Planimetric Technique Research Articles

Measurement of placental volume with real‐time ultrasound in mid‐pregnancy

A new method to measure placental volume in mid-pregnancy using real-time ultrasound is described. The method is an adaptation of the B-mode parallel planimetric technique. The mean error of in vitro measurements on 45 balloons (mean volume 186 mL range: 88-485 mL) was -2.24 mL, standard deviation 6.76 mL. The error standard deviation of in vivo placental volume measurements was 16.4 mL (volume range: 173-396.5 mL). Placental measurements were made on 175 women between 14.3 weeks and 21.4 weeks, menstrual age (MA) and a smooth centile curve derived. Median volume increased linearly from 144 to 329 mL. The size of the ultrasound probe limits the technique to use before 20 weeks, MA.

Comparison in women versus men of composition of atherosclerotic plaques in native coronary arteries and in saphenous veins used as aortocoronary conduits

Objectives. This study quantifies and compares the components of atherosclerotic plaques in native coronary arteries and in saphenous vein grafts used for aortocoronary bypass surgery in women versus those in men.Background. Plaque composition has been described in various manifestations of fatal coronary artery disease and after the bypass operation, but no reports have investigated this composition according to gender.Methods. A total of 979 5-mm segments of native coronary arteries and 842 5-mm segments of saphenous vein grafts were examined by computerized planimetric technique in 11 women and 11 men who were matched for survival time after the bypass operation.Results. Comparison of the plaque components revealed that atherosclerotic plaques in women, compared with those in men, contained significantly more cellular fibrous tissue, both in native coronary arteries (mean 38% vs. 4%, p < 0.001) and in saphenous vein grafts (mean 70% vs. 36%, p < 0.05). In contrast, the proportion of dense fibrous tissue was significantly less in the atherosclerotic plaques of women than in those of men, both in native coronary arteries (mean 50% vs. 85%, p < 0.001) and in saphenous vein grafts (mean 25% vs. 57%, p < 0.05).Conclusions. Cellular fibrous tissue is often found at an early stage of plaque development, whereas dense fibrous tissue is a major component in later stages. Thus, the plaque composition of the native coronary arteries and saphenous venous conduits differed in men and women, with the plaques of the women appearing younger than those of the men.

Comparison of composition of atherosclerotic plaques in saphenous veins used as aortocoronary bypass conduits with plaques in native coronary arteries in the same men

This study describes quantitatively the components of atherosclerotic plaques In saphenous vein grafts used for aortocoronary bypass and compares the findings with the plaques in the native coronary arteries in the same men. A total of 607 five-mm segments of saphenous veins and 797 five-mm segments of native coronary arteries were examined by computerized planimetric technique in 19 men, aged 39 to 82 years (mean 61), who had survived bypass operation for >1 year. Comparison of the mean percentages of the plaque components in saphenous vein grafts in place for 14 to 26 months with those of the native coronary arteries revealed significant differences: cellular fibrous tissue, 86 vs 7%; dense fibrous tissue, 13 vs 82%; p < 0.05. As survival time after the bypass operation increased, composition of the plaques in the saphenous veins changed so that by approximately 80 months the amounts of cellular and dense fibrous tissue in both saphenous vein grafts and native coronary arteries were similar: 10 vs 16%, and 75 vs 71%; p = not significant. Thus, by about 7 years after a coronary bypass operation the composition of plaques in saphenous vein grafts is similar to that in the native coronary arteries of the same patients.

A rapid technique for recording and measuring the leaf area of conifer needle samples.

An optical planimetric technique for measuring projected leaf area of conifer needle samples was developed that combines a rapid field recording method with an inexpensive hand-held optical scanner. The field recording method utilizes strips of diazo paper (blueprint paper), 10 x 28 cm, to make positive images of the needle samples. An analysis program calculates leaf area from the output files produced by the hand-held scanner. The results from this system were compared with results from a Li-Cor 3100 leaf area meter and from a digital camera-based image analysis system using both standard samples of known area and needle samples from three conifer species. All three systems produced similar results in terms of means and variances. The digital camera system typically had the lowest variances between successive measurements of the same sample. Most differences among the systems were not statistically significant. The system presented in this paper is inexpensive, easy to use, and provides a rapid and permanent method for recording and measuring the leaf area of conifer samples.

An imaging routine for assessing the efficacy of instruments used for scaling and root planing.

Deposits of dental plaque or calculus are typically quantified using planimetric techniques. However, error is introduced into a quantitative analysis of plaque deposits using these methods, since they require a significant amount of human intervention. The purpose of this study is to describe and validate a computerized imaging routine which has the potential to objectively identify material on dental roots and measure the area covered by these deposits. Dentiform teeth with simulated plaque were videorecorded. A computer routine was developed based on a flood-fill algorithm which analyzed images of the dentiform teeth and determined the amount of simulated plaque on their root surfaces. Results showed that the dentiform teeth and their simulated plaque patterns are duplicated by the imaging routine in a rapid and reliable fashion. The system shows a high degree of accuracy with an average error factor of only 0.58%. As well, the system enables precise reproducibility with an average error factor of only 0.71%.

Intra- and inter-observer variation of optic nerve head measurements in glaucoma suspects using disc-data.

The aim of this study was to determine the intra- and inter-observer variation in the use of a system designed for exact measurements from standard optic nerve head photographs. The commercially available system consisted of a colour CCD Videocamera, a dedicated frame grabber and customized software run on a IBM AT compatible computer. Masked measurements were made 3 times by 2 observers, from stereophotographs of the optic nerve head of 56 eyes from 30 glaucoma suspects. The cup was defined on the basis of contour, not pallor and the disc area was defined as the area inside Elschnig's ring. Intra-observer variances were 0.001 +/- 0.001 mm2 for cup area (mean +/- SD), 0.002 +/- 0.002 mm2 for disc area and 0.002 +/- 0.003 mm2 for rim area. These values for intra-observer variance were comparable with the results obtained using manual planimetric techniques. Intra-observer variance for disc area was significantly larger for the less trained of the two experienced observers. Inter-observer variances were 0.004 +/- 0.009 mm2 for cup area, 0.008 +/- 0.013 mm2 for disc area and 0.009 +/- 0.014 mm2 for rim area. These inter-observer variances were significantly larger than those previously reported for manual planimetry. The absolute differences between the two observers ranged from -0.35 to +0.20 mm2 (-0.08 +/- 0.11 mm2) for cup area, from -0.38 to +0.15 mm2 (-0.08 +/- 0.11 mm2) for disc area and from -0.29 to +0.34 mm2 (-0.06 +/- 0.12 mm2) for rim area.(ABSTRACT TRUNCATED AT 250 WORDS)

Patterns of Recovery from Homonymous Hemianopia Subsequent to Infarction in the Distribution of the Posterior Cerebral Artery

The authors performed a prospective study of recovery from complete homonymous hemianopia in 69 patients who had suffered ischemic occipital lobe infarction. Findings documented with kinetic perimetry were evaluated with a planimetric technique. Improvement was found in 32 patients (47.8%), and the temporal course of improvement as well as the location of improvement in the visual fields in these patients were investigated.Recovery of function was more common in the lower quadrants (46.9%) and in the temporal crescent (75%). Initial improvement was observed most often in the lower quadrants (37.5%) and was associated with preservation of the cuneus in CT studies. This structure was involved in brain infarction in 71.7% of patients in whom recovery of the upper quadrants was observed. The occipito-temporal gyri were affected much less frequently (28.6%) in the latter group of patients. The results suggest that vascular mechanisms were operant in the recovery process.

Computerized tomography brain scan tumor volume determinations

In an effort to define more precisely and objectively computerized tomography (CT) brain scan evidence of glioma patient response to treatment, planimetric measurements of serial CT images of enhancing tumor areas were made using a digitizing tablet interfaced to a microcomputer for computing three-dimensional tumor volumes. The ability of a single investigator to measure a "significant change" in tumor volume was determined from that investigator's coefficient of variation (COV) for triplicate volume measurements (a total of 1701) on 155 scans of 27 patients with malignant gliomas. Planimetric volume data were compared with geometric computation of volumes based upon the product of the maximum diameter of enhancing tumor and the perpendicular diameter for each image made simultaneously with each planimetric measurement. The planimetric method COV was less than that for geometric computation, and the former method was employed for analysis of response to therapy in these same patients. Overall, for a tumor volume change to be significant (COV plus 2 standard errors of the means), the percentage change was determined to be 20%. However, the smaller the tumor volume being measured, the greater was the percentage change required in order to be significant. Thus, minimal measurable changes (%) were separately defined for large (greater than 14 cc), medium (8 to 14 cc), and small (less than 8 cc) tumor volumes. Tumor volumes computed from baseline (prior to investigational therapy) and from subsequent serial CT scans were compared, with response defined as a significant change. Responses to therapy based on significant volume changes were compared in each instance to the conventional visual viewbox comparison ("Gestalt") of serial scans. In 28% of scan comparisons, planimetric technique sensitivity permitted determination of significant enlargement or reduction in tumor size, while Gestalt comparison suggested no change. The use of quantitative tumor volume analysis of planimetric determinations of changes in tumor size during investigational therapy appears to permit recognition of either progression or regression of tumor size earlier than by Gestalt comparison in one-fourth of instances.

Alterations in developing rat uterine cell populations after neonatal exposure to estrogens and antiestrogens.

Exposure of rats to either estrogens or antiestrogens during early postnatal development reduces subsequent uterine growth as measured by uterine weight. However, individual uterine cell types respond differently to these agents and uterine weight alone cannot discern subtle or even large alterations in individual cell populations. Using a computerized planimetric technique, we estimated the prepubertal growth of the uterine luminal epithelium, endometrial stroma, glands, and circular and longitudinal muscle after exposure of neonatal rats (postnatal days 1-5) to the estrogens 17 beta-estradiol (E2), diethylstilbestrol (DES), or ethynylestradiol (EE), and the antiestrogens tamoxifen or clomiphene citrate. On postnatal day 26, the cross-sectional areas of the luminal epithelium, endometrial stroma, and circular muscle were reduced after estrogen exposure, compared to untreated controls, while longitudinal muscle cross-sectional area was not affected. Since cell densities (cell number/unit area) were increased, these estrogen-induced area reductions demonstrate a decrease in cell size. Total cell numbers, estimated as the product of cell type areas and their respective cell densities, were also reduced by neonatal estrogen exposure. The synthetic estrogens DES and EE were more potent than E2 with respect to reduction of uterine growth. Neonatal antiestrogen exposure caused large area reductions only in the uterine glands and luminal epithelium. Little change in cell density occurred in any cell population exposed to antiestrogen. These data demonstrate that the decreased uterine growth resulting from estrogen exposure during early postnatal development is a consequence of combined hypotrophy and hypoplasia in all cell types except longitudinal muscle while antiestrogen-induced morphological alterations were limited to hypoplasia having epithelial cell specificity.

RIB REGENERATION AREA AS AN INDICATOR OF FUSION AREA IN ADOLESCENT IDIOPATHIC SCOLIOSIS

This retrospective study of 24 patients with adolescent idiopathic scoliosis who underwent L-rod instrumentation, posterior thoracoplasty, and rib-bone grafting analyzed the correlation between the quality of rib regeneration and the host response to the rib-bone grafts. A planimetric technique was used to quantitate the coronal plane area of the resected ribs and of an L1-L2 concave fusion area immediately after surgery and at the end of the first postsurgical year. Using computerized regression analysis, these and other variables such as age, Cobb angle, and grafting technique were studied. Rib regeneration correlated with spinal fusion but not with age or Cobb angle. A better host response with strip vs. morseled graft was suggested, but not statistically proven. The data strongly support the belief that systemic biologic factors are a major variable affecting the quality of the fusion procedure.

Albumin adsorption and retention on C18-alkyl-derivatized polyurethane vascular grafts.

The short-term albumin affinity and thrombo-resistance of a polyether polyurethane vascular graft have been improved. The method is based on the C18 alkylation of the polymer. Thrombus formation by a planimetric technique and albumin retention on wire-reinforced polyurethane tubes, both C18 alkylated and untreated, were measured in short-term (4-h) exposure at femoral arterial sites in the dog. 125I-Albumin was preabsorbed on tubes and then exposed to blood for successive 2-h periods. Albumin uptake on alkylated tubes prior to blood exposure and retention following 2 h of blood exposure were significantly greater than on controls. Following a fast desorption phase in blood, the remaining albumin was more slowly desorbed from alkylated than from control tubes. Reincubation with albumin and blood reexposure produced a similar tendency, suggesting blood conditioning does not reduce the albumin affinity-enhancing property of C18 alkylation in the short term. Blood-preconditioning experiments suggested endogenous albumin has a high affinity for the C18-alkylated surface. Scanning electron microscopic examination showed thrombus and platelet densities were higher on control than on alkylated surfaces. These results suggest in vivo albumin affinity is increased for C18-alkylated polyurethane, which may be linked to decreased thrombus formation on these surfaces.

Rib regeneration area as an indicator of fusion area in adolescent idiopathic scoliosis.

This retrospective study of 24 patients with adolescent idiopathic scoliosis who underwent L-rod instrumentation, posterior thoracoplasty, and rib-bone grafting analyzed the correlation between the quality of rib regeneration and the host response to the rib-bone grafts. A planimetric technique was used to quantitate the coronal plane area of the resected ribs and of an L1-L2 concave fusion area immediately after surgery and at the end of the first postsurgical year. Using computerized regression analysis, these and other variables such as age, Cobb angle, and grafting technique were studied. Rib regeneration correlated with spinal fusion but not with age or Cobb angle. A better host response with strip vs. morseled graft was suggested, but not statistically proven. The data strongly support the belief that systemic biologic factors are a major variable affecting the quality of the fusion procedure.

Nucleo-cytoplasmic ratio in ageing skeletal muscle.

In order to investigate possible changes in the nucleo-cytoplasmic ratio of the muscle fibres during ageing, samples of quadriceps femoris from 15 normal individuals whose age ranged from 17 to 82 years were studied (autopsy material). The mean lesser diameter and the number and size of the muscle fibre nuclei were calculated using a planimetric technique. It was found that nucleo-cytoplasmic ratio increased significantly after the age of 60 years. This was due to a decrease in the mean fibre size whilst the number and the size of myonuclei remained unchanged. The resemblance of this finding to denervation atrophy changes is noted.

Anti-inflammatory drugs in experimental atherosclerosis Part 6. Combination therapy with steroid and non-steroid agents

The pathological changes which accompany enhanced cholesterol deposition in atherosclerosis include inflammatory reponses mediated by the prostaglandin cyclooxygenase and lipoxygenase-leukotriene metabolite of the arachidonic acid cascade. Cortisone suppresses arachidonic acid release, whereas non-steroid anti-inflammatory drugs inhibit principally the cyclooxygenase enzyme. Groups of New Zealand white rabbits were fed a 1% cholesterol diet for 12 weeks. Diets of selected groups were further supplemented daily with the non-steroid anti-inflammatory drugs phenylbutazone (100 mg), oxyphenylbutazone (240 mg), flufenamic acid (100 mg), either singly or in combination with cortisone acetate (10 mg or 5 mg), or 9-α-fluorohydrocortisone (30 μg or 200 μg). Serum lipid levels were measured at 0, 4, 8 and 12 weeks, and atherosclerotic plaque intensity in thoracic aorta was measured at 12 weeks using a planimetric technique: serum cholesterol levels in control groups increased from 38 ± 5 to 1190 ± 139 mg/100 ml. Neither the rate of increase nor the final lipid values attained were significantly changed by the non-steroid drugs. The non-steroid drugs reduced plaque coverage by about one third (phenylbutazone 34 ± 10%, flufenamic acid 36 ± 11 %) compared to controls. In combination therapy, addition of cortisone acetate resulted in further plaque suppression. Cortisone 10 mg + phenylbutazone gave 100% suppression; cortisone 5 mg + phenylbutazone gave 82 ± 18%, and cortisone 5 mg + flufenamic acid gave 84 ± 3%. However, when a suboptimal dose of steroid was administered there was no additive effect between the steroid and the non-steroid drugs (F-cort. 30 μg alone gave 56 ± 7% protection and + phenylbutazone gave 44 ± 16%). In general, combination of a steroid with a non-steroid did not provide greater protection than that afforded by the optimum dose of steroid alone. Thus both classes of drugs can suppress plaques when administered singly, but the non-steroids do not enhance the level of protection provided by a steroid alone. The result confirm that anti-inflammatory drugs can mitigate the effects of hypercholesterolemia in rabbits without affecting the degree of hypercholesterolemia per se and indicate that both classes of drugs may act in a similar fashion, probably by suppressing eicosanoid-mediated inflammatory responses of vascular tissues to the hypercholesterolemic insult.

Limitations of postmortem assessment of human coronary artery size and luminal narrowing: Differential effects of tissue fixation and processing on vessels with different degrees of atherosclerosis

Numerous studies have utilized histologic sections of coronary arteries as the standard for testing the validity of the angiographic determination of coronary artery dimensions. However, little attention has been given to artifactual dimensional changes that occur during fixation and histologic processing of tissues (dehydration, clearing, embedding, sectioning and staining). Using planimetric techniques, the dimensional changes that occurred with fixation and processing were quantitated in 61 coronary artery segments with minimal or moderate to severe atherosclerosis obtained from 12 patients studied at autopsy. In vessels with minimal atherosclerotic narrowing, fixation and processing resulted in a decrease in total vessel cross-sectional area and luminal cross-sectional area (p less than or equal to 0.05), whereas absolute wall area (total vessel cross-sectional area minus luminal cross-sectional area) did not change (p = NS). These disproportionate changes resulted in an alteration in the relation between lumen and wall areas so that luminal cross-sectional area decreased from 47.6 +/- 8.5% of the total vessel cross-sectional area observed before fixation to 36.2 +/- 7% after processing (p less than or equal to 0.05). In vessels with moderate to severe atherosclerosis, both the total cross-sectional area and wall area decreased after fixation and processing (p less than or equal to 0.05), but luminal area did not change (p = NS). As a result, the percent luminal cross-sectional area in these vessels increased from 21.1 +/- 10.1% before fixation to 28.7 +/- 9.7% after processing (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

A planimetric technique for measuring deformation of the carotid sinus region.

This paper describes a planimetric technique for measuring the volume of the carotid sinus region from still photographs taken during pressure and volume forcings. The method consists of first digitizing the curves defining the boundary of the carotid sinus and then calculating its volume by assuming that the carotid sinus region is made up of a finite number of circular "pancake" slices. Plots of the calculated volume (Vc) vs. applied pressure forcings (P) were compared with plots of injected volume (Vi) vs. recorded pressure to assess the sensitivity of the method used to calculate volume changes from still photographs. The plots of Vc vs. P were remarkably similar to the plots of Vi vs. recorded pressure, and a plot of Vc vs. Vi was linear, suggesting that this method provides a good estimate of volume changes. Application of this method can yield useful data on mechanisms of the baroreceptor process.

1197 FORAMEN OVALE SIZE AS A MARKER OF TRANS-ATRIAL BLOOD FLOW DURING CARDIAC DEVELOPMENT

We studied the ratio of the foramen ovale area to the total atrial septum area in 18 normal hearts and 33 hearts with congenital cardiac anomalies. The congenital defects included tricuspid atresia, 5; pulmonary atresia, 4; secundum atrial septal defect, 9; coarctation of the aorta, 8; and aortic stenosis, 7. In the 10% formalin fixed specimens, the margins of the atrial septum were defined and marked with India ink. The hearts were coded, positioned with the septum flat and photographed with a grid. The areas of the atrial septum and foramen ovale were measured using standard planimetric techniques. A ratio of the foramen ovale to atrial septal area was calculated. The area of the atrial septum did not differ significantly among the six groups. The foramen ovale/atrial septal ratio in normal hearts was 0.19 ± .01 (SEM). The ratios in tricuspid atresia (0.41 ± .02), pulmonary atresia (0.38 ± .02), and secundum atrial septal defect (.37 ± .01) were significantly larger than normal (p<.05) while the ratio in coarctation of the aorta (0.15 ± .01) and aortic stenosis (0.11 ± .01) were significantly smaller (p<.05). These data indicate that foramen ovale size is directly related to the magnitude of trans-atrial blood flow during embryonic and fetal development, and provide support for the role of intracardiac blood flow in cardiac morphogenesis.

An evaluation of DNA fluorochromes, staining techniques, and analysis for flow cytometry. I. Unperturbed cell populations.

Several preparative techniques (detergent treatment, ethanol fixation, and hypotonic cell lysis), DNA fluorochromes, and methods of numerical analysis (planimetric or curve-fitting) were compared for the estimation of cell-cycle kinetic parameters (G1, S, G2 + M) by flow cytometry. In addition, coefficients of variation (CV), relative fluorescence, and G1/chicken erythrocyte (CRBC) ratios were measured and the effects of the proportion of cycling cells and cellular RNA content were examined. DNA fluorochromes were ranked by relative fluorescence: 4,6-diamidino-2-phenylindole > ethidium bromide/mithramycin > Hoechst 33342 > mithramycin > ethidium bromide > acridine orange approximately equal to propidium iodide. The first four (DNA-specific stains) gave lower CVs than the remainder (DNA intercalators). Detergent treatment also increased relative fluorescence and slightly lowered CVs. Comparable results were obtained for the kinetic parameters independently of stain or staining procedure; intercalating dyes with cells of a high RNA content not treated with RNAse and acridine orange being the exceptions. Of the two methods of numerical analysis, the planimetric technique was more consistant. Although highly consistant G1/CRBC ratios were obtained for any one stain, independently of staining procedures, variations between stains were noted. It is suggested that the detergent treatment in combination with DNA-specific stains provide optimal results.

Leg temperature profiles with a simplified thermographic technique in the diagnosis of acute venous thromboses

A simplified thermographic technique has been developed to provide continuous leg temperature profiles by manual scanning with a noncontactile infrared radiation transducer connected to a linear potentiometer for determination of the transducer position. The clinical value of the technique in the diagnosis of acute venous thromboses has been estimated in seventy patients and thirty controls, using plethysmography and phlebography as methods of reference. The thermographic diagnosis was based on side differences in temperature levels within different segments of the limbs, as calculated from the temperature profiles by means of planimetric technique. Standardized temperature profiles from the medial side of the limbs were found to demonstrate a side difference above the reference level in fifty-seven of fifty-nine patients with acute venous thromboses, which means a diagnostic sensitivity corresponding to that of conventional thermography. Skin temperature profiles were superior to plethysmography, particularly in the diagnosis of thromboses located distally. Falsely positive results were obtained, as expected, in some cases of varicose veins or acute arthritis and skin infections. The presented type of thermography has obvious qualifications as a screening method in the early diagnosis of acute venous thromboses, being far less expensive but never the less more suited for objective numerical analyses and evaluation than conventional thermography with scanning cameras.

Reliability of symptom assessment, les pressure (LESP) and barium meal to predict rate of esophageal emptying in achalasia

RELIABILITY OF SYMPTOM ASSESSMENT, LES PRESSURE (LESP) AND BARIUM MEAL TO PREDICT RATE OF ESOPHAGEAL EMPTYING IN ACHALASIA. R. Gross, L. F. Johnson, R. J. Kaminski, GI and Nuclear Medicine Service, Walter Reed A.M.C., Wash., D.C. Esophageal emptying of food in patients with achalasia has been assessed indirectly by subjective symptoms, LESP and esophageal retention of a barium meal. A new technique measuring esophageal emptying of a radiolabelled meal sharply discriminates between symptomatic achalasia and normal controls (Clin Research 26:17A, Jan 78). In the present study, we examined the reliability of symptoms, LESP and barium retention to predict the rate of esophageal emptying of the isotope meal. The study population consisted of 19 consecutive symptomatic achalasia patients referred For evaluation, 12 untreated and 7 previously treated. All patients quantitated the severity of dysphagia by estimating the excess length of time required to finish a meal as compared with other household members. Resting LESP and residual LESP after swallowing was measured by perfused catheters. Esophageal retention of barium was determined by an upright chest X-ray taken 5 min after ingestion of 8 oz of barium. The residual barium, height of column and volume (estimated by planimetric technique) was determined. We found that residual LESP had a significant correlation with esophageal emptying of the radiolabelled meal (r = .55, P <.05), however, in the individual patient, residual LESP was not always a reliable indicator of esophageal emptying. Resting LESP poorly correlated with esophageal emptying of the isotope meal. The residual barium, height of column and volume both had a significant correlation with esophageal emptying of the radiolabelled meal (r = .74 P c.001, r = .81 P <.OOl, respectively). Symptoms poorly correlated with esophageal emptying of the radiolabelled meal. In conclusion, the severit) of delayed esophageal emptying in achalasia cannot be inferred from a patient's subjective symptoms. Residual LESP better correlated to esophageal emptying of food than resting LESP. The residual volume, 5 min after ingestion of 8 oz of barium, closely approximates esophageal retention of the radiolabelled meal and may be a convenient substitute for directly measuring esophageal emptying in achalasia.