Measuring the outcomes of lateral ridge augmentation using cone-beam computed tomography.

OBJECTIVES: Lateral ridge augmentation (LRA) is a surgical technique to gain bone prior to implant placement. Performing cone-beam computed tomography (CBCT) pre- and post-surgery allows for quantitative comparison of the buccal-lingual width and the vertical height of the edentulous ridges. This study used CBCT images to evaluate the bone regeneration following surgery. METHODS: A total of 30 cases from adult patients who underwent LRA and had high-quality CBCT images taken pre- and post-surgery from the same CBCT scanner were available for the retrospective study. Study data included linear measurements of the bone ridge width and height obtained from the middle of the edentulous ridge and a volumetric measurement of bone growth at the edentulous site observed on the CBCT scan. RESULTS: The reliability of the measurements was excellent as indicated by Intra-Class Coefficient values of 0.974 or higher. There was a significant mean bone increase from pre-surgery compared to post-surgery for both the linear and volumetric measurements. The linear bone gain ranged from 1.5 to 2.5 mm and volumetric gain from 250 to 750 mm3 . However, two patients did not gain any bone. Multivariate regression showed the strongest predictors of bone gain post-surgery were the pre-surgery bone volume and a surgical site being in the mandible. For maxillary surgical sites, particularly anterior areas, the LRA surgeries were the least successful. CONCLUSIONS: LRA before implant placement helped to increase bone for the majority of patients, particularly for surgical sites in the mandible. The quantitative analyses in the CBCT images showed excellent intra-examiner agreement.

Exploring stressors and coping strategies among dental students during COVID-19 pandemic in British Columbia.

OBJECTIVE: The COVID-19 pandemic has caused stress among undergraduate dental students; coping mechanisms might be employed to deal with such stress. A cross-sectional study was conducted to explore the coping strategies employed by dental students at the University of British Columbia (UBC) in response to their self-perceived stressors during the pandemic. METHODS: An anonymous 35-item survey was distributed to all four cohorts of UBC undergraduate dental students enrolled in the 2021-2022 academic year, 229 students in total. The survey gathered sociodemographic information, self-perceived COVID-19-related stressor, and coping strategies via the Brief Cope Inventory. Adaptive and maladaptive coping were compared among the years of study, self-perceived stressors, sex, ethnicity, and living situations. RESULTS: Of the 229 eligible students, 182 (79.5%) responded to the survey. Of the 171 students that reported a major self-perceived stressor, 99 (57.9%) of them were stressed about clinical skill deficit due to the pandemic; fear of contraction was reported by 27 (15.8%). Acceptance, self-distraction, and positive reframing were the most used coping strategies among all students. The one-way ANOVA test revealed a significant difference in the adaptive coping scores among the four student cohorts (p = 0.001). Living alone was found to be a significant predictor for maladaptive coping (p < 0.001). CONCLUSION: The main cause of stress related to the COVID-19 pandemic for dental students at UBC is their clinical skills being negatively affected. Coping strategies including acceptance and self-distraction were identified. Continued mitigation efforts should be made to address students' mental health concerns and create a supportive learning environment.

In vivo measurements of lung function using respiratory-gated micro-computed tomography in a smoke-exposure model of chronic obstructive pulmonary disease.

Purpose: We hypothesize that in vivo respiratory-gated micro computed tomography (micro-CT) imaging can noninvasively provide structural and functional information about the lungs in a cigarette-exposure model of chronic obstructive pulmonary disease in mice. Approach: Female C57BL/6 mice were exposed to cigarette smoke or ambient air for 1, 3, or 6 months. Each mouse received a respiratory-gated micro-CT scan at baseline and another scan following the exposure period, while anaesthetized and free-breathing. Images were obtained representing end-expiration and peak inspiration, and measurements were performed to characterize the lung structure and compute functional metrics. Following the final micro-CT session, the mice were euthanized and the lungs prepared for histology. Results: Following 6 months of smoke-exposure, the mice exhibited larger increases in end-expiration lung volume and functional residual capacity, and a reduction in weight gain when compared with air-exposed mice. The histogram of CT numbers in the lung obtained during end-expiration also showed a shift to lower CT numbers following 6 months of smoke-exposure, indicating increased air content within the lungs. The metrics suggested air-trapping in the lung, which is consistent with emphysema. In the 3-month exposure group, only the reduction in weight gain was significant compared with the air-exposed group. Histological analysis confirmed that the 6-month smoke-exposed mice likely developed centrilobular emphysema as measured by the mean linear intercept. Conclusions: Respiratory-gated micro-CT imaging of free-breathing mice at multiple respiratory phases is noninvasive and provides additional information about lung structure and function that complements postmortem techniques and could be used to monitor changes over time.

Measurement Accuracy in Cone Beam Computed Tomography in the Presence of Metal Artifact.

PURPOSE: Cone beam computed tomography (CBCT) image quality is known to be affected by artifacts produced by metal restorations, causing image deterioration via bright streaks and loss of gray values in the vicinity of the metallic structure. The aim of the study was to determine the impact of progressively increasing metal artifacts on the measurement accuracy of commonly evaluated points in implant treatment planning. MATERIALS AND METHODS: Holes were drilled into porcine mandibles at known distances from the alveolar crest on the buccal and lingual surfaces and filled with gutta-percha. Repeated CBCT images were taken, with progressively increasing amalgam restorations and stainless steel crowns (up to a total of eight restorations per jaw). The imaging field of view (FOV) was of a single site (5 × 5 cm2) in two different locations in the mandible, as well as a full-arch FOV (10 × 5 cm2). Images were taken using clinical settings, and with increased kVp and exposure time, without metal artifact reduction (MAR) corrections. Measurements between the buccal and lingual gutta-percha points on the mandible were performed using a digital caliper and compared to the same measurements taken digitally on the CBCT images. Measurements were obtained with no restorations (baseline) and compared with increasing number of restorations. RESULTS: Comparison between caliper measurements and baseline CBCT with no metal artifact demonstrated differences ranging from 0 to 1.7 mm, with no clear detectable pattern of change related to the restorations. Compared to baseline measurements, scans with amalgam and stainless steel restorations showed a maximum difference of 0.54 ± 0.64 mm and 0.62 ± 0.64 mm, respectively, with no significant differences with increasing metal restorations. CONCLUSION: There may be a variation of up to 1.7 mm between measured anatomical points and CBCT imaging under commonly used settings. While this result may be clinically important, it does not appear to be affected by increasing metal artifact due to amalgam restorations or stainless steel crowns. The findings of this study support current clinical practices accounting for a safety margin of up to 2 mm with any CBCT image, and not limiting CBCT scans for patients with multiple metal restorations.

A three-dimensional virtual mouse generates synthetic training data for behavioral analysis.

We developed a three-dimensional (3D) synthetic animated mouse based on computed tomography scans that is actuated using animation and semirandom, joint-constrained movements to generate synthetic behavioral data with ground-truth label locations. Image-domain translation produced realistic synthetic videos used to train two-dimensional (2D) and 3D pose estimation models with accuracy similar to typical manual training datasets. The outputs from the 3D model-based pose estimation yielded better definition of behavioral clusters than 2D videos and may facilitate automated ethological classification.

Detectability of fluorescent gold nanoparticles under micro-CT and optical projection tomography imaging.

Purpose: Preclinical studies often compare micro-computed tomography (micro-CT) imaging with histology using optical microscopy of fluorescently labeled slides. However, correlating the images is difficult because the tissues appear differently in the two modalities. It would be valuable to have a single contrast medium visible on both radiographic and optical imaging. Approach: We have explored the detectability of fluorescently labeled gold nanoparticles under micro-CT and optical projection tomography (OPT) in agarose phantoms and a murine melanoma tumor model. Murine melanoma cells were used to induce tumor growth in the right hind legs of 12 C57Bl6 mice, with the maximal tumor size of 1 cm 3 . We injected Cy3 fluorescently coated gold nanorods directly into the tumors. The mice were scanned with in vivo micro-CT (for pre- and post-contrast scans). Once euthanized, the hind leg was dissected and scanned with a higher resolution specimen micro-CT and OPT. Results: The distribution of the gold nanoparticles appeared to be contained and isolated to the tumor. Alignment of micro-CT specimen scans with the OPT scans was possible, although there was also autofluorescence of the surrounding muscle tissue. Conclusions: This study highlights the potential use of fluorescently labeled gold nanoparticles for imaging murine melanoma tumors using micro-CT and OPT.

Optimization of cone beam computed tomography image quality in implant dentistry.

This study was conducted to optimize the cone beam computed tomography image quality in implant dentistry using both clinical and quantitative image quality evaluation with measurement of the radiation dose. A natural bone human skull phantom and an image quality phantom were used to evaluate the images produced after changing the exposure parameters (kVp and mA). A 10 × 5 cm2 field of view was selected for average adult. Five scans were taken with varying kVp (70-90 kVp) first at fixed 4 mA. After assessment of the scans and selecting the best kVp, nine scans were taken with 2-12 mA, and the kVp was fixed at the optimal value. A clinical assessment of the implant-related anatomical landmarks was done in random order by two blinded examiners. Quantitative image quality was assessed for noise/uniformity, artifact added value, contrast-to-noise ratio, spatial resolution, and geometrical distortion. A dosimetry index phantom and thimble ion chamber were used to measure the absorbed dose for each scan setting. The anatomical landmarks of the maxilla had good image quality at all kVp settings. To produce good quality images, the mandibular landmarks demanded higher exposure parameters than the maxillary landmarks. The quantitative image quality values were acceptable at all selected exposure settings. Changing the exposure parameters does not necessarily produce higher image quality outcomes but does affect the radiation dose to the patient. The image quality could be optimized for implant treatment planning at lower exposure settings and dose than the default settings.

Marginal Fit of Lithium Disilicate Crowns Fabricated Using Conventional and Digital Methodology: A Three-Dimensional Analysis.

PURPOSE: To compare the marginal fit of lithium disilicate (LD) crowns fabricated with digital impression and manufacturing (DD), digital impression and traditional pressed manufacturing (DP), and traditional impression and manufacturing (TP). MATERIALS AND METHODS: Tooth #15 was prepared for all-ceramic crowns on an ivorine typodont. There were 45 LD crowns fabricated using three techniques: DD, DP, and TP. Microcomputed tomography (micro-CT) was used to assess the 2D and 3D marginal fit of crowns in all three groups. The 2D vertical marginal gap (MG) measurements were done at 20 systematically selected points/crown, while the 3D measurements represented the 3D volume of the gap measured circumferentially at the crown margin. Frequencies of different marginal discrepancies were also recorded, including overextension (OE), underextension (UE), and marginal chipping. Crowns with vertical MG > 120 µm at more than five points were considered unacceptable and were rejected. The results were analyzed by one-way ANOVA with Scheffe post hoc test (α = 0.05). RESULTS: DD crowns demonstrated significantly smaller mean vertical MG (33.3 ± 19.99 µm) compared to DP (54.08 ± 32.34 µm) and TP (51.88 ± 35.34 µm) crowns. Similarly, MG volume was significantly lower in the DD group (3.32 ± 0.58 mm3 ) compared to TP group (4.16 ± 0.59 mm3 ). The mean MG volume for the DP group (3.55 ± 0.78 mm3 ) was not significantly different from the other groups. The occurrence of underextension error was higher in DP (6.25%) and TP (5.4%) than in DD (0.33%) group, while overextension was more frequent in DD (37.67%) than in TP (28.85%) and DP (18.75%) groups. Overall, 4 out of 45 crowns fabricated were deemed unacceptable based on the vertical MG measurements (three in TP group and one in DP group; all crowns in DD group were deemed acceptable). CONCLUSION: The results suggested that digital impression and CAD/CAM technology is a suitable, better alternative to traditional impression and manufacturing.

Comparison of the CTDI and AAPM report No. 111 methodology in adult, adolescent, and child head phantoms for MSCT and dental CBCT scanners.

This study investigates the dosimetry methodology proposed by the American Association of Physicists in Medicine (AAPM) task group 111 and compares with the computed tomography dose index (CTDI) method and the SEDENTEXCT DI method on one clinical multislice CT and two dental cone beam CT (CBCT) scanners using adult, adolescent, and child head phantoms. Following the AAPM method, the normalized (100 mAs) equilibrium doses ([Formula: see text]) for Toshiba Aquilion One MSCT computed using dose measurements from the central hole of the phantom ([Formula: see text]), the peripheral hole of the phantom, ([Formula: see text]), and by the [Formula: see text] equation ([Formula: see text]) are in the range from 20 to 25 mGy. For i-CAT Next Generation dental CBCT, the normalized [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] by the two SEDENTEXCT DI methods are in the range from 12 to 15 mGy. Fitting the AAPM equation is not possible for the limited scan lengths available on the CS 9300 dental CBCT. This study offers a simple CTDI-like measurement that can approximate the AAPM [Formula: see text] in clinical CBCT scanners capable of providing four or more scan lengths.

Dosimetry analysis of panoramic-imaging devices in different-sized phantoms.

The aim of this study is to measure the radiographic dose in adult, adolescent, and child head-sized PMMA phantoms for three panoramic-imaging devices: the panoramic mode on two CBCT machines (Carestream 9300 and i-CAT NG) and the Planmeca ProMax 2D. A SEDENTEXCT dose index adult phantom and custom-built adolescent and pediatric PMMA dosimetry phantoms were used. Panoramic radiographs were performed using a Planmeca ProMax 2D and the panoramic mode on a Carestream 9300 CBCT and an i-CAT NG using the protocols used clinically. Point dose measurements were performed at the center, around the periphery and on the surface of each phantom using a thimble ionization chamber. Five repeat measurements were taken at each location. For each machine, single-factor ANOVA was conducted to determine dose differences between protocols in each phantom, as well as determine the differences in absorbed dose when the same protocol was used for different-sized phantoms. For any individual phantom, using protocols with lower kVp, mA, or acquisition times resulted in statistically significant dose savings, as expected. When the same protocol was used for different-sized phantoms, the smaller phantom had a higher radiation dose due to less attenuation of x-rays by the smaller phantom and differences in the positioning of the ion chamber relative to the focal trough. The panoramic-mode on the CBCT machines produce images suitable for clinical use with similar dose levels to the stand-alone panoramic device. Significant dose savings may result by selecting age- and size- appropriate protocols for pediatric patients, but a wider range of protocols for children and adolescents may be beneficial.

A respiratory-gated micro-CT comparison of respiratory patterns in free-breathing and mechanically ventilated rats.

In this study, we aim to quantify the differences in lung metrics measured in free-breathing and mechanically ventilated rodents using respiratory-gated micro-computed tomography. Healthy male Sprague-Dawley rats were anesthetized with ketamine/xylazine and scanned with a retrospective respiratory gating protocol on a GE Locus Ultra micro-CT scanner. Each animal was scanned while free-breathing, then intubated and mechanically ventilated (MV) and rescanned with a standard ventilation protocol (56 bpm, 8 mL/kg and PEEP of 5 cm H2O) and again with a ventilation protocol that approximates the free-breathing parameters (88 bpm, 2.14 mL/kg and PEEP of 2.5 cm H2O). Images were reconstructed representing inspiration and end expiration with 0.15 mm voxel spacing. Image-based measurements of the lung lengths, airway diameters, lung volume, and air content were compared and used to calculate the functional residual capacity (FRC) and tidal volume. Images acquired during MV appeared darker in the airspaces and the airways appeared larger. Image-based measurements showed an increase in lung volume and air content during standard MV, for both respiratory phases, compared with matched MV and free-breathing. Comparisons of the functional metrics showed an increase in FRC for mechanically ventilated rats, but only the standard MV exhibited a significantly higher tidal volume than free-breathing or matched MV Although standard mechanical ventilation protocols may be useful in promoting consistent respiratory patterns, the amount of air in the lungs is higher than in free-breathing animals. Matching the respiratory patterns with the free-breathing case allowed similar lung morphology and physiology measurements while reducing the variability in the measurements.

Patient and surgeon radiation exposure during spinal instrumentation using intraoperative computed tomography-based navigation.

BACKGROUND CONTEXT: Imaging modalities used to visualize spinal anatomy intraoperatively include X-ray studies, fluoroscopy, and computed tomography (CT). All of these emit ionizing radiation. PURPOSE: Radiation emitted to the patient and the surgical team when performing surgeries using intraoperative CT-based spine navigation was compared. STUDY DESIGN/SETTING: This is a retrospective cohort case-control study. PATIENT SAMPLE: Seventy-three patients underwent CT-navigated spinal instrumentation and 73 matched controls underwent spinal instrumentation with conventional fluoroscopy. OUTCOME MEASURES: Effective doses of radiation to the patient when the surgical team was inside and outside of the room were analyzed. The number of postoperative imaging investigations between navigated and non-navigated cases was compared. METHODS: Intraoperative X-ray imaging, fluoroscopy, and CT dosages were recorded and standardized to effective doses. The number of postoperative imaging investigations was compared with the matched cohort of surgical cases. A literature review identified historical radiation exposure values for fluoroscopic-guided spinal instrumentation. RESULTS: The 73 navigated operations involved an average of 5.44 levels of instrumentation. Thoracic and lumbar instrumentations had higher radiation emission from all modalities (CT, X-ray imaging, and fluoroscopy) compared with cervical cases (6.93 millisievert [mSv] vs. 2.34 mSv). Major deformity and degenerative cases involved more radiation emission than trauma or oncology cases (7.05 mSv vs. 4.20 mSv). On average, the total radiation dose to the patient was 8.7 times more than the radiation emitted when the surgical team was inside the operating room. Total radiation exposure to the patient was 2.77 times the values reported in the literature for thoracolumbar instrumentations performed without navigation. In comparison, the radiation emitted to the patient when the surgical team was inside the operating room was 2.50 lower than non-navigated thoracolumbar instrumentations. The average total radiation exposure to the patient was 5.69 mSv, a value less than a single routine lumbar CT scan (7.5 mSv). The average radiation exposure to the patient in the present study was approximately one quarter the recommended annual occupational radiation exposure. Navigation did not reduce the number of postoperative X-rays or CT scans obtained. CONCLUSIONS: Intraoperative CT navigation increases the radiation exposure to the patient and reduces the radiation exposure to the surgeon when compared with values reported in the literature. Intraoperative CT navigation improves the accuracy of spine instrumentation with acceptable patient radiation exposure and reduced surgical team exposure. Surgeons should be aware of the implications of radiation exposure to both the patient and the surgical team when using intraoperative CT navigation.

Quantitative performance characterization of image quality and radiation dose for a CS 9300 dental cone beam computed tomography machine.

This paper aims to characterize the radiation dose and image quality (IQ) performance of a dental cone beam computed tomography (CBCT) unit over a range of fields of view (FOV). IQ and dose were measured using a Carestream 9300 dental CBCT. Phantoms were positioned in the FOV to imitate clinical positioning. IQ was assessed by scanning a SEDENTEXCT IQ phantom, and images were analyzed in ImageJ. Dose index 1 was obtained using a thimble ionization chamber and SEDENTEXCT DI phantom. Mean gray values agreed within 93.5% to 99.7% across the images, with pixel-to-pixel fluctuations of 6% to 12.5%, with poorer uniformity and increased noise for child protocols. CNR was fairly constant across FOVs, with higher CNR for larger patient settings. The measured limiting spatial resolution agreed well with 10% MTF and bar pattern measurements. Dose was reduced for smaller patient settings within a given FOV; however, smaller FOVs obtained with different acquisition settings did not necessarily result in reduced dose. The use of patient-specific acquisition settings decreased the radiation dose for smaller patients, with minimal impact on the IQ. The full set of IQ and dose measurements is reported to allow dental professionals to compare the different FOV settings for clinical use.

Investigating the effect of longitudinal micro-CT imaging on tumour growth in mice.

The aim of this study is to determine the impact of longitudinal micro-CT imaging on the growth of B16F1 tumours in C57BL/6 mice. Sixty mice received 2 × 10(5) B16F1 cells subcutaneously in the hind flank and were divided into control (no scan), 'low-dose' (80 kVp, 70 mA, 8 s, 0.07 Gy), 'medium-dose' (80 kVp, 50 mA, 30 s, 0.18 Gy) and 'high-dose' (80 kVp, 50 mA, 50 s, 0.30 Gy) groups. All imaging was performed on a fast volumetric micro-CT scanner (GE Locus Ultra, London, Canada). Each mouse was imaged on days 4, 8, 12 and 16. After the final imaging session, each tumour was excised, weighed on an electronic balance, imaged to obtain the final tumour volume and processed for histology. Final tumour volume was used to evaluate the impact of longitudinal micro-CT imaging on the tumour growth. An ANOVA indicated no statistically significant difference in tumour volume (p = 0.331, α = ß = 0.1) when discriminating against a treatment-sized effect. Histological samples revealed no observable differences in apoptosis or cell proliferation. We conclude that four imaging sessions, using standard protocols, over the course of 16 days did not cause significant changes in final tumour volume for B16F1 tumours in female C57BL/6 mice (ANOVA, α = ß = 0.1, p = 0.331).

Longitudinal follow-up of cardiac structure and functional changes in an infarct mouse model using retrospectively gated micro-computed tomography.

OBJECTIVES: Mouse models of myocardial infarction are valuable in studying the effect of genetic modifications on structural and functional remodeling of the heart. Our group recently developed a method for acquiring three-dimensional images of the beating mouse heart using micro-computed tomography (micro-CT) and retrospective gating. In this study, we evaluated cardiac function in sham and infarcted mice longitudinally, using this novel technique. MATERIALS AND METHODS: Thirteen mice (7 sham-operated, 6 infarcted; male, C57BL/6) were imaged at baseline and at weeks 1, 2, 3, and 4 postligation of the left anterior descending coronary artery. Animals were anesthetized with 1.5% isoflurane; mechanical ventilation was not used. Contrast between blood and tissue was provided by an iodinated blood-pool contrast agent (0.01 mL/g Fenestra VC). The cardiac and respiratory waveforms were recorded during the 50-second scan time, to enable retrospective gating. Once scanning was completed on week 4 postsurgery, hemodynamic measurements were performed using a Millar pressure conductance catheter. RESULTS: There were significant differences in systolic and diastolic volumes, and ejection fraction, between sham and myocardial infarction groups (P < 0.0001). A comparison of ejection fraction derived from both CT and hemodynamic measurements was not significantly different (P > 0.1). CONCLUSIONS: We have demonstrated the first use of dynamic micro-CT for monitoring cardiac remodeling, resulting from myocardial infarction, over time. The fast scan times (<1 minute) and ability to track individual animals over an entire study make this quantitative noninvasive technique a promising tool for in vivo studies of cardiac disease in mouse models.

Noninvasive quantification of tumor volume in preclinical liver metastasis models using contrast-enhanced x-ray computed tomography.

OBJECTIVES: To determine a timepoint after contrast injection that yields equal liver parenchymal and vascular enhancement in micro-computed tomography images. To evaluate the utility of images acquired during this time period for the noninvasive measurement of liver-tumor volume. MATERIALS AND METHODS: The imaging timepoint was determined by quantifying the enhancement kinetics of Fenestra VC (0.015 mL/g) in NIH III mice. In respiratory-gated images of tumor bearing mice, the ability to measure tumor volume was evaluated with a measurement variability study, and by comparing in vivo and histologically measured tumor volume. RESULTS: Eight hours after contrast injection the liver parenchyma and vasculature were equally enhanced allowing for clear delineation of the unenhanced tumors. The smallest tumor detected in this study was 1.1 mm in diameter. The coefficient of variation for tumor-volume measurement ranged from 3.6% to 12.9% and from 6.3% to 25.8% for intra and interobserver variability, respectively. In vivo and histologic tumor-volume measurements were closely correlated (r = 0.98, P < 0.0001). CONCLUSIONS: Imaging at a time period of equal liver parenchyma and vascular enhancement after contrast injection allows for clear delineation of liver-tumor borders, thereby enabling quantitative tumor-volume monitoring.

Optimization of a retrospective technique for respiratory-gated high speed micro-CT of free-breathing rodents.

The objective of this study was to develop a technique for dynamic respiratory imaging using retrospectively gated high-speed micro-CT imaging of free-breathing mice. Free-breathing C57Bl6 mice were scanned using a dynamic micro-CT scanner, comprising a flat-panel detector mounted on a slip-ring gantry. Projection images were acquired over ten complete gantry rotations in 50 s, while monitoring the respiratory motion in synchrony with projection-image acquisition. Projection images belonging to a selected respiratory phase were retrospectively identified and used for 3D reconstruction. The effect of using fewer gantry rotations--which influences both image quality and the ability to quantify respiratory function--was evaluated. Images reconstructed using unique projections from six or more gantry rotations produced acceptable images for quantitative analysis of lung volume, CT density, functional residual capacity and tidal volume. The functional residual capacity (0.15 +/- 0.03 mL) and tidal volumes (0.08 +/- 0.03 mL) measured in this study agree with previously reported measurements made using prospectively gated micro-CT and at higher resolution (150 microm versus 90 microm voxel spacing). Retrospectively gated micro-CT imaging of free-breathing mice enables quantitative dynamic measurement of morphological and functional parameters in the mouse models of respiratory disease, with scan times as short as 30 s, based on the acquisition of projection images over six gantry rotations.

Fast retrospectively gated quantitative four-dimensional (4D) cardiac micro computed tomography imaging of free-breathing mice.

OBJECTIVE: We sought to demonstrate retrospectively gated dynamic 3D cardiac micro computed tomography (CT) of free-breathing mice. MATERIALS AND METHODS: Five C57Bl6 mice were scanned using a cone-beam scanner with a slip-ring-mounted flat-panel detector. After the injection of an intravascular iodinated contrast agent, projection images were acquired over the course of 50 seconds, while the scanner rotated through 10 complete rotations. The mouse respiratory and electrocardiogram signals were recorder simultaneously with image acquisition. After acquisition, the projection images were retrospectively sorted into projections belonging to different cardiac time points, occurring only during expiration. RESULTS: Dynamic 3D cardiac images, with isotropic 150-microm voxel spacing, were reconstructed at 12-millisecond intervals throughout the cardiac cycle in all mice. The average ejection fraction and cardiac output were 58.2+/-4.6% and 11.4+/-1.3 mL/min, respectively. The measured entrance dose for the entire scan was 28 cGy. Repeat scans of the same animals showed that intrasubject variability was smaller than intersubject variability. CONCLUSIONS: We have developed a high-resolution micro computed tomography method for evaluating the cardiac function and morphology of free-breathing mice in acquisition times shorter than 1 minute.

Time-course characterization of the computed tomography contrast enhancement of an iodinated blood-pool contrast agent in mice using a volumetric flat-panel equipped computed tomography scanner.

OBJECTIVE: The objective of this study was to determine the time-course of computed tomography (CT) contrast enhancement of an iodinated blood-pool contrast agent. METHODS: Five C57BL/6 mice were anesthetized, imaged at baseline, and given an iodinated blood-pool contrast agent. Micro-CT scans were acquired at 0, 0.25, 0.5, 1, 2, 4, 8, and 24 hours after injection. The mean CT number was determined in a region of interest in 7 organs. RESULTS: The CT contrast enhancement was plotted as a function of time for each organ. We identified an imaging window immediately after injection suitable for visualizing the vascular system and a second imaging window at 24 hours for visualizing liver and spleen. CONCLUSIONS: A single injection of the blood-pool contrast agent can be used for dual-phase investigations of the vasculature (t = 0 hours) and liver (t = 24 hours), which can be applied to studies of liver tumors or disease.

Prospective respiratory-gated micro-CT of free breathing rodents.

Microcomputed tomography (Micro-CT) has the potential to noninvasively image the structure of organs in rodent models with high spatial resolution and relatively short image acquisition times. However, motion artifacts associated with the normal respiratory motion of the animal may arise when imaging the abdomen or thorax. To reduce these artifacts and the accompanying loss of spatial resolution, we propose a prospective respiratory gating technique for use with anaesthetized, free-breathing rodents. A custom-made bed with an embedded pressure chamber was connected to a pressure transducer. Anaesthetized animals were placed in the prone position on the bed with their abdomens located over the chamber. During inspiration, the motion of the diaphragm caused an increase in the chamber pressure, which was converted into a voltage signal by the transducer. An output voltage was used to trigger image acquisition at any desired time point in the respiratory cycle. Digital radiographic images were acquired of anaesthetized, free-breathing rats with a digital radiographic system to correlate the respiratory wave form with respiration-induced organ motion. The respiratory wave form was monitored and recorded simultaneously with the x-ray radiation pulses, and an imaging window was defined, beginning at end expiration. Phantom experiments were performed to verify that the respiratory gating apparatus was triggering the micro-CT system. Attached to the distensible phantom were 100 microm diameter copper wires and the measured full width at half maximum was used to assess differences in image quality between respiratory-gated and ungated imaging protocols. This experiment allowed us to quantify the improvement in the spatial resolution, and the reduction of motion artifacts caused by moving structures, in the images resulting from respiratory-gated image acquisitions. The measured wire diameters were 0.135 mm for the stationary phantom image, 0.137 mm for the image gated at end deflation, 0.213 mm for the image gated at peak inflation, and 0.406 mm for the ungated image. Micro-CT images of anaesthetized, free-breathing rats were acquired with a General Electric Healthcare eXplore RS in vivo micro-CT system. Images of the thorax were acquired using the respiratory cycle-based trigger for the respiratory-gated mode. Respiratory gated-images were acquired at inspiration and end expiration, during a period of minimal respiration-induced organ motion. Gated images were acquired with a nominal isotropic voxel spacing of 44 microm in 20-25 min (80 kVp, 113 mAs, 300 ms imaging window per projection). The equivalent ungated acquisitions were 11 min in length. We observed improved definition of the diaphragm boundary and increased conspicuity of small structures within the lungs in the gated images, when compared to the ungated acquisitions. In this work, we have characterized the externally monitored respiratory wave form of free-breathing, anaesthetized rats and correlated the respiration-induced organ motion to the respiratory cycle. We have shown that the respiratory pressure wave form is an excellent surrogate for the radiographic organ motion. This information facilitates the definition of an imaging window at any phase of the breathing cycle. This approach for prospectively gated micro-CT can provide high quality images of anaesthetized free-breathing rodents.