Biomedical subjects

Nobutoku Motomura

Publications and source records attributed to Nobutoku Motomura.

8 recordsLinked to original sources

PubMed2006

Development of a collimator blurring compensation method using fine angular sampling projection data in SPECT.

Due to the collimator aperture, spatial resolution of SPECT data varies with source-to-detector distance. Since the radius of detector rotation is bigger when scanning larger patients, spatial resolution is degraded in these cases. Emitted gamma rays travel not only along the central axis of the collimator hole but also off-axis due to the collimator aperture. However, an off-axis ray at one angle would be a central-axis ray at another angle; therefore, raw projection data at one angle can be thought of as an ensemble of central-axis rays collected from a small arc equal to the collimator aperture. Thus, fine angular sampling can compensate for collimator blurring. By using a sampling pitch of less than half the collimator aperture angle, compensation was performed by subtracting the weighted sum of the projection data from the raw projection data. Collimator geometry and detector rotation radius determined the weighting function. Cylindrical phantom with four different-sized rods and torso phantom for Tl-201 cardiac SPECT simulation were used for evaluation. Aperture angle of the collimator was 7 degrees. Projection sampling pitch was 2 degrees. In both phantom studies, the proposed method showed improvement in contrast and reduction of partial volume effect, thereby indicating that the proposed method can compensate adequately for image blurring caused by the collimator aperture.

Artifacts↗

PubMed2005

[Effectiveness of deep breath-hold SPECT in torso area: examination concerning improvement of resolution].

Because SPECT images are acquired under normal respiration, the respiratory motion induces artifacts and decreases resolution. In this study we developed a novel method of acquiring SPECT data during deep inhalation breath-hold (BrST) and assessed its efficacy in reducing motion artifacts and improving resolution. Reproducibility studies found that variations in SPECT image homogeneity were reduced using the BrST method to within a clinically non-problematic range. An experiment using a custom-built respiration phantom showed almost complete elimination of motion artifacts and significant improvement in resolution using the BrST method. Clinical assessment confirmed a significant reduction in motion artifacts along with the improvement in resolution. The BrST method enabled visualization of lesions that previously had been impossible to detect by standard acquisition under normal respiration. The BrST method is expected to both significantly reduce motion artifacts and improve resolution.

Artifacts↗

PubMed2005

Evaluating performance of a pixel array semiconductor SPECT system for small animal imaging.

OBJECTIVES: Small animal imaging has recently been focused on basic nuclear medicine. We have designed and built a small animal SPECT imaging system using a semiconductor camera and a newly designed collimator. We assess the performance of this system for small object imaging. METHODS: We employed an MGC 1500 (Acrorad Co.) camera including a CdTe semiconductor. The pixel size was 1.4 mm/pixel. We designed and produced a parallel-hole collimator with 20-mm hole length. Our SPECT system consisted of a semiconductor camera with the subject holder set on an electric rotating stage controlled by a computer. We compared this system with a conventional small animal SPECT system comprising a SPECT-2000H scanner with four Anger type cameras and pinhole collimators. The count rate linearity for estimation of the scatter was evaluated for a pie-chart phantom containing different concentrations of 99mTc. We measured the FWHM of the 99mTc SPECT line source along with scatter. The system volume sensitivity was examined using a flood source phantom which was 35 mm long with a 32-mm inside diameter. Additionally, an in vivo myocardial perfusion SPECT study was performed with a rat. RESULTS: With regards to energy resolution, the semiconductor camera (5.6%) was superior to the conventional Anger type camera (9.8%). In the count rate linearity evaluation, the regression lines of the SPECT values were y = 0.019x + 0.031 (r2 = 0.999) for our system and y = 0.018x + 0.060 (r2 = 0.997) for the conventional system. Thus, the scatter count using the semiconductor camera was less than that using the conventional camera. FWHMs of our system and the conventional system were 2.9 +/- 0.1 and 2.0 +/- 0.1 mm, respectively. Moreover, the system volume sensitivity of our system [0.51 kcps/(MBq/ ml)/cm] was superior to that of the conventional system [0.44 kcps/(MBq/ml)/cm]. Our system provided clear images of the rat myocardium, sufficient for practical use in small animal imaging. CONCLUSIONS: Our SPECT system, utilizing a semiconductor camera, permits high quantitative analysis by virtue of its low scatter radiation and high sensitivity. Therefore, this system may contribute to molecular imaging of small animals and basic medical research.

Animals↗

PubMed2004

Attenuation correction using asymmetric fanbeam transmission CT on two-head SPECT system.

For transmission computed tomography (TCT) systems using a centered transmission source with a fan-beam collimator, the transmission projection data are truncated. To achieve sufficiently large imaging field of view (FOV), we have designed the combination of an asymmetric fan-beam (AsF) collimator and a small uncollimated sheet-source for TCT, and implemented AsF sampling on a two-head SPECT system. The purpose of this study is to evaluate the feasibility of our TCT method for quantitative emission computed tomography (ECT) in clinical application. Sequential Tc-99m transmission and Tl-201 emission data acquisition were performed in a cardiac phantom (30 cm in width) with a myocardial chamber and a patient study. Tc-99m of 185 MBq was used as the transmission source. Both the ECT and TCT images were reconstructed with the filtered back-projection method after scatter correction with the triple energy window (TEW) method. The attenuation corrected transaxial images were iteratively reconstructed with the Chang algorithm utilizing the attenuation coefficient map computed from the TCT data. In this AsF sampling geometry, an imaging FOV of 50 cm was yielded. The attenuated regions appeared normal on the scatter and attenuation corrected (SAC) images in the phantom and patient study. The good quantitative accuracy on the SAC images was also confirmed by the measurement of the Tl-201 radioactivity in the myocardial chamber in the phantom study. The AsF collimation geometry that we have proposed in this study makes it easy to realize TCT data acquisition on the two-head SPECT system and to perform quantification on Tl-201 myocardial SPECT.

Aged↗

PubMed2004

Attenuation correction using combination of a parallel hole collimator and an uncollimated non-uniform line array source.

Attenuation correction is very important for quantitative SPECT imaging. We designed an uncollimated non-uniform line array source (non-uniform LAS) for attenuation correction based on transmission computed tomography (TCT) using Tc-99m and compared its performance with an uncollimated uniform line array source (uniform LAS) in a thorax phantom study. This non-uniform LAS was attached to one camera head of a dual-head gamma camera, and transmission data were acquired with another camera head with a low-energy, general purpose, parallel-hole collimator at 50 cm-distance apart from the source. The modified TEW using a subtraction factor of 1.0 was employed to correct scattered Tc-99m photons for transmission data. In the phantom experiment, eight TCT data were acquired with the scanning time changed from 2 minutes to 20 minutes for each LAS. The Tc-99m attenuation coefficient (mu) maps with the non-uniform LAS and uniform LAS improved the statistical count variation in the mediastinum filled with water as the scanning time got longer. The Tc-99m mu-map with the non-uniform LAS and 6 minutes of scanning time had equal quality at the center of the thorax phantom to that with the uniform LAS and 16 minutes of scanning time. In conclusion, for the TCT imaging with combination of the parallel hole collimator and uncollimated Tc-99m external source the non-uniform LAS can reduce the Tc-99m radioactivity or the TCT scanning time compared with the uniform LAS.

Humans↗

PubMed2004

Accurate scatter correction for transmission computed tomography using an uncollimated line array source.

We investigated scatter correction in transmission computed tomography (TCT) imaging by the combination of an uncollimated transmission source and a parallel-hole collimator. We employed the triple energy window (TEW) as the scatter correction and found that the conventional TEW method, which is accurate in emission computed tomography (ECT) imaging, needs some modification in TCT imaging based on our phantom studies. In this study a Tc-99m uncollimated line array source (area: 55 cm x 40 cm) was attached to one camera head of a dual-head gamma camera as a transmission source, and TCT data were acquired with a low-energy, general purpose (LEGP), parallel-hole collimator equipped on the other camera head. The energy spectra for 140 keV-photons transmitted through various attenuating material thicknesses were measured and analyzed for scatter fraction. The results of the energy spectra showed that the photons transmitted had an energy distribution that constructs a scatter peak within the 140 keV-photopeak energy window. In TCT imaging with a cylindrical water phantom, the conventional TEW method with triangle estimates (subtraction factor, K = 0.5) was not sufficient for accurate scatter correction (micro = 0.131 cm(-1) for water), whereas the modified TEW method with K = 1.0 gave the accurate attenuation coefficient of 0.153 cm(-1) for water. For the TCT imaging with the combination of the uncollimated Tc-99m line array source and parallel hole collimator, the modified TEW method with K = 1.0 gives the accurate TCT data for quantitative SPECT imaging in comparison with the conventional TEW method with K = 0.5.

Equipment Failure Analysis↗

PubMed2004

Truncation correction of fan beam transmission data for attenuation correction using parallel beam emission data on a 3-detector SPECT system.

BACKGROUND: When the simultaneous transmission computed tomography (TCT)/single photon emission CT (SPECT) acquisition protocol is applied to myocardial studies using a 3-detector SPECT, the narrow effective field of view of a fan beam collimator used for TCT acquisition may cause truncation artifacts on TCT images. In this paper, we propose a new method of correcting for the truncation of TCT. METHODS: The truncated parts of the TCT projection data are corrected using quadratic functions, based on the properties that the integral of non-truncated TCT projection data is constant at any projection angle and the position of the centre of gravity is focused on a fixed point. The usefulness of our method was investigated in phantom and human studies using a 3-detector SPECT equipped with one cardiac fan beam collimator for TCT and two parallel beam collimators for SPECT. We used Tl as a tracer for SPECT and Tc as an external source for TCT. RESULTS: The phantom and human studies showed that our method can adequately correct for the truncation of TCT data acquired using a fan beam collimator in a 3-detector SPECT, as long as there is no truncation in SPECT data. CONCLUSION: Our method appears to be useful for improving the SPECT images obtained using simultaneous TCT/SPECT acquisition in a 3-detector SPECT. However, further studies will be necessary to establish the clinical usefulness of this method.

Algorithms↗

PubMed2002

Attenuation correction of myocardial SPECT images with X-ray CT: effects of registration errors between X-ray CT and SPECT.

PURPOSE: Attenuation correction with an X-ray CT image is a new method to correct attenuation on SPECT imaging, but the effect of the registration errors between CT and SPECT images is unclear. In this study, we investigated the effects of the registration errors on myocardial SPECT, analyzing data from a phantom and a human volunteer. METHODS: Registerion (fusion) of the X-ray CT and SPECT images was done with standard packaged software in three dimensional fashion, by using linked transaxial, coronal and sagittal images. In the phantom study, an X-ray CT image was shifted 1 to 3 pixels on the x, y and z axes, and rotated 6 degrees clockwise. Attenuation correction maps generated from each misaligned X-ray CT image were used to reconstruct misaligned SPECT images of the phantom filled with 201Tl. In a human volunteer, X-ray CT was acquired in different conditions (during inspiration vs. expiration). CT values were transferred to an attenuation constant by using straight lines; an attenuation constant of 0/cm in the air (CT value = -1,000 HU) and that of 0.150/cm in water (CT value = 0 HU). For comparison, attenuation correction with transmission CT (TCT) data and an external gamma-ray source (99mTc) was also applied to reconstruct SPECT images. RESULTS: Simulated breast attenuation with a breast attachment, and inferior wall attenuation were properly corrected by means of the attenuation correction map generated from X-ray CT. As pixel shift increased, deviation of the SPECT images increased in misaligned images in the phantom study. In the human study, SPECT images were affected by the scan conditions of the X-ray CT. CONCLUSION: Attenuation correction of myocardial SPECT with an X-ray CT image is a simple and potentially beneficial method for clinical use, but accurate registration of the X-ray CT to SPECT image is essential for satisfactory attenuation correction.

Artifacts↗