Volume Measurement Error Research Articles

Calibrating volume measurements made using the dual-field conductance catheter

The conductance catheter technique allows real- time measurements of ventricular volume based on changes in the electrical conductance of blood within the ventricular cavity. Conductance volume measurements are corrected with a calibration coefficient, α, in order to improve accuracy. However, conductance volume measurements are also affected by parallel conductance, which may confound cali-bration coefficient estimation. This study was un-dertaken to examine the variation in α using a physical model of the left ventricle without parallel conductance. Calibration coefficients were calculated as the conductance-volume quotient (αV(t)) or the stroke conductance-stroke volume quotient (αSV). Both calibration coefficients varied as a non-linear function of the ventricular volume. Conductance volume measurements calibrated with αV(t) estimated ventricular volume to within 2.0 ± 6.9%. By contrast, calibration with αSV substantially over-estimated the ventricular volume in a volume-dependent manner, increasing from 26 ± 20% at 100ml to 106 ± 36% at 500ml. The accuracy of conductance volume measurements is affected by the choice of calibration coefficient. Using a fixed or constant calibration coeffi-cient will result in volume measurement errors. The conductance-stroke volume quotient is associated with particularly significant and volume-dependent measurement errors. For this reason, conductance volume measurements should ideally be calibrated with an alternative measurement of ventricular vol-ume.

Electrocardiographic interference and conductance volume measurements

The conductance catheter technique enables continuous ventricular volume measurements based on the electrical conductance of blood within the ventricular cavity. However, ventricular excitation also produces a measurable electrical signal within the ventricular cavity. This study was undertaken to investigate the relationship between the ventricular electrogram and conductance volume measurements in a physical model of the left ventricle without parallel conductance. The ventricular electrogram was simulated with an ECG signal, ECGinput connected to two ring electrodes within the model ventricle. Conductance volume measurements were made with and without ECGinput. The difference between these measurements, GECG(t), represented the conductance volume due to ECGinput. GECG(t) varied as a function of the first-derivative of ECGinput with respect to time (r2=0.92, P<0.001). GECG(t), This primarily affected volume measurements during ventricular depolarisation; during this phase the volume measurement error varied widely between –12% and +9%. As a re-sult, end-diastole could not be reliably identified on the pressure-volume loop. The accuracy of conduc-tance volume measurements during late diastole and early isovolumic contraction are substantially affected by the ventricular electrogram. This may result in a significant error in end-diastolic volume estimates, which has important implications for the quantitative assessment of ventricular function including, in particular, the assessment of chamber compliance.

Usefulness of Renal Volume Measurements Obtained by a 3-Dimensional Sonographic Transducer With Matrix Electronic Arrays

The purpose of this study was to examine the feasibility of 3-dimensional (3D) sonography using a matrix array transducer to measure renal volume. One hundred consecutive patients with a normal serum creatinine level and kidney appearance on computed tomography (CT) performed within 2 months before sonography were enrolled in this study. Two hundred individual renal volumes were blindly obtained by the ellipsoid formula, the stacked ellipse method, the voxel count method using routine 2-dimensional (2D) sonographic data, 3D sonographic data using a matrix array transducer, and CT data, respectively. The voxel count method was validated as the reference standard by the water displacement method in 10 cadaveric pig kidneys (r = 0.99; P < .001). Renal volumes determined by 2D and 3D sonography were compared with volumes determined by CT. Volumes determined by 2D sonography were significantly lower than those determined by CT (P < .001) but similar to those determined by 3D sonography (P = .78). The percent volume error of 3D sonography (mean +/- SD, -2.2% +/- 3.7%) was significantly lower than that of 2D sonography (-15.7% +/- 11.8%) with CT as the standard (P < .001). The correlation coefficient between 3D sonography and CT (r = 0.98; P < .0001) was better than that between 2D sonography and CT (r = 0.83; P < .0001). In addition, Bland-Altman analysis revealed that the limits of agreement between 3D sonography and CT (-9.7% to 5.1%) were narrower than those between 2D sonography and CT (-45.6% to 9.8%). Three-dimensional sonography with a matrix array transducer can significantly reduce renal volume measurement errors and offers a reliable means of determining renal volumes.

Three‐dimensional endoanal ultrasound assessment of the anal sphincters: Reproducibility

Volume measurement of the anal sphincter can be a future method for assessing volume loss, muscle atrophy or laceration. Three-dimensional (3D) endoanal ultrasound is a technique for assessing the volume of the anal sphincters, but the reproducibility of the method is scarcely known. Cross-sectional, repeated measurements. Twenty women were recruited for the study after written consent according to an ethically approved protocol, nine 0-gravida and 11 with traumatic vaginal deliveries. Endoanal 3D-ultrasound volume was obtained during rest and squeeze. The length of the anal canal and the volume of the external and internal sphincters were determined by two observers. Observer 1 repeated the measurements three times for all 20 women, and observer 2 for the nine 0-gravida, and intra- and inter-observer variation was assessed. During rest, the anal length measurement had intra-class correlation coefficients of 0.91 for observer 1 and 0.85 for observer 2. The limits of agreement for inter-observer measurement were (-0.81 to 1.61) measured in centimeters. For the external anal sphincter volume, the intra-class correlation coefficients and the limits of agreement were correspondingly: 0.89, 0.78 and (-7.29 to 6.03) measured in cm(3), and for the internal anal sphincter volume: 0.85, 0.69 and (-1.72 to 2.95). The variation in identifying the external anal sphincter could rise to a corresponding 30% error in volume measurement. Although intra-class correlation coefficients showed good reproducibility for endoanal ultrasound measurements, the limits of agreement were less reassuring with sizeable variation in the volume assessment, probably due to uncertainty in landmark identification.

Interexaminer Difference in Infarct Volume Measurements on MRI

The measurement of ischemic lesion volume on diffusion- (DWI) and perfusion-weighted MRI (PWI) is examiner dependent. We sought to quantify the variance imposed by measurement error in DWI and PWI lesion volume measurements in ischemic stroke. Fifty-eight consecutive patients with DWI and PWI within 12 hours of symptom onset and follow-up MRI on >or= day-5 were studied. Two radiologists blinded to each other measured lesion volumes by manual outlining on each image. Interexaminer reliability was evaluated by intraclass correlation coefficients (ICC) and relative paired difference or RPD (ratio of difference between 2 measurements to their mean). The ratio of between-examiner variability to between-subject variability (variance ratio) was calculated for each imaging parameter. The correlation (ICC) between examiners ranged from 0.93 to 0.99. The median RPD was 10.0% for DWI, 14.1% for mean transit time, 18.9% for cerebral blood flow, 21.0% for cerebral blood volume, 16.8% for DWI/MTT mismatch, and 6.3% for chronic T2-weighted images. There was negative correlation between RPD and lesion volume in all but chronic T2-weighted images. The variance ratio ranged between 0.02 and 0.10. Despite high correlation between volume measurements of abnormal regions on DWI and PWI by different examiners, substantial differences in individual measurements can still occur. The magnitude of variance from measurement error is primarily determined by the type of imaging and lesion volume. Minimizing this source of variance will better enable imaging to deliver on its promise of smaller sample size.

Growth-limiting size of atoll-islets: Morphodynamics in nature

Several linear models have been proposed for islet evolution. These models do not address the non-linear processes contributing to islet evolution or account for feedback between islet morphology and the fluid dynamics leading to sediment sequestration. The non-linear Sediment Allocation Model (SAM) has also been proposed for atoll-islet evolution. The SAM is a quantitative model of atoll-islet development implemented assuming that there is morphodynamic feedback between islet topography and the fluid dynamics leading to sediment sequestration in islet sinks. The SAM requires measurements of islet volume to recover parameters in the model using a data inversion algorithm. The SAM was developed and tested using synthetic data in order to determine the effect of errors in the islet volume measurements on model parameters. In this study the model parameters are estimated using radiocarbon-dated samples from published field studies of islet development on atolls. These calibration procedures involved reanalysis of the data using methods consistent with the morphodynamic principles of islet growth underlying the SAM. The results support a pattern of islet growth characterized by rapid lateral expansion followed by diminishing vertical accretion and shoreface rotation due to morphodynamic feedback.

Quantifying Sources of Error in Ultrasonic Measurements of Citrus Orchards

Ultrasonic sensors can be used to estimate tree canopy volume variability within orchards, which is useful for planning site-specific management practices and estimating crop yield. The objective of this study was to investigate the errors in tree canopy volume measured with a 10-transducer ultrasonic orchard measurement array and Trimble AgGPS 132 DGPS. Sensitivity analysis was used to investigate the magnitude of individual errors in ultrasonically-sensed tree canopy volume measurement (eUCV) caused by several factors including ground speed accuracy measured by DGPS, uncalibrated air temperature, ultrasonic transducers, and deviation in driving path from the centerline between two rows. The height error in the transducer array due to improper tire inflation and uneven ground was also estimated. Canopy volume of a selected tree measured with the ultrasonic system was used as the basis to simulate eUCV caused by each error factor. One hundred data points were simulated within the selected range of each factor to calculate eUCV and the ranges were determined on the basis of measured data and literature. The overall ranking of error sources affecting canopy volume were, from high to low 1) DGPS ground speed (6.78%), 2) air temperature (+4.83% to -4.69% for the temperature range 5C to 45C), 3) ultrasonic transducer performance (2.29%), and 4) deviations in driving path (1.56%). The height error due to uneven ground and wheel tracks ranged from 0.025 to 0.12 m. These results could be used to control error in ultrasonically-sensed canopy volumes within orchards.

Prostate volume and prostate-specific antigen levels in men enrolled in a large screening trial

Objectives Prostate volume correlates both with prostate-specific antigen (PSA) values and with the presence of benign prostatic hyperplasia (BPH). Here we examine the relationship between prostate volume and PSA level in a large, geographically diverse sample of men undergoing prostate cancer screening. Methods We followed 35,323 men enrolled in the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. Each man was screened with digital rectal examination (DRE) and PSA levels for up to 4 years. Prostate volume was estimated by DRE performed by trained examiners at the PLCO sites. Linear and logistic regression was used to assess the effect of prostate volume and age on PSA levels. Regression coefficients were adjusted for the effect of prostate volume measurement error. Results Prostate volume estimated by DRE showed considerable measurement error. Averaging volume over screening visits and accounting for examiner bias greatly reduced this error. Linear regression analysis showed a slope of 0.030/cm 3 of log PSA on prostate volume when correcting for measurement error (95% confidence interval [CI], 0.029 to 0.031). Age was independently associated with (log) PSA, with a slope of 0.022 per year. Logistic regression analysis of the risk of having an elevated PSA value (exceeding 4 ng/mL) showed an odds ratio of 1.9 (95% CI, 1.8 to 2.0) associated with a 10 cm 3 increase in prostate volume. The correlation of log PSA and prostate volume was 0.37. Prostate volume was not correlated with body mass index and showed weak correlation ( r = 0.14) with age. Conclusions Prostate volume and age are independently associated with increased PSA levels in a population of men undergoing screening.

Polyp Volume Versus Linear Size Measurements at CT Colonography: Implications for Noninvasive Surveillance of Unresected Colorectal Lesions

Proposed surveillance of unresected medium-sized (6.0-9.9 mm) polyps will require reliable detection of small incremental changes. The purpose of this study was to assess the reproducibility of linear versus volume measurements of polyp size at CT colonography (CTC) and to correlate results with a hemispheric model. The study group consisted of 30 polyps on supine and prone CTC data sets. Measurements were performed separately by two experienced radiologists using the same CTC system (Vitrea 2), resulting in 120 linear and volume measurements. Linear size was defined as the longest dimension among the 2D multiplanar reconstruction views. Semiautomated volume determination required manual tracing of polyp boundaries on 2D multiplanar reconstruction views. The relative error between reviewers 1 and 2 was defined as 100 x (/D1 - D2/)/D(ave) for linear size (D) and as 100 x (/V1 - V2)/V(ave) for volume (V), where ave is average. The mean relative error for linear size and volume measurement was 10.4% +/- 10.7% and 16.9% +/- 13.2%, respectively. Median linear size and volume of polyps were 9.4 mm and 270 mm3, respectively. CTC-derived volumes for medium-sized polyps closely approximated hemispheric volume (V = (pi/12) x D(b), where b =3.13, r2 = 0.90). Small incremental changes in hemispheric size result in a 3:1 relative change in volume versus diameter, such that a 1-mm diameter change in a medium-sized hemispheric polyp results in a relative change in linear size and volume ranging from approximately 11-18% and 31-53%, respectively. Because changes in polyp volume are amplified compared with linear dimension, volume measurement rather than diameter measurement will better allow detection of small incremental changes in polyp size using CTC.

Accuracy of fetal lung volume assessed by three‐dimensional sonography

To determine the accuracy and precision of prenatal three-dimensional (3D) ultrasound in estimating fetal lung volume using the rotational multiplanar technique (VOCAL) by comparing it to postmortem volume measurements. Fetal lung volume was measured during 3D ultrasound examination using a rotational multiplanar technique in eight cases of congenital diaphragmatic hernia (CDH) (six left and two right-sided) and in 25 controls without pulmonary malformation, immediately before termination. Prenatal 3D sonographic estimates of fetal lung volume were compared with postmortem measurement of fetal lung volume achieved by water displacement. The intraclass correlation coefficient of fetal lung volume estimated by 3D ultrasound and measured at postmortem examination was 0.95 in CDH cases and 0.99 in controls. Based on Bland-Altman analysis, the bias, precision and limits of agreement were, respectively, 0.35 cm(3), 1.46 cm(3) and between -2.51 and + 3.21 cm(3) in cases with CDH and 0.08 cm(3), 2.80 cm(3) and between -5.41 and + 5.57 cm(3) in controls. The mean relative error of 3D ultrasound fetal lung volume measurement was -7.19% (from -42.70% to + 18.11%) in CDH cases and -0.72% (from -30.25% to + 19.22%) in controls, while the mean absolute error of 3D ultrasound fetal lung volume measurement was 1.40 (range, 0.71-2.52) cm(3) and 2.12 (range, 0.05-4.98) cm(3), respectively. Accuracy of 3D ultrasound for measuring fetal lung volumes was 84.86 (range, 57.30-99.48)% in cases with CDH and 91.38 (range, 69.75-99.45)% in controls. The mean intraobserver variability for lung volume estimated by 3D ultrasound was 0.28 cm(3) in controls and 0.17 cm(3) in CDH cases. Prenatal 3D ultrasound can estimate accurately fetal lung volume using the rotational multiplanar technique for volume measurements (VOCAL), even in fetuses with very small lungs, such as cases with isolated CDH.

Uncertainty in NAPL Volume Estimates Due to Random Measurement Errors during Partitioning Tracer Tests

The uncertainty in NAPL volume estimates obtained through partitioning tracers can be quantified as a function of random errors in volume and concentration measurements when moments are calculated from experimentally measured breakthrough curves using the trapezoidal rule for numerical integration. The methodology is based upon standard stochastic methods for random error propagation. Monte Carlo simulations using a synthetic data set derived from the one-dimensional solution of the advective-dispersive equation serve to verify the process. It is shown that the uncertainty in NAPL volume predictions nonlinearly increases as the retardation factor decreases. An important result of this observation is that there is a large degree of uncertainty in using partitioning tracers to conclude NAPL is absent from the swept zone. Under the conditions investigated, random errors in concentration measurements are shown to have a greater impact on NAPL volume uncertainty than random errors in volume measurements, and it is also shown that uncertainty in NAPL volume decreases as the resolution of the breakthrough curves increases. The impact of uncertainty in background retardation (i.e., sorption of partitioning tracers in the absence of NAPL) was also investigated, and it likewise indicated that the relative uncertainty in NAPL volume estimates increases as the retardation factor decreases.

Errors in NAPL Volume Estimates Due to Systematic Measurement Errors during Partitioning Tracer Tests

During moment-based analyses of partitioning tracer tests, systematic errors in volume and concentration measurements propagate to yield errors in the saturation and volume estimates for nonaqueous phase liquid (NAPL). Derived expressions could be applied to help practitioners bracket their estimates of NAPL saturation and volume obtained from such tests. In practice, many of these effects may be overshadowed by other complications experienced in the field. Errors are propagated for systematic constant (offset) volume, proportional volume, and constant (offset) concentration errors. Previous efforts to quantify the impact of these errors were predicated upon the specific assumption that nonpartitioning and partitioning masses were equal. The current work relaxes that assumption and is therefore more general in scope. Through the use of nondimensional concentration, systematic proportional concentration errors do not affect the accuracy of the method. Specific consideration needs to be given to accurate flow measurements and minimizing baseline concentration errors when performing partitioning tracer tests in order to prevent the propagation of systematic errors.

Errors of measurement for blood volume parameters: a meta-analysis

The volume of red blood cells (V(RBC)) is used routinely in the diagnostic workup of polycythemia, in assessing the efficacy of erythropoietin administration, and to study factors affecting oxygen transport. However, errors of various methods of measurement of V(RBC) and related parameters are not well characterized. We meta-analyzed 346 estimates of error of measurement of V(RBC) for techniques based on Evans blue (V(RBC,Evans)), 51chromium-labeled red blood cells (V(RBC,51Cr)), and carbon monoxide (CO) rebreathing (V(RBC,CO)), as well as hemoglobin mass with the carbon-monoxide method (M(Hb,CO)), in athletes and active and inactive subjects undergoing various experimental and control treatments lasting minutes to months. Subject characteristics and experimental treatments had little effect on error of measurement, but measures with the smallest error showed some increase in error with increasing time between trials. Adjusted to 1 day between trials and expressed as coefficients of variation, mean errors for M(Hb,CO) (2.2%; 90% confidence interval 1.4-3.5%) and V(RBC,51Cr) (2.8%; 2.4-3.2%) were much less than those for V(RBC,Evans) (6.7%; 4.9-9.4%) and V(RBC,CO) (6.7%; 3.4-14%). Most of the error of V(RBC,Evans) was due to error in measurement of volume of plasma via Evans blue dye (6.0%; 4.5-7.8%), which is the basis of V(RBC,Evans). Most of the error in V(RBC,CO) was due to estimates from laboratories with a relatively large error in M(Hb,CO), the basis of V(RBC,CO). V(RBC,51Cr) and M(Hb,CO) are the best measures for research on blood-related changes in oxygen transport. With care, V(RBC,Evans) is suitable for clinical applications of blood-volume measurement.

Aortic aneurysm volume calculation: effect of operator experience

We have successfully applied sequential volumetric analysis of abdominal aortic aneurysms to exclude endoleak in patients who have an aortic endostent. This study compared the effect of variable operator experience on volumetric calculation accuracy. Four operators with different experience levels calculated abdominal aneurysm volumes in 10 patients at two different times (>/= 1 week apart). The four reviewers were ranked as having a high level of experience (one full-time laboratory worker specializing in three dimensions with 3 years of experience), a moderate level of experience (one part-time laboratory worker specializing in three dimensions/computed tomographic technician with 1 year of part-time experience), and a low level of experience (two individuals taught volumetric measurements for the purposes of this study: a fellow in abdominal imaging and a computed tomographic technician). All volumes were calculated with a GE Advantage 4.0 workstation (General Electric, Waukesha, WI, USA). Mean aneurysm volume and volume difference between two measurements were calculated for four operators. The average (standard deviation) percent volume differences were 1.2% (0.2%) for the experienced reader, 3.2% (0.3%) for the moderately experienced reader, and 6.0% (1.0%) and 5.8% (1.1%) for the two readers with light experience. Differences between averages were statistically significant (p < 0.005). We have defined a percent margin of error for aortic aneurysm volume measurement and have shown a direct correlate to level of experience. Diagnosis of endoleak based on aneurysm volume enlargement on serial scans needs to account for the level of operator experience.

Measurement of cartilage volumes in rheumatoid arthritis using MRI

MRI is a valuable imaging modality for assessment of the articular cartilage in rheumatoid arthritis (RA) and is potentially of use in monitoring disease progression and response to therapy. In this study, we investigated the sources of error in volume measurements obtained by segmentation of MR images of knee cartilage in patients with RA and followed cartilage volume in a group of RA patients for 12 months. 23 RA patient volunteers were recruited for knee imaging. Six subjects were imaged at baseline only, six were imaged at baseline and again within an hour in the same imaging session, six subjects were imaged at baseline and 7 days, and 17 subjects were imaged at baseline, 4+/-2 months and 12 months. Imaging was performed at 1.0 T using a three-dimensional spoiled gradient-echo sequence with fat-suppression. Manual image segmentation was performed once or twice on the lateral tibial, medial tibial, patellar and femoral compartment by either one or two segmenters. Coefficients of variation (CoV) for repeated volume measurement of total cartilage were 2.2% (same segmenter, same scan), 5.2% (different segmenter, same scan), 4.9% (same segmenter, different scan, same session), and 4.4% (same segmenter, different scan, different session). Over the 12 month duration of the study there was no significant change in total cartilage volume, nor were there significant changes in volume in any individual compartment. This measurement technique is reproducible, but any net change in cartilage volume over 1 year is very small.

Analysis of errors in the measurement of the volume of natural gas under standard conditions using measurement complexes that incorporate counters

Analysis of errors in the measurement of the volume of natural gas under standard conditions using measurement complexes that incorporate counters

Quantifying uncertainty due to random errors for moment analyses of breakthrough curves

The uncertainty in moments calculated from breakthrough curves (BTCs) is investigated as a function of random measurement errors in the data used to define the BTCs. The method presented assumes moments are calculated by numerical integration using the trapezoidal rule, and is theoretically applicable to moments of any order. Moreover, the method is applicable to either temporal or volumetric moments, and in the latter case, explicitly accounts for errors in volume measurements. The complexity of the calculations for the zeroth moment is comparable to that associated with the typical propagation-of-errors formula based on a Taylor series expansion. However, the formulae for higher moments are substantially more complex than the typical propagation-of-errors formula. For the zeroth and normalized first moments, moment uncertainties are more sensitive to random errors in concentration measurements compared to random errors in volume measurements. The robust nature of moment calculations is exemplified by the fact that relative uncertainty in moments is less than the relative error in volume and concentration measurements. Furthermore, moment uncertainty decreases as more data points are collected to define the BTC. For a BTC (based upon the solution to the one-dimensional advective-dispersion equation with a Peclet number of 10) with 100 data points, the zeroth moment and normalized first moment coefficient of variations are approximately 6 and 2%, respectively, for concentration coefficient of variation equal to 25% over a range of volume errors.

Development of a portable 3D ultrasound imaging system for musculoskeletal tissues

3D ultrasound is a promising imaging modality for clinical diagnosis and treatment monitoring. Its cost is relatively low in comparison with CT and MRI, no intensive training and radiation protection is required for its operation, and its hardware is movable and can potentially be portable. In this study, we developed a portable freehand 3D ultrasound imaging system for the assessment of musculoskeletal body parts. A portable ultrasound scanner was used to obtain real-time B-mode ultrasound images of musculoskeletal tissues and an electromagnetic spatial sensor was fixed on the ultrasound probe to acquire the position and orientation of the images. The images were digitized with a video digitization device and displayed with its orientation and position synchronized in real-time with the data obtained by the spatial sensor. A program was developed for volume reconstruction, visualization, segmentation and measurement using Visual C++ and Visualization toolkits (VTK) software. A 2D Gaussian filter and a Median filter were implemented to improve the quality of the B-scan images collected by the portable ultrasound scanner. An improved distance-weighted grid-mapping algorithm was proposed for volume reconstruction. Temporal calibrations were conducted to correct the delay between the collections of images and spatial data. Spatial calibrations were performed using a cross-wire phantom. The system accuracy was validated by one cylinder and two cuboid phantoms made of silicone. The average errors for distance measurement in three orthogonal directions in comparison with micrometer measurement were 0.06 ± 0.39, −0.27 ± 0.27, and 0.33 ± 0.39 mm, respectively. The average error for volume measurement was −0.18% ± 5.44% for the three phantoms. The system has been successfully used to obtain the volume images of a fetus phantom, the fingers and forearms of human subjects. For a typical volume with 126 × 103 × 109 voxels, the 3D image could be reconstructed from 258 B-scans (640 × 480 pixels) within one minute using a portable PC with Pentium IV 2.4 GHz CPU and 512 MB memories. It is believed that such a portable volume imaging system will have many applications in the assessment of musculoskeletal tissues because of its easy accessibility.

Impact of photon energy recovery on the assessment of left ventricular volume using myocardial perfusion SPECT

Background Photon energy recovery (PER) is a spectral deconvolution technique validated for scatter removal in patients and phantom studies. The purpose of this study was to examine the impact of PER on left ventricular volume measurement based on myocardial perfusion single photon emission computed tomography (SPECT). Methods and results SPECT acquisitions were performed by use of a static cardiac phantom and in 25 patients after a rest injection of technetium 99m sestamibi by use of multiple energy windows (126-136, 137-144, and 145-154 keV). Data were successively reconstructed with and without PER, by use of iterative reconstruction and post-processing filtering (Butterworth filter; order, 5; cutoff, 0.30 cycles/pixel). Image contrast was evaluated in reconstructed data, and volumes were calculated by use of QGS. PER increased reconstructed image contrast from 62% ± 2.7% to 84.3% ± 5.7% in the phantom studies ( P < .0001) and from 49% ± 2% to 73% ± 2% in patients ( P < .0001). Although it remained underestimated ( P < .0001), phantom volume was higher after PER correction compared with uncorrected data (50.9 ± 0.8 mL vs 44.6 ± 1 mL, P < .0001). The error in volume measurement was decreased by PER correction (16.6% ± 1.3% vs 27% ± 1.7% [uncorrected data], P < .0001). In patients, left ventricular volume increased from 83 ± 10 mL to 91 ± 10 mL ( P < .0001), and the PER-induced volume increase was correlated with the image contrast increase ( r = 0.61, P = .001). Finally, the percentage of volume increase was higher in patients with small left ventricular volumes. Conclusions PER has a significant impact on image contrast and left ventricular volume measurement by use of perfusion SPECT. PER improves the accuracy of phantom volume assessment. In patients, volume increase is correlated to image contrast increase and is higher in those with small ventricles.

소형 공기챔버를 센서소자로 사용하는 새로운 호식기류 계측기술

Asthma is one of the important respiratory diseases requiring home self care usually performed by commercialized peak expiratory flow meter (PEFM). However, this simple device can measure only single parameter, PEF, due to its purely mechanical principle, significantly limiting desease management quality. The present study introduced a new expiratory flow measurement technique by miniatured air expansion chamber easily installed within PEFM. Continuous pressure signal obtained from the chamber demonstrated an accurate quadratic relationship with flow. The volume measurement error was <TEX>$</TEX><TEX><</TEX><TEX>{\pm}1%$</TEX> well within the American Thoracic Society (ATS) criteria of 3%. Important spirometric parameters of FVC, PEF, and FEF25-75% were all accurately estimated with correlation coefficients > 0.95. The present technique obtains continuous expiratory air flow signal, making possible and convenient to perform spirometric test at home. Electronic interface capability would be also useful for remote asthma management.