Biomedical subjects

Kenneth H Wong

Publications and source records attributed to Kenneth H Wong.

6 recordsLinked to original sources

PubMed2006

Geometric accuracy of a real-time target tracking system with dynamic multileaf collimator tracking system.

PURPOSE: Dynamically compensating for target motion during radiotherapy will increase treatment accuracy. A laboratory system for real-time target tracking with a dynamic MLC has been developed. In this study, the geometric accuracy limits of this DMLC target tracking system were evaluated. METHODS AND MATERIALS: A motion simulator was programmed to follow patient-derived tumor motion paths, parallel to the leaf motion direction. A target attached to the simulator was optically tracked, and the leaf positions adjusted to continually align the DMLC beam aperture to the target. Analysis of the tracking accuracy was based on video images of the target and beam alignment. The system response time was determined and the tracking error measured. Response time-corrected tracking accuracy was also calculated to investigate the accuracy limits of an improved system. RESULTS: The response time of the system is 160 +/- 2 ms. The geometric precision for tracking patient motion is 0.6 to 1.1 mm (1 sigma) for the 3 patient datasets tested, with tracking errors relative to the original patient motion of 35, 40, and 100%. CONCLUSIONS: A DMLC target tracking system has been developed that can account for detected motion parallel to the leaf motion direction. The tracking error has a negligible systematic component. Reducing the response time will further increase the overall system accuracy.

Calibration↗

PubMed2006

Progress in SPECT/CT imaging of prostate cancer.

Prostate cancer is the most common type of cancer (other than skin cancer) among men in the United States. Although prostate cancer is one of the few cancers that grow so slowly that it may never threaten the lives of some patients, it can be lethal once metastasized. Indium-111 capromab pendetide (ProstaScint, Cytogen Corporation, Princeton, NJ) imaging is indicated for staging and recurrence detection of the disease, and is particularly useful to determine whether or not the disease has spread to distant metastatic sites. However, the interpretation of 111In-capromab pendetide is challenging without correlated structural information mostly because the radiopharmaceutical demonstrates nonspecific uptake in the normal vasculature, bowel, bone marrow, and the prostate gland. We developed an improved method of imaging and localizing 111In-Capromab pendetide using a SPECT/CT imaging system. The specific goals included: i) development and application of a novel iterative SPECT reconstruction algorithm that utilizes a priori information from coregistered CT; and ii) assessment of clinical impact of adding SPECT/CT for prostate cancer imaging with capromab pendetide utilizing the standard and novel reconstruction techniques. Patient imaging studies with capromab pendetide were performed from 1999 to 2004 using two different SPECT/CT scanners, a prototype SPECT/CT system and a commercial SPECT/CT system (Discovery VH, GE Healthcare, Waukesha, WI). SPECT projection data from both systems were reconstructed using an experimental iterative algorithm that compensates for both photon attenuation and collimator blurring. In addition, the data obtained from the commercial system were reconstructed with attenuation correction using an OSEM reconstruction supplied by the camera manufacturer for routine clinical interpretation. For 12 sets of patient data, SPECT images reconstructed using the experimental algorithm were interpreted separately and compared with interpretation of images obtained using the standard reconstruction technique. The experimental reconstruction algorithm improved spatial resolution, reduced streak artifacts, and yielded a better correlation with anatomic details of CT in comparison to conventional reconstruction methods (e.g., filtered back-projection or OSEM with attenuation correction only). Images produced with the experimental algorithm produced a subjective improvement in the confidence of interpretation for 11 of 12 studies. There were also changes in interpretations for 4 of 12 studies although the changes were not sufficient to alter prognosis or the patient treatment plan.

Algorithms↗

PubMed2005

Calculation and validation of the use of effective attenuation coefficient for attenuation correction in In-111 SPECT.

Nuclear medicine tracers using 111In as a radiolabel are increasing in their use, especially in the domain of oncologic imaging. In these applications, it often is critical to have the capability of quantifying radionuclide uptake and being able to relate it to the biological properties of the tumor. However, images from single photon emission computed tomography (SPECT) can be degraded by photon attenuation, photon scattering, and collimator blurring; without compensation for these effects, image quality can be degraded, and accurate and precise quantification is impossible. Although attenuation correction for SPECT is becoming more common, most implementations can only model single energy radionuclides such as 99mTc and 123I. Thus, attenuation correction for 111In is challenging because it emits two photons (171 and 245 keV) at nearly equal rates (90.2% and 94% emission probabilities). In this paper, we present a method of calculating a single "effective" attenuation coefficient for the dual-energy emissions of 111In, and that can be used to correct for photon attenuation in radionuclide images acquired with this radionuclide. Using this methodology, we can derive an effective linear attenuation coefficient Micro(eff) and an effective photon energy E(eff) based on the emission probabilities and linear attenuation coefficients of the 111In photons. This approach allows us to treat the emissions from 111In as a single photon with an effective energy of 210 keV. We obtained emission projection data from a tank filled with a uniform solution of 111In. The projection data were reconstructed using an iterative maximum-likelihood algorithm with no attenuation correction, and with attenuation correction assuming photon energies of 171, 245, and 210 keV (the derived E(eff)). The reconstructed tomographic images demonstrate that the use of no attenuation correction, or correction assuming photon energies of 171 or 245 keV introduces inaccuracies into the reconstructed radioactivity distribution when compared against the effective energy method. In summary, this work provides both a theoretical framework and experimental methodology of attenuation correction for the dual-energy emissions from 111In. Although these results are specific to 111In, the foundation could easily be extended to other multiple-energy isotopes.

Biophysical Phenomena↗

PubMed2005

Correction of photon attenuation and collimator response for a body-contouring SPECT/CT imaging system.

UNLABELLED: (111)In-Capromab pendetide imaging is indicated for postprostatectomy patients at risk for residual or recurrent disease. However, this study is complicated by relatively long times for tumor uptake and background washout that require imaging to be performed several days after radiopharmaceutical administration. In addition, (111)In-capromab pendetide demonstrates uptake in normal structures that produce images that are interpreted best using correlation with anatomic imaging. Finally, the visual quality of radionuclide imaging can be improved with corrections for photon attenuation and for the geometric response of the radionuclide collimator. Therefore, we have evaluated the advantages of using a commercially available dual-modality SPECT/CT system. In this article, we evaluate a novel iterative reconstruction algorithm using the SPECT/CT data obtained from phantoms and (111)In-capromab pendetide patient studies. METHODS: Phantom data acquired with the dual-head SPECT camera were reconstructed using both filtered backprojection (FBP) and an iterative maximum-likelihood expectation maximization (MLEM) algorithm incorporating corrections for (a) attenuation coefficient at the effective energy of the radionuclide (either (99m)Tc or (111)In) and (b) collimator response based on experimentally measured depth-dependent spatial resolution of the camera. The collimator response model used the coregistered CT image to estimate the source-target distances produced by the patient-contouring logic of the SPECT camera. Spatial resolution was measured using SPECT images of 2 line sources and uniformity from a uniform cylindric tank. Clinical (111)In-capromab pendetide SPECT/CT data were acquired according to the radiopharmaceutical manufacturer's protocol. Region-of-interest (ROI) analysis of a transverse slice at the level of the sacral base produced mean, median, maximum, and minimum counts per pixel for bone marrow and surrounding soft-tissue ROIs. Ratios of the mean capromab pendetide uptake within marrow to uptake within soft tissue were compared for images reconstructed with FBP versus that obtained from the MLEM method with photon attenuation and collimator response corrections. RESULTS: The source-target distances reconstructed from the patient-specific CT image agreed well with the corresponding values recorded manually from the camera display unit. This information was incorporated into the iterative reconstruction algorithms and improved the quality of SPECT images from phantoms and patients versus SPECT images reconstructed without the depth-dependent collimator response model. Qualitatively, SPECT images reconstructed with corrections for photon attenuation and collimator response showed less background activity and improved target contrast compared with those images reconstructed with FBP. The target-to-background ratio (marrow uptake-to-soft-tissue uptake) was significantly better using MLEM reconstruction than with FBP when mean uptake values were measured. CONCLUSION: A priori anatomic data can be used to enhance the quality of the SPECT image when reconstructed using iterative techniques (e.g., MLEM) that use the CT data to produce a patient-specific attenuation map and a collimator response model based on the body contour produced during the SPECT acquisition.

Algorithms↗

PubMed2002

Dual-modality imaging of function and physiology.

Dual-modality imaging is a technique in which computed tomography (CT) or magnetic resonance imaging is combined with positron emission tomography or single-photon emission CT to acquire structural and functional images with an integated system. The data are acquired in a single procedure; the patient remains on the scanner table while undergoing both x-ray and radionuclide studies to facilitate correlation between the structural and functional images. The resulting data can aid in localization, enabling more specific diagnosis than can be obtained with a conventional imaging study. In addition, the anatomic information can be used to compensate the correlated radionuclide data for physical perturbations such as photon attenuation, scatter radiation, and partial volume errors. Thus, dual-modality imaging provides a priori information that can improve both the visual quality and the quantitative accuracy of the radionuclide images. Dual-modality imaging systems are also being developed for biologic research involving small animals. Small-animal dual-modality systems offer advantages for measurements that currently are performed invasively with autoradiography and tissue sampling. By acquiring data noninvasively, dual-modality imaging permits serial studies in a single animal, enables measurements to be performed with fewer animals, and improves the statistical quality of the data.

Animals↗

PubMed2002

Dual-modality imaging of cancer with SPECT/CT.

Dual-modality imaging is an in vivo diagnostic technique that obtains structural and functional information directly from patient studies in a way that cannot be achieved with separate imaging systems alone. Dual-modality imaging systems are configured by combining computed tomography (CT) with radionuclide imaging (using positron emission tomography (PET) or single-photon emission computed tomography (SPECT)) on a single gantry which allows both functional and structural imaging to be performed during a single imaging session without having the patient leave the imaging system. A SPECT/CT system developed at UCSF is being used in a study to determine if dual-modality imaging offers advantages for assessment of patients with prostate cancer using (111)In-ProstaScint, a radiolabeled antibody for the prostate-specific membrane antigen. (111)In-ProstaScint images are reconstructed using an iterative maximum-likelihood expectation-maximization (ML-EM) algorithm with correction for photon attenuation using a patient-specific map of attenuation coefficients derived from CT. The ML-EM algorithm accounts for the dual-photon nature of the 111In-labeled radionuclide, and incorporates correction for the geometric response of the radionuclide collimator. The radionuclide image then can be coregistered and overlaid in color on a grayscale CT image for improved localization of the functional information from SPECT. Radionuclide images obtained with SPECT/CT and reconstructed using ML-EM with correction for photon attenuation and collimator response improve image quality in comparison to conventional radionuclide images obtained with filtered backprojection reconstruction. These results illustrate the potential advantages of dual-modality imaging for improving the quality and the localization of radionuclide uptake for staging disease, planning treatment, and monitoring therapeutic response in patients with cancer.

Algorithms↗