital malformations such as retentio testis, but also with congenital heart disease, cleft lip/palate, anal atresia, and neural tube defects. The analysis indicates that this association was not random, but possibly indicates common teratogenic pathways.