Biomedical subjects

Kyeong Min Kim

Publications and source records attributed to Kyeong Min Kim.

11 recordsLinked to original sources

PubMed2006

Quantitative mapping of basal and vasareactive cerebral blood flow using split-dose 123I-iodoamphetamine and single photon emission computed tomography.

A new method has been developed for diffusible tracers, to quantify CBF at rest and after pharmacological stress from a single session of dynamic scans with dual bolus administration of a radiotracer. The calculation process consisted of three steps, including the procedures of incorporating background radioactivity contaminated from the previous scan. Feasibility of this approach was tested on clinical SPECT studies on 16 subjects. Two sequential SPECT scans, 30 min apart, were carried out on each subject, after each of two split-dose administrations of 111 MBq IMP. Of these, 11 subjects received acetazolamide at 10 min before the second IMP injection. Additional PET scans were also carried out on 6 subjects on a separate day, at rest and after acetazolamide administration. The other 5 subjects were scanned only at rest during the whole study period. Quantitative CBF obtained by this method was in a good agreement with those determined with PET (y(ml/100 g/min)=1.07x(ml/100 g/min)-1.14, r=0.94). Vasareactivity was approximately 40% over the whole cerebral area on healthy controls, which was consistent with a literature value. Reproducibility of CBF determined in the rest-rest study was 1.5+/-5.7%. Noise enhancement of CBF images, particularly the second CBF, was reduced, providing reasonable image quality. Repeat assessment of quantitative CBF from a single session of scans with split-dose IMP is accurate, and may be applied to clinical research for assessing vascular reactivity in patients with chronic cerebral vascular disease.

Aged↗

PubMed2006

Widespread decrease of nicotinic acetylcholine receptors in Parkinson's disease.

OBJECTIVE: Nicotinic acetylcholine receptors have close interactions with the dopaminergic system and play critical roles in cognitive function. The purpose of this study was to compare these receptors between living PD patients and healthy subjects. METHODS: Nicotinic acetylcholine receptors were imaged in 10 nondemented Parkinson's disease patients and 15 age-matched healthy subjects using a single-photon emission computed tomography ligand [(123)I]5-iodo-3-[2(S)-2-azetidinylmethoxy]pyridine. Using an arterial input function, we measured the total distribution volume (V; specific plus nondisplaceable), as well as the delivery (K(1)). RESULTS: Parkinson's disease showed a widespread significant decrease (approximately 10%) of V in both cortical and subcortical regions without a significant change in K(1). INTERPRETATION: These results indicate the importance of extending the study to demented patients.

Aged↗

PubMed2006

Use of a compact pixellated gamma camera for small animal pinhole SPECT imaging.

OBJECTIVES: Pinhole SPECT which permits in vivo high resolution 3D imaging of physiological functions in small animals facilitates objective assessment of pharmaceutical development and regenerative therapy in pre-clinical trials. For handiness and mobility, the miniature size of the SPECT system is useful. We developed a small animal SPECT system based on a compact high-resolution gamma camera fitted to a pinhole collimator and an object-rotating unit. This study was aimed at evaluating the basic performance of the detection system and the feasibility of small animal SPECT imaging. METHODS: The gamma camera consists of a 22 x 22 pixellated scintillator array of 1.8 mm x 1.8 mm x 5 mm NaI(Tl crystals with 0.2-mm gap between the crystals coupled to a 2" flat panel position-sensitive photomultiplier tube (Hamamatsu H8500) with 64 channels. The active imaging region of the camera was 43.8 mm x 43.8 mm. Data acquisition is controlled by a personal computer (Microsoft Windows) through the camera controller. Projection data over 360 degrees for SPECT images are obtained by synchronizing with the rotating unit. The knife-edge pinhole collimators made of tungsten are attached on the camera and have 0.5-mm and 1.0-mm apertures. The basic performance of the detection system was evaluated with 99mTc and 201Tl solutions. Energy resolution, system spatial resolution and linearity of count rate were measured. Rat myocardial perfusion SPECT scans were sequentially performed following intravenous injection of 201TlCl. Projection data were reconstructed using a previously validated pinhole 3D-OSEM method. RESULTS: The energy resolution at 140 keV was 14.8% using a point source. The system spatial resolutions were 2.8-mm FWHM and 2.5-mm FWHM for 99mTc and 201Tl line sources, respectively, at 30-mm source distance (magnification factor of 1.3) using a 1.0-mm pinhole. The linearity between the activity and count rate was good up to 10 kcps. In a rat study, the left ventricular walls were clearly visible in all scans. CONCLUSIONS: We developed a compact SPECT system using compact gamma camera for small animals and evaluated basic physical performances. The present system may be of use for quantitation of biological functions such as myocardial blood flow in small animals.

Animals↗

PubMed2005

Development of a practical image-based scatter correction method for brain perfusion SPECT: comparison with the TEW method.

PURPOSE: An image-based scatter correction (IBSC) method was developed to convert scatter-uncorrected into scatter-corrected SPECT images. The purpose of this study was to validate this method by means of phantom simulations and human studies with 99mTc-labeled tracers, based on comparison with the conventional triple energy window (TEW) method. METHODS: The IBSC method corrects scatter on the reconstructed image I(mub)AC with Chang's attenuation correction factor. The scatter component image is estimated by convolving I(mub)AC with a scatter function followed by multiplication with an image-based scatter fraction function. The IBSC method was evaluated with Monte Carlo simulations and 99mTc-ethyl cysteinate dimer SPECT human brain perfusion studies obtained from five volunteers. The image counts and contrast of the scatter-corrected images obtained by the IBSC and TEW methods were compared. RESULTS: Using data obtained from the simulations, the image counts and contrast of the scatter-corrected images obtained by the IBSC and TEW methods were found to be nearly identical for both gray and white matter. In human brain images, no significant differences in image contrast were observed between the IBSC and TEW methods. CONCLUSION: The IBSC method is a simple scatter correction technique feasible for use in clinical routine.

Algorithms↗

PubMed2005

Rapid quantitative measurement of CMRO(2) and CBF by dual administration of (15)O-labeled oxygen and water during a single PET scan-a validation study and error analysis in anesthetized monkeys.

Cerebral blood flow (CBF) and rate of oxygen metabolism (CMRO(2)) may be quantified using positron emission tomography (PET) with (15)O-tracers, but the conventional three-step technique requires a relatively long study period, attributed to the need for separate acquisition for each of (15)O(2), H(2)(15)O, and C(15)O tracers, which makes the multiple measurements at different physiologic conditions difficult. In this study, we present a novel, faster technique that provides a pixel-by-pixel calculation of CBF and CMRO(2) from a single PET acquisition with a sequential administration of (15)O(2) and H(2)(15)O. Experiments were performed on six anesthetized monkeys to validate this technique. The global CBF, oxygen extraction fraction (OEF), and CMRO(2) obtained by the present technique at rest were not significantly different from those obtained with three-step method. The global OEF (gOEF) also agreed with that determined by simultaneous arterio-sinus blood sampling (gOEF(A-V)) for a physiologically wide range when changing the arterial PaCO(2) (gOEF=1.03gOEF(A-V)+0.01, P<0.001). The regional values, as well as the image quality were identical between the present technique and three-step method for CBF, OEF, and CMRO(2). In addition, a simulation study showed that error sensitivity of the present technique to delay or dispersion of the input function, and the error in the partition coefficient was equivalent to that observed for three-step method. Error sensitivity to cerebral blood volume (CBV) was also identical to that in the three-step and reasonably small, suggesting that a single CBV assessment is sufficient for repeated measures of CBF/CMRO(2). These results show that this fast technique has an ability for accurate assessment of CBF/CMRO(2) and also allows multiple assessment at different physiologic conditions.

Algorithms↗

PubMed2004

A new reconstruction strategy for image improvement in pinhole SPECT.

Pinhole single-photon emission computed tomography (SPECT) is able to provide information on the biodistribution of several radioligands in small laboratory animals, but has limitations associated with non-uniform spatial resolution or axial blurring. We have hypothesised that this blurring is due to incompleteness of the projection data acquired by a single circular pinhole orbit, and have evaluated a new strategy for accurate image reconstruction with better spatial resolution uniformity. A pinhole SPECT system using two circular orbits and a dedicated three-dimensional ordered subsets expectation maximisation (3D-OSEM) reconstruction method were developed. In this system, not the camera but the object rotates, and the two orbits are at 90 degrees and 45 degrees relative to the object's axis. This system satisfies Tuy's condition, and is thus able to provide complete data for 3D pinhole SPECT reconstruction within the whole field of view (FOV). To evaluate this system, a series of experiments was carried out using a multiple-disk phantom filled with 99mTc solution. The feasibility of the proposed method for small animal imaging was tested with a mouse bone study using 99mTc-hydroxymethylene diphosphonate. Feldkamp's filtered back-projection (FBP) method and the 3D-OSEM method were applied to these data sets, and the visual and statistical properties were examined. Axial blurring, which was still visible at the edge of the FOV even after applying the conventional 3D-OSEM instead of FBP for single-orbit data, was not visible after application of 3D-OSEM using two-orbit data. 3D-OSEM using two-orbit data dramatically reduced the resolution non-uniformity and statistical noise, and also demonstrated considerably better image quality in the mouse scan. This system may be of use in quantitative assessment of bio-physiological functions in small animals.

Algorithms↗

PubMed2004

Effect of scatter correction on the compartmental measurement of striatal and extrastriatal dopamine D2 receptors using [123I]epidepride SPET.

Prior studies with anthropomorphic phantoms and single, static in vivo brain images have demonstrated that scatter correction significantly improves the accuracy of regional quantitation of single-photon emission tomography (SPET) brain images. Since the regional distribution of activity changes following a bolus injection of a typical neuroreceptor ligand, we examined the effect of scatter correction on the compartmental modeling of serial dynamic images of striatal and extrastriatal dopamine D(2) receptors using [(123)I]epidepride. Eight healthy human subjects [age 30+/-8 (range 22-46) years] participated in a study with a bolus injection of 373+/-12 (354-389) MBq [(123)I]epidepride and data acquisition over a period of 14 h. A transmission scan was obtained in each study for attenuation and scatter correction. Distribution volumes were calculated by means of compartmental nonlinear least-squares analysis using metabolite-corrected arterial input function and brain data processed with scatter correction using narrow-beam geometry micro (SC) and without scatter correction using broad-beam micro (NoSC). Effects of SC were markedly different among brain regions. SC increased activities in the putamen and thalamus after 1-1.5 h while it decreased activity during the entire experiment in the temporal cortex and cerebellum. Compared with NoSC, SC significantly increased specific distribution volume in the putamen (58%, P=0.0001) and thalamus (23%, P=0.0297). Compared with NoSC, SC made regional distribution of the specific distribution volume closer to that of [(18)F]fallypride. It is concluded that SC is required for accurate quantification of distribution volumes of receptor ligands in SPET studies.

Adult↗

PubMed2003

Dependency of energy and spatial distributions of photons on edge of object in brain SPECT.

OBJECTIVES: Accurate mu maps are important for quantitative image reconstruction in SPECT. The Compton scatter energy window (CSW) technique has been proposed to define the outline of objects. In this technique, a lower energy window image is acquired in addition to the main photo-peak energy window. The image of the lower energy window is used to estimate the edge of the scanned object to produce a constant attenuation map. The aim of this study was to investigate the dependency of CSW on the spatial and energy distribution of radioisotope to predict the edges of objects. METHODS: Two particular cases of brain study were considered, namely uniform distribution and non-uniform distribution using Monte Carlo simulation and experiments with uniform cylindrical phantom and hotspot phantom. The phantoms were filled with water and a radioactive solution of 99mTc. For each phantom, 20%, 30%, 40% and 50% thresholds of the mean profile were applied to estimate Ewt, the energy window for minimum difference between the estimated and true edge of objects. RESULTS: The Ewt's were 100-120 keV with a 40% threshold and 92-114 keV with a 30% threshold for uniform and hotspot phantoms, respectively. CONCLUSIONS: Edge of the objects with CSW technique varies with energy window and thresholds. Careful setting of the energy window is required to use the CSW technique.

Algorithms↗

PubMed2003

A theoretical model of oxygen delivery and metabolism for physiologic interpretation of quantitative cerebral blood flow and metabolic rate of oxygen.

The coupling of cerebral blood flow (CBF) and metabolic rate of oxygen (CMRO2) during physiologic and pathophysiologic conditions remains the subject of debate. In the present study, we have developed a theoretical model for oxygen delivery and metabolism, which describes the diffusion of oxygen at the capillary-tissue interface and the nonlinear nature of hemoglobin (Hb) affinity to oxygen, allowing a variation in simple-capillary oxygen diffusibility, termed "effective oxygen diffusibility (EOD)." The model was used to simulate the relationship between CBF and CMRO2, as well as oxygen extraction fraction (OEF), when various pathophysiologic conditions were assumed involving functional activation, ischemia, hypoxia, anemia, or hypo- and hyper-capnic CBF variations. The simulations revealed that, to maintain CMRO2 constant, a variation in CBF and Hb required active change in EOD. In contrast, unless the EOD change took place, the brain allowed small but significant nonlinear change in CMRO2 directly dependent upon oxygen delivery. Application of the present model to quantitative neuroimaging of CBF and CMRO2 enables us to evaluate the biologic response at capillary level other than Hb- and flow-dependent properties of oxygen transport and may give us another insight regarding the physiologic control of oxygen delivery in the human brain.

Biological Transport↗

PubMed2003

Contribution of scatter and attenuation compensation to SPECT images of nonuniformly distributed brain activities.

UNLABELLED: Correction of scatter and attenuation is essential for quantitative SPECT. In this work, we evaluated the accuracy gained from a method of transmission-dependent convolution subtraction (TDCS) in the quantitation of activity that is highly concentrated in the striatum (STR). METHODS: SPECT data were acquired from an (123)I-containing phantom with a constant activity in the STR but differing background (BKG) activities, so as to simulate various STR/BKG ratios (19.7:1, 9.7:1, 4.8:1, 1.9:1, and 1:1). In a study of healthy humans (n = 6), a transmission scan followed by an emission scan was performed 24 h after injection of (123)I-2beta-carbomethoxy-3beta-(4-iodophenyl)-tropane ((123)I-beta-CIT). All SPECT data was reconstructed with ordered-subset expectation maximization. TDCS was applied for scatter correction. Values of activity in the STR and occipital lobe (for BKG) were used to calculate binding potential V(3)" (= [STR - BKG]/BKG). The effect of SPECT collimator dependency on scatter correction was also evaluated for 6 collimators from 3 different SPECT cameras in the phantom experiment. RESULTS: Scatter correction in the phantom experiment increased the measured values of STR activity (36.2%), resulting in a substantial increase in V(3)" (66.1%). Scatter and attenuation corrections with recovery correction showed an overall bias of -7.3% for the STR, -4.0% for BKG activity, and -7.8% for V(3)". TDCS corrections of phantom activities were relatively uniform for the 6 different collimators, with variabilities of <5.5% for the STR and <3.0% for BKG activities. TDCS correction of human (123)I-beta-CIT images was of a similar, although slightly larger, magnitude than for the phantom data, with increased V(3)" values of 9.4 +/- 2.3 and 4.9 +/- 0.6, with and without scatter correction, respectively. CONCLUSION: The TDSC method significantly improved the accuracy of SPECT images with a nonuniform distribution of activity highly concentrated in central regions. The value of V(3)" was significantly increased in phantom and human data, with most of the improvement derived from an increase in STR activity. This scatter correction method was approximately equally useful with data from the 6 different collimators and is recommended for more accurate quantitation of nonuniformly distributed brain activities.

Adult↗

PubMed2002

Evaluation of a commercial PET tomograph-based system for the quantitative assessment of rCBF, rOEF and rCMRO2 by using sequential administration of 15O-labeled compounds.

The purpose of this study was to develop a reliable and practical strategy that generates quantitative CBF and OEF maps accurately from PET data sets obtained with 15O-tracers. Sequential sinogram data sets were acquired after the administration of 15O-tracers, and combined single-frame images were obtained. The delay time between sampled input function and the brain was estimated from the H2(15)O study with the whole brain and the arterial time-activity curves (TACs). The whole-brain TACs were obtained from the reconstructed images (image-base method) and the sinogram data (sinogram-base method). Six methods were also evaluated for the dead-time and decay correction procedures in the process of generating a single-frame image from the dynamic sinogram. The estimated delay values were similar with both the sinogram-based and image-based methods. A lumped correction factor to a previously added single-frame sinogram caused an underestimation of CBF, OEF and CMRO2 by 16% at maximum, as compared with the correction procedure for a short sinogram. This suggested the need for a dynamic acquisition of a sinogram with a short interval. The proposed strategy provided an accurate quantification of CBF and OEF by PET with 15O-tracers.

Adult↗