Observations on two nests of the Black-headed Siskin Serinus nigriceps in the Bale Mountains National Park, Ethiopia

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Effectiveness and cost efficiency of monitoring mountain nyala in the Bale Mountains National Park, Ethiopia

Due to the financial limitations faced by many protected areas today, identifying cost-efficient monitoring protocols has become important in ensuring the long-term sustainability of conservation. The selection of monitoring protocols is usually driven by a range of factors, such as widespread practice or accuracy, but the cost efficiency of protocols is rarely considered. The mountain nyala Tragelaphus buxtoni, classified by the IUCN as Endangered, is endemic to the Ethiopian highlands. This species has high economic potential for local communities through tourism and trophy hunting, but the expansion of human settlement is causing habitat degradation and fragmentation. A significant proportion of the global mountain nyala population occurs in Bale Mountains National Park (BMNP); thus the development of a long-term monitoring protocol was identified as a priority. Like many protected areas, the BMNP is operating well below its financial needs; hence developing a robust, cost-effective method that can detect changes in population size is important. We compared the effectiveness and cost efficiency of distance sampling and total counts. Results showed that while the population estimates were relatively similar, total counts underestimated population size but were more precise, had a greater power to detect changes in population size and required only 12% of the resources needed compared to distance sampling. We suggest that investing in initial comparisons of the effectiveness and costs of different methods can result in significant cost savings, without jeopardizing the effectiveness of a survey

Assessment of Threat Status in the Northern Woodlands of the Bale Mountains, Ethiopia: Indicator for Management Effectiveness

The present study was carried out to identify the types and quantify the magnitude of human disturbances in six forest patches in the northern Bale Mountains, southeast Ethiopia. The principal objective was to compare three protected forest patches within the Bale Mountains National Park with three unprotected patches outside the park in terms of the severity of human-induced disturbances. Data was collected along five 1-km long transects in each patch. Eight major disturbance types were identified and quantified in the six forest patches: settlement, agriculture, selective logging, livestock herbivory, fuel wood collection, charcoal production, path/track formation and forest-fire. Results showed some degree of human disturbances in all patches, with logging, fuel wood collection, path/track formation and livestock grazing being the most widespread. Crop production, settlement and charcoal making, however, were only recorded in unprotected patches. Sixty percent and 47% of transects in these patches showed crop cultivation and houses respectively, covering 40% ha-1.  The unprotected patches were characterized by significantly higher level of incidences of logged trees, fuel wood collection and livestock herbivory compared to the protected patches. For tree logging, this difference was however only observed for trees logged in recent years (estimated to be logged < 20 years) with  logging of larger trees (DBH > 10 cm) than smaller trees. Generally the protected areas had reduced human disturbance as indicated by low logging activity. This is a positive indicator of effective management practices in the protected area. Key Words: Bale Mountains, Disturbance, Logging, Management effectiveness, Threa

Low-Dose Dual-Energy Computed Tomography for PET Attenuation Correction with Statistical Sinogram Restoration

Dual-energy (DE) X-ray computed tomography (CT) has been proposed as an useful tool in various applications. One promising application is DECT with low radiation doses used for attenuation correction in positron emission tomography (PET). In low-dose DECT, conventional methods for sinogram decomposition have been based on logarithmic transformations and ignored noise properties, leading to very noisy component sinogram estimates. In this paper, we propose two novel sinogram restoration methods that are statistically motivated; penalized weighted least square (PWLS) and penalized likelihood (PL), producing less noisy component sinogram estimates for low-dose DECT than the conventional approaches. The restored component sinograms can improve attenuation correction, thus allowing better image quality in PET. Experiments with a digital phantom indicate that the proposed methods produce less noisy sinograms, reconstructed images, and attenuation correction factors (ACF) than the conventional one, showing promise for CT-based attenuation correction in emission tomography.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85933/1/Fessler230.pd

Statistical Sinogram Restoration in Dual-Energy CT for PET Attenuation Correction

Dual-energy (DE) X-ray computed tomography (CT) has been found useful in various applications. In medical imaging, one promising application is using low-dose DECT for attenuation correction in positron emission tomography (PET). Existing approaches to sinogram material decomposition ignore noise characteristics and are based on logarithmic transforms, producing noisy component sinogram estimates for low-dose DECT. In this paper, we propose two novel sinogram restoration methods based on statistical models: penalized weighted least square (PWLS) and penalized likelihood (PL), yielding less noisy component sinogram estimates for low-dose DECT than classical methods. The proposed methods consequently provide more precise attenuation correction of the PET emission images than do previous methods for sinogram material decomposition with DECT. We report simulations that compare the proposed techniques and existing approaches.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85900/1/Fessler11.pd

Fast kVp-Switching Dual Energy CT for PET Attenuation Correction

X-ray CT images are used routinely for attenuation correction in PET/CT systems. However, conventional CT-based attenuation correction (CTAC) can be inaccurate in regions containing iodine contrast agent. Dual-energy (DE) CT has the potential to improve the accuracy of attenuation correction in PET, but conventional DECT can suffer from motion artifacts. Recent X-ray CT systems can collect DE sinograms by rapidly switching the X-ray tube voltage between two levels for alternate projection views, reducing motion artifacts. The goal of this work is to study statistical methods for image reconstruction from both fast kVp-switching DE scans and from conventional dual-rotate DE scans in the context of CTAC for PET.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86003/1/Fessler244.pd

Quantitative Attenuation Correction for PET/CT Using Iterative Reconstruction of Low-Dose Dual-Energy CT

We present the results of using iterative reconstruction of dual-energy CT (DECT) to perform accurate CT-based attenuation correction (CTAC) for PET emission images. Current methods, such as bilinear scaling, introduce quantitative errors in the PET emission image for bone, metallic implants, and contrast agents. DECT has had limited use in the past for quantitative CT imaging due to increased patient dose and high noise levels in the decoupled CT basis-material images. Reconstruction methods that model the acquisition physics impose a significant computational burden due to the large image matrix size (typically 512 × 512). For CTAC, however, three factors make DECT feasible: (1) a smaller matrix is needed for the transmission image, which reduces the noise per pixel, (2) a smaller matrix significantly accelerates an iterative CT reconstruction algorithm, (3) the monoenergetic transmission image at 511 keV is the sum of the two decoupled basis-material images. Initial results using a 128 × 128 matrix size for a test object comprised of air, soft tissue, dense bone, and a mixture of tissue and bone demonstrate a significant reduction of bias using DECT (from 20% to ?0% for the tissue/bone mixture). FBP reconstructed images, however, have significant noise. Noise levels are reduced from ?8% to ?3% by the use of PWLS reconstruction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85861/1/Fessler203.pd

Performance assessment of a NaI(Tl) gamma counter for PET applications with methods for improved quantitative accuracy and greater standardization

BACKGROUND: Although NaI(Tl) gamma counters play an important role in many quantitative positron emission tomography (PET) protocols, their calibration for positron-emitting samples has not been standardized across imaging sites. In this study, we characterized the operational range of a gamma counter specifically for positron-emitting radionuclides, and we assessed the role of traceable (68)Ge/(68)Ga sources for standardizing system calibration. METHODS: A NaI(Tl) gamma counter was characterized with respect to count rate performance, adequacy of detector shielding, system stability, and sample volume effects using positron-emitting radionuclides (409- to 613-keV energy window). System efficiency was measured using (18)F and compared with corresponding data obtained using a long-lived (68)Ge/(68)Ga source that was implicitly traceable to a national standard. RESULTS: One percent count loss was measured at 450 × 10(3) counts per minute. Penetration of the detector shielding by 511-keV photons gave rise to a negligible background count rate. System stability tests showed a coefficient of variation of 0.13% over 100 days. For a sample volume of 4 mL, the efficiencies relative to those at 0.1 mL were 0.96, 0.94, 0.91, 0.78, and 0.72 for (11)C, (18)F, (125)I, (99m)Tc, and (51)Cr, respectively. The efficiency of a traceable (68)Ge/(68)Ga source was 30.1% ± 0.07% and was found to be in close agreement with the efficiency for (18)F after consideration of the different positron fractions. CONCLUSIONS: Long-lived (68)Ge/(68)Ga reference sources, implicitly traceable to a national metrology institute, can aid standardization of gamma counter calibration for (18)F. A characteristic feature of positron emitters meant that accurate calibration could be maintained over a wide range of sample volumes by using a narrow energy window centered on the 511-keV peak

Noise Characteristics of the FORE+OSEM(DB) Reconstruction Method for the MiCES PET Scanner

The FORE+OSEM(DB) image reconstruction method has been proposed for the fully-3D MiCES PET scanner under construction at the University of Washington. It is based on Fourier rebinning followed by 2D OSEM and an incorporated model of detector blurring (DB). As an extension, this paper presents the noise/resolution characteristics of this method. Multiple realizations were simulated to estimate the noise properties of the algorithm. The results are compared with OSEM followed by post reconstruction 3D Gaussian smoothing. The results show that the incorporation of detector blurring (OSEM(DB)) into the system matrix improves resolution compared to OSEM, while also inducing an increased variance at all radial locations. In addition, radially-varying noise characteristics are more apparent with OSEM(DB) than with OSEM.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85836/1/Fessler204.pd

Reconstruction of 3D Whole-Body PET Data Using Blurred Anatomical Labels

The diagnostic utility of whole-body PET is often limited by the high level of statistical noise in the images. An improvement in image quality can be obtained by incorporating correlated anatomical information during the reconstruction of the PET data. The combined PET/CT (SMART) scanner allows the acquisition of accurately aligned PET and CT whole-body data. The authors present results of incorporating aligned anatomical information from the CT during the reconstruction of 3D whole-body PET data. They use the FORE+PWLS method for the reconstruction and a label model to incorporate anatomical information via penalty weights. Since in practice mismatches between anatomical and functional data are unavoidable, the labels are “blurred” to reflect the uncertainty associated with the anatomical information. Results show the potential advantage of incorporating anatomical information by using a blurred labels with the penalty weights.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85864/1/Fessler153.pd