Hounsfield Unit Value of Interpeduncular Cistern Hematomas Can Predict Symptomatic Vasospasm.

Background and Purpose- Symptomatic vasospasm is an important factor that affects the outcomes of aneurysmal subarachnoid hemorrhage. Subarachnoid blood volume can predict symptomatic vasospasm, and we postulated that the blood clot density would also be an important factor involved in such events. The present study aimed to determine the relationship between the incidence of symptomatic vasospasm and the Hounsfield unit (HU) value of the interpeduncular cistern that reflects the density of hematomas. Methods- Data from 323 patients admitted and treated at a single center between 2008 and 2017 within 24 hours of subarachnoid hemorrhage onset were retrospectively analyzed. Initial HU values of the interpeduncular cistern were measured using CT, then correlations with the incidence of symptomatic vasospasm and HU values as well as other variables were assessed. Results- Symptomatic vasospasm developed in 54 (16.7%) of the 323 patients. The incidence of symptomatic vasospasm was low (1.8%, 2/166) for HU <50, but this incidence increased greatly when the HU value exceeded 50 (23.7%, 22/93 for HU >50 to ≤60, and 45.3%, 29/64 for HU >60). The odds ratio for symptomatic vasospasm was 2.0 (95% CI, 1.6-2.4) per 5 HU increase. Symptomatic vasospasm correlated significantly with intraventricular hemorrhage (P=0.05) and with intracerebral hematoma (P=0.046) but even more significantly with the HU value of the interpeduncular cistern (P<0.0001). Conclusions- The HU value of the interpeduncular cistern on initial CT is an accurate and reliable predictor of symptomatic vasospasm.

The effect of the section thickness used for 2- and 3-dimensional quantification of dual-energy perfusion computed tomography.

PURPOSE: To retrospectively investigate the effect of the section thickness used for quantifying dual-energy perfusion computed tomography (DEpCT) during 2- and 3-dimensional evaluation. METHODS: Sixty-six patients (22 males and 44 females; mean age, 59.3 years) suspected of having an acute pulmonary embolism underwent DEpCT, and 15patients were diagnosed to have intrapulmonary clots (IPCs). Two-dimensional DEpCT images were reconstructed into various section thicknesses from 1 to 10 mm at the main pulmonary artery, and the ratios of the low attenuation area (LAA) ranging from 1 to 5 HU (%LAA5) and 10 HU (%LAA10) on DEpCT were compared with the relative areas of the lung with attenuation coefficients lower than -950 HU (RA-950) using the lung CT images of each section thickness. Three-dimensional values of DEpCT were reconstructed with 3 different section thicknesses (1, 3, and 10 mm) and were analyzed for the presence of IPC burden using the factors suggesting IPC burden, including the right/left ventricular diameter ratio and CT obstruction index. RESULTS: The mean attenuation and image noise were decreased as the section thickness increased. In the 2-dimensional analysis, the %LAA5 and %LAA10 had the smallest value at 1-mm section, and DEpCT with thinner sections had a correlation with the RA-950 (r = 0.22-0.23, P < 0.05). The 3-dimensional values of DEpCT reconstructed with a 1- or 3-mm section thickness had a correlation with the CT obstruction index (r = 0.52-0.59, P < 0.05) and right/left ventricular diameter ratio (r = 0.60-0.68, P < 0.01). CONCLUSIONS: The thinner images should be used for 2- and 3-dimensional quantification of DEpCT.

The effect of a pre-reconstruction process in a filtered back projection reconstruction on an image quality of a low tube voltage computed tomography.

This study aims to evaluate the effect of pre-reconstruction process for low tube voltage computed tomography (CT) on image quality of filtered back projection (FBP) reconstruction. Small and large quality assurance water phantoms (19 and 33 cm diameter) were scanned on a third-generation dual-source CT with 70 kVp and 120 kVp at various dose levels. Image quality was assessed in terms of the noise power spectrum (NPS) and task-based transfer function (TTF). NPSs and TTFs in the small phantom were comparable between 70 and 120 kVp protocols. In the large phantom, the curves of the NPS changed and the TTF decreased even at the high-dose levels for 70 kVp protocol compared to 120 kVp protocol. Our results indicated that the pre-reconstruction process is performed in low tube voltage CT for large objects even for the FBP reconstruction and has an effect on the image quality.

Patient dose reduction for a localizer radiograph with an additional tin filter in chest-abdomen-pelvis, spine, and head computed tomography examinations.

This study aimed to evaluate the dose reduction potential of adding a tin filter to localizer radiographs (LR) on computed tomography (CT) examinations in both phantom and clinical studies. LRs were performed using combinations of 120 kVp and 20 mA (120/20), 100 kVp with a tin filter, and 50 mA or 20 mA (Sn100/50, Sn100/20). For the phantom experiment, entrance surface doses (ESD) of the LRs were evaluated for each protocol using an anthropomorphic phantom. This retrospective clinical study included 700 patients (300 for chest-pelvis, 200 for spine, and 200 for head CTs). The volume CT dose indices (CTDIvols) of the main CT scans were recorded and placed into one of three groups based on body mass index (BMI): underweight, normal-weight, and overweight, to evaluate the effect of LR acquisition conditions on the performance of the automatic tube current modulation technique of subsequent CT scans. The ESDs of all LRs with the Sn100/50 protocol were 0.03 mGy, a decrease of more than 80% compared to those of the 120/20 protocol. Moreover, the Sn100/20 protocol reduced ESD to 0.02 mGy. In chest-pelvis CT, there were no significant differences in the CTDIvol between with and without a tin filter for each BMI group. However, the lateral LRs with the tin filter on the spine CT slightly reduced the CTDIvol in normal-weight and overweight patients. Although there is room to optimize the acquisition conditions for larger patients, an additional tin filter for LR is a useful means to efficiently reduce ESDs.

A Triphasic Split-bolus Contrast Injection Protocol for Artery-vein Separation During Pulmonary Computed Tomographic Angiography.

PURPOSE: Accurate artery-vein separation on pulmonary computed tomographic (CT) angiography is desirable for preoperative 3-dimensional image simulation, while using a minimal amount of contrast medium. This study aimed to verify whether a split-bolus contrast enhancement protocol with test-bolus tracking would provide contrast differentiation between the pulmonary arteries (PA) and pulmonary veins (PV) during high-pitch single-pass CT angiography. MATERIALS AND METHODS: Fifty patients underwent pulmonary CT angiography with a triphasic split-bolus injection protocol with the main bolus of contrast medium for 6 seconds, followed by a subsequent bolus of 20% diluted contrast medium/80% saline for another 6 seconds and a 5-second saline chaser. The single-scan timing was individually tailored to the peak enhancement at the left atrium, that is, the pulmonary-venous dominant phase, by monitoring a time-enhancement curve with test bolus. RESULTS: Time-enhancement curves of the test bolus demonstrated that the interval times between the peak enhancements at the PA and PV were ~6 seconds. For contrast enhancement image analyses with our protocol, the attenuation measurements at the main PA and left atrium were performed. The mean (SD) CT numbers were 246.4 (50.0) HU at the main PA, and 410.8 (59.0) HU at the left atrium. The mean difference in the CT numbers was 164.4 HU (95% confidence interval: 149.2-179.6, P <0.001) between the main PA and left atrium. CONCLUSIONS: Our contrast enhancement protocol for high-pitch single-pass pulmonary CT angiography could provide the desired artery-vein separation while maintaining adequate attenuations of the pulmonary vasculature.

Biological fingerprint for patient verification using trunk scout views at various scan ranges in computed tomography.

Immediate verification of whether a patient being examined is correct is desirable, even if the scan ranges change during different examinations for the same patient. This study proposes an advanced biological fingerprint technique for the rapid and reliable verification of various scan ranges in computed tomography (CT) scans of the torso of the same patient. The method comprises the following steps: geometric correction of different scans, local feature extraction, mismatch elimination, and similarity evaluation. The geometric magnification correction was aligned at the scanner table height in the first two steps, and the local maxima were calculated as the local features. In the third step, local features from the follow-up scout image are matched to those in the corresponding baseline scout image via template matching and outlier elimination via a robust estimator. We evaluated the correspondence rate based on the inlier ratio between corresponding scout images. The ratio of inliers between the baseline and follow-up scout images was assessed as the similarity score. The clinical dataset, including chest, abdomen-pelvis, and chest-abdomen-pelvis scans, included 600 patients (372 men, 68 ± 12 years) who underwent two routine torso CT examinations. The highest area under the receiver operating characteristic curve (AUC) was 0.996, which was sufficient for patient verification. Moreover, the verification results were comparable to the conventional method, which uses scout images in the same scan range. Patient identity verification was achieved before the main scan, even in follow-up torso CT, under different scan ranges.

[Evaluation of image quality of multiplanar reconstruction images: Effect of Z-increment of original axial images].

PURPOSE: The aim of our study was to evaluate the image quality of multiplanar reconstruction images (MPRs) focusing on the effect of z-increment of original axial images using signal to noise ratio (SNR) measurement in in- plane and longitudinal directions. METHODS AND MATERIALS: SNRs of MPRs were calculated using modulation transfer function (MTF) and noise power spectrum (NPS). We scanned a bead phantom with a diameter of 0.1 mm and a water phantom with a diameter of 250 mm for calculating MTF and NPS using a MDCT with 0.5 s per rotation, 1.0 pitch and 64 x 0.6 mm collimation, and 50 mm field of view. Axial images for generating MPRs were reconstructed with standard kernel (B40), and 1.00 mm slice width. Coronal images were generated from two datasets with 0.1 mm and 0.5 mm z-increments of axial images respectively. For measuring the SNRs, the MTFs and NPSs in in-plane and longitudinal directions of each dataset were calculated from coronal bead images and coronal uniform noise images, respectively. Differences of MTF, NPS, and SNR were compared in in-plane and longitudinal directions. RESULTS: The MTF of longitudinal direction of the dataset with 0.1 mm z-increment was higher than the dataset with 0.5 mm z-increment. 10% MTFs of longitudinal direction with 0.1 mm and 0.5 mm z-increments were 0.75 cycles/mm and 0.68 cycles/mm, respectively. Conversely, the NPS of longitudinal direction of the dataset with a 0.1 mm z-increment was lower than the dataset with a 0.5 mm z-increment. As a consequence, the SNRs of longitudinal direction had relatively no difference between the datasets. In in-plane direction, MTFs, NPSs and SNRs had no differences between the datasets. CONCLUSION: A tradeoff relationship was indicated between spatial resolution and noise characteristic in the longitudinal direction due to the effects of different z-increment of original axial images used in generating MPRs. MPR using 0.5 mm z-increment of axial images had comparable SNR to MPR using 0.1 mm z-increment of axial images in our experimental condition. CLINICAL RELEVANCE/APPLICATION: Using 0.5 mm z-increment of original axial images for generating MPRs is effective for reducing the data volume, reconstruction time and transfer time without reducing image quality.

[Measurement of residual effect in the amorphous selenium flat panel detector system].

The purpose of this study was to evaluate the residual effect generated by the amorphous selenium flat panel detector system (a-Se FPD). A residual effect occurs as a result of the addition of delayed electrons by previous X-ray irradiation joining the signal and change in detector sensitivity caused by hole-electron recombination or trapped electrons in a-Se. To evaluate the effect of previous radiation exposure, we irradiated a-Se FPD that were half-shielded by a 3 mm thick lead plate. A residual effect was generated in irradiated areas, with the unirradiated areas serving as reference points. Next, we removed the lead plate and took a new image using uniform irradiation. The difference in pixel value between irradiated and nonirradiated areas was measured using a variety of time intervals between each exposure. Through a comparison of pixel values from images taken over various time intervals, we discovered our system needs 20 hours to return to a normal state and become capable of producing a residual-free image.

Usefulness of biological fingerprint in magnetic resonance imaging for patient verification.

The purpose of our study is to investigate the feasibility of automated patient verification using multi-planar reconstruction (MPR) images generated from three-dimensional magnetic resonance (MR) imaging of the brain. Several anatomy-related MPR images generated from three-dimensional fast scout scan of each MR examination were used as biological fingerprint images in this study. The database of this study consisted of 730 temporal pairs of MR examination of the brain. We calculated the correlation value between current and prior biological fingerprint images of the same patient and also all combinations of two images for different patients to evaluate the effectiveness of our method for patient verification. The best performance of our system were as follows: a half-total error rate of 1.59 % with a false acceptance rate of 0.023 % and a false rejection rate of 3.15 %, an equal error rate of 1.37 %, and a rank-one identification rate of 98.6 %. Our method makes it possible to verify the identity of the patient using only some existing medical images without the addition of incidental equipment. Also, our method will contribute to patient misidentification error management caused by human errors.

Automatic ROI construction for analyzing time-signal intensity curve in dynamic contrast-enhanced MR imaging of the breast.

Our purpose in this study was to construct a 3-dimensional (3D) region of interest (ROI) for analyzing the time-signal intensity curve (TIC) semi-automatically in dynamic contrast-enhanced magnetic resonance (DCE-MR) imaging of the breast. DCE-MR breast imaging datasets were acquired by a 3.0-Tesla MR system with the use of a 3D fast gradient echo sequence. The essential idea in the new method was to analyze each pixel and to construct an ROI made up of pixels with similar TICs. First, an analyst selected a starting point in the contrast media-enhanced tumor. Second, we calculated Pearson's correlation coefficients (CCs) between the TIC in the starting coordinate selected by the analyst and the TIC in the other coordinates. Third, ROI pixels were selected if their CC threshold satisfied a level of coefficient variation of the ROI determined by prior research performed in our institution. We made a retrospective review of patients who underwent breast DCE-MR examination for pre-operative diagnosis. To confirm the feasibility of the resulting 3D-ROI from TIC analysis, we compared Fischer's score obtained from 3D-ROI by applying a new method to a score obtained from a manually selected 2-dimensional (2D) ROI which was used during routine clinical examination. The Fischer's scores obtained from both the automatically selected 3D-ROI and the manually selected 2D-ROI showed almost equivalent results. Thus, we considered that the new method was comparable to the conventional method. Furthermore, the new method has the potential to be used for evaluation of the extent of tumors.

Added value of lung perfused blood volume images using dual-energy CT for assessment of acute pulmonary embolism.

PURPOSE: To investigate the added value of lung perfused blood volume (LPBV) using dual-energy CT for the evaluation of intrapulmonary clot (IPC) in patients suspected of having acute pulmonary embolism (PE). MATERIALS AND METHODS: Institutional review board approval was obtained for this retrospective study. Eighty-three patients suspected of having PE who underwent CT pulmonary angiography (CTPA) using a dual-energy technique were enrolled in this study. Two radiologists who were blinded retrospectively and independently reviewed CTPA images alone and the combined images with color-coded LPBV over a 4-week interval, and two separate sessions were performed with a one-month interval. Inter- and intraobserver variability and diagnostic accuracy were evaluated for each reviewer with receiver operating characteristic (ROC) curve analysis. RESULTS: Values for inter- and intraobserver agreement, respectively, were better for CTPA combined with LPBV (ICC=0.847 and 0.937) than CTPA alone (ICC=0.748 and 0.861). For both readers, diagnostic accuracy (area under the ROC curve [Az]) were also superior, when CTPA alone (Az=0.888 [reader 1] and 0.912 [reader 2]) was compared with that after the combination with LPBV images (Az=0.966 [reader 1] and 0.959 [reader 2]) (p<0.001). However, Az values of both images might not have significant difference in statistics, because Az value of CTPA alone was high and 95% confidence intervals overlapped in both images. CONCLUSION: Addition of dual-energy perfusion CT to CTPA improves detection of peripheral IPCs with better interobserver agreement.

Dual-energy perfusion CT of non-diseased lung segments using dual-source CT: correlation with perfusion SPECT.

PURPOSE: To determine the utility of dual-energy perfusion CT (DEpCT) of non-diseased lung segments, using dual-source CT, in comparison with perfusion single-photon emission computed tomography (SPECT). MATERIALS AND METHODS: 28 patients (18 male and 10 female; mean age 63 years; age range 18-86 years) underwent DEpCT and SPECT within a 3-day interval. The presence and location of perfusion defects in each segment of the lungs were evaluated. RESULTS: Perfusion defects were noted in 7 of 361 segments (1.9%) by DEpCT and in 19 of 361 segments (5.3%) by perfusion SPECT. DEpCT was in good agreement with perfusion SPECT for 338 of 361 segments (93.6%). Intraobserver agreement was also good, ranging from 93.4 to 93.6% (κ = 0.64-0.75, p < 0.01). CONCLUSION: For non-diseased lung segments, DEpCT correlated well with SPECT.

Comparison of lumbar drainage and external ventricular drainage for clearance of subarachnoid clots after Guglielmi detachable coil embolization for aneurysmal subarachnoid hemorrhage.

OBJECTIVE: Subarachnoid clots play an important role in development of delayed vasospasm after subarachnoid hemorrhage (SAH). The purpose of this study was to compare clearance of subarachnoid clots using external ventricular drainage (EVD) or lumbar drainage (LD) after Guglielmi detachable coil (GDC) embolization for aneurysmal SAH. METHODS: The subjects were 51 treated with GDC coil embolization for aneurysmal Fisher group 3 SAH within 72 h of ictus. Software-based volumetric quantification of the subarachnoid clots was performed on CT scans and the hemoglobin (Hb) level was measured in CSF drained from each catheter. RESULTS: Clearance of subarachnoid clots was more rapid in patients treated with LD (n=34) compared to those treated with EVD (n=17). The Hb level in CSF was significantly higher in the LD group on Days 4-5 after onset of SAH (P<0.05), but was higher in the EVD group on Days 8-9. The incidence of symptomatic vasospasm did not differ between the two groups. The rate of occurrence of a new low density area on CT scans was higher in patients treated with EVD, but not significantly higher than the rate in the LD group. CONCLUSION: GDC embolization followed by lumbar drainage accelerates the reduction of subarachnoid clots, but EVD may contribute to stasis of hemorrhage within subarachnoid spaces.

Correction of liver displacement due to irregular respiration for SPECT images obtained using a multiple short-time acquisition with breath-holding technique.

Recently, a new method for acquiring single photon emission computed tomography (SPECT) data during breath-holding with a high-speed rotation (HSR-SPECT) technique was applied to hepatic-function scintigraphy. This technique can suppress motion artifact caused by respiration. However, it is challenging to apply this technique to patients with respiratory problems. Our purpose in this study was to analyze projection data and correct liver displacement due to irregular respiration during technetium-99m-diethylenetriaminepentaacetic acid galactosyl human serum albumin ((99m)Tc-GSA) liver SPECT scans. We calculated cross-correlation functions (CCFs) for both intra- and inter-projections to correct irregular projections by shifting them in the longitudinal direction enough to maximize the CCFs. We integrated all of the shifted projections and created a synthesis projection which was used to reconstruct SPECT images. To confirm the effectiveness of our method, we did both a phantom study and a clinical retrospective review. In the phantom study, blurring artifacts due to displacement were reduced using our method. Post-processing using our method showed improvements in the normalized mean square error values ranging from 0.18 to 0.06. Furthermore, our method showed no disadvantage or miss-correction if we applied our method to data without displacement. In the clinical review, our method improved the image clarity for patients who could not repeat consistent respiration. In both the phantom simulation and the clinical application, the results showed the usefulness of our method. The efficiency of our method has the potential to reduce the displacement problem caused by respiration and provides excellent matching SPECT/CT fusion images.

The low attenuation area on dual-energy perfusion CT: correlation with the pulmonary function tests and quantitative CT measurements.

PURPOSE: To retrospectively investigate the distribution of the low attenuation area (LAA) on dual energy perfusion CT (DEpCT) in comparison with the results of pulmonary function tests (PFTs) and quantitative CT measurements. MATERIALS AND METHODS: Twenty-eight patients (15 male and 13 female; mean age: 62.21 years) underwent DEpCT and PFTs within a 1-month interval. The ranges of the LAA on DEpCT were classified into six groups with attenuation values of 0-3, 0-5, 0-8, 0-10, 0-13 and 0-15 HU and the ratios of LAA in each group were compared with the percentage of forced expiratory volume in the 1st second (%FEV(1.0)), FEV(1.0)/forced vital capacity (FEV(1.0)/FVC) and the relative area of the lung with attenuation coefficients lower than -950 HU (RA(-950)). RESULTS: The LAAs on the DEpCT images were significantly correlated with the RA(-950), %FEV(1.0) and FEV(1.0)/FVC, and the regression analysis showed that the best values of LAA on DEpCT were 0-10 HU with RA(-950) (r=0.63), 0-8 HU with %FEV(1.0) (r=-0.52) and 0-8HU with FEV(1.0)/FVC (r=-0.61) per patient. CONCLUSION: The iodine disturbance on DEpCT had a moderate correlation with the results of the PFTs and RA(-950), but further examination would be needed for evaluation of iodine distribution.

Fate of clots in patients with subarachnoid hemorrhage after different surgical treatment modality: a comparison between surgical clipping and Guglielmi detachable coil embolization.

BACKGROUND: Subarachnoid clot is important in the development of delayed vasospasm after subarachnoid hemorrhage (SAH). OBJECTIVE: To compare the clearance of subarachnoid clot and the incidence of symptomatic vasospasm in surgical clipping and embolization with Guglielmi detachable coils for aneurysmal SAH. METHODS: The subjects were 115 patients with Fisher group 3 aneurysmal SAH on computed tomography scan at admission whose aneurysm was treated by surgical clipping (clip group; n = 86) or Guglielmi detachable coil embolization (coil group; n = 29) within 72 hours of ictus. Software-based volumetric quantification of the subarachnoid clot was performed, and the amount of hemoglobin in drained cerebrospinal fluid was measured. RESULTS: Clearance of the subarachnoid clot on the computed tomography scan was rapid in the clip group until the day after the operation but slow in the coil group (58.9% removed vs 27.8% removed; P = .008). However, postoperative clearance of the clot occurred more rapidly in the coil group. Reduction of the clot until days 3 through 5 did not differ significantly between the 2 groups (72.9% removed vs 75.2% removed). The amount of hemoglobin in the clip group was > 0.8 g/d until day 3 and then gradually decreased (n = 15), but hemoglobin in the coil group remained at > 0.8 g/d until day 5 (n = 17). The incidence of symptomatic vasospasm did not differ between the groups. CONCLUSION: Subarachnoid clot can be removed directly during surgical clipping, which is not possible with endovascular treatment. However, the percentage reduction of the clot on days 3 through 5 did not differ between the 2 groups.

Evaluation of the spatial resolution of multiplanar reconstruction images.

We present a simple method for evaluating the spatial resolution of multi-slice computed tomography (MSCT) multiplanar reconstruction images (MPRs). We scanned a bead phantom to obtain the three-dimensional point spread function (PSF), and bead-centric MPRs were generated. The modulation transfer function (MTF) was calculated from the MPRs via a two-dimensional Fourier transform (2DFFT) of the PSF. The results showed that, when MPRs were reconstructed using axial images less than or equal to a nominal 1.0-mm slice-width with a standard kernel for the abdomen, the MTF in the longitudinal direction (z-direction) was superior to that in the in-plane (x-y plane) direction. It was also found that the arbitrary-angle MTFs of MPRs were between the MTFs of the in-plane and longitudinal directions. It was confirmed that this method can be used to evaluate MPR spatial resolution.