Effects of organ dose modulation applied to a part of the scan range on radiation dose in computed tomography of the body.

In computed tomography (CT), organ dose modulation (ODM) reduces radiation exposure from the anterior side to reduce radiation dose received by the radiosensitive organs located anteriorly. We investigated the effects of ODM applied to a part of the scan range on radiation dose in body CT. The thorax and thoraco-abdominopelvic region of an anthropomorphic whole-body phantom were imaged with and without ODM. ODM was applied to various regions, and the tube current modulation curves were compared. Additionally, the dose indices were compared with and without ODM in thoracic and thoraco-abdominopelvic CTs in 800 patients. ODM was applied to the thyroid in male patients and to the thyroid and breast in female patients. In phantom imaging of the thorax, the application of ODM below the scan range decreased the tube current, and that to the breast showed a further decrease. Decreased tube current was also observed in phantom imaging of the thoraco-abdominopelvic regions with ODM below the scan range, and the application of ODM to the whole scan range, thyroid, breast, and both thyroid and breast further reduced the tube current in the region to which ODM was applied. In patient imaging, the dose indices were significantly lower with ODM than without ODM, regardless of the scan range or sex. The absolute reduction in dose-length product was larger for thoraco-abdominopelvic CT (male, 43.2 mGy cm; female, 59.7 mGy cm) than for thoracic CT (male, 30.8 mGy cm; female, 37.6 mGy cm) in both sexes, indicating dose reduction in the abdominopelvic region to which ODM was not applied. In conclusion, The application of ODM in body CT reduces radiation dose not only in the region to which ODM is applied but also outside the region. In radiation dose management, it should be considered that even ODM applied to a limited region affects the dose indices.

Effects of genome instability of parental CHO cell clones on chromosome number distribution and recombinant protein production in parent-derived subclones.

Chinese hamster ovary (CHO) cells are the de facto standard host cells for biopharmaceuticals, and there is great interest in developing methods for constructing stable production cell lines. In this study, clones with a wide chromosome number distribution were selected from isolated antibody-producing strains, and subclones obtained from these clones were evaluated. The transgene copy number varied between the subclones. Even among subclones with similar copy numbers of antibody genes and maintained insertion sites, clones with different productivity were generated. Although the chromosome number distribution differed between these subclones, there was no correlation between the variability in chromosome number after cloning (genome instability) and productivity. Most of the subclones obtained from a parental strain with a wide chromosome number had the same wide chromosome number distribution as the parental strain. Less frequently, cells with less variation (remaining in one distribution) in chromosome number were isolated from cells with a wide chromosome number distribution, from which subclones with less variation in chromosome number were obtained when subcloning was performed again. These results imply that the characteristics of clones with chromosomal instability are inherited by subclones, and thus provide a better understanding of cell line stability/instability.

Relationships of Radiation Dose Indices with Body Size Indices in Adult Body Computed Tomography.

We investigated the relationships between radiation dose indices and body size indices in adult body computed tomography (CT). A total of 3200 CT scans of the thoracic, abdominal, abdominopelvic, or thoraco-abdominopelvic regions performed using one of four CT scanners were analyzed. Volume CT dose index (CTDIvol) and dose length product (DLP) were compared with various body size indices derived from CT images (water-equivalent diameter, WED; effective diameter, ED) and physical measurements (weight, weight/height, body mass index, and body surface area). CTDIvol showed excellent positive linear correlations with WED and ED. CTDIvol also showed high linear correlations with physical measurement-based indices, whereas the correlation coefficients were lower than for WED and ED. Among the physical measurement-based indices, weight/height showed the strongest correlations, followed by weight. Compared to CTDIvol, the correlation coefficients with DLP tended to be lower for WED, ED, and weight/height and higher for weight. The standard CTDIvol values at 60 kg and dose increase ratios with increasing weight, estimated using the regression equations, differed among scanners. Radiation dose indices closely correlated with body size indices such as WED, ED, weight/height, and weight. The relationships between dose and body size differed among scanners, indicating the significance of dose management considering body size.

SIZE-SPECIFIC DOSE ESTIMATES IN PEDIATRIC BRAIN CT IN RELATION TO AGE AND WEIGHT.

The size-specific dose estimate (SSDE) is used for radiation dose management in computed tomography (CT) and represents patient's absorbed dose more accurately than volume CT dose index. The relationship between SSDE and age or weight was investigated using 980 pediatric brain CT scans. Monolinear, power, and bilinear functions were fitted to the plots of SSDE against age or weight, and SSDE was estimated using the obtained functions. SSDE showed a biphasic increase with increasing age and weight: a rapid initial increase and subsequent a slow increase. Bilinear and power functions were successfully fitted to the plots, and mean estimation errors were close to 0, irrespective of the age or weight group. The standard SSDE values estimated from the obtained functions agreed well with the median values for each age or weight group. The curve-fitting method is expected to aid radiation dose management for pediatric brain CT using SSDE.

Effects of Post-Labeling Delay on Magnetic Resonance Evaluation of Brain Tumor Blood Flow Using Arterial Spin Labeling.

We investigated the effect of post-labeling delay (PLD) on the evaluation of brain tumor blood flow using arterial spin labeling (ASL) magnetic resonance (MR) imaging to assess the need for imaging with two PLDs. Retrospective analysis was conducted on 63 adult patients with brain tumors who underwent contrast-enhanced MR imaging including ASL imaging with PLDs of both 1525 and 2525 ms on a 1.5 T or 3 T MR unit. Blood flow was estimated in the tumors and normal-appearing brain parenchyma, and tumor blood flow was normalized by parenchymal flow. Estimates of tumor blood flow, parenchymal flow, and normalized tumor flow showed no statistically significant differences between PLDs of 1525 and 2525 ms. Close correlations between different PLDs were found, with the closest correlation for normalized tumor flow. These results were similarly observed for the 1.5 T and 3 T units. The blood flow estimates obtained using ASL MR imaging in patients with brain tumors were highly concordant between PLDs of 1525 and 2525 ms, irrespective of the magnetic field strength. It is indicated that imaging with a single, standard PLD is acceptable for ASL assessment of brain tumor perfusion and that additional imaging with a long PLD is not required.

Artificial induction of chromosome aneuploidy in CHO cells alters their function as host cells.

Chinese hamster ovary (CHO) cells are major host cells for biopharmaceuticals. During culture, the chromosome number of CHO cells alters spontaneously. Here, we investigated the effects of artificial changes in the chromosome number on productivity. When cell fusion between antibody-producing CHO-K1-derived cells was induced, we observed a wide range of aneuploidy that was not detected in controls. In particular, antibody productivities were high in clone-derived cell populations that retained a diverse chromosome number distribution. We also induced aneuploid cells using 3-aminobenzamide that causes chromosome non-disjunction. After induction of aneuploidy by 3-aminobenzamide, cells with an increased chromosome number were isolated, but cells with a decreased chromosome number could not be isolated. When antibody expression vectors were introduced into these isolated clones, productivity tended to increase in cells with an increased chromosome number. Further analysis was carried out by focusing on clone 5E8 with an average chromosome number of 37. When 5E8 cells were used as host, the productivity of multiple antibodies, including difficult-to-express antibodies, was improved compared with CHO-K1 cells. The copies of exogenous genes integrated into the genome were significantly increased in 5E8 cells. These findings expand the possibilities for host cell selection and contribute to the efficient construction of cell lines for recombinant protein production.

Age-Dependent Changes in Effective Dose in Pediatric Brain CT: Comparisons of Estimation Methods.

The effective dose (ED) in computed tomography (CT) may be calculated by multiplying the dose-length product (DLP) by a conversion factor. As children grow, automatic exposure control increases the DLP, while the conversion factor decreases; these two changes affect the ED in opposite ways. The aim of this study was to investigate the methods of ED estimation according to age in pediatric brain CT. We retrospectively analyzed 980 brain CT scans performed for various clinical indications in children. The conversion factor at each age, in integer years, was determined based on the values at 0, 1, 5, and 10 years provided by the International Commission on Radiological Protection (ICRP), using a curve (curve method) or lines (linear method). In the simple method, the ED was estimated using the ICRP conversion factor for the closest age. We also analyzed the ED estimated by a radiation dose management system. Although the median DLP at each age increased with age, the median ED estimated by the curve method was highest at 0 years, decreased with age, and then plateaued at 9 years. The linear method yielded mildly different results, especially at 2 and 3 years. The ED estimated by the simple method or the radiation dose management system showed inconsistent, up-and-down changes with age. In conclusion, the ED in pediatric brain CT decreases with age despite increased DLP. Determination of the conversion factor at each age using a curve is expected to contribute to estimating the ED in pediatric CT according to age.

Automatic Exposure Control Attains Radiation Dose Modulation Matched with the Head Size in Pediatric Brain CT.

We investigated the relationship between the head size and radiation dose in pediatric brain computed tomography (CT) to evaluate the validity of automatic exposure control (AEC). Phantom experiments were performed to assess image noise with and without AEC, and indicated that AEC decreased differences in noise between slices of different section sizes. Retrospective analysis was conducted on 980 pediatric brain CT scans where the tube current was determined using AEC. The water equivalent diameter (WED) was employed as an index of the head size, and mean WED for each image set (WEDmean) and WED for each slice (WEDslice) were used for analysis. For the image-set-based analysis, volume CT dose index (CTDIvol) was compared to WEDmean. For the slice-based analysis, the tube current was compared to WEDslice using 20 of the 980 sets. Additionally, CTDIvol and WEDmean were compared between male and female patients matched for age, weight, or WEDmean. CTDIvol increased with increasing WEDmean, and an exponential curve was closely fitted to the relationship. Tube current changed similarly to the change in WEDslice for each image set, and an exponential curve was well-fitted to the plots of tube current against WEDslice when data from the 20 sets were pooled together. Although CTDIvol and WEDmean were slightly but significantly larger for male than female patients after matching for age or weight, a sex-dependent difference in CTDIvol was not found after matching for WEDmean. This study indicated successful dose modulation using AEC according to the head size for each patient and each slice location. The application of AEC to pediatric brain CT is recommended for radiation dose optimization.

Clinical Evaluation of Left Ventricular Diastolic Function Using Phase-contrast Cine Cardiovascular Magnetic Resonance Imaging: A Comparison With Steady-state Free Precession Cine Cardiovascular Magnetic Resonance Imaging and Echocardiography.

OBJECTIVE: We investigated a practical method using phase-contrast (PC) cine cardiovascular magnetic resonance imaging to estimate peak filling rate and early/atrial velocity (E/A) as left ventricular diastolic function indicators. METHODS: Peak filling rate and E/A were estimated in 32 patients using PC imaging with high spatial or high temporal resolution and compared with those estimated using steady-state free precession cine cardiovascular magnetic resonance imaging and echocardiography. RESULTS: Peak filling rate estimated using PC imaging significantly correlated with those estimated using steady-state free precession imaging despite apparent underestimation using PC imaging with high spatial resolution. The E/A estimated using PC imaging significantly correlated with those estimated using echocardiography. CONCLUSIONS: Peak filling rate and E/A measurements using PC imaging with high temporal resolution is convenient and acceptably accurate, suggesting its potential for clinical use.

Evaluation of a novel reconstruction method based on the compressed sensing technique: Application to cervical spine MR imaging.

Compressed sensing-based reconstruction (CSR) is a new magnetic resonance (MR) image reconstruction method based on the compressed sensing (CS) technique. CSR suppresses ringing artifacts from truncated k-space sampling by estimating the high spatial frequency information required to support the acquired k-space data. CSR is intended to replace the existing zero-fill interpolation (ZIP) reconstruction. We investigated the usefulness of the CSR technique by obtaining sagittal T2-weighted images of the cervical spine and phantom images using CSR or ZIP. Our results indicated that the CSR technique reduces truncation artifacts compared to ZIP without prolonging the scan time or impairing image sharpness.

Quantitative Evaluation of Display Contrast of Gd-EOB-DTPA-Enhanced Magnetic Resonance Images: Effects of the Flip Angle and Grayscale Gamma Value.

INTRODUCTION: Display contrast can be changed nonlinearly by manipulating the gamma value of the grayscale. We investigated the contrast of the hepatobiliary-phase images acquired with different flip angles (FAs) and displayed with different gamma values in Gd-EOB-DTPA-enhanced magnetic resonance imaging. MATERIAL AND METHODS: Twenty patients with liver tumors were studied. Hepatobiliary-phase images were acquired at low (12°) and high (30°) FAs. Low-FA images were converted to simulate images displayed with different gamma values, using ImageJ software. To assess image contrast, the liver-to-muscle signal ratio (LMR), liver-to-spleen signal ratio (LSR), contrast ratio (CR), liver signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were calculated. RESULTS: The LMR, LSR, and CR were higher in the high-FA images than in the low-FA original images. Although the SNR was lower in the high-FA images, indicating an increase in noise, the CNR was higher. Raising the gamma value increased the LMR, LSR, and CR, notably decreased the SNR, and slightly decreased the CNR. CONCLUSION: Increasing the FA enhanced image contrast, supporting its usefulness for improving the delineation of focal liver lesions. Although the associated increase in noise may be problematic, raising the grayscale gamma value enhances the display contrast of low-FA images.

Safe Stereotactic Biopsy for Basal Ganglia Lesions: Avoiding Injury to the Basal Perforating Arteries.

BACKGROUND: One of the most serious complications of stereotactic biopsy is postoperative symptomatic hemorrhage due to injury to the basal perforating arteries such as the lenticulostriate arteries neighboring the basal ganglia lesions. OBJECTIVES: A new target-planning method was proposed to reduce hemorrhagic complications by avoiding injury to the perforating arteries. METHODS: Three-dimensional 3-T time-of-flight (3D 3-T TOF) imaging was applied to delineate the basal perforating arteries such as the lenticulostriate arteries. The incidence of postoperative hemorrhage in basal ganglia cases was compared between a new method using 3D 3-T TOF and a conventional target-planning method based on contrast-enhanced T1-weighted magnetic resonance images obtained by 1.5-T scanning. RESULTS: 3D 3-T TOF imaging could delineate the basal perforating arteries sufficiently in target planning. No postoperative hemorrhage occurred with the new method (n = 10), while 6 postoperative hemorrhages occurred with the conventional method (n = 14). The new method significantly reduced the occurrence of postoperative hemorrhages (p = 0.017). CONCLUSIONS: 3D 3-T TOF MR imaging with contrast medium administration provides useful information about the perforating arteries and allows safe stereotactic biopsy of basal ganglia lesions.

Reliability of 3D arterial spin labeling MR perfusion measurements: The effects of imaging parameters, scanner model, and field strength.

The aim of this study was to investigate the reliability of cerebral blood flow (CBF) measurements obtained by 3D pseudo-continuous arterial spin labeling (pCASL) imaging according to imaging parameters, scanner model, and field strength. We acquired 3D pCASL images in 12 healthy volunteers using four different scanners: two 3.0 T scanners and two 1.5 T scanners. Reliability was evaluated using intraclass correlation coefficient. Our results indicate that the influence of the post-labeling delay and scanner model on CBF measurements should be taken into consideration. If two scanners of the same model are used, scannerdependent differences may be small.

Methods for optimizing the display conditions of brain magnetic resonance images.

PURPOSE: To investigate a method for optimizing the display conditions of brain magnetic resonance (MR) images. MATERIALS AND METHODS: We retrospectively analyzed brain MR images of 120 adults classified into screening, acute cerebral infarction, and brain tumor groups (n = 40 each). Two observers independently displayed the images on a monitor and optimized the display conditions using the W/L and U/L methods. In the W/L method, the observers manipulated the width and level of the display window, while in the U/L method they manipulated the upper and lower levels of the window. The times required were compared between the two methods. Additionally, the appropriateness of the determined window setting was evaluated visually by the respective observer to exclude the possibility that rough, suboptimal adjustment shortened the adjustment time. RESULTS: For both observers and all groups, the time required for optimization was significantly shorter for the U/L method than for the W/L method. The appropriateness of the window setting for the U/L method was equal to or better than that for the W/L method. CONCLUSION: Manipulating the upper and lower levels of the display window appears to improve the efficiency of interpreting brain MR images through rapid optimization of the display condition.

Two-Dimensional Spoiled Gradient-Recalled Echo Magnetic Resonance Imaging of the Liver Using Respiratory Navigator-Gating Techniques.

OBJECTIVE: We assessed the feasibility of T1-weighted 2-dimensional spoiled gradient-recalled (2D SPGR) acquisition in steady-state imaging of the liver with various respiratory navigator gating techniques. METHODS: A total of 12 healthy volunteers underwent in-phase and out-of-phase 2D SPGR imaging of the liver during breath-holding and free-breathing. Four techniques for respiratory navigation, 2 conventional navigator techniques and 2 self-navigator techniques, were used for free-breathing imaging. RESULTS: Good navigator waveforms were obtained in conventional navigation, whereas fluctuations were evident in self navigation. All of the 4 navigator-based methods provided better images in terms of background signals and visual image quality compared with images obtained with no respiratory control. However, differences remained in comparison with breath-holding. Superiority of self-navigation to conventional navigation was not shown. CONCLUSIONS: Navigator-gating techniques improved 2D SPGR images of the liver acquired during free-breathing, suggesting feasibility and beneficial effects, although navigator-based images were still inferior to breath-hold images.

Influence of the Magnetic Field Strength on Image Contrast in Gd-EOB-DTPA-enhanced MR Imaging: Comparison between 1.5T and 3.0T.

PURPOSE: We quantitatively investigated hepatic enhancement in gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance (MR) imaging at 1.5T and 3.0T. METHODS: A total of 40 patients who underwent Gd-EOB-DTPA-enhanced MR imaging were included in the study. Precontrast and hepatobiliary-phase images acquired at a low flip angle (FA, 12°) and hepatobiliary-phase images acquired at a high FA (30°) were analyzed. From these images, the liver-to-muscle signal intensity ratio (LMR) and liver-to-spleen signal intensity ratio (LSR) were estimated, and the contrast enhancement ratio (CER) was calculated from the liver signal, LMR, and LSR as the ratio of the low-FA hepatobiliary-phase value to the precontrast value. The coefficient of variance in the liver signal was determined to represent image noise. RESULTS: LMR and LSR indicated similar image contrast between 1.5T and 3.0T. A higher FA provided larger LMRs and LSRs, and the degree of the FA-dependent increase was similar between 1.5T and 3.0T. CER did not differ significantly between 1.5T and 3.0T, regardless of the calculation method. A better correlation to CER calculated from the liver signal was found for the LMR-based CER values than for the LSR-based CER. The coefficient of variance in the liver signal was significantly smaller at 3.0T for precontrast and low-FA hepatobiliary-phase images, but not for high-FA hepatobiliary-phase images. CONCLUSION: The indices of hepatic enhancement were similar between 1.5T and 3.0T, indicating that the magnetic field strength does not substantially influence image contrast after administration of Gd-EOB-DTPA.

Image Non-Uniformity Correction for 3-T Gd-EOB-DTPA-Enhanced MR Imaging of the Liver.

PURPOSE: Image non-uniformity may cause substantial problems in magnetic resonance (MR) imaging especially when a 3-T scanner is used. We evaluated the effect of image non-uniformity correction in gadolinium ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced MR imaging using a 3-T scanner. METHODS: Two commercially available methods for image non-uniformity correction, surface coil intensity correction (SCIC), and phased-array uniformity enhancement (PURE), were applied to Gd-EOB-DTPA-enhanced images acquired at 3-T in 20 patients. The calibration images were used for PURE and not for SCIC. Uniformity in the liver signal was evaluated visually and using histogram analysis. The liver-to-muscle signal ratio (LMR) and liver-to-spleen signal ratio (LSR) were estimated, and the contrast enhancement ratio (CER) was calculated from the liver signal, LMR, and LSR. RESULTS: Without non-uniformity correction, hyperintensity was consistently observed near the liver surface. Both SCIC and PURE improved uniformity in the liver signal; however, the superficial hyperintensity remained after the application of SCIC, especially in the hepatobiliary-phase images, and focal hyperintensity was shown in the lateral segment of the left hepatic lobe after the application of PURE. PURE increased LMR dramatically and LSR mildly, with no changes in CERs. SCIC depressed temporal changes in LMR and LSR and obscured contrast effects, regardless of the method used for calculation of CER. CONCLUSION: SCIC improves uniformity in the liver signal; however, it is not suitable for a quantitative assessment of contrast effects. PURE is indicated to be a useful method for non-uniformity correction in Gd-EOB-DTPA-enhanced MR imaging using a 3-T scanner.

Cardiovascular magnetic resonance evaluation of left ventricular peak filling rate using steady-state free precession and phase contrast sequences.

BACKGROUND: We investigated a practical method to measure peak filling rate (PFR) as an indicator of diastolic function of the left ventricle. Ten adult volunteers underwent cine MR imaging using steady-state free precession (SSFP) and phase contrast (PC) sequences to measure PFR. Two PC image sets were acquired at the mitral valve orifice, and PFR was determined from the set with high true temporal resolution (temporal PC method) or with high spatial resolution (spatial PC method). SSFP images covering the left ventricle were acquired, and a time-volume curve was generated around the peak filling phase. PFR was determined using parabolic curve fitting on the first-derivative curve of the LV time-volume curve. FINDINGS: PFR values estimated by the PC methods correlated well with those estimated by the SSFP method, despite apparent underestimation. The underestimation was smaller for the temporal PC method (12 %) than for the spatial PC method (28 %). Intra- and inter-observer repeatabilities were better for the PC methods than for the SSFP method. CONCLUSIONS: PFR measurement by PC imaging with high true temporal resolution is convenient and offers excellent repeatability and acceptable accuracy, indicating suitability for clinical use.

Evaluation of a respiratory navigator-gating technique in Gd-EOB-DTPA-enhanced magnetic resonance imaging for the assessment of liver tumors.

OBJECTIVES: We investigated the clinical usefulness of respiratory navigator-gating technique for the assessment of liver tumors in Gd-EOB-DTPA-enhanced magnetic resonance (MR) imaging. METHODS: Eighty patients who underwent Gd-EOB-DTPA-enhanced MR imaging to evaluate known or suspected liver tumors were enrolled. Three-dimensional spoiled gradient-recalled echo images of the liver were acquired in the hepatobiliary phase by the following three methods: breath-hold imaging, navigator-gated low-resolution imaging, and navigator-gated high-resolution imaging. Navigator-gated imaging was performed during free breathing. Spatial resolution was identical between breath-hold imaging and gated low-resolution imaging. Signal intensities in the liver, muscle, and spleen were measured in 20 patients. Image quality was visually evaluated in all 80 patients. The detection rate and lesion conspicuity were assessed for 71 malignant liver lesions identified in 29 patients. RESULTS: The liver-to-muscle and liver-to-spleen signal ratios were significantly lower for gated images compared to breath-hold images. Images of acceptable quality were obtained in most patients by all three methods, and the overall image quality of axial images did not differ significantly among the imaging methods, although superior reformatted coronal images were obtained by gated high-resolution imaging. The detection rates of malignant liver lesions were similar among the three imaging methods, although lesion conspicuity was significantly better for breath-hold imaging compared to gated imaging. CONCLUSIONS: Navigator-gated imaging provided image qualities and detection rates of malignant liver lesions comparable to breath-hold imaging in Gd-EOB-DTPA-enhanced MR imaging; however, no additional benefits of high-resolution imaging were proven for lesion evaluation.

MONITORING DOSE-LENGTH PRODUCT IN COMPUTED TOMOGRAPHY OF THE CHEST CONSIDERING SEX AND BODY WEIGHT.

Dose-length product (DLP) is widely used as an indicator of the radiation dose in computed tomography. The aim of this study was to investigate the significance of sex and body weight in DLP-based monitoring of the radiation dose. Eight hundred computed tomographies of the chest performed using four different scanners were analysed. The DLP was compared with body weight by linear regression in men and women separately. The DLP was positively correlated with body weight, and dependence on sex and weight differed among scanners. Standard DLP values adjusted for sex and weight facilitated interscanner comparison of the radiation dose and its dependence on sex and weight. Adjusting the DLP for sex and weight allowed one to identify examinations with possibly excessive doses independently of weight. Monitoring the DLP in relation to sex and body weight appears to aid detailed comparison of the radiation dose among imaging protocols and scanners and daily observations to find unexpected variance.