No abstract

We present a solution to meet an unmet clinical need of an in‐situ “close look” at a pulmonary nodule or at the margins of a pulmonary cyst revealed by a primary (screening) chest CT while the patient is still in the scanner. We first evaluated options available on current whole‐body CT scanners for high resolution screening scans, including ROI reconstruction of the primary scan data and HRCT, but found them to have insufficient SNR in lung tissue or discontinuous slice coverage. Within the capabilities of current clinical CT systems, we opted for the solution of a secondary, volume‐of‐interest (VOI) protocol where the radiation dose is focused into a short‐beam axial scan at the z position of interest, combined with a small‐FOV reconstruction at the xy position of interest. The objective of this work was to design a VOI protocol that is optimized for targeted lung imaging in a clinical whole‐body CT system. Using a chest phantom containing a lung‐mimicking foam insert with a simulated cyst, we identified the appropriate scan mode and optimized both the scan and recon parameters. The VOI protocol yielded 3.2 times the texture amplitude‐to‐noise ratio in the lung‐mimicking foam when compared to the standard chest CT, and 8.4 times the texture difference between the lung mimicking and reference foams. It improved details of the wall of the simulated cyst and better resolution in a line‐pair insert. The Effective Dose of the secondary VOI protocol was 42% on average and up to 100% in the worst‐case scenario of VOI positioning relative to the standard chest CT. The optimized protocol will be used to obtain detailed CT textures of pulmonary lesions, which are biomarkers for the type and stage of lung diseases.

In pathology protocols, a tissue block, such as one containing a mouse brain or a biopsy sample from a patient, can produce several hundred thin sections. Substantial time may be required to analyse all sections. In cases of uncertainty regarding which sections to focus on, noninvasive scout imaging of intact blocks can help in guiding the pathology procedure. The scouting step is ideally done in a time window of minutes without special sample preparation that may interfere with the pathology procedures. The challenge is to obtain some visibility of unstained tissue structures at sub‐10 µm resolution. We explored a novel x‐ray tomosynthesis method as a way to maximise contrast‐to‐noise ratio, a determinant of tissue visibility. It provided a z‐stack of thousands of images at 7.3 μm resolution (10% contrast, half‐period of 68.5 line pairs/mm), in scans of 5‐15 minutes. When compared with micro‐CT scans, the straight‐line tomosynthesis scan did not need to rotate the sample, which allowed flat samples, such as paraffin blocks, to be kept as close as possible to the x‐ray source. Thus, given the same hardware, scan time and resolution, this mode maximised the photon flux density through the sample, which helped in maximising the contrast‐to‐noise ratio. The tradeoff of tomosynthesis is incomplete 3D information. The microtomosynthesis scanner has scanned 110 unstained human and animal tissue samples as part of their respective pathology protocols. In all cases, the z‐stack of images showed tissue structures that guided sectioning or provided correlative structural information. We describe six examples that presented different levels of visibility of soft tissue structures. Additionally, in a set of coronary artery samples from an HIV patient donor, microtomosynthesis made a new discovery of isolated focal calcification in the internal elastic lamina of coronary wall, which was the onset of medial calcific sclerosis in the arteries.

To evaluate the accuracy of cyst score measurements by standard high-resolution helical volume chest CT (HRCT) in patients with lymphangioleiomyomatosis (LAM), using a short z-length ultra-high resolution rescan (UH re-scan) as the reference. In cystic lung diseases, cyst score is derived from CT scans and defined as the percentage of the total lung parenchymal volume occupied by cysts, a biomarker which measures the severity of the disease. Methods: In a prospective study of 73 LAM patients, each patient received the standard HRCT chest scan and a short z-length UH re-scan. Cyst scores were acquired from both scans using a standard FDA-approved scoring software on the CT scanner. Results: The limited UH re-scan resolved small cysts that were not resolved in the HRCT. The HRCT-derived cyst scores were on average 59.6% of the reference values from the UH re-scan (p = 4.7e-25). The amount of underestimation by HRCT varied from patient to patient, with an inter-quartile range of 29.8% and standard deviation of 20.7%. The overall trend was more pronounced underestimation for patients with lower cyst scores. For patients whose reference cyst scores were below 15 (n = 29), the HRCT cyst scores were 46.9 ± 21.6% of reference values (p = 7.4e-12), while for the rest of the patients (n = 44) the HRCT cyst scores were 68.0 ± 15.3% of reference values (p = 1.2E-19). Reconstructing the HRCT images to the resolution of the UH re-scan further widened the spread of the discrepancy between HRCT and reference values due to increased image noise, and did not provide accurate cyst scores. Conclusion: Cyst scores derived from standard high-resolution helical volume chest CT significantly underestimates the percentage lung volume occupied by cysts. This inaccuracy needs to be taken into consideration when cyst score is used as part of the CT assessment of the patient's condition.

Histopathology protocols often require sectioning and processing of numerous microscopy slides to survey a sample. Trade-offs between workload and sampling density means that small features can be missed. Aiming to reduce the workload of routine histology protocols and the concern over missed pathology in skipped sections, we developed a prototype x-ray tomographic scanner dedicated to rapid scouting and identification of regions of interest in pathology specimens, thereby allowing targeted histopathology analysis to replace blanket searches. In coronary artery samples of a deceased HIV patient, the scanner, called Tomopath, obtained depth-resolved cross-sectional images at 15 µm resolution in a 15-minute scan, which guided the subsequent histological sectioning and microscopy. When compared to a commercial tabletop micro-CT scanner, the prototype provided several-fold contrast-to-noise ratio in 1/11th the scan time. Correlated tomographic and histological images revealed two types of micro calcifications: scattered loose calcifications typically found in atherosclerotic lesions; isolated focal calcifications in one or several cells in the internal elastic lamina and occasionally in the tunica media, which we speculate were the initiation of medial calcification linked to kidney disease, but rarely detected at this early stage due to their similarity to particle contaminants introduced during histological processing, if not for the evidence from the tomography scan prior to sectioning. Thus, in addition to its utility as a scouting tool, in this study it provided complementary information to histological microscopy. Overall, the prototype scanner represents a step toward a dedicated scouting and complementary imaging tool for routine use in pathology labs.

Ultrahigh-resolution, low-dose rescans in a region of interest following a general screening computed tomography (CT) scan is motivated by the need to reduce invasive tissue biopsy procedures in cancer screening. We describe a new method to meet the conflicting demands of ultrahigh resolution, high-speed and ultralow-dose, and the first proof-of-concept experiment. With improving detector resolution, the limiting factor for the system resolution of whole-body CT scanners shifts to the penumbra of the source focal spot. The penumbra unsharpness is minimized by inserting flat-panel detector(s) that are in direct contact with the body. In the hybrid system, the detector insert and the CT detector acquire data simultaneously, whereby the standard CT images give the position and orientation of the detector insert(s) as needed for tomosynthesis reconstruction. Imaging tests were performed with a compact photon-counting detector insert on resolution targets of both high- and low-contrast as well as a mouse specimen, all inside a body phantom. Detector insert tomosynthesis provided twice the resolution of the CT scanner alone at the same dose concentration. The short 2-cm beam collimation of the tomosynthesis rescan gave an effective dose equivalent to 6% of an average CT scan in the chest or abdomen.

No abstract

Purpose: Two Varian on‐board imaging (OBI) systems have been installed and commissioned in our clinic. Over recent months, a daily QA procedure was developed to monitor system's performance and a clinical study was implemented to transition electronic portal image (EPI) guided to OBI guided prostate treatments. Method and Materials: A Penta‐Guide phantom (QUASAR™) is used for daily QA. The functions of match and couch auto motion in the OBI kilo‐voltage (kV) and OBI‐CBCT systems are tested. For the clinical study, to be finished in April, 2008, 14 prostate (78Gy/39) patients have been recruited. CBCT soft tissue‐based (ST) match and couch shift are performed twice a week and kV‐orthogonal fudical marker (FM) match and shift are executed 3 times a week for each patient before treatment. EPI FM match, our standard image guided procedure is used to verify the OBI match and couch motion. The differences are recorded. Results: Daily QA data over 5 months show that the coincidence between EPI and OBI after couch motion is 0.1±0.5mm, −0.2±0.6mm and −1.3±0.6mm (2σ) in RL, SI and AP direction, respectively. The AP mean was caused by the systematic couch motion error. For the clinical study, the preliminary data from the first 8 patients have been analyzed. The differences between OBI‐kV FM match and EPI FM match are −0.1±1.6mm, −0.4±1.8mm and −1.2±2.6mm (2σ) in RL, SI and AP direction, respectively. The differences between OBI‐CBCT ST match and EPI‐FM match are −0.9±4.1mm, −0.8±5.0mm and −1.6±5.1mm (2σ) in RL, SI and AP direction respectively. The AP mean is largely due to the systematic treatment couch motion error. Conclusion: The daily QA is comprehensive to capture systematic errors; OBI‐kV FM and EPI FM match agree within 3 mm in all three directions and CBCT‐ST match demonstrates larger variations of 5mm compared with EPI‐FM in three directions.