Biomedical subjects

Keiichi Matsumoto

Publications and source records attributed to Keiichi Matsumoto.

18 recordsLinked to original sources

PubMed2006

[Comparison of noise equivalent count rate and image quality for two-dimensional and three-dimensional PET scans].

The aim of this study was to investigate the correlation between noise equivalent count (NEC) rates and the signal-to-noise ratio (S/N) in reconstructed images. The NEC rates were determined using uniform 20 cm and 70 cm tall, 20 cm diameter cylinders filled with 11C. The phantoms were scanned in both two-dimensional and three-dimensional modes. The reconstructed image noise was evaluated using FBP and OSEM algorithms (4 iterations and 8 subsets). The images were filtered to a final image resolution of 6.5 mm. From the reconstructed image sets, averages and standard deviations of images were generated, from which the average image S/N (=average/standard deviation) was calculated within an 18 cm central ROI. The S/N of a central slice and an end slice was compared with the NEC. The NEC was found to have a linear relationship to the image S/N of all slices, depending on differences in noise properties specific to the reconstruction algorithm. In two-dimensional mode, although the image S/N of the central slice and the edge slice showed a linear relationship with the NEC, in three-dimensional mode, the S/N of the central slice did not show a relationship with the NEC. The linear relationship was also found in both two- and three-dimensional acquisition modes, as well as for the different activity distributions. These results indicate that the NEC is not only a measure for comparing the count rate performance of imaging systems. However, an absolute evaluation is impossible to depend on reconstruction algorithm, slice number, and phantom type.

Algorithms↗

PubMed2006

[Accuracy of attenuation coefficient obtained by 137Cs single-transmission scanning in PET: comparison with conventional germanium line source].

UNLABELLED: Transmission scanning can be successfully performed with a Cs-137 single-photon-emitting point source for three-dimensional PET imaging. This method was effective for postinjection transmission scanning because of differences in physical energy. However, scatter contamination in the transmission data lowers measured attenuation coefficients. The purpose of this study was to investigate the accuracy of the influence of object scattering by measuring the attenuation coefficients on the transmission images. We also compared the results with the conventional germanium line source method. METHODS: Two different types of PET scanner, the SET-3000 G/X (Shimadzu Corp.) and ECAT EXACT HR(+) (Siemens/CTI) , were used. For the transmission scanning, the SET-3000 G/X and ECAT HR(+) were the Cs-137 point source and Ge-68/Ga-68 line source, respectively. With the SET-3000 G/X, we performed transmission measurement at two energy gate settings, the standard 600-800 keV as well as 500-800 keV. The energy gate setting of the ECAT HR(+) was 350-650 keV. The effects of scattering in a uniform phantom with different cross-sectional areas ranging from 201 cm(2) to 314 cm(2) to 628 cm(2) (apposition of the two 20 cm diameter phantoms) and 943 cm(2) (stacking of the three 20 cm diameter phantoms) were acquired without emission activity. First, we evaluated the attenuation coefficients of the two different types of transmission scanning using region of interest (ROI) analysis. In addition, we evaluated the attenuation coefficients with and without segmentation for Cs-137 transmission images using the same analysis. The segmentation method was a histogram-based soft-tissue segmentation process that can also be applied to reconstructed transmission images. RESULTS: In the Cs-137 experiment, the maximum underestimation was 3% without segmentation, which was reduced to less than 1% with segmentation at the center of the largest phantom. In the Ge-68/Ga-68 experiment, the difference in mean attenuation coefficients was stable with all phantoms. CONCLUSION: We evaluated the accuracy of attenuation coefficients of Cs-137 single-transmission scans. The results for Cs-137 suggest that scattered photons depend on object size. Although Cs-137 single-transmission scans contained scattered photons, attenuation coefficient error could be reduced using by the segmentation method.

Cesium Radioisotopes↗

PubMed2006

[Optimization of basic adjustable data-acquisition parameters for continuous three-dimensional whole-body FDG-PET].

UNLABELLED: The SET-3000 G/X (Shimadzu Corp., Kyoto, Japan) has a large aperture and functions as a three-dimensional (3D) dedicated PET scanner. However, the large number of line of responses in the SET-3000 G/X scanner creates a large volume of sinogram data and prolongs reconstruction time in iterative reconstruction. The purpose of this study was to optimize basic acquisition parameters (maximum ring difference and span) for sensitivity and spatial resolution for 3D whole-body (18)F-FDG PET. METHODS: Detector rings and image planes numbered 50 and 99, respectively. In sensitivity measurement, the maximum ring difference (MRD) was changed from 1 to 49. In the measurement of spatial resolution, the span was changed from 3 to 21. For sensitivity and spatial resolution measurements, the standard protocols defined by the Japan Radioisotope Association (JRIA) 1994 and the National Electrical Manufacturers Association (NEMA) NU 2-2001 were used. We also evaluated the corresponding image noise by placing identical ROI on the reconstructed images. RESULTS: The total sensitivity of MRD=49 was 85.7 cps/Bq/ml in a uniform phantom (15 cm diameter, 30 cm tall cylinder) filled with (18)F. This was approximately two times higher than MRD=13. The image noise in the center of the axial FOV decreased with increasing MRD. Spatial resolution was slightly decreased as MRD increased, but axial resolution deteriorated with a span of more than 11. CONCLUSION: Optimum basic data-acquisition parameters for whole-body (18)F-FDG PET were MRD 49 to obtain maximum sensitivity and span 9 to avoid decreasing spatial resolution. Additionally, it was concluded that the basic data-acquisition parameters should be carefully selected for 3D whole-body (18)F-FDG PET in order to maximize the efficiency of PET measurement.

Electronic Data Processing↗

PubMed2006

Performance of list mode data acquisition with ECAT EXACT HR and ECAT EXACT HR+ positron emission scanners.

Recently, list mode (event-by-event) data acquisition with positron emission tomography (PET) has been widely noticed because list mode acquisition is superior to conventional frame mode data acquisition in terms of (1) higher efficiency of data storage, (2) higher temporal resolution, and (3) higher flexibility of data manipulation. The aim of this study is to investigate the performance of list mode data acquisition with ECAT EXACT HR and HR+ PET scanners (CTI PET Systems) and its feasibility in clinical applications. A cylindrical phantom (16 cm in diameter and length) filled with a 11C solution for the HR and a 15O solution for the HR+ was scanned several times by varying the radioactivity concentration with the list mode and frame mode acquisitions. The scans were also carried out with a septa (2D mode) and without a septa (3D mode) in order to evaluate the effect of the interplane septa on the quality of the list mode data. The acquired list mode data were sorted into a sinogram and reconstructed using a filtered back-projection algorithm. The count rate performance of the list mode data was comparable to that of the frame mode data. However, the list mode acquisition could not be performed when the radioactivity concentration in the field-of-view was high (exceeding 24 kBq/ml for the 3D mode) due to a lack of sufficient transfer speed for sending data from the memory to hard disk. In order to estimate the pixel noise in a reconstructed image, ten replicated data sets were generated from one list mode data. The reconstructed images with the 3D mode had a signal-to-noise ratio that was more than 60% better than that of the image with the 2D mode. The file size of the generated list mode data was also evaluated. In the case of ECAT EXACT HR+ with the 3D list mode, the list mode data with a generated file size of 2.31 Mbytes/ s were generated for 37 MBq injections. Our results suggest that careful attention must be paid to the protocol of the list mode data acquisition in order to obtain the highest performance of the PET scanner.

Algorithms↗

PubMed2006

Performance characteristics of a new 3-dimensional continuous-emission and spiral-transmission high-sensitivity and high-resolution PET camera evaluated with the NEMA NU 2-2001 standard.

UNLABELLED: The SET-3000 G/X (clinical tomograph with high resolution and a large axial field of view) is a 3-dimensional (3D) (only) dedicated PET camera with germanium oxyorthosilicate (GSO) and bismuth germanate (BGO) scintillators. The main characteristic of the SET-3000 G/X PET scanner is 3D continuous-emission and spiral-transmission (CEST) scanning, yielding a reduction in whole-body scan time. We evaluated the physical performance of the SET-3000 G/X PET scanner with the National Electrical Manufacturers Association (NEMA) NU 2-2001 standard. METHODS: A GSO 3D emission scanner is combined with a BGO transmission scanner separated axially by a lead shield. In the GSO scanner, small and thick scintillators (2.45 x 5.1 x 30 mm(3)) are arranged in small blocks (23.1 x 52 mm) to achieve high resolution and a high counting rate. The detector ring has a large solid angle with a diameter of 664 mm and an axial coverage of 260 mm (50 rings). The transmission scanner consists of BGO block detectors with a diameter of 798 mm and an axial width of 23.1 mm and is equipped with a rotating (137)Cs point source of 740 MBq and a tungsten collimator. The low- and high-energy thresholds are set to 400 and 700 keV, respectively, in the emission system. The coincidence time window is set to 6 ns. In CEST acquisition, the patient couch moves continuously through the emission and transmission scanners in a 1-way motion. Emission coincidence data are acquired in the histogram mode with on-the-fly Fourier rebinning, and transmission single data are acquired with emission contamination correction. RESULTS: With the NEMA NU 2-2001 standard, the main performance results were as follows: the average (radial and tangential) transverse and axial spatial resolutions (full width at half maximum) at 1 cm and at 10 cm off axis were 3.49 and 5.04 mm and 4.48 and 5.40 mm, respectively; the average sensitivity for the 2 radial positions (0 and 10 cm) was 20.71 cps/kBq; the scatter fraction was 50%; the peak noise equivalent count rate was 62.3 kcps at 9.8 kBq/mL; and the peak random rate was 542.1 kcps at 37.6 kBq/mL. CONCLUSION: The new integrated SET-3000 G/X PET scanner has good overall performance, including high resolution and sensitivity, and has the potential of reducing whole-body acquisition time to less than 10 min while improving small-lesion detectability with a low radiation dose.

Equipment Design↗

PubMed2005

An intra-operative positron probe with background rejection capability for FDG-guided surgery.

For radio-guided surgery on tumors using F-18-FDG, detection of annihilation gamma photons emanating from other parts of the body produces background radiation counts and limits its use in clinical situations. To overcome this limitation, we have developed an intra-operative positron probe with background-rejection capability. The positron probe uses a phoswich detector composed of a plastic scintillator and a bismuth germinate (BGO). A positron from a positron emitter such as F-18 is detected by the plastic scintillator and emits annihilation photons. The BGO detects one of the annihilation photons while a photo-multiplier tube (PMT) detects scintillation photons from both scintillators. The decay time differences of these two scintillators are used to distinguish whether the event is a true event where a positron and a following annihilation photon are detected simultaneously, or a background event. In this configuration, only positrons can be selectively detected, even in an environment of high background gamma photon flux. Spatial resolution was 11-mm full width at half maximum (FWHM) 5 mm from the detector surface. Measured sensitivity for the F-18 point source was 2.6 cps/kBq 5 mm from the detector surface. The background count rate was less than 0.5 cps for a 20-cm diameter cylindrical phantom containing 37 MBq of F-18 solution measured on the phantom surface, while the positron count rate was almost linear over a range of approximately 6 kcps. These results indicate that our developed intra-operative positron probe is valuable for radio-guided surgery on tumors using F-18-FDG in a high flux of background annihilation gamma photons.

Background Radiation↗

PubMed2005

Investigation of single, random, and true counts from natural radioactivity in LSO-based clinical PET.

OBJECTIVE: Lutetium oxyorthosilicate (LSO) contains natural radioactivity that emits beta particles and three gamma photons simultaneously. These beta particles and gamma photons increase the single and random rates in a positron emission tomography (PET) system while a beta particle and gamma photon produced in the same decay of Lu-176 and detected by another detector can be beta-gamma coincidence true events. The purpose of this work is to measure the single, random, and true count rates due to the natural radioactivity in LSO and determine the optimum lower energy threshold level for an energy window in an LSO-based clinical PET. METHODS: First, we measured the energy spectra of these beta particles and gamma photons in LSO using a single crystal to obtain the basic data. Then, we measured single, random, and true count rates of an LSO-based clinical PET from the natural radioactivity as a function of the lower energy threshold. RESULTS: In the PET, single and random count rates due to the natural background activity were gradually decreased as the lower energy threshold level increased. The true count rates due to the beta-gamma coincidence were more than 10 kcps below a lower energy threshold of 250 keV. However, these true count rates due to the natural radioactivity in LSO can be decreased to less than 1 kcps at a lower energy threshold level set at more than 350 keV. CONCLUSION: With these considerations, in an LSO-based clinical PET, a lower energy threshold level set at above 350 keV is recommended.

Artifacts↗

PubMed2005

Accuracy of image fusion using a fixation device for whole-body cancer imaging.

OBJECTIVE: The purpose of this study was to evaluate the clinical feasibility of a simple image fusion technique with PET and CT images acquired separately using a vacuum cushion as a fixation device. SUBJECTS AND METHODS: Forty-four patients underwent whole-body PET using 18F-fluoro-2-deoxy-D-glucose (FDG) followed by CT with IV contrast material. The patients were carefully fixed in an individually molded cushion to provide the same positioning for both examinations. The PET and CT images were fused on a workstation by using the lower margin of the urinary bladder as a reference. The degree of misregistration was evaluated for the physiologic uptake of the liver and kidneys and for the pathologic uptake of lesions. RESULTS: The average deviation of the center point of the liver between the two images was 6.6 +/- 8.7 (SD) mm in the craniocaudal direction, 1.9 +/- 5.1 mm in the anteroposterior direction, and 2.3 +/- 7.0 mm in the right-left direction. This value in the craniocaudal direction was 4.7 +/- 8.7 mm in the right kidney and 4.0 +/- 8.8 mm in the left kidney. Above the diaphragm, the deviations of the center point of movable and static lesions were 11.7 +/- 3.4 mm and 10.4 +/- 5.3 mm, respectively. Below the diaphragm, those of movable and static lesions were 9.7 +/- 2.5 mm and 6.9 +/- 2.9 mm, respectively. CONCLUSION: Our preliminary data indicate that this technique is a simple and practical method for manual image fusion that may be acceptable in clinical settings.

Feasibility Studies↗

PubMed2004

What is the most appropriate scan timing for intraoperative detection of malignancy using 18F-FDG-sensitive gamma probe? Preliminary phantom and preoperative patient study.

PURPOSE: To evaluate the appropriate post-injection timing for hand-held-gamma-ray-detecting probe (GDP) scanning for the intraoperative detection of malignancy after preoperative F-18 FDG (FDG) injection. METHODS: Patient study with superficially located cancer was performed on three patients before operation by dual-phase whole-body PET at 2 and 6-7 hr post-injection of FDG (370 MBq), and by probe scanning from the skin at several points at 1, 3, 5, and 7 hr after FDG injection. TNRa (tumor-adjacent-normal ratio) and TNRc (tumor-contralateral-normal ratio) were calculated. Phantom study was also performed to determine basic GDP function. RESULTS: The patient study revealed that tumors showed constant TNRa (0.9-1.3) and TNRc (1.1-3.0) by GDP count rate, and that there was no tendency of an increase in TNRa with time. The standard deviations of GDP count rate were lower at 1-3 hr post-injection compared with those of delayed scans. While delayed PET showed an increase or no change in the tumor FDG uptake, the decrease of normal tissue FDG uptake was not adequate to create higher TNRs. The phantom study revealed that LN model showed TNRa of 1.7 or greater by GDP count rate (cps) when background contained no FDG, but that they showed TNRa of 1.3 or less when the background contained 4% of the LN FDG activity per ml. CONCLUSION: The present study suggests that higher FDG count rate of tumors at 1-3 hr postinjection would be more suitable for the gamma-probe detection compared with lower count rate at 6-7 hr delayed scans with wide standard deviations.

Adult↗

PubMed2004

[Reduction of reconstruction time and data volume of sinogram by angular compression for clinical three-dimensional whole body FDG-PET].

In positron emission tomography (PET), the large number of lines of responses in three-dimensional (3D) acquisition mode creates a high volume of sinogram data and increases reconstruction time in iterative reconstruction. We tried to decrease sinogram data volume by reducing the number of views using angular compression and then evaluated the accuracy of this mashed mode. Three methods were compared, conventional mode (CONV), X2 mashed mode (X2: two adjacent projection angles are added together), and X4 mashed mode (X4: four adjacent angles added). A point source of (18)F was used to measure spatial resolution. A hot spot phantom made of 6 hot spheres (10-38 mm in diameter) within water of 20 cm in diameter was scanned to evaluate the recovery coefficient (RC). A lung-heart-liver phantom made of homogeneous radioactive myocardium, a spherical hot mass in the lung (10 mm in diameter), and background activity in the liver was scanned to evaluate the homogeneity of the myocardial wall. The quality of the reconstructed images was evaluated in terms of the normalized mean square error (NMSE), Bull's eye map, profile curve, and peak value of the spherical hot mass. The reconstruction times of X2 and X4 were one-half and one-quarter, respectively, of that of CONV. In terms of spatial resolution, FWHM of CONV, X2, and X4 were, 4.26, 4.33, and 4.48 (mm) at the center, 4.81, 5.68, and 8.73 tangentially, and 8.01, 8.19, and 8.27 radially at R=200 mm, respectively. RC was similar for all methods. The NMSE values of X2 and X4 compared with CONV were 0.0003 and 0.0014, respectively. In the hot mass, these methods showed almost the same profile curves, although the peak value of X4 was only -1.95% less than that of CONV. Although the result of spatial resolution of X4 was slightly degraded, image quality and physical performance were good. Therefore, the X4 mashed mode used with angular compression was considered clinically useful.

Humans↗

PubMed2004

[Evaluation of noise equivalent count per line of response: new parameter for count statistics for PET systems].

OBJECTIVE: The noise equivalent count (NEC) is a useful, widely accepted method of evaluating image quality in positron emission tomography (PET) from the standpoint of effective count statistics. However, NEC cannot be used when different types of PET scanners are compared owing to the differences in slice thickness and field of view. Moreover, NEC should be treated differently depending on whether the 2D or 3D mode is used for a given PET scanner. A new parameter "Specific NEC," which is NEC per line of response (LOR) was devised to compare image quality between different PET scanners and acquisition modes. METHODS: Two PET scanners were employed, the CTI-Siemens ECAT EXACT HR(+) and ECAT EXACT 47. Images of a cylindrical (68)Ge phantom were scanned in 2D and 3D modes using various acquisition times ranging from 15 secx20 frames to 120 secx20 frames in order to examine the effect of count statistics on the quality of image reconstruction. The data were reconstructed using a ramp filter with a cutoff frequency of 0.5 cycles/pixel, corrected for dead time, random, attenuation, and scatter. The quality of the reconstructed images was evaluated with the coefficient of variation (COV; SD/average for the pixels within a 16 cm region of interest). Specific NEC was defined as NEC divided by the number of LOR for the entire scanner at detector level. RESULTS: COV showed a linear relationship with Specific NEC in double logarithmic plot within a given experiment. When the Specific NEC was used, all 2D and 3D mode showed the same relationship. The slight difference between the two scanners was attributed to the difference in slice thickness. CONCLUSION: Image quality was dependent on effective count statistics per number of LOR. Our method was considered effective for evaluating image quality in both 2D and 3D modes.

Artifacts↗

PubMed2004

[Evaluation of optimized injection dose and acquisition time using body mass index for three-dimensional whole-body FDG-PET].

OBJECTIVE: The standardized uptake value (SUV) is a relative measure of tracer uptake in tissue used in (18)F-FDG PET. However, the quality of ordered subset expectation maximization (OS-EM) images is sensitive to the number of iterations, because a large number of iterations leads to images with checkerboard noise. The main advantage of data acquisition in the three-dimensional (3D) mode is the high sensitivity to better exploit the intrinsic spatial resolution and the lower injection dose given to patients. In the 3D mode, the scatter fraction is higher, and, for a given administered dose, the random fraction is higher than that in the two-dimensional mode, which implies that correction methods need to be more accurate. Moreover, in clinical oncology (18)F-FDG PET studies, patients have a wide variety of body shapes and sizes, which may impact image statistics. Consequently, it is necessary to make constant the acquisition (true) counts. The purpose of this study was to optimize injection dose and acquisition time in consideration of body mass index (BMI) for 3D whole-body (18)F-FDG PET. METHODS: A dedicated PET scanner, SIEMENS ECAT EXACT HR(+), was used to scan images of clinical data. The injection dose for BMI of <14-19, 19-22, 22-25, and 25< (kg/m(2)) were, 92.5 MBq, 111.0 MBq, 129.5 MBq, and 148.0 MBq, respectively. The emission scan time per bed position for BMI of <14-19, 19-22, 22-25, and >25 (kg/m(2)) were, 120, 120, 180, and 240 sec, respectively. A total of 20 patient subjects were evaluated as to true counts per bin (T/bin) of sinogram data and measured activity concentrations for the region of interest in the liver section. RESULTS: T/bin was stable using an optimized protocol that took into consideration the BMI for any type of body morphology. The overall coefficient of variation was 7.27% for radioactivity concentration. Additionally, Gaussian filtering (8 mm FWHM) after reconstruction by the OS-EM method provided stable SUV values even when the iteration number was increased 30 times over. CONCLUSION: Optimization of injection dose and acquisition time indicated that BMI was a clinically useful acquisition protocol for 3D whole-body (18)F-FDG PET.

Body Mass Index↗

PubMed2004

[Development of method to estimate delay time for arterial imput function with [15O]CO2-PET study using sinogram data and attenuation map].

The difference in tracer arrival times between the external radiation detector and the brain following administration of radioactivity (delay time) must be estimated correctly in order to quantitatively measure regional cerebral blood flow (rCBF) with positron emission tomography and [15O]H2O by autoradiographic method. Instead of intervenous injection of [15O]H2O, bolus inhalation of [15O]CO2 gas is sometimes used to simplify the measurement of rCBF. In the case of [15O]CO2, radioactive gas in mask and nasal cavity contributes large artifact on the sinogram data and it is difficult to estimate delay time from the sinogram data. In this paper, we proposed a new method to estimate the delay time using the sinogram data and the attenuation map (attenuation weighted sinogram method). In the present method, the attenuation map was used to eliminate the effect of the gas outside the brain region from the sinogram data. For the validation of the present method, PET data with [15O]CO2 (n = 10) were analyzed. Three methods, namely the image method, the sinogram method and the attenuation weighted sinogram method were used to estimate the delay time. The estimated delay times and calculated rCBF images by three methods were compared. Due to the radioactivity outside of the brain, the sinogram method significantly overestimated the delay time and thus underestimated the rCBF value compared with the image base method. On the other hand, there were good agreements between the delay times estimated by the attenuation weighted sinogram method and the image method. The present method can eliminate the effect of the radioactivity outside of the brain on the sinogram data and estimate the delay time accurately and fast enough for clinical use.

Autoradiography↗

PubMed2003

Comparison of whole-body 18F-FDG PET, 99mTc-MIBI SPET, and post-therapeutic 131I-Na scintigraphy in the detection of metastatic thyroid cancer.

UNLABELLED: The usefulness of fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in differentiated thyroid cancer (DTC) has been demonstrated by many investigators, but in only a small number of studies have FDG-PET images been compared with those obtained using other non-iodine tumour-seeking radiopharmaceuticals. In most of the studies, planar imaging was performed for comparison using thallium-201 chloride or technetium-99m 2-methoxyisobutylisonitrile ((99m)Tc-MIBI). Furthermore, FDG-PET studies were not always performed in the hypothyroid state with increased levels of thyroid stimulating hormone (TSH), which are known to increase FDG uptake by DTC. The aim of this study was to compare the ability of FDG-PET to detect metastatic DTC with that of (99m)Tc-MIBI whole-body single-photon emission tomography (SPET) and post-therapeutic iodine-131 scintigraphy, evaluated under TSH stimulation. Nineteen patients (8 men, 11 women; age range, 38-72 years, mean 60 years; 17 thyroidectomised and 2 inoperable patients following (131)I ablation of the remaining thyroid tissue; 16 papillary and 3 follicular carcinomas) with metastatic DTC underwent FDG-PET whole-body scan (WBS) and (99m)Tc-MIBI SPET WBS at an interval of less than 1 week, followed by (131)I therapy. The SPET images were reconstructed using the maximum likelihood expectation maximisation (ML-EM) method. All patients were hypothyroid at the time of each scan. (131)I WBS was performed 3-5 days after oral administration of the therapeutic dose. A total of 32 lesions [10 lymph node (LN), 15 lung, 6 bone, 1 muscle] were diagnosed as metastases, as confirmed by histopathology and/or other imaging modalities (X-ray, US, CT, MRI, bone, (201)Tl and (131)I scans). FDG-PET, (99m)Tc-MIBI SPET and post-therapeutic (131)I scintigraphy respectively revealed a total of 26 (81.3%), 20 (62.5%) and 22 (68.8%) lesions. These techniques respectively demonstrated nine (90.0%), eight (80.0%) and six (60.0%) LN metastases, and eleven (73.3%), seven (46.7%) and ten (66.7%) lung metastases. They each demonstrated five of the six bone metastases (83.3%). FDG-PET and (99m)Tc-MIBI SPET were positive in 17 (78.3%) and 14 (63.6%) of the 22 (131)I-positive lesions, respectively, and also in nine (90.0%) and six (60.0%) of the ten (131)I-negative lesions, respectively. Three of the five (131)I-positive and FDG-PET-negative lesions were miliary type lung metastases with a maximal nodular diameter of less than 10 mm. Comparison of FDG-PET with (99m)Tc-MIBI SPET revealed concordant results in 24 lesions, and discordant results in eight lesions (seven with positive FDG-PET alone and one with positive (99m)Tc-MIBI SPET alone). IN CONCLUSION: (a) even using whole-body SPET, FDG PET is superior to (99m)Tc-MIBI in terms of ability to detect metastases of DTC; (b) the higher sensitivity of FDG-PET compared with the previous studies could partly be due to increased serum TSH.

Adenocarcinoma, Follicular↗

PubMed2003

[A multicenter evaluation of seven commercial ML-EM algorithms for SPECT image reconstruction using simulation data].

The maximum likelihood expectation maximization (ML-EM) algorithm has become available as an alternative to filtered back projection in SPECT. The actual physical performance may be different depending on the manufacturer and model, because of differences in computational details. The purpose of this study was to investigate the characteristics of seven different types of ML-EM algorithms using simple simulation data. Seven ML-EM algorithm programs were used: Genie (GE), esoft (Siemens), HARP-III (Hitachi), GMS-5500UI (Toshiba), Pegasys (ADAC), ODYSSEY-FX (Marconi), and Windows-PC (original software). Projection data of a 2-pixel-wide line source in the center of the field of view were simulated without attenuation or scatter. Images were reconstructed with ML-EM by changing the number of iterations from 1 to 45 for each algorithm. Image quality was evaluated after a reconstruction using full width at half maximum (FWHM), full width at tenth maximum (FWTM), and the total counts of the reconstructed images. In the maximum number of iterations, the difference in the FWHM value was up to 1.5 pixels, and that of FWTM, no less than 2.0 pixels. The total counts of the reconstructed images in the initial few iterations were larger or smaller than the converged value depending on the initial values. Our results for the simplest simulation data suggest that each ML-EM algorithm itself provides a simulation image. We should keep in mind which algorithm is being used and its computational details, when physical and clinical usefulness are compared.

Algorithms↗

PubMed2002

[Fundamental evaluation of segmented attenuation correction method for clinical FDG-PET studies: simulation of pulmonary mass lesions in phantom studies].

OBJECTIVE: Both the segmented attenuation correction (SAC) method and post-injection transmission scanning are useful and widespread in clinical whole-body FDG-PET studies. The SAC method usually accomplishes smoothing of the transmission data. This calculation segments a micro -map into three degrees (lung, soft tissue, and bone) of attenuation coefficient. This method is used to reduce transmission scan time without deteriorating the quality of PET images. However, the SAC method has a tendency to underestimate the attenuation coefficient, resulting lower detectability for lung field mass lesions. We therefore evaluated the quantitative accuracy of the SAC method using transmission scanning and emission scanning data in a phantom study. METHODS: A dedicated 3D PET scanner, the Siemens ECAT EXACT HR+, was used to scan images of two types of phantoms, a spherical phantom (Japan Radioisotope Association phantom) and a cylindrical phantom (20 cm in diameter). We evaluated differences between transmission images ( micro -map) of the SAC method and measured attenuation correction (MAC) method, these two kinds of attenuation-corrected emission data (emission + SAC method, emission + MAC method), and emission data only (without attenuation correction). RESULTS: In the micro -map, recovery coefficient (RC) values at 10 mm in diameter were 0.27 and 0.00 in the MAC and SAC methods, respectively, in the spherical hot area. For the emission data, the emission + SAC method and emission + MAC method showed almost the same RC values for all sizes of hot area diameter. The SAC method, however, resulted in 20% underestimation for all sizes of hot area diameter as compared with the MAC method. CONCLUSION: In pulmonary mass lesions, it is necessary to correct for the partial volume effect in quantitative PET measurement. However, from our data, the SAC method is not appropriate for partial volume effect correction.

Evaluation Studies as Topic↗

PubMed2002

[Evaluation of median filtering after reconstruction with maximum likelihood expectation maximization (ML-EM) by real space and frequency space].

Maximum likelihood expectation maximization (ML-EM) image quality is sensitive to the number of iterations, because a large number of iterations leads to images with checkerboard noise. The use of median filtering in the reconstruction process allows both noise reduction and edge preservation. We examined the value of median filtering after reconstruction with ML-EM by comparing filtered back projection (FBP) with a ramp filter or ML-EM without filtering. SPECT images were obtained with a dual-head gamma camera. The acquisition time was changed from 10 to 200 (seconds/frame) to examine the effect of the count statistics on the quality of the reconstructed images. First, images were reconstructed with ML-EM by changing the number of iterations from 1 to 150 in each study. Additionally, median filtering was applied following reconstruction with ML-EM. The quality of the reconstructed images was evaluated in terms of normalized mean square error (NMSE) values and two-dimensional power spectrum analysis. Median filtering after reconstruction by the ML-EM method provided stable NMSE values even when the number of iterations was increased. The signal element of the image was close to the reference image for any repetition number of iterations. Median filtering after reconstruction with ML-EM was useful in reducing noise, with a similar resolution achieved by reconstruction with FBP and a ramp filter. Especially in images with poor count statistics, median filtering after reconstruction with ML-EM is effective as a simple, widely available method.

Filtration↗

PubMed2002

[Performance evaluation of continuous blood sampling system for PET study: comparison of three detector-systems].

OBJECTIVES: To measure cerebral blood flow with 15O'PET, it is necessary to measure the time course of arterial blood radioactivity. We examined the performance of three different types of continuous blood sampling system. METHODS: Three kinds of continuous blood sampling system were used: a plastic scintillator-based beta detector (conventional beta detector (BETA)), a bismuth germanate (BGO)-based coincidence gamma detector (Pico-count flow-through detector (COINC)) and a Phoswich detector (PD) composed by a combination of plastic scintillator and BGO scintillator. Performance of these systems was evaluated for absolute sensitivity, count rate characteristic, sensitivity to background gamma photons, and reproducibility for nylon tube geometry. RESULTS: The absolute sensitivity of the PD was 0.21 cps/Bq for 68Ga positrons at the center of the detector. This was approximately three times higher than BETA, two times higher than COINC. The value measured with BETA was stable, even when background radioactivity was increased. The count rate characteristic of the PD and COINC was linear up to 8 kcps. The reproducibility of sensitivity for nylon tube geometry of COINC was the smallest (C.V. = 1.00%) among the three. PD was the weights the least (3.5 kg) among the three, which is convenient for clinical use. CONCLUSIONS: Each detector has unique characteristics derived from its own structure. Although the performance of all three detectors meets clinical requirement, PD had the highest physical performance.

Cerebrovascular Circulation↗