Influence of imaging conditions on the spatial resolution of PET/CT images from different models / 中国辐射卫生

Objective To investigate the influence of PET/CT imaging conditions (acquisition time, bed overlap, reconstruction matrix, iteration times, filter kernel size, and attenuation correction) on the spatial resolution of images. Methods Two PET/CT devices, GE Discovery Elite and GE Discovery ST-16, were used to scan the elliptical column resolution model in one and two beds (list mode, acquisition time of 6 min). Images were reconstructed under the commonly used clinical reconstruction conditions (Elite: VPFX-S algorithm, ST-16: VUE Point HD algorithm) at 1-6 min/bed, different iteration times of 2-10 times, different filter kernel sizes of 2.0-10.0 mm (Elite), and different reconstruction matrices, with attenuation correction or not. The spatial resolution of reconstructed PET images was represented by the full width at half maximum (FWHM) of the line spread function. Results Under the clinical acquisition conditions, when the acquisition time was 1 min, 2 min, 3 min, 4 min, 5 min, and 6 min, the FWHMElite of spatial resolution at the center of field of view was (4.06 ± 0.08) mm, (4.05 ± 0.20) mm, (4.01 ± 0.01) mm, (4.05 ± 0.07) mm, (4.05 ± 0.03) mm, and (4.08 ± 0.06) mm, and the FWHMST-16 was (5.76 ± 0.12) mm, (5.72 ± 0.11) mm, (5.74 ± 0.09) mm, (5.78 ± 0.05) mm, (5.75 ± 0.09) mm, and (5.77 ± 0.07) mm. When the phantom was located in the center of one bed and the overlap of two beds, the line FWHMElite at the center was (4.04 ± 0.01) mm and (4.04 ± 0.01) mm, and the FWHMST-16 was (5.39 ± 0.19) mm and (5.38 ± 0.07) mm, respectively. The FWHMElite at the center was (4.07 ± 0.18) mm, (4.25 ± 0.10) mm, and (4.73 ± 0.08) mm at the matrices of 256 × 256, 192 × 192, and 128 × 128, respectively. The FWHMElite at the center was (4.65 ± 0.43) mm, (4.77 ± 0.27) mm, (4.02 ± 0.01) mm, (4.11 ± 0.04) mm, and (9.94 ± 0.01) mm at the filter kernel sizes of 2.0 mm-10.0 mm (interval of 2.0 mm), respectively. The FWHMElite at the center was (4.17 ± 0.27) mm, (4.27 ± 0.21) mm, (4.11 ± 0.05) mm, (4.18 ± 0.04) mm, and (4.12 ± 0.06) mm at 2-10 iterations (interval of 2 times), respectively. The FWHMElite at the center was (4.14 ± 0.01) mm and (4.18 ± 0.08) mm with and without attenuation correction, respectively. At the same acquisition time and bed, the spatial resolution of Elite images was improved by about 40.57% compared with that of ST-16 images. Conclusion The spatial resolution of images obtained at the matrix of 256 × 256 is higher than that of images obtained at the matrices of 192 × 192 and 128 × 128 in the same model. Elite images have the best spatial resolution at the reconstruction filter kernel size of 6.0 mm. Under the same imaging conditions, Elite images show significantly better spatial resolution compared with ST-16 images. Acquisition time, overlap of beds, iteration times, and attenuation correction have no significant effect on the spatial resolution of PET images.

The Effects of Breathing Motion on DCE-MRI Images: Phantom Studies Simulating Respiratory Motion to Compare CAIPIRINHA-VIBE, Radial-VIBE, and Conventional VIBE

OBJECTIVE: To compare the breathing effects on dynamic contrast-enhanced (DCE)-MRI between controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA)-volumetric interpolated breath-hold examination (VIBE), radial VIBE with k-space-weighted image contrast view-sharing (radial-VIBE), and conventional VIBE (c-VIBE) sequences using a dedicated phantom experiment. MATERIALS AND METHODS: We developed a moving platform to simulate breathing motion. We conducted dynamic scanning on a 3T machine (MAGNETOM Skyra, Siemens Healthcare) using CAIPIRINHA-VIBE, radial-VIBE, and c-VIBE for six minutes per sequence. We acquired MRI images of the phantom in both static and moving modes, and we also obtained motion-corrected images for the motion mode. We compared the signal stability and signal-to-noise ratio (SNR) of each sequence according to motion state and used the coefficients of variation (CoV) to determine the degree of signal stability. RESULTS: With motion, CAIPIRINHA-VIBE showed the best image quality, and the motion correction aligned the images very well. The CoV (%) of CAIPIRINHA-VIBE in the moving mode (18.65) decreased significantly after the motion correction (2.56) (p < 0.001). In contrast, c-VIBE showed severe breathing motion artifacts that did not improve after motion correction. For radial-VIBE, the position of the phantom in the images did not change during motion, but streak artifacts significantly degraded image quality, also after motion correction. In addition, SNR increased in both CAIPIRINHA-VIBE (from 3.37 to 9.41, p < 0.001) and radial-VIBE (from 4.3 to 4.96, p < 0.001) after motion correction. CONCLUSION: CAIPIRINHA-VIBE performed best for free-breathing DCE-MRI after motion correction, with excellent image quality.

The first phantom study on the diagnostic accuracy of quantitative ultrasound elastography / 中华超声影像学杂志

Objective To evaluate the effects of the range and the frequency of the compression load on the accuracy for discerning target stiffness differences in ultrasound elastography.Methods Quantitative ultrasound elastography was achieved by integrating two compression force sensors,a laptop computer and a clinical ultrasound elastographic system.The force sensors and the ultrasound probe were assembled in a 3D printed mounting bracket for continuous monitoring of compression loads during ultrasound elastography. Both the force measurements and the elastographic maps were acquired and displayed on the laptop computer in real time.Four targets of the same diameter(10.4 mm),the same depth (3 cm) and different stiffness levels (8,14,45 and 80 kPa) were examined by a HITACHI preirus,L74M linear-array transducer.Each target was evaluated 45 times with two different method(i.e.,freehand elastography and quantitative elastography),yielding 1 80 evaluations.The data were divided into the following three groups:group Ⅰ(80 kPa vs 45,14 and 8 kPa),group Ⅱ(80,45kPa vs 14,8 kPa)and group Ⅲ(80,45 and 14 kPa vs 8 kPa).Area under ROC curves(AUC)were calculated for different stiffness levels.Results In group Ⅲ, quantitative elastography yielded an greater AUC level than that of freehand elastography(P =0.0379).In group Ⅰ and group Ⅱ,two methods yielded the similar AUC levels (P = 1 .000).However,quantitative elastography was able to discern 8 kPa and 14 kPa targets (P <0.001),while freehand elastography was hard to differentiate them(P =0.258).Conclusions In comparison with freehand elastography,quantitative ultrasound elastography is able to improve the accuracy for discerning different target stiffnesses.

Effects of MR Parameter Changes on the Quantification of Diffusion Anisotropy and Apparent Diffusion Coefficient in Diffusion Tensor Imaging: Evaluation Using a Diffusional Anisotropic Phantom

OBJECTIVE: To validate the usefulness of a diffusional anisotropic capillary array phantom and to investigate the effects of diffusion tensor imaging (DTI) parameter changes on diffusion fractional anisotropy (FA) and apparent diffusion coefficient (ADC) using the phantom. MATERIALS AND METHODS: Diffusion tensor imaging of a capillary array phantom was performed with imaging parameter changes, including voxel size, number of sensitivity encoding (SENSE) factor, echo time (TE), number of signal acquisitions, b-value, and number of diffusion gradient directions (NDGD), one-at-a-time in a stepwise-incremental fashion. We repeated the entire series of DTI scans thrice. The coefficients of variation (CoV) were evaluated for FA and ADC, and the correlation between each MR imaging parameter and the corresponding FA and ADC was evaluated using Spearman's correlation analysis. RESULTS: The capillary array phantom CoVs of FA and ADC were 7.1% and 2.4%, respectively. There were significant correlations between FA and SENSE factor, TE, b-value, and NDGD, as well as significant correlations between ADC and SENSE factor, TE, and b-value. CONCLUSION: A capillary array phantom enables repeated measurements of FA and ADC. Both FA and ADC can vary when certain parameters are changed during diffusion experiments. We suggest that the capillary array phantom can be used for quality control in longitudinal or multicenter clinical studies.

Intervention Planning Using a Laser Navigation System for CT-Guided Interventions: A Phantom and Patient Study

OBJECTIVE: To investigate the accuracy, efficiency and radiation dose of a novel laser navigation system (LNS) compared to those of free-handed punctures on computed tomography (CT). MATERIALS AND METHODS: Sixty punctures were performed using a phantom body to compare accuracy, timely effort, and radiation dose of the conventional free-handed procedure to those of the LNS-guided method. An additional 20 LNS-guided interventions were performed on another phantom to confirm accuracy. Ten patients subsequently underwent LNS-guided punctures. RESULTS: The phantom 1-LNS group showed a target point accuracy of 4.0 +/- 2.7 mm (freehand, 6.3 +/- 3.6 mm; p = 0.008), entrance point accuracy of 0.8 +/- 0.6 mm (freehand, 6.1 +/- 4.7 mm), needle angulation accuracy of 1.3 +/- 0.9degrees (freehand, 3.4 +/- 3.1degrees; p < 0.001), intervention time of 7.03 +/- 5.18 minutes (freehand, 8.38 +/- 4.09 minutes; p = 0.006), and 4.2 +/- 3.6 CT images (freehand, 7.9 +/- 5.1; p < 0.001). These results show significant improvement in 60 punctures compared to freehand. The phantom 2-LNS group showed a target point accuracy of 3.6 +/- 2.5 mm, entrance point accuracy of 1.4 +/- 2.0 mm, needle angulation accuracy of 1.0 +/- 1.2degrees, intervention time of 1.44 +/- 0.22 minutes, and 3.4 +/- 1.7 CT images. The LNS group achieved target point accuracy of 5.0 +/- 1.2 mm, entrance point accuracy of 2.0 +/- 1.5 mm, needle angulation accuracy of 1.5 +/- 0.3degrees, intervention time of 12.08 +/- 3.07 minutes, and used 5.7 +/- 1.6 CT-images for the first experience with patients. CONCLUSION: Laser navigation system improved accuracy, duration of intervention, and radiation dose of CT-guided interventions.

Adaptive Iterative Dose Reduction Algorithm in CT: Effect on Image Quality Compared with Filtered Back Projection in Body Phantoms of Different Sizes

OBJECTIVE: To evaluate the impact of the adaptive iterative dose reduction (AIDR) three-dimensional (3D) algorithm in CT on noise reduction and the image quality compared to the filtered back projection (FBP) algorithm and to compare the effectiveness of AIDR 3D on noise reduction according to the body habitus using phantoms with different sizes. MATERIALS AND METHODS: Three different-sized phantoms with diameters of 24 cm, 30 cm, and 40 cm were built up using the American College of Radiology CT accreditation phantom and layers of pork belly fat. Each phantom was scanned eight times using different mAs. Images were reconstructed using the FBP and three different strengths of the AIDR 3D. The image noise, the contrast-to-noise ratio (CNR) and the signal-to-noise ratio (SNR) of the phantom were assessed. Two radiologists assessed the image quality of the 4 image sets in consensus. The effectiveness of AIDR 3D on noise reduction compared with FBP were also compared according to the phantom sizes. RESULTS: Adaptive iterative dose reduction 3D significantly reduced the image noise compared with FBP and enhanced the SNR and CNR (p < 0.05) with improved image quality (p < 0.05). When a stronger reconstruction algorithm was used, greater increase of SNR and CNR as well as noise reduction was achieved (p < 0.05). The noise reduction effect of AIDR 3D was significantly greater in the 40-cm phantom than in the 24-cm or 30-cm phantoms (p < 0.05). CONCLUSION: The AIDR 3D algorithm is effective to reduce the image noise as well as to improve the image-quality parameters compared by FBP algorithm, and its effectiveness may increase as the phantom size increases.

Evaluation of intra-cellular lipid of skeletal muscle by 1H-MR spectroscopy: in vivo and phantom study / 中华放射学杂志

Objective To elucidate the spectrum of lipid peaks in 1H-MRS of skeletal muscle and it's interpretation,to investigate the utility of 1H-MRS in evaluating intramyecellular lipid (IMCL).Methods 1H-MRS was acquired in vivo on tibialis anterior muscle (TA) and soleus muscle (S) on 5 healthy volunteers.The spectrum of the lipid peak between 0.80 and 1.80 ppm was observed with different angle between the long axis of the calf and B0.Ex vivo phantom was an cluster of capillary tubers filled with soybean oil and fat emulsion,simulating the extramyecellular lipid (EMCL) and IMCL,respectively.The spectra of the lipid peaks were compared using different angles between the phantom and Bo field.Results The lipid spectrum split to 3 to 4 peaks between 0.80 and 1.80 ppm on calf muscles,with 0.20 to 0.30 ppm interval between each neighbouring peak.The methylene peak of EMCL shifted to the right when the angle between long axis of the calf and B0 increased.The phantom could simulate the spectrum of 1H-MRS of the muscle,presenting two peaks with 0.20 to 0.30 ppm chemical shift difference between 0.80 and 1.80 ppm.They are methyl triglyceride and methylene,representing IMCL and EMCL,respectively.The peak splitting could be attributed to the high ordered muscle fibers and their chemical shift difference between inta-and extra-cellular distribution.The interval of IMCL and EMCL peaks attenuated when the angle between the muscle fiber and B0 increased from 0 to the magic angle(54.7°).Conclusion On 1H- MRS spectrum,the peak of the EMCL and IMCL splits.This indicated that 1H-MRS is an applicable method to detect IMCL noninvasively.TA is an optimizing muscle for 1H-MRS study.

Semi-Automatic Measurement of the Airway Dimension by Computed Tomography Using the Full-With-Half-Maximum Method: a Study of the Measurement Accuracy according to the Orientation of an Artificial Airway

OBJECTIVE: To develop an algorithm to measure the dimensions of an airway oriented obliquely on a volumetric CT, as well as assess the effect of the imaging parameters on the correct measurement of the airway dimension. MATERIALS AND METHODS: An airway phantom with 11 poly-acryl tubes of various lumen diameters and wall thicknesses was scanned using a 16-MDCT (multidetector CT) at various tilt angles (0, 30, 45, and 60degree). The CT images were reconstructed at various reconstruction kernels and thicknesses. The axis of each airway was determined using the 3D thinning algorithm, with images perpendicular to the axis being reconstructed. The luminal radius and wall thickness was measured by the full-width-half-maximum method. The influence of the CT parameters (the size of the airways, obliquity on the radius and wall thickness) was assessed by comparing the actual dimension of each tube with the estimated values. RESULTS: The 3D thinning algorithm correctly determined the axis of the oblique airway in all tubes (mean error: 0.91 +/- 0.82degree). A sharper reconstruction kernel, thicker image thickness and larger tilt angle of the airway axis resulted in a significant decrease of the measured wall thickness and an increase of the measured luminal radius. Use of a standard kernel and a 0.75-mm slice thickness resulted in the most accurate measurement of airway dimension, which was independent of obliquity. CONCLUSION: The airway obliquity and imaging parameters have a strong influence on the accuracy of the airway wall measurement. For the accurate measurement of airway thickness, the CT images should be reconstructed with a standard kernel and a 0.75 mm slice thickness.

Assessment of Imaging Distortion in Magnetic Resonance Imaging for Stereotactic Radiosurgery: Through Phantom Study

PURPOSE: To assess the distortion of MRI with the Leksell stereotactic radiosurgery system in variable pulse sequence and imaging plane through phantom study, to find most adequate imaging plane and pulse sequence for stereotactic radiosurgery system. MATERIALS AND METHODS: We made the phantoms for MRI and get images in variable conditions and analyzed the image distortion using image analysis program, and statistically using paired student t-test. RESULTS: The transeverse plane images had acceptable error ranges (less than 1.5mm) in all pulse sequence in both the analysis of fiducial marker in stereotactic G-frame and the phantom study. The coronal plane images had unacceptable large errors (more than 1.5mm) in the analysis of fiducial marker in the stereotactic G-frame, but had corrected small errors (less than 1.5mm) in the phantom study. CONCLUSION: We find from the phantom study that the present MR machines are adequate for stereotactic surgery system in frequently used pulse sequences, and imaging planes.