Browsing by Subject "Quantification"

Single-walled carbon nanotubes (SWCNT) are unique, anthropogenic allotropes of nanoparticulate black carbon. As numerous industrial and commercial uses of SWCNT result the heavy expansion of production of this material, the release of SWCNT is likely to occur, increasing their level in air, water and soil. SWCNTs have been shown to cause adverse impact in organisms from direct exposure through ingestion or inhalation. In addition to direct exposure, SWCNT can also induce toxicity to organisms by indirect exposure such as adsorption of hydrophobic contaminants (HOCs). One unique property of SWCNT is the quantized nature of their electronic structure, which is dependent on the chiral wrapping angle of the sp2 hybridized graphene sheet that comprises the wall of each SWNT species. Using probe HOCs – one planar polycyclic aromatic hydrocarbon (PAH)14 C-naphthalene and one halogenated aromatic 14 C-hexachlorobenzene and purified conductive and semiconductive SWCNT species, my first study aimed at assessing the role of SWCNT electronic structure on HOC sorption. Despite their differences in electronic structures, the results indicated that overall the electronic structure does not influence the adsorption of HOCs. However, due to the large specific surface area, SWCNT have a general high affinity for HOCs. Upon release of SWCNT into aquatic environment, SWCNT have the potential to affect the distribution of organic contaminants by acting as strong sorbent.

A significant barrier to studying toxicity of SWCNT to animal models is the lack of in vivo techniques to track and quantify SWCNT for assessing their distribution, transport and bioaccumulation. The fluorescence resulting from the unique band gap of each species of semiconductive SWCNT allows the detection and quantification of a bulky SWCNT sample using near infrared fluorescence spectroscopy (NIRF). NIRF is highly sensitive to detect SWCNT in biological tissues due to the low fluorescence in the near infrared region from biological samples. Two exposure routes were investigated using NIRF: ingestion from dietary track using fathead minnow (FHM) fish model in an aquatic environment and inhalation through lung using mouse model. The SWCNT extraction conditions were optimized and validated using spike recovery experiments. SWCNT were extracted from fish tissues, intestine, and liver using ultrasonic extraction in 2% sodium deoxycholate1extraction. Proteinase K digestion was needed for dissolving mouse lung prior to SDC extraction. The quantification results showed that while SWCNT readily passed through fish dietary track with minimal partition into the lumen tissue and caused no acute toxicity; SWCNT was less mobile in respiratory system and was responsible for the lung-term pulmonary disease induced.

The fate, transport and bioaccumulation of SWCNT are essential information for risk assessment and making environmental regulations for nanomaterials. Currently the lack of standardized sensitive characterization and quantitative analytical methods for SWCNT determination at the current levels in the environment is one major barrier for evaluation of their real impact to the environment. NIRF is sensitive for environmental samples. However, this technique is not sensitive to all types of SWCNT. Metal catalysts are widely used in synthetic production of SWCNTs, leading to total metal content ranging from 5 - 30%. The metal: metal ratios and metal: carbon ratios of SWCNT are very distinctive from many geological materials. A metal fingerprinting approach was developed by monitoring the metal type and metal: metal ratios, along with elemental carbon content. SWCNT can be principally quantified using inductive coupled plasma mass spectrometry (ICP-MS). Metal content, metal: metal ratios, elemental carbon and metal: carbon ratios were analyzed for two aerosol matrices, the urban dust NIST SRM 1649b and aerosol collected at Duke University using three types of SWCNT: SG65 SWCNT, SG65i SWCNT and P2 SWCNT. Results demonstrated that the metal finger approach worked well with all aerosol matrices with detection limits near ng m-3. It worked best with elements that were less abundant in the background such as Co and Y. This method offers a robust and economic approach for application to occupational spaces for monitoring possible SWCNT release.

Applying a similar approach in sediment presents a significant challenge as background metals present in sediment complicates such analyses. To overcome these challenges, we have applied density gradient ultracentrifuge (DGU) to isolate and separate SWCNT in sediment extracts prior to both NIRF and ICP-MS analysis. Several types of SWCNTs (arc discharge, CoMoCat, and HiPCO) were spiked and subsequently extracted from estuarine sediments. SWCNTs were separated into different bands after DGU, primarily into two distinct horizons (one showed near infrared fluorescence, while the other did not). Two techniques,near-infrared spectroscopy (NIRF) and ICP-MS, were applied for quantitation of SWCNTs in these bands. Results indicate excellent separation of SWCNT from interferences in sediments. We have also discovered an apparent disconnect between the metal catalyst particles and SWCNT during density gradient ultracentrifuge separation. It is clear that the SWCNT (within the NIRF band) is not physically associated with metal catalyst. This result was further confirmed using single-particle ICP-MS. Although DGU separation seems to be an outstanding method for isolating SWCNT from aquatic sediment for analysis, our current findings indicate that metal fingerprints derived from residual catalyst may not be a good tracer for SWCNT occurrence and fate in marine sediments, as the associated metal catalyst particles in SWCNT preparations might be transported in different ways relative to the SWCNT.

Overall, my research explored several analytical techniques to detect and quantify SWCNTs at their relevant concentration in various environmental matrices. These techniques will provide essential information for evaluating the environmental impact based on SWCNTs fate, transport and bioaccumulation in the environment.

This work investigates phantom and subject positioning as well as collecting data with a variety of angular sampling and acquisition trajectories. The overall goal of this work has been to utilize the dedicated, breast SPECT-CT system to acquire the best possible images. A large portion of this work has been to apply corrections to the system for quantitative imaging. The system has been shown to provide high quality images with minimal out-of-field signal contribution. Additionally, the quantification procedure has been shown to be within 10% of the known activity concentration present at the time of imaging for both VAOR and PROJSINE trajectories.

The work presented in this dissertation focuses on evaluation of absolute quantification accuracy in dedicated breast SPECT-CT. The overall goal was to investigate through simulations and measurements the impact and utilization of various correction methods for scattered and attenuated photons, characterization of incomplete charge collection in Cadmium Zinc Telluride detectors as a surrogate means of improving scatter correction, and resolution recovery methods for modeling collimator blur during image reconstruction. The quantification accuracy of attenuation coefficients in CT reconstructions was evaluated in geometric phantoms, and a slice-by-slice breast segmentation algorithm was developed to separate adipose and glandular tissue. All correction and segmentation methods were then applied to a pilot study imaging parathyroid patients to determine the average uptake of Tc-99m Sestamibi in healthy breast tissue, including tissue specific uptake in adipose and glandular tissue.

Monte Carlo methods were utilized to examine the changes in incident scatter energy distribution on the SPECT detector as a function of 3D detector position about a pendant breast geometry. A simulated prone breast geometry with torso, heart, and liver was designed. An ideal detector was positioned at various azimuthal and tilted positions to mimic the capabilities of the breast SPECT subsystem. The limited near-photopeak scatter energy range in simulated spectra was linearly fit and the slope used to characterize changes in scatter distribution as a function of detector position. Results show that the detected scatter distribution changes with detector tilt, with increasing incidence of high energy scattered photons at larger detector tilts. However, reconstructions of various simulated trajectories show minimal impact on quantification (<5%) compared to a primary-only reconstruction.

Two scatter compensation methods were investigated and compared to a narrow photopeak-only windowing for quantification accuracy in large uniform regions and small, regional uptake areas: 1) a narrow ±4% photopeak energy window to minimize scatter in the photopeak window, 2) the previously calibrated dual-energy window scatter correction method, and 3) a modified dual-energy window correction method that attempts to account for the effects of incomplete charge collection in Cadmium Zinc Telluride detectors. Various cylindrical phantoms, including those with imbedded hot and cold regions, were evaluated. Results show that the Photopeak-only and DEW methods yield reasonable quantification accuracy (within 10%) for a wide range of activity concentrations and phantom configurations. The mDEW demonstrated highly accurate quantification measurements in large, uniform regions with improved uniformity compared to the DEW method. However, the mDEW method is susceptible to the calibration parameters and the activity concentration of the scanned phantom. The sensitivity of the mDEW to these factors makes it a poor choice for robust quantification applications. Thus, the DEW method using a high-performance CZT gamma camera is still a better choice for quantification purposes

Phantoms studies were performed to investigate the application of SPECT vs CT attenuation correction. Minor differences were observed between SPECT and CT maps when assuming a uniformly filled phantom with the attenuation coefficient of water, except when the SPECT attenuation map volume was significantly larger than the CT volume. Material specific attenuation coefficients reduce the corresponding measured activity concentrations compared to a water-only correction, but the results do not appear more accurate than a water-only attenuation map. Investigations on the impact of image registration show that accurate registration is necessary for absolute quantification, with errors up to 14% observed for 1.5cm shifts.

A method of modeling collimator resolution within the SPECT reconstruction algorithm was investigated for its impact on contrast and quantification accuracy. Three levels of resolution modeling, each with increasing ray-sampling, were investigated. The resolution model was applied to both cylindrical and anthropomorphic breast phantoms with hot and cold regions. Large volume quantification results (background measurements) are unaffected by the application of resolution modeling. For smaller chambers and simulated lesions, contrast generally increases with resolution modeling. Edges of lesions also appear sharper with resolution modeling. No significant differences were seen between the various levels of resolution modeling. However, Gibbs artifacts are amplified at the boundaries of high contrast regions, which can significantly affect absolute quantification measurements. Convergence with resolution modeling is also notably slower, requiring more iterations with OSEM to reach a stable mean activity concentration. Additionally, reconstructions require far more computing time with resolution modeling due to the increase in number of sampling rays. Thus while the edge enhancement and contrast improvements may benefit lesion detection, the artifacts, slower convergence, and increased reconstruction time limit the utility of resolution modeling for both absolute quantification and clinical imaging studies.

Finally, a clinical pilot study was initiated to measure the average uptake of Tc-99m Sestamibi in healthy breast tissue. Subjects were consented from those undergoing diagnostic parathyroid studies at Duke. Each subject was injected with 25mCi of Sestamibi as part of their pre-surgical parathyroid SPECT imaging studies and scanned with the dedicated breast SPECT-CT system before their diagnostic parathyroid SPECT scan. Based on phantom studies of CT reconstructed attenuation coefficient accuracy, a slice-by-slice segmentation algorithm was developed to separate breast CT data into adipose and glandular tissue. SPECT data were scatter, attenuation, and decay corrected to the time of injection. Segmented CT images were used to measure average radiotracer concentration in the whole breast, as well as adipose and glandular tissue. With 8 subjects scanned, the average measured whole breast activity concentration was found to be 0.10µCi/mL. No significant differences were seen between adipose and glandular tissue uptake.

In conclusion, the application of various characterization and correct methods for quantitative SPECT imaging were investigated. Changes in detected scatter distribution appear to have minimal impact on quantification, and characterization of low-energy tailing for a modified scatter subtraction method yields inferior overall quantification results. Comparable quantification accuracy is seen with SPECT and CT-based attenuation maps, assuming the SPECT-based volume is fairly accurate. In general, resolution recovery within OSEM yields higher contrast, but quantification accuracy appears more susceptible to measurement location. Finally, scatter, attenuation, and resolution recovery methods, along with a breast segmentation algorithm, were implemented in a clinical imaging study for quantifying Tc-99m Sestamibi uptake. While the average whole breast uptake was measured to be 0. 10µCi/mL, no significant differences were seen between adipose and glandular tissue or when implementing resolution recovery. Thus, for future clinical imaging, it's recommended that the application of the investigated correction methods should be limited to the traditional DEW method and CT-based attenuation maps for quantification studies.

Purpose: Lung ventilation imaging offers guidance for functional avoidance during radiation therapy. Ventilation imaging modalities such as radioactive aerosols PET and SPECT, and hyperpolarized gas MRI, are not widely available at many institutions. In contrast, 4DCT images are part of standard treatment planning for lung malignancies and contain characteristics that reflect changes in the air content of the lungs due to ventilation. The purpose of this work was to develop a voxel-based delta radiomic feature extraction process using 4DCT images to quantify lung ventilation.

Materials and Methods: Twenty-five patients from the VAMPIRE dataset were used in this study with 4DCT/Galligas 4DPET images. For each patient, end-of-exhalation (EOE) and end-of-inhalation (EOI) phase CT images were both registered to the average phase CT using a contour-based deformable image registration algorithm. Next, 62 radiomic features were extracted spatially throughout the lungs using a sliding-window technique. The resulting tensor images were extracted to create 62 delta radiomic feature maps. Delta feature maps were compared with corresponding Galligas PET images by calculating Spearman correlation, mutual information. Delta feature distributions in clinical defect and non-defect lung regions were compared. The effect of sliding window kernel size was characterized to investigate its impact on correlation with Galligas PET.

Results: The best agreement between delta feature maps and Galligas PET images using a 5x5x5cm3 kernel was obtained by first-order energy, which demonstrates a mean Spearman correlation of r(s)=0.45±0.16. Other highly correlated filtered images were of features designed to capture high gray level intensities. Correlations with Galligas PET were found to increase and then saturate with increasing kernel size.

Conclusion: We have developed a promising method to quantify lung ventilation using voxel-based delta radiomics extracted from thoracic 4DCT. The results were comparable with a HU-based CT ventilation imaging (CTVI) method. Voxel-based radiomics is a potentially useful technique that can be used to generate synthetic ventilation images from standard-of-care image data.