Phantom Volume Research Articles

Evaluating and Validating Two Methods for Estimating Brain Structure Volumes: Tessellation and Simple Pixel Counting

Developments in imaging technology have made three-dimensional visualization of internal brain structures possible with excellent resolution. Since improved visualization implies improved measurement, these advances hold promise to more accurately measure the volumes of internal structures. As new technologies and techniques emerge, evaluating the relative benefits of measurement methods becomes necessary. We compared and evaluated two methods of estimating volumes from images of brain structures. One method counted pixels within a region of interest, while the other method tessellated the surface between tracings on adjacent slices. Our study assessed both measurement error for true phantom volumes and method disparity for in vivo structures in a randomly selected sample of subjects ( n = 100). For our comparisons, we focused on the temporal lobe, ventricular system, and hippocampus. Bias, independence of measurement errors and maximal discrimination of individual differences are properties that are relevant to validating and evaluating measurements of cerebral structure. Pixel counting proved to be the more robust of the two methods, being less sensitive to nuisance interactions between size of object, shape, and slice thickness. Clinical and research applications of imaging techniques may have distinctive but overlapping needs when evaluating and validating new developments in imaging.

Kidney volume estimation using 99Tcm-DMSA RSPECT

Renal parenchymal volume is important for clinical interpretation. The phantom study was carried out to validate the volume calculation. The volume of kidney phantom was determined using reoriented single photon emission computed tomography (RSPECT). The phantom volume range was 20-300 ml. There are two major factors in the determination of volume which are radioactivity concentration and organ/background ratio. Our results showed that the effect of radioactivity concentration on the volume in the kidney phantom is -3.3 to 7.5% whereas the effect of organ/background ration was only 2.2%. Our relative volume deviation, therefore, from the real volume was 1.43%. We concluded that it is feasible to use kidney volume in clinical work.

Three-dimensional echocardiographic measurement of left ventricular volume in vitro: Comparison with two-dimensional echocardiography and cineventriculography

Objetives. This study was designed to compare three-dimensional echocardiography, two-dimensional echocardiography and cineventriculography for the purpose of measuring left ventricular volume in vitro.Background. Three-dimensional echocardiographic systems have been shown to be highly accurate in measuring the volumes of balloon phantoms, However, three-dimensional techniques have not been compared with standard two-dimensional echocardiography in vitro or with cineventriculography, the clinical standard for left ventricular volume measurement.Methods. Excised porcine hearts were prepared with an internal latex sheath that could be filled and maintained with a known (“true”) volume of liquid. Each heart was then imaged by cineventriculography, standard two-dimensional echocardiography and three-dimensional echocardiography. Left ventricular volumes were calculated from 15 hearts at 25 volumes ranging from 50 to 280 ml by the following methods: 1) biplane cineventriculography using the area-length method; 2) two-dimensional echocardiography by the apical biplane method using a summation of discs algorithm in 15 cases and the single-plane, four-chamber method using a summation of discs algorithm in 10 cases; and 3) three-dimensional echocardiography using a polyhedral surface reconstruction volume computation algorithm based on multiple nonparallel, nonevenly spaced short-axis cross sections.Results. Results were compared with true volume, and a nonparametric analysis of variance was performed. Both measurement bias (systematic error) and imprecision (random error) were assessed. All methods tended to underestimate the true volume (two-dimensional echocardiography −6.1 ± 17.6%, three-dimensional echocardiography −4.7 ± 5.0% and biplane cineventriculography −3.9 ± 8.2%), although differences were not significant. Although there was a significant correlation between the magnitude of measurement bias and the size of the volume being measured for two-dimensional echocardiography and cineventriculography, the bias of three-dimensional echocardiography was fairly constant over the range of volumes. When bias was accounted for, two-dimensional echocardiography was significantly less precise than cineventriculography and three-dimensional echocardiography in terms of percent error (15.3 ± 11.9%, 5.6 ± 5.7% and 3.9 ± 3.4%, respectively).Conclusions. Three-dimensional echocardiography using a polyhedral surface reconstruction algorithm for volume computation provides accuracy comparable to that of biplane cineventri-culography in this in vitro model. Standard two-dimensional echocardiographic volume computation is significantly less accurate than the other two methods.

Photoneutron dose in soft tissue phantoms irradiated by 25 MV X-rays

The photoneutron production and the absorbed dose in two soft tissue phantoms irradiated with 25 MV X-ray beams were estimated by means of the MCNP4 Monte Carlo code. Both single-beam and four-field box irradiations were considered. The neutron and photon therapy dose was calculated in various regions of the phantoms. An experimental verification of the photoneutron yield as a function of depth in a water phantom was also carried out by means of photoactivation reactions on 16O. An average photoneutron and X-ray integral dose ratio of 3.7*10-5 (photoneutron Gy kg-1)/(X-ray therapy Gy kg-1) was estimated inside the target volume of the four-field box irradiation phantom, whilst outside the integral dose ratio is 9.2*10-6 (photoneutron Gy kg-1)/(X-ray therapy Gy kg-1).

Fast, interactive algorithm for segmentation of a series of related images: application to volumetric analysis of MR images of the heart.

Magnetic resonance (MR) cine images of the beating heart have excellent spatial and temporal resolution. Extracting the boundaries of the heart from MR images for volumetric measurements is of considerable interest; however, since the number of images involved is large, tracing the boundaries by hand is tedious and prohibitively time consuming. The authors have developed an interactive method of boundary detection that uses the correlation between the cardiac boundaries on temporally or spatially adjacent images to increase the speed of the process and reproducibility of the measurement. A simulated cine MR study of a phantom (total of 155 images) and cardiac cine studies of two patients (192 images each) were analyzed by two independent observers. Analysis of the phantom data was completed in 5.6 minutes (2.16 seconds per image) by observer 1 and 6.3 minutes (2.4 seconds per image) by observer 2. The percent measurement errors for 31 phantom volumes (30-120 mL) were 0.96% and 0.83% for observers 1 and 2, respectively. The observers analyzed the patient studies in 14-23 minutes (4.4-7.2 seconds per image), with interobserver variabilities of 5.8% and 3.7% for the two patients, respectively. The authors conclude that their flexible, semiautomatic, interactive algorithm allows rapid and reproducible detection of structural boundaries.

A Monte Carlo Investigation of the Dosimetric Properties of Monoenergetic Neutron Beams for Neutron Capture Therapy

A Monte Carlo simulation study has been carried out to investigate the suitability of neutron beams of various energies for therapeutic efficacy in boron neutron capture therapy. The dosimetric properties of unidirectional, monoenergetic neutron beams of varying diameters in two different phantoms (a right-circular cylinder and an ellipsoid) made of brain-equivalent material were examined. The source diameter was varied from 0.0 to 20.0 cm; neutron energies ranged from 0.025 eV up to 800 keV, the maximum neutron energy generated by a tandem cascade accelerator using 2.5-MeV protons in a 7Li(p,n)7Be reaction. Such a device is currently under investigation for use as a neutron source for boron neutron capture therapy. The simulation studies indicate that the maximum effective treatment depth (advantage depth) in the brain is 10.0 cm and is obtainable with a 10-keV neutron beam. A useful range of energies, defined as those neutron energies capable of effectively treating to a depth of 7 cm in brain tissue, is found to be 4.0 eV to 40.0 keV. Beam size is shown not to affect advantage depth as long as the entire phantom volume is used in determining this depth. Dose distribution in directions parallel to and perpendicular to the beam direction are shown to illustrate this phenomenon graphically as well as to illustrate the differences in advantage depth and advantage ratio and the contribution of individual dose components to tumor dose caused by the geometric differences in phantom shape.

2. MRI 装置によるスペクトロスコピーの基礎的検討(MRS の現状と技術的課題)

Technical aspects of image selected in vivo spectroscopy (ISIS) and fast rotating gradient spectroscopy (FROGS) are reported. Experiments were performed on a 1.5 T MRI system for human body by using a surface coil tuned to phosphorus-31. Phantoms filled with phosphoricacid solustions and normal ten volunteers were examined. We focused on the dependence of the signal intensity on RF transmitter power, volume selectivity, and the positional shift due to chemical shift. Results are as follows : Transmitter power to excite spins increased with conductivity and volume of phantoms. The peak hight of the spectrum of the heart of human volunteers changed depending on the transmitter power and repetition time. In ISIS, volume selectivity was good in large volume selection. While, in FROGS, it was good in thin slice selection. Positional shift due to chemical shift was not negligible in both techniques, but the distance changed depending on the strength of the gradient field used.

Validation of Ultrafast Computed Tomographic Left Ventricular Volume Measurement

Left ventricular volume has been measured with ultrafast computed tomography. However, the accuracy with which this can be done is unknown. We therefore imaged with ultrafast computed tomography 11 rectangular phantoms, 20 to 225 ml, and 17 left ventricular casts, 15 to 112 ml. Two observers planimetered serial tomographic images and computed volume from sequential tomograms. There was no significant inter- or intraobserver difference in measurement of phantoms. Deviation of ultrafast computed tomographic volume from true phantom volume was -0.1 +/- 3.5% SD, range 9.0 to -7.6%. Correlation of true phantom volume with ultrafast computed tomographic volume was 0.99, SEE = 1.9 ml. No significant difference was observed between merged and single ultrafast computed tomographic scanning sequences. Left ventricular cast volume determined by ultrafast computed tomography deviated from true volume by 6% +/- 20%, range 54% to -45%. Correlation of true volume with ultrafast computed tomographic volume was 0.99, SEE = 5.1 ml. There was no interobserver significant difference in measurement of left ventricular cast volume. Correlation between ultrafast computed tomographic volume and cineradiographic volume of the same left ventricular casts was 0.99, SEE = 4.4 ml. Thus, phantom volumes can be measured accurately without significant intra- or interobserver variation. Merged scanning sequences did not influence volume determination. Left ventricular cast volume determination was comparable to that obtained with cineradiography.

Analysis of brain and cerebrospinal fluid volumes with MR imaging. Part I. Methods, reliability, and validation.

A computerized system was developed to process standard spin-echo magnetic resonance (MR) imaging data for estimation of brain parenchyma and cerebrospinal fluid (CSF) volumes. In phantom experiments, the estimated volumes corresponded closely to the true volumes (r = .998), with a mean error less than 1.0 cm3 (for phantom volumes ranging from 5 to 35 cm3), with excellent intra- and interobserver reliability. In a clinical validation study with actual brain images of 10 human subjects, the average coefficient of variation between observers for the measurement of absolute brain and CSF volumes was 1.2% and 6.4%, respectively. The intraclass correlations for three expert operators is greater than .99 in the measurement of brain and ventricular volumes and greater than .94 for total CSF volume. Therefore, the authors believe that their technique to analyze MR images of the brain performed with acceptable levels of accuracy and reliability and that it can be used to measure brain and CSF volumes for clinical research. This technique could be helpful in the correlation of neuroanatomic measurements to behavioral and physiologic parameters in neuropsychiatric disorders.

ＳＰＥＣＴによる｀９９ｍ´Ｔｃ‐ジメルカプトコハク酸腎摂取率測定法における最適いき値の基礎的，臨床的検討

To calculate renal uptake of 99mTc-dimercaptosuccinic acid (DMSA) more accurately using single photon emission computed tomography (SPECT), it is necessary to estimate values of threshold level, which corresponds to the ratio of kidney to background (BG ratio). Thus the phantom and clinical studies were conducted. Six kinds of renal phantoms of 80 to 339 ml, contained different radioactivity of 37 to 485 MBq were prepared. These phantoms were placed in a larger body phantom filled with 1 to 50% of radioactivity representing background. Clinical application of this method was also performed. Results were as follows. 1) A significant correlation between phantom volumes and estimated volumes obtained using threshold level based on BG ratio calculated on tomographic images was found (r = 0.99). 2) A significant correlation between total counts in estimated volumes and radioactivities in phantoms was recognized (r = 0.94). 3) Known radioactivity in phantoms and radioactivity in estimated volumes were highly related (r = 0.98). 4) Clinical application showed valuable results in patients with renal dysfunction. Thus, this method can calculate more accurate renal uptake of 99mTc-DMSA.

A practical SPECT technique for quantitation of drug delivery to human tumors and organ absorbed radiation dose

A practical quantitative single photon emission computed tomographic (SPECT) technique based on an empirical threshold analysis permits accurate measurements in humans of drug delivery and absorbed radiation dose. The limits of the method have been explored using a wide range of phantom volumes, concentrations, and target-to-nontarget ratios. A threshold of 43% was found to give the best results using volumes of 30 to 3,800 cc. An excellent correlation (r = .99 with a standard error of estimate [SEE] of 41 cc) was found between SPECT measured volumes and actual phantom volumes. A similarly high correlation (r = .98, SEE = 260 counts/voxel) was found in 77 measurements of concentrations between 0.01 and 3.6 microCi/cc. There was a direct relationship between the target-to-nontarget ratio of phantoms and the accuracy of volume measurements. The technique has been validated by an excellent in vivo/in vitro correlation of uptake in human tumors. The tumor cumulative concentration and tumor-to-blood ratio were used for assessment of drug delivery. In vivo quantitative measurements of the pharmacokinetics of technetium-99m (99mTc) glucoheptonate, cobalt-57 (57Co) bleomycin and platinum-195m (195mPt) cisplatin in human tumors in vivo indicates that, in contrast with tumor models in animals, there is a marked variability in drug delivery even in tumors with the same histology. Future development of labeled drugs should make it possible to use quantitative SPECT for predicting tumor response to therapy and for tailoring chemotherapy for the individual patient under treatment. SPECT quantitation of organ concentration was used for Medical Internal Radiation Dose committee (MIRD) calculations of organ absorbed radiation dose from 99mTc-labeled RBCs. Excellent in vivo/in vitro correlations were obtained between SPECT measured concentrations of blood radioactivity in the heart and in vitro measurements of blood samples. The possibilities and limitations of this technique are discussed and its use for in vivo measurement in humans of absorbed radiation dose from radiopharmaceuticals is suggested.

Quantitative evaluation of postembolized splenic tissue using technetium-99m sulfur colloid.

Tc-99m sulfur colloid scans were used to quantitate the percent of residual splenic tissue after partial splenic embolization (PSE) performed for the treatment of hypersplenism in 17 renal transplant patients. A liver-spleen phantom was designed which simulated the human liver and spleen configuration to evaluate the technique. This phantom contained a solution of tc-99m sulfur colloid, which allowed precise quantities of the spleen phantom volume to be displaced using lucite pseudo-emboli. After each lucite embolus, computer images of the spleen phantom were collected and analyzed in the same manner used for the transplant patients. Correlation of the actual volume displaced or embolized with the computer estimated values was 0.996 (P less than 0.001). This technique was superior to both CT and MRI, which were more difficult to perform and less precise in measuring a decrease in postinfarction functioning splenic tissue.

Determination of thyroid volume using computerized ultrasonography and its clinical application

A new method for determining thyroid gland volume was developed by means of computerized ultrasonography. A maximum area of the thyroid (S) was obtained from coronal sections and a maximum thickness (C) was obtained from sagittal sections. The thyroid volume was then calculated by SXC. The volume of phantoms and pig thyroids obtained by this method was identical with the actual volume. The thyroid volume in this method correlated well with the estimated volume in patients with Graves' disease undergoing thyroidectomy (r = 0.954). The measurement was then performed in 56 healthy subjects (male 28, female 28, age 15-68 y.o.) and 126 patients with thyroid diseases. The thyroid volume in healthy men was significantly larger than that in women (18.4 +/- 6.1 ml vs 13.9 +/- 4.9 ml, Mean +/- SD, p less than 0.01). The thyroid volume in normal subjects correlated with body height, body weight or body surface area (p less than 0.01), which may explain the sex differences. An attempt was made to calculate the prospective thyroid volume (Y ml) from body height as follows; Y = 0.425 X - 52.8, X; body height (cm). Four out of thirty patients with untreated Graves' disease had a gland volume of the normal range, but in all patients the thyroid volume was larger than the prospective volume. The thyroid volume and the rate of volume increase (determined thyroid volume/calculated prospective volume) were correlated with the serum levels of T3, T4 concentration in the untreated stage. The volume and the rate of volume increase did not correlate with serum TSH receptor antibody activity. The thyroid volume in patients with Graves' disease who had been in remission (33.0 +/- 13.5 ml) was significantly smaller than that in untreated patients (51.8 +/- 24.4 ml, p less than 0.02). These findings indicate that the present method is reliable and clinically useful for the investigation of thyroid diseases.

CONTRIBUTION OF TIME-OF-FLIGHT INFORMATION TO LIMITED ANGLE POSITRON TOMOGRAPHY

Limited-angle emission tomography has been investigated using a two-dimensional phantom to generate positron events simulating a camera with two opposed parallel position-sensitive detectors collecting data within a 90° cone. The data, backprojected onto lines passing through the phantom volume, is used with a matrix reconstruction method to provide two-dimensional images. Image quality has been measured using the standard deviation of the reconstructions with respect to the original phantom. The application of Phillips-Twomey smoothing to the deconvolution matrices has substantially improved the original reconstructions, a factor of 1.9 in signal to noise ratio, giving S/N = 3.4 for a phantom having an average of 150 events/pixel. Using photon time-of-flight to restrict the reconstruction volume a further considerable improvement is made. When the time-of-flight limited the contributing volume to 4 lines out of 11 the improvement was another factor of 1.9 giving SN = 6.0 for the same phantom. Comparable increases in signal to noise ratios are expected for three-dimensional reconstructions.

A Method for Volume Estimation by Using Vector Areas and Centroids of Serial Cross Sections

A technique is developed to estimate the volume of an organ from its cross-sectional images. It is applicable even if each section is multiply-connected or not parallel with the others. The volume is calculated by using the vector areas and the centroids of serial sections. When ten sections were used, it estimated the volumes of computer-generated phantoms at an error of less than 3 percent, using six-different cutting modes. The technique may be efficiently applicable to the two-dimensional ultrasound images.

Contribution of Time-of-Flight Information to Limited Angle Positron Tomography

Limited-angle emission tomography has been investigated using a two-dimensional phantom to generate positron events simulating a camera with two opposed parallel position-sensitive detectors collecting data within a 90° cone. The data, backprojected onto lines passing through the phantom volume, is used with a matrix reconstruction method to provide two-dimensional images. Image quality has been measured using the standard deviation of the reconstructions with respect to the original phantom. The application of Phillips-Twomey smoothing to the deconvolution matrices has substantially improved the original reconstructions, a factor of 1.9 in signal to noise ratio, giving S/N = 3.4 for a phantom having an average of 150 events/pixel. Using photon time-of-flight to restrict the reconstruction volume a further considerable improvement is made. When the time-of-flight limited the contributing volume to 4 lines out of 11 the improvement was another factor of 1.9 giving SN = 6.0 for the same phantom. Comparable increases in signal to noise ratios are expected for three-dimensional reconstructions.

Left ventricular volumes by gated equilibrium radionuclide angiography: a new method.

To compare radionuclide end-diastolic (EDV) and end-systolic (ESV) volumes with angiographic volume, we studied 52 patients with equilibrium radionuclide angiography using 99mTc-human serum albumin within 48 hours of contrast angiography. Each RR interval was divided into 20--28 equally timed frames and a time-activity curve generated. End-diastolic counts were taken at the early peak of the curve and end-systolic counts at its nadir. Counts were divided by the total number of processed heart beats and normalized for: 1) dose per body surface area; 2) plasma volume; and 3) counts/ml of plasma. A cardiac phantom was developed and serial volumes were studied using a normalization factor. Radionuclide values were expressed as dimensionless units and compared with either biplane angiographic volumes (in the patient studies) or known phantom volumes. Good correlations were obtained with methods 1 and 2 in 35 patients (r greater than 0.84), but the best correlation was obtained in 17 patients when normalization for counts/ml of plasma was used (r = 0.98; y = 0.255 x -0.121). The standard error of the estimate (SEE) was +/- 11.5 ml for EDV and +/- 7.3 ml for ESV. The phantom study also showed an excellent correlation (r = 0.99), with a SEE of +/- 6.5 ml. We conclude that a radionuclide method independent of geometric assumptions can be used to estimate left ventricular volume in man.

Perception of Subjective Lines, Surfaces and Volumes in 3-Dimensional Constructions

Psychologists of visual perception have used special pictures, some made by artists, to investigate the phenomenon of subjective or phantom lines and surfaces. The authors have extended the investigations to 3-dimensional constructions of their design. Eight constructions are described and an account is given of the results obtained with human subjects. Differences between the phenomenon perceived in pictures and in the constructions are pointed out and attention is drawn to a new phenomenon—the perception of a subjective or phantom volume.

Quantitation of tumor volumes and response to therapy with ultrasound B-scans.

A technique employing serial ultrasonic B-scans and a computer for measuring volumes of internal anatomical structures is described. Phantom studies indicate that this method is accurate to within 5% for phantom volumes in the 200–2000 cm3 range. The technique was applied to monitor the spleen-tumor volume in a patient with chronic lymphocytic leukemia and the liver-tumor volume in a patient with retroperitoneal rhabdomyosarcoma. The data suggest that the method is clinically useful for determining normal organ and tumor volumes and for evaluating response to therapy.

The Effects of Total-Body Irradiation of Dogs with Simulated Fission Neutrons

Mongrel male dogs were exposed to neutrons obtained by bombarding a thick Be target with 12 Mev protons. The distribution of neutron and associated gamma-ray dose was measured throughout the volume of a tissue equivalent phantom constructed to simulate an average dog. The median lethal midline tissue dose is 239 rads, of which 165 rads are from neutrons and 74 rads are from gamma rays. The potency ratio, compared with 250 kvp x rays is approximately 0.9, in good agreement with the value of 0.95 found by other workers with a higher energy neutron beam. Thc significance of this potency ratio in terms of the gastrointestinal and bone marrow injuring potential of neutrons is discussed and the idea is presented that death after neutron irradiation of dogs is almost purely the result of bone marrow injury while death in rodents is the result largely of injury to the gastrointestinal tract. (auth)