Showing papers on "Imaging phantom published in 1989"

Temperature mapping with MR imaging of molecular diffusion: application to hyperthermia.

Abstract: Efficacy and safety considerations for hyperthermia (HT) cancer therapy require accurate temperature measurements throughout the heated volume. Noninvasive thermometry methods have been proposed, including magnetic resonance (MR) imaging based on the temperature dependence of the relaxation time T1. However, the temperature accuracy achieved to date with T1 measurements does not fulfill the HT requirements (1 degree C/cm). The authors propose to use molecular diffusion, for which temperature dependence is well known. Molecular diffusion is more sensitive than T1 and can be determined with high accuracy with MR imaging. Diffusion and derived temperature images were obtained with a 2 X 2-mm pixel size in a polyacrylamide gel phantom heated inside the head coil of a clinical 0.5-T whole-body MR imaging system by means of a modified clinical HT device made compatible with the system. Temperatures determined from these images with 0.8-cm2 regions of interest were found to be within 0.5 degrees C of those recor...

Irradiation synchronized with respiration gate

Abstract: A respiratory gating technique was developed for radiotherapy of tumors unable to remain stable due to respiration. Irradiation was started and stopped with a microwave oscillator of a linear accelerator controlled by gating signals at specific points in the respiratory cycle. This technique was tested in a phantom specially designed to simulate a patient with lung cancer and in clinical therapy for lung tumors of seven patients. A mask was used to check ventilation in the phantom and airbags were used to measure thoracoabdominal pressure in patients and in the phantom; this enabled us to detect the excursion of the tumors. Low sensitivity film for verification demonstrated the efficacy of this technique. The gated irradiation was proved to ensure more precise radiotherapy for tumors located close to the diaphragm.

Correction of nonuniform attenuation in cardiac SPECT imaging.

Abstract: Correction for photon attenuation in cardiac SPECT imaging using a measured attenuation distribution with an iterative expectation maximization (EM) algorithm and an iterative Chang algorithm were compared with the conventional filtered backprojection and an iterative EM algorithm without attenuation correction. The attenuation distribution was determined from a transmission computed tomography study that was obtained using an external collimated sheet source. The attenuation of the emitting photons was modeled in the EM algorithm by an attenuated projector-backprojector that used the estimated attenuation distribution to calculate attenuation factors for each pixel along each projection and backprojection ray. Results from a heart-lung phantom study and a 201Tl patient study demonstrated that the iterative EM algorithm with attenuation correction provided improved image quality in terms of reduced streak artifacts and noise, and more accurate quantitative information in terms of improved radioactivity distribution uniformity where uniformity existed, and better anatomic object definition.

Authenticating edges produced by zero-crossing algorithms

Abstract: It is shown that zero-crossing edge detection algorithms can produce edges that do not correspond to significant image intensity changes. Such edges are called phantom or spurious. A method for classifying zero crossings as corresponding to authentic or phantom edges is presented. The contrast of an authentic edge is shown to increase and the contrast of phantom edges to decrease with a decrease in the filter scale. Thus, a phantom edge is truly a phantom in that the closer one examines it, the weaker it becomes. The results of applying the classification schemes described to synthetic and authentic signals in one and two dimensions are given. The significance of the phantom edges is examined with respect to their frequency and strength relative to the authentic edges, and it is seen that authentic edges are denser and stronger, on the average, than phantom edges. >

Clinical percutaneous imaging of coronary anatomy using an over-the-wire ultrasound catheter system

Abstract: This manuscript describes initial applications of a unique new intravascular ultrasound imaging catheter. This 5.5F catheter uses an over-the-wire design and incorporates a phased array transducer at its tip. There are no moving parts. A 360° image is produced perpendicular to the catheter axis using a 20 MHz center frequency. A dedicated minicomputer is used for initial image processing, as well as enhancement and analysis. Initial studies using phantoms demonstrated excellent accuracy for linear dimensions (r = 0.99, range 3.0 to 7.6mm, image = 1.0 phantom + 0.1). Serial imaging of the same arterial segment in vitro showed good reproducibility (coefficients of variance 2.5–5.2%). Likewise, intra- and inter-observer variability in image analysis was minimal (r = 0.92−0.99). Initial in vivo studies were performed in dogs. The catheter was easily passed over a wire into mesenteric, cerebral and coronary vessels without evidence of significant vessel trauma. Subsequently, 20 patients had percutaneous coronary imaging performed during cardiac catheterization. Cardiac motion was rarely a problem and acceptable images were obtained in all but two patients. Areas of calcification, mild stenoses, branching vessels and graft atherosclerosis could be identified. We conclude that intracoronary ultrasound imaging will be useful for assessing vascular pathology, for studying both rapid change in vessel size as well as chronic progression or regression of atherosclerosis, and for assisting with new therapeutic interventions.

Automated image detail localization method

Abstract: An automated image detail localization system for digital image systems, such as CT, MRI, digital radiograph, includes a calibration phantom having plural reference samples of materials having known, fixed imaging properties. The phantom is positioned with respect to a patient and scanned simultaneously to produce an image that includes a cross-section of the patient and a cross-section of the phantom. The cross-sectional image of the phantom includes cross-sectional images of the reference samples. The system automatically finds the phantom and the centers of the reference sample images and then positions regions of interest (ROIs) within the reference sample images to define the portions of the images that are included in a step of averaging the intensities of the reference sample images. The system further automatically places an ROI of regular (e.g., elliptical) or irregular shape in a specific region of the image of the patient's anatomy, such as the trabecular bone region of the patient's spine. The system automatically performs a histogram analysis of the tissue within an ROI to exclude tissue components that are undesirable in the calculation of tissue density. By using the phantom in combination with the histogram analysis, component tissues that cannot be readily separated spatially can be isolated by density or signal intensity and thus quantified in an automated manner. Small or irregularly-shaped tissues, such as lung nodules, can be accurately quantified without requiring precise placement of an ROI in the tissue image.

Spin locking for magnetic resonance imaging with application to human breast.

Abstract: The dependence of rotating frame spin-lattice relaxation, T1 rho on locking field frequency, f1, was measured for phantom materials and human breast tissues. These data were used to predict the relative signal strengths obtainable in a spin-locking imaging sequence. This imaging sequence was implemented on a 0.15-T imaging system and measurements of phantom and tissue signal strength for various imaging parameters agreed with predicted signal strengths. Compared to T1 and T2, T1 rho appears to have unique capability to distinguish tumor from normal fat and fibrous breast tissues. The applications of T1 rho to tissue characterization and imaging at high static field strengths are discussed.

A technique for using CT images in attenuation correction and quantification in SPECT.

Abstract: A technique is described for using computed tomography (CT) images for attenuation correction and quantification in SPECT. The CT images are aligned with the corresponding SPECT slices and the Hounsfield units are converted to linear attenuation coefficient values for the SPECT radionuclide. The attenuation coefficient map thus produced is used to provide the attenuation correction required in the SPECT reconstruction. The technique has been evaluated in both a non-anatomical and an anatomical phantom giving a mean accuracy in quantifying activity of various features in the phantoms of 2.6% (range 0.3%-4.0%). The value of performing scatter correction prior to attenuation correction in obtaining accurate quantification is demonstrated. The practicalities of applying the technique in patient studies are discussed.

T1 and T2 measurements on a 1.5-T commercial MR imager.

Abstract: In order for relaxation times to be used in clinical diagnosis, the precision of the measurement must be determined. The authors measured T1, T2, and proton density in a phantom and in human volunteers to determine the reproducibility of the method. The coefficient of variance of T1 measurements in the phantom during a 15-month period with two software upgrades was 5%. Variance of T2 measurements with any given software was 4% or less, and overall in the 15-month period, with two software changes, the T2 reproducibility was between 6% and 9%. The reproducibility is sufficiently high that precise clinical measurements of T1, T2, and proton density are feasible.

MRI of "diffusion" in the human brain: new results using a modified CE-FAST sequence.

Abstract: “Diffusion-weighted” MRI in the normal human brain and in a patient with a cerebral metastasis is demonstrated. The method employed was a modified CE-FAST sequence with imaging times of only 6-10 s using a conventional 1.5-T whole-body MRI system (Siemens Magnetom). As with previous phantom and animal studies, the use of strong gradients together with macroscopic motions in vivo causes unavoidable artifacts in diffusion-weighted images of the human brain. While these artifacts are shown to be considerably reduced by averaging of 8-16 images, the resulting diffusion contrast is compromised by unknown signal losses due to motion. © 1989 Academic press, Inc.

A dual-frequency electrical impedance tomography system

Abstract: An electrical impedance tomography (EIT) system has been constructed, operating at two frequencies, 40.96 and 81.92 kHz, for investigating the practicability of the dual-frequency imaging method discussed theoretically in a previous paper (Griffiths and Ahmed, 1987). For testing the system, a phantom with a frequency-dependent electrical conductivity was designed. The properties of the phantom can be adjusted to match the frequency dependence observed in a given type of tissue. Dual-frequency images were obtained from a phantom simulating liver and also from 200 g of porcine liver in a saline tank. Prior to image reconstruction, it was necessary to apply a correction to the data to cancel the effects of stray capacitance within the electronics.

Investigation of causes of geometric distortion in 180 degrees and 360 degrees angular sampling in SPECT.

Abstract: To investigate geometric distortion when 180 degrees or 360 degrees angular sampling techniques are used in single photon emission computed tomography (SPECT), a study of point sources imaged at different positions in a water filled cylindrical phantom, and reconstructed using filtered back projection, was conducted. A simulation study, based upon a serial model of the system point spread function (PSF), was used to investigate the contributions of attenuation, spatial resolution and scatter on distortion of the reconstructed PSFs. To study the geometric distortion in transverse (x-y plane), coronal (x-z plane), and sagittal (y-z plane) sections, the ratios of the full widths at half maximum (FWHM) and full widths at tenth maximum (FWTM) in the x/y, x/z, and y/z directions were calculated for the real and simulated PSFs. These results showed that, in an attenuating medium, there is more distortion of point sources into ovals for 180 degrees than for 360 degrees sampling. The simulation study indicated that the primary cause of geometrical distortion in SPECT studies, is the inconsistency of projections due to variable attenuation and spatial resolution. The impact of scatter on geometric distortion was small as measured by the ratios of FWHMs and FWTMs for PSFs. Attenuation correction applied to acquired PSFs significantly reduced geometric distortion in both 180 degrees and 360 degrees studies. To investigate distortion in extended objects, an Iowa heart phantom was placed inside an Alderson body phantom and 201Tl heart SPECT studies acquired. The phantom images confirmed the conclusion that in transverse sections of 360 degrees studies with arithmetic averaging of opposite views, geometric distortion is reduced compared to 180 degrees. The coronal and sagittal sections were equally distorted in both, the 180 degrees and 360 degrees studies, and the 180 degrees studies yielded better contrast.

Preliminary validation of the opposing view method for quantitative gamma camera imaging

Abstract: We perform gamma cameraimaging to generate data for estimation of internal radiation dose in our radioimmunotherapy candidates. Because of the inability of single photon emission computed tomography(SPECT) to account for patient attenuation variability without serious error, quantitative planar imaging was performed to estimate the radioactive content of normal organs. We undertook the following studies to further validate this method. A realistic fillable human phantom was used to determine the accuracy of I‐131 filled organ estimation. A transmission scan of the unfilled phantom was produced with an I‐131 filled flat flood source. Anterior and posterior planar images of the filled organs were acquired with region of interest determination of the activity in the organ. Correction by the attenuation factor and a cameracalibration factor yielded the MBq in the organ. The procedure was also performed in a simple phantom. Three dogs were imaged and sacrificed to validate the technique i n v i v o. A high degree of accuracy in estimation of organ radioactive content was found to be present using the phantom and dog models. Use of this method requires further validation but provides a solid basis for estimation of internal radiationdosimetry in radioimmunotherapy planning.

Calibration phantom for computer tomography system

Abstract: A calibration phantom for the quantitative computer tomography (QCT) system for bone or other tissue measurement in which a series of graduated reference solutions are retained within cavities formed in a translucent member having x-ray attenuation characteristics closely approximate to human tissue. In preferred embodiment, the reference solutions are sealed under pressure in direct contact with the material forming the base of the phantom. Only a very thin wall separates the solution from the upper and lower surfaces of the phantom. In addition, the cavities are closely adjacent one another. As a result, phantoms constructed in accordance with this invention minimize the size and mass of the phantom and thus minimize x-ray beam hardening, scatter and image are the facts.

Three-dimensional magnetic resonance image distortion correction method and system

Abstract: A method and system in Nuclear Magnetic Resonance (NMR) medical imaging systems corrects for three-dimensional distortions arising from the apparatus and patient specific distortions using a phantom and a helmet, both of which have fiducial markers in a three-dimensional matrix. The positions of the phantom and helmet fiducial markers are automatically detected and compared in a computer system which uses image transform algorithms to correct for the various distortions.

Anthropomorphic cardiac ultrasound phantom

Abstract: A phantom which simulates the human cardiac anatomy for applications in ultrasound imaging, ultrasound Doppler, and color-flow Doppler imaging is described. The phantom consists of a polymer left ventricle which includes a prosthetic mitral and aortic valve and is connected to a mock circulatory loop. Aerated tap water serves as a blood simulating fluid and ultrasound contrast medium within the circulatory loop. The left ventricle is housed in a Lexan ultrasound visualization chamber which includes ultrasound viewing ports and acoustic absorbers. A piston pump connected to the visualization chamber by a single port pumps degassed water within the chamber which in turn pumps the left ventricle. Real-time ultrasound images and Doppler studies measure flow patterns through the valves and within the left ventricle. >

Precise measurement of vertebral bone density using computed tomography without the use of an external reference phantom

Abstract: Bone density measurement by quantitative computed tomography (QCT) commonly uses an external reference phantom to decrease scan-to-scan and scanner-to-scanner variability. However, the peripheral location of these phantoms and other phantom variables is also responsible for a measurable degradation in accuracy and precision. Due to non-uniform artifacts such as beam hardening, scatter, and volume averaging, the ideal reference phantom should be as close to the target tissue as possible. This investigation developed and tested a computer program that uses paraspinal muscle and fat tissue as internal reference standards in an effort to eliminate the need for an external phantom. Because of their proximity, these internal reference tissues can be assumed to reflect more accurately the local changes in the x-ray spectra and scatter distribution at the target tissue. A user interactive computerized histogram plotting technique enabled the derivation of reproducible CT numbers for muscle, fat, and trabecular bone. Preliminary results indicate that the use of internal reference tissues with the histogram technique may improve reproducibility of scan-to-scan measurements as well as inter-scanner precision. Reproducibility studies on 165 images with intentional region-of-interest (ROI) mispositioning of 1.5, 2.5, or 3.5 mm yielded a precision of better than 1% for normals and 1% to 2% for osteoporotic patients—a twofold improvement over the precision from similar tests using the standard technique with an external reference phantom. Such improvements in precision are essential for QCT to be clinically useful as a noninvasive modality for measurement of the very small annual changes in bone mineral density.

Quantification techniques for dual-energy cardiac imaging.

Abstract: We have previously reported a motion immune dual-energy subtraction technique in which x-ray tube voltage and x-ray beam filtration are switched at 30 Hz between 60 kVp (2.0-mm Al filter) and 120 kVp (2.0-mm Al + 2.5-mm Cu filtration). In this paper we consider the suitability of these dual-energy images for quantitative measurements of iodine thickness and volume. Optimized iodine signal-to-noise ratio (S/N) was measured as a function of phantom thickness. Using a fixed mAs, the S/N of the dual-energy images was found to decrease by sevenfold as lucite thickness increased from 10 to 25 cm. For the same increase in lucite thickness S/N for time subtraction images decreased by fivefold. Image quality in two human volunteers was subjectively judged to be good. In order to quantitate physiological parameters such as ejection fraction and left ventricular volume, energy dependent corrections for scatter and veiling glare, beam hardening, detector nonuniformity, heel effect, and uncanceled bone signals were developed. Since the dual-energy technique does not completely cancel bone, a preinjection dual-energy subtraction image was used to estimate integrated bone contributions to iodine volume measurements. In a phantom measurement simulating exercise ventriculography, the known (Vk) and videodensitometrically measured (Vm) volumes of 19 mg/cm3 solution of iodine were related by Vm = 0.95 Vk + 1.50 cm3 (r greater than 0.99).

Energy-weighted acquisition of scintigraphic images using finite spatial filters.

Abstract: Energy weighted acquisition (EWA) is a technique for improving image contrast by correcting for some of the blurring effects of Compton scattering within the patient. We outline image formation theory as it applies to energy weighting and present a pre-processing implementation that acquires images with real-number energy-dependent weighting functions of finite spatial extent. The effect of scattered radiation on quantitative accuracy, with and without EWA, is demonstrated with sheet and point sources at various depths. A planar phantom and a clinical {sup 201}TI study demonstrate enhanced contrast and edge definition. The performance of EWA in SPECT is shown by {sup 99m}Tc and {sup 123}I phantom studies and a clinical {sup 125}I study.

A model of the peritoneal cavity for use in internal dosimetry.

Abstract: Several therapeutic and diagnostic techniques involve injection of radioactive material into the peritoneal cavity. Estimation of the radiation dose to the surface of the peritoneum or to surrounding organs is hampered by the lack of a suitable source region in the phantom commonly used for such calculations. We have modified the Fisher-Snyder phantom to include a region representing the peritoneal cavity which may be employed to estimate such radiation doses. A geometric model is described which is coordinated with the existing organ regions in the phantom. Specific absorbed fractions (derived by Monte Carlo techniques) for photon emissions originating within the cavity are listed. Photon S-values for several radionuclides which have been administered intraperitoneally are shown. Dose conversion factors for electrons irradiating the peritoneal cavity wall, from either a thin plane or volume source of activity within the cavity, are also given for several nuclides.

Magnetic movement of a brain thermoceptor.

Abstract: Hyperthermia has significant potential as an adjuvant form of brain tumor therapy. Current intracranial hyperthermia methods, however, are limited in their ability to control spatiotemporal thermal distribution. A stereotaxic magnetic movement system that may be capable of heating discrete regions of brain to a preselected temperature is described. With this system, a ferromagnetic object (referred to as a thermoceptor) is directed through the brain by an external drive magnet. Real time thermoceptor position is monitored with biplanar fluoroscopy and superimposed on a preoperative magnetic resonance imaging scan using a computer. Once in position, the thermoceptor can be inductively heated by externally generated radiofrequency signals. Experiments on the magnetic drive and imaging aspects of this system have been conducted in vitro and in vivo. Mechanical studies of cadaver dog brains revealed that a mean force of 0.07 +/- 0.03 N was required to move a 3-mm diameter sphere through brain at a speed of less than 1 cm/15 s. A cranial phantom with mechanical properties similar to brain was constructed of gelatin and Plexiglas. With the use of a "neck loop" design drive magnet with a maximum magnetic field strength of 0.10 T, a 3 x 3 mm cylindrical neodymium iron boron thermoceptor was smoothly directed through the phantom in two dimensions. Additional experiments were conducted with a larger drive magnet in five anesthetized dogs. Neodymium iron boron and samarium cobalt thermoceptors of various shapes and sizes were placed into the cerebral cortex through a burr hole, then directed with the drive magnet. Fluoroscopy was used to follow the thermoceptor movements.(ABSTRACT TRUNCATED AT 250 WORDS)

X-ray energy optimisation in computed microtomography.

Abstract: Expressions describing the absorbed dose and the number of incident photons necessary for the detection of a contrasting detail in x-ray transmission CT imaging of a circular phantom are derived as functions of the linear attenuation coefficients of the materials comprising the object and the detail. A shell of a different material can be included to allow simulation of CT imaging of the skulls of small laboratory animals. The equations are used to estimate the optimum photon energy in x-ray transmission computed microtomography. The optimum energy depends on whether the number of incident photons or the absorbed dose at a point in the object is minimised. For a water object of 300 mm diameter the two optimisation criteria yield optimum photon energies differing by an order of magnitude.

Improved control of image optical density with low-dose digital and conventional radiography in bedside imaging.

Abstract: The technical and diagnostic performance of simultaneously acquired low-dose (44% of standard dose) storage-phosphor digital radiographs (system resolution = 0.2 mm, 10 bits) were compared with those of standard-dose conventional bedside radiographs of the chest in 32 patients. The mean optical density (OD) of the lungs (800 measurements) was closer to the ideal density with digital radiography (1.45 OD +/- 0.20 [standard deviation] vs 1.75 OD +/- 0.53) and was less often outside the usable range (2.5% vs 42.5%). Receiver operating characteristic analysis for detection of simulated nodules and monitoring devices (nine readers, 4,608 observations) showed that digital radiography was superior to conventional radiography (P less than .05) for four of the nine readers and equivalent to conventional radiography for five readers. The authors concluded that digital radiography produces more consistent and ideal image density and performs at least as well as conventional radiography under phantom test conditions.

Labat lecture. Phantom limbs.

Abstract: A phantom limb is universally experienced after a limb has been amputated or its sensory roots have been destroyed. A complete break of the spinal cord also often leads to a phantom body below the level of the break. Furthermore, phantom breasts, genitals and other body areas occur in a substantial number of people after surgical removal or denervation of the body part. The most astonishing feature of a phantom limb (or other body area) is its incredible "reality" to the person. An examination of phantom limb phenomena has led to a new theory. It is proposed that we are born with a widespread neural network--the neuromatrix--for the body-self, which is subsequently modified by experience. The neuromatrix imparts a pattern--the neurosignature--on all inputs from the body, so that experiences of one's own body have a quality of self and are imbued with affective tone and cognitive meaning. The theory is presented with supporting evidence as well as implications for research.

Solitary pulmonary nodules: evaluation with a CT reference phantom.

Abstract: The Zerhouni computed tomographic (CT) reference phantom was used to study 112 solitary pulmonary nodules that were indeterminate with plain tomography. Of the 112 nodules, 33 were more attenuating than the reference phantom and 79 less attenuating. One patient with a previous endometrial malignancy had a pulmonary metastatic lesion that was more attenuating than the reference phantom, presumably due to microscopic calcification. The nodule in the other 32 cases was benign, as determined from follow-up studies of up to 4.5 years or by means of surgical sampling (two patients). Among the 79 nodules that were less attenuating than the reference phantom, 26 were malignant, 22 were benign, and 31 were followed up for up to 4.5 years with no evidence of malignancy. In this series, the CT reference phantom proved to be a useful adjuvant to plain tomography in patients whose nodules were uncalcified and had an indeterminate shape.

Tomographic image diagnostic method and apparatus including automatic ROI setting means

Abstract: In a tomographic image diagnostic apparatus, a region of interest is automatically set on a tomographic image by recognizing actual positions of a phantom based upon CT (computerized tomographic) values of the phantom. The phantom is made of a base portion having a first reference CT value and a plurality of rods each having a second reference CT value. The region of interest is defined by recognizing the gravity centers of these rods. Said apparatus comprises: image memory for storing image data of an object and a phantom made of a plurality of reference substances and a base portion; a storage for previously storing a first reference CT value used for the base portion of the phantom, and also a second reference CT value used for each of the reference substances; a first detector for detecting a position of the phantom by comparing an actually measured first CT value of the base portion with the first reference CT value previously stored in the storage; a processor for performing both profile and filtering processes on the detected position of the phantom so as to obtain processed positional data of the phantom; a second detector for detecting positions of the reference substances contained in phantom by comparing an actually measured second CT value of each of the reference substances with the second reference CT value previously stored in the storage; and, a defining units for automatically defining a position of a region of interest with respect to the tomographic image data based upon the detected positions of the reference substances.