Correction for 'X-ray CT observation and characterization of water transformation in heavy objects' by Satoshi Takeya
et al.
,
Phys. Chem. Chem. Phys.
, 2020,
22
, 3446-3454, DOI:
10.1039/c9cp05983k
.
Background
Photon‐counting CT (PCCT) is the next‐generation CT scanner that enables improved spatial resolution and spectral imaging. For full spectral processing, higher tube voltages compared to ...conventional CT are necessary to achieve the required spectral separation. This generated interest in the potential influence of thin slice high tube voltage PCCT on overall image quality and consequently on radiation dose.
Purpose
This study first evaluated tube voltages and radiation doses applied in patients who underwent coronary CT angiography with PCCT and energy‐integrating detector CT (EID‐CT). Next, image quality of PCCT and EID‐CT was objectively evaluated in a phantom study simulating different patient sizes at these tube voltages and radiation doses.
Methods
We conducted a retrospective analysis of clinical doses of patients scanned on a conventional and PCCT system. Average patient water equivalent diameters for different tube voltages were extracted from the dose reports for both EID‐CT and PCCT. A conical phantom made of polyethylene with multiple diameters (26/31/36 cm) representing different patient sizes and containing an iodine insert was scanned with a EID‐CT scanner using tube voltages and phantom diameters that match the patient scans and characteristics. Next, phantom scans were made with PCCT at a fixed tube voltage of 120 kV and with CTDIVOL values and phantom diameters identical to the EID‐CT scans. Clinical image reconstructions at 0.6 mm slice thickness for conventional CT were compared to PCCT images with 0.4 mm slice thickness. Image quality was quantified using the detectability index (d′), which estimated the visibility of a 3 mm diameter contrast‐enhanced coronary artery by considering noise, contrast, resolution, and human visual perception. Alongside d′, noise, contrast and resolution were also individually assessed. In addition, the influence of various kernels (Bv40/Bv44/Bv48/Bv56), quantum iterative reconstruction strengths (QIR, 3/4) and monoenergetic levels (40/45/50/55 keV) for PCCT on d′ was investigated.
Results
In this study, 143 patients were included: 47 were scanned on PCCT (120 kV) and the remaining on EID‐CT (74 small‐sized at 70 kV, 18 medium‐sized at 80 kV and four large‐sized at 90 kV). EID‐CT showed 7%–17% higher d′ than PCCT with Bv40 kernel and strength four for small/medium patients. Lower monoenergetic images (40 keV) helped mitigate the difference to 1%–6%. For large patients, PCCT's detectability was up to 31% higher than EID‐CT. PCCT has thinner slices but similar noise levels for similar reconstruction parameters. The noise increased with lower keV levels in PCCT (≈30% increase), but higher QIR strengths reduced noise. PCCT's iodine contrast was stable across patient sizes, while EID‐CT had 33% less contrast in large patients than in small‐sized patients.
Conclusion
At 120 kV, thin slice PCCT enables CCTA in phantom scans representing large patients without raising radiation dose or affecting vessel detectability. However, higher doses are needed for small and medium‐sized patients to obtain a similar image quality as in EID‐CT. The alternative of using lower mono‐energetic levels requires further evaluation in clinical practice.
Objectives
The purpose of this study was to compare the image quality of coronary computed tomography angiography (CTA) subjected to deep learning–based image restoration (DLR) method with images ...subjected to hybrid iterative reconstruction (IR).
Methods
We enrolled 30 patients (22 men, 8 women) who underwent coronary CTA on a 320-slice CT scanner. The images were reconstructed with hybrid IR and with DLR. The image noise in the ascending aorta, left atrium, and septal wall of the ventricle was measured on all images and the contrast-to-noise ratio (CNR) in the proximal coronary arteries was calculated. We also generated CT attenuation profiles across the proximal coronary arteries and measured the width of the edge rise distance (ERD) and the edge rise slope (ERS). Two observers visually evaluated the overall image quality using a 4-point scale (1 = poor, 4 = excellent).
Results
On DLR images, the mean image noise was lower than that on hybrid IR images (18.5 ± 2.8 HU vs. 23.0 ± 4.6 HU,
p
< 0.01) and the CNR was significantly higher (
p
< 0.01). The mean ERD was significantly shorter on DLR than on hybrid IR images, whereas the mean ERS was steeper on DLR than on hybrid IR images. The mean image quality score for hybrid IR and DLR images was 2.96 and 3.58, respectively (
p
< 0.01).
Conclusions
DLR reduces the image noise and improves the image quality at coronary CTA.
Key Points
• Deep learning–based image restoration is a new technique that employs the deep convolutional neural network for image quality improvement.
• Deep learning–based restoration reduces the image noise and improves image quality at coronary CT angiography.
• This method may allow for a reduction in radiation exposure.
Bone metastases are common, especially in more prevalent malignancies such as breast and prostate cancer. They cause significant morbidity and draw on health-care resources. Molecular and hybrid ...imaging techniques, including SPECT/CT, PET/CT, and whole-body MRI with diffusion-weighted imaging, have improved diagnostic accuracy in staging the skeleton compared with previous standard imaging methods, allowing earlier tailored treatment. With the introduction of several effective treatment options, it is now even more important to detect and monitor response in bone metastases accurately. Conventional imaging, including radiographs, CT, MRI, and bone scintigraphy, are recognized as being insensitive and nonspecific for response monitoring in a clinically relevant time frame. Early reports of molecular and hybrid imaging techniques, as well as whole-body MRI, promise an earlier and more accurate prediction of response versus nonresponse but have yet to be adopted routinely in clinical practice. We summarize the role of new molecular and hybrid imaging methods, including SPECT/CT, PET/CT, and whole-body MRI. These modalities are associated with improvements in diagnostic accuracy for the staging and response assessment of skeletal metastases over standard imaging methods, being able to quantify biologic processes related to the bone microenvironment as well as tumor cells. The described improvements in the imaging of bone metastases and their response to therapy have led to adoption of some of these methods into routine clinical practice in some centers. These methods also provide a better way to assess the treatment response of bone metastases in clinical trials.
Emerging data from published studies are demonstrating the superiority of Ga-68 PSMA PET/CT imaging in prostate cancer. However, the low yield of the Ge-68/Ga-68 from which Gallium-68 is obtained and ...fewer installed PET/CT systems compared to the SPECT imaging systems may limit its availability. We, therefore, evaluated in a head-to-head comparison, the diagnostic sensitivity of Ga-68 PSMA PET/CT and Tc-99m PSMA SPECT/CT in patients with prostate cancer.
A total of 14 patients with histologically confirmed prostate cancer were prospectively recruited to undergo Ga-68 PSMA PET/CT and Tc-99m HYNIC PSMA SPECT/CT. The mean age of patients was 67.21 ± 8.15 years and the median PSA level was 45.18 ng/mL (range = 1.51-687 ng/mL). SUVmax of all lesions and the size of lymph nodes with PSMA avidity on Ga-68 PSMA PET/CT were determined. Proportions of these lesions detected on Tc-99m HYNIC PSMA SPECT/CT read independent of PET/CT findings were determined.
A total of 46 lesions were seen on Ga-68 PSMA PET/CT localized to the prostate (n = 10), lymph nodes (n = 24), and bones (n = 12). Of these, Tc-99m HYNIC PSMA SPECT/CT detected 36 lesions: Prostate = 10/10 (100%), lymph nodes = 15/24 (62.5%), and bones = 11/12 (91.7%) with an overall sensitivity of 78.3%. Lesions detected on Tc-99m HYNIC PSMA SPECT/CT were bigger in size (P < 0.001) and had higher SUVmax (P < 0.001) as measured on Ga-68 PSMA PET/CT compared to those lesions that were not detected. All lymph nodes greater than 10 mm in size were detected while only 28% of nodes less than 10 mm were detected by Tc-99m HYNIC PSMA SPECT/CT. In a univariate analysis, Lymph node size (P = 0.033) and the SUVmax of all lesions (P = 0.007) were significant predictors of lesion detection on Tc-99m HYNIC PSMA SPECT/CT.
Tc-99m HYNIC PSMA may be a useful in imaging of prostate cancer although with a lower sensitivity for lesion detection compared to Ga-68 PSMA PET/CT. Its use is recommended when Ga-68 PSMA is not readily available, in planning radio-guided surgery or the patient is being considered for radio-ligand therapy with Lu-177 PSMA. It performs poorly in detecting small-sized lesions hence its use is not recommended in patients with small volume disease.
Purpose:
To assess image quality and image-guidance capabilities of a cone-beam CT based small-animal image-guided irradiation unit (micro-IGRT).
Methods:
A micro-IGRT system has been developed in ...collaboration with the authors’ laboratory as a means to study the radiobiological effects of conformal radiation dose distributions in small animals. The system, the X-Rad 225Cx, consists of a 225 kVp x-ray tube and a flat-panel amorphous silicon detector mounted on a rotational C-arm gantry and is capable of both fluoroscopic x-ray and cone-beam CT imaging, as well as image-guided placement of the radiation beams. Image quality (voxel noise, modulation transfer, CT number accuracy, and geometric accuracy characteristics) was assessed using water cylinder and micro-CT test phantoms. Image guidance was tested by analyzing the dose delivered to radiochromic films fixed to BB’s through the end-to-end process of imaging, targeting the center of the BB, and irradiation of the film/BB in order to compare the offset between the center of the field and the center of the BB. Image quality and geometric studies were repeated over a 5–7 month period to assess stability.
Results:
CT numbers reported were found to be linear
(
R
2
≥
0.998
)
and the noise for images of homogeneous water phantom was 30 HU at imaging doses of approximately 1 cGy (to water). The presampled MTF at 50% and 10% reached 0.64 and
1.35
mm
−
1
, respectively. Targeting accuracy by means of film irradiations was shown to have a mean displacement error of
Δ
x
,
Δ
y
,
Δ
z
=
−
0.12
,
−
0.05
,
−
0.02
mm
, with standard deviations of 0.02, 0.20, 0.17 mm. The system has proven to be stable over time, with both the image quality and image-guidance performance being reproducible for the duration of the studies.
Conclusions:
The micro-IGRT unit provides soft-tissue imaging of small-animal anatomy at acceptable imaging doses
(
≤
1
cGy
)
. The geometric accuracy and targeting systems permit dose placement with submillimeter accuracy and precision. The system has proven itself to be stable over 2 yr of routine laboratory use
(
>
1800
irradiations
)
and provides a platform for the exploration of targeted radiation effects in small-animal models.
ABSTRACTSome patients undergoing routine SPECT/CT and PET/CT examinations during the COVID-19 pandemic may incidentally reveal findings of COVID-19–associated pneumonia (C-19AP) on localizing CT. It ...is critical for nuclear medicine physicians to develop diagnostic skills for timely recognition of typical findings of C-19AP on a localizing CT. Furthermore, it is our responsibility to know the optimal practices for safely isolating and managing such patients while protecting the staff, other patients at the facility, family and/or friend accompanying the patients, and the public in general from risky exposure to COVID-19 sources. We offer several steps following an encounter suspicious of C-19AP.
Abstract
Aims
To determine the ranges of pre-test probability (PTP) of coronary artery disease (CAD) in which stress electrocardiogram (ECG), stress echocardiography, coronary computed tomography ...angiography (CCTA), single-photon emission computed tomography (SPECT), positron emission tomography (PET), and cardiac magnetic resonance (CMR) can reclassify patients into a post-test probability that defines (>85%) or excludes (<15%) anatomically (defined by visual evaluation of invasive coronary angiography ICA) and functionally (defined by a fractional flow reserve FFR ≤0.8) significant CAD.
Methods and results
A broad search in electronic databases until August 2017 was performed. Studies on the aforementioned techniques in >100 patients with stable CAD that utilized either ICA or ICA with FFR measurement as reference, were included. Study-level data was pooled using a hierarchical bivariate random-effects model and likelihood ratios were obtained for each technique. The PTP ranges for each technique to rule-in or rule-out significant CAD were defined. A total of 28 664 patients from 132 studies that used ICA as reference and 4131 from 23 studies using FFR, were analysed. Stress ECG can rule-in and rule-out anatomically significant CAD only when PTP is ≥80% (76–83) and ≤19% (15–25), respectively. Coronary computed tomography angiography is able to rule-in anatomic CAD at a PTP ≥58% (45–70) and rule-out at a PTP ≤80% (65–94). The corresponding PTP values for functionally significant CAD were ≥75% (67–83) and ≤57% (40–72) for CCTA, and ≥71% (59–81) and ≤27 (24–31) for ICA, demonstrating poorer performance of anatomic imaging against FFR. In contrast, functional imaging techniques (PET, stress CMR, and SPECT) are able to rule-in functionally significant CAD when PTP is ≥46–59% and rule-out when PTP is ≤34–57%.
Conclusion
The various diagnostic modalities have different optimal performance ranges for the detection of anatomically and functionally significant CAD. Stress ECG appears to have very limited diagnostic power. The selection of a diagnostic technique for any given patient to rule-in or rule-out CAD should be based on the optimal PTP range for each test and on the assumed reference standard.
Fractional flow reserve (FFR) computation from coronary computed tomography angiography (CTA) datasets (FFRCT) has emerged as a promising noninvasive test to assess hemodynamic severity of coronary ...artery disease (CAD), but has not yet been compared with traditional functional imaging.
The purpose of this study was to evaluate the diagnostic performance of FFRCT and compare it with coronary CTA, single-photon emission computed tomography (SPECT), and positron emission tomography (PET) for ischemia diagnosis.
This subanalysis involved 208 prospectively included patients with suspected stable CAD, who underwent 256-slice coronary CTA, 99mTc-tetrofosmin SPECT, 15OH2O PET, and routine 3-vessel invasive FFR measurements. FFRCT values were retrospectively derived from the coronary CTA images. Images from each modality were interpreted by core laboratories, and their diagnostic performances were compared using invasively measured FFR ≤0.80 as the reference standard.
In total, 505 of 612 (83%) vessels could be evaluated with FFRCT. FFRCT showed a diagnostic accuracy, sensitivity, and specificity of 87%, 90%, and 86% on a per-vessel basis and 78%, 96%, and 63% on a per-patient basis, respectively. Area under the receiver-operating characteristic curve (AUC) for identification of ischemia-causing lesions was significantly greater for FFRCT (0.94 and 0.92) in comparison with coronary CTA (0.83 and 0.81; p < 0.01 for both) and SPECT (0.70 and 0.75; p < 0.01 for both), on a per-vessel and -patient level, respectively. FFRCT also outperformed PET on a per-vessel basis (AUC 0.87; p < 0.01), but not on a per-patient basis (AUC 0.91; p = 0.56). In the intention-to-diagnose analysis, PET showed the highest per-patient and -vessel AUC followed by FFRCT (0.86 vs. 0.83; p = 0.157; and 0.90 vs. 0.79; p = 0.005, respectively).
In this study, FFRCT showed higher diagnostic performance than standard coronary CTA, SPECT, and PET for vessel-specific ischemia, provided coronary CTA images were evaluable by FFRCT, whereas PET had a favorable performance in per-patient and intention-to-diagnose analysis. Still, in patients in whom 3-vessel FFRCT could be analyzed, FFRCT holds clinical potential to provide anatomic and hemodynamic significance of coronary lesions.
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