Repetitive transcranial magnetic stimulation restores altered functional connectivity of central poststroke pain model monkeys.

Central poststroke pain (CPSP) develops after a stroke around the somatosensory pathway. CPSP is hypothesized to be caused by maladaptive reorganization between various brain regions. The treatment for CPSP has not been established; however, repetitive transcranial magnetic stimulation (rTMS) to the primary motor cortex has a clinical effect. To verify the functional reorganization hypothesis for CPSP development and rTMS therapeutic mechanism, we longitudinally pursued the structural and functional changes of the brain by using two male CPSP model monkeys (Macaca fuscata) developed by unilateral hemorrhage in the ventral posterolateral nucleus of the thalamus. Application of rTMS to the ipsilesional primary motor cortex relieved the induced pain of the model monkeys. A tractography analysis revealed a decrease in the structural connectivity in the ipsilesional thalamocortical tract, and rTMS had no effect on the structural connectivity. A region of interest analysis using resting-state functional magnetic resonance imaging revealed inappropriately strengthened functional connectivity between the ipsilesional mediodorsal nucleus of the thalamus and the amygdala, which are regions associated with emotion and memory, suggesting that this may be the cause of CPSP development. Moreover, rTMS normalizes this strengthened connectivity, which may be a possible therapeutic mechanism of rTMS for CPSP.

Accuracy of Dual-Energy Virtual Monochromatic CT Numbers: Comparison between the Single-Source Projection-Based and Dual-Source Image-Based Methods.

RATIONALE AND OBJECTIVES: To investigate the accuracy of dual-energy virtual monochromatic computed tomography (CT) numbers obtained by two typical hardware and software implementations: the single-source projection-based method and the dual-source image-based method. MATERIALS AND METHODS: A phantom with different tissue equivalent inserts was scanned with both single-source and dual-source scanners. A fast kVp-switching feature was used on the single-source scanner, whereas a tin filter was used on the dual-source scanner. Virtual monochromatic CT images of the phantom at energy levels of 60, 100, and 140 keV were obtained by both projection-based (on the single-source scanner) and image-based (on the dual-source scanner) methods. The accuracy of virtual monochromatic CT numbers for all inserts was assessed by comparing measured values to their corresponding true values. Linear regression analysis was performed to evaluate the dependency of measured CT numbers on tissue attenuation, method, and their interaction. RESULTS: Root mean square values of systematic error over all inserts at 60, 100, and 140 keV were approximately 53, 21, and 29 Hounsfield unit (HU) with the single-source projection-based method, and 46, 7, and 6 HU with the dual-source image-based method, respectively. Linear regression analysis revealed that the interaction between the attenuation and the method had a statistically significant effect on the measured CT numbers at 100 and 140 keV. CONCLUSIONS: There were attenuation-, method-, and energy level-dependent systematic errors in the measured virtual monochromatic CT numbers. CT number reproducibility was comparable between the two scanners, and CT numbers had better accuracy with the dual-source image-based method at 100 and 140 keV.

The Detectability of Iterative CT Reconstruction for Low-contrast Lesions in Hyperacute Cerebral Infarction: Assessment with Newly Developed Dedicated Head Phantoms.

Iterative reconstruction techniques, such as adaptive statistical iterative reconstruction (ASiR), improve the contrast-to-noise ratio of computed tomography (CT) images; however, underlying anatomical structures may nevertheless hamper detectability of low-contrast areas in clinical situations, despite using such a technique. We therefore conducted a phantom study to investigate the efficacy of ASiR in improving the detectability of low-contrast areas in the presence of brain anatomical structures. We developed dedicated head phantoms simulating hyperacute cerebral infarction and confirmed that their CT numbers were sufficiently reproducible and that observer performance in detecting low-contrast areas using these phantoms more closely resembled that in clinical situations than that using a simple phantom. The efficacy of ASiR in improving low-contrast detectability was evaluated via receiver operating characteristics analysis. The mean area under the curve (AUC) values at ASiR blend rates of 0%, 30%, 60%, and 100% were 0.57, 0.57, 0.59, and 0.59 at 200 mA; 0.83, 0.84, 0.84, and 0.90 at 500 mA; and 0.79, 0.77, 0.76, and 0.79 at 800 mA, respectively. No significant differences were noted in AUC values among ASiR blend rates at any mA setting, suggesting that ASiR does not improve the detectability of subtle low-contrast lesions seen in hyperacute cerebral infarction in clinical situations.

Comparison of Diffusion-Weighted Imaging in the Human Brain Using Readout-Segmented EPI and PROPELLER Turbo Spin Echo With Single-Shot EPI at 7 T MRI.

OBJECTIVES: The purpose of the present study was to compare periodically rotated overlapping parallel lines with enhanced reconstruction-type turbo spin echo diffusion-weighted imaging (pTSE-DWI) and readout-segmented echo planar imaging (rsEPI-DWI) with single-shot echo planar imaging (ssEPI-DWI) in a 7 T human MR system. We evaluated the signal-to-noise ratio (SNR), image distortion, and apparent diffusion coefficient values in the human brain. MATERIALS AND METHODS: Six healthy volunteers were included in this study. The study protocol was approved by our institutional review board. All measurements were performed at 7 T using pTSE-DWI, rsEPI-DWI, and ssEPI-DWI sequences. The spatial resolution was 1.2 × 1.2 mm in-plane with a 3-mm slice thickness. Signal-to-noise ratio was measured using 2 scans. RESULTS: The ssEPI-DWI sequence showed significant image blurring, whereas pTSE-DWI and rsEPI-DWI sequences demonstrated high image quality with low geometrical distortion compared with reference T2-weighted, turbo spin echo images. Signal loss in ventral regions near the air-filled paranasal sinus/nasal cavity was found in ssEPI-DWI and rsEPI-DWI but not pTSE-DWI. The apparent diffusion coefficient values for ssEPI-DWI were 824 ± 17 × 10 and 749 ± 25 × 10 mm/s in the gray matter and white matter, respectively; the values obtained for pTSE-DWI were 798 ± 21 × 10 and 865 ± 40 × 10 mm/s; and the values obtained for rsEPI-DWI were 730 ± 12 × 10 and 722 ± 25 × 10 mm/s. The pTSE-DWI images showed no additional distortion comparison to the T2-weighted images, but had a lower SNR than ssEPI-DWI and rsEPI-DWI. The rsEPI-DWI sequence provided high-quality images with minor distortion and a similar SNR to ssEPI-DWI. CONCLUSIONS: Our results suggest that the benefits of the rsEPI-DWI and pTSE-DWI sequences, in terms of SNR, image quality, and image distortion, appear to outweigh those of ssEPI-DWI. Thus, pTSE-DWI and rsEPI-DWI at 7 T have great potential use for clinical diagnoses. However, it is noteworthy that both sequences are limited by the scan time required. In addition, pTSE-DWI has limitations on the number of slices due to specific absorption rate. Overall, rsEPI-DWI is a favorable imaging sequence, taking into account the SNR and image quality at 7 T.

Radiotherapy treatment planning with contrast-enhanced computed tomography: feasibility of dual-energy virtual unenhanced imaging for improved dose calculations.

BACKGROUND: In radiotherapy treatment planning, intravenous administration of an iodine-based contrast agent during computed tomography (CT) improves the accuracy of delineating target volumes. However, increased tissue attenuation resulting from the high atomic number of iodine may result in erroneous dose calculations because the contrast agent is absent during the actual procedure. The purpose of this proof-of-concept study was to present a novel framework to improve the accuracy of dose calculations using dual-energy virtual unenhanced CT in the presence of an iodine-based contrast agent. METHODS: Simple phantom experiments were designed to assess the feasibility of the proposed concept. By utilizing a "second-generation" dual-source CT scanner equipped with a tin filter for improved spectral separation, four CT datasets were obtained using both a water phantom and an iodine phantom: "true unenhanced" images with attenuation values of 2 ± 11 Hounsfield Units (HU), "enhanced" images with attenuation values of 274 ± 23 HU, and two series of "virtual unenhanced" images synthesized from dual-energy scans of the iodine phantom, each with a different combination of tube voltages. Two series of virtual unenhanced images demonstrated attenuation values of 12 ± 29 HU (with 80 kVp/140 kVp) and 34 ± 10 HU (with 100 kVp/140 kVp) after removing the iodine component from the contrast-enhanced images. Dose distributions of the single photon beams calculated from the enhanced images and two series of virtual unenhanced images were compared to those from true unenhanced images as a reference. RESULTS: The dose distributions obtained from both series of virtual unenhanced images were almost equivalent to that from the true unenhanced images, whereas the dose distribution obtained from the enhanced images indicated increased beam attenuation caused by the high attenuation characteristics of iodine. Compared to the reference dose distribution from the true unenhanced images, the dose distribution pass rates from both series of virtual unenhanced images were greater than 90%, while those from the enhanced images were less than approximately 50-60%. CONCLUSIONS: Dual-energy virtual unenhanced CT improves the accuracy of dose distributions in radiotherapy treatment planning by removing the iodine component from contrast-enhanced images.

Paradoxical signal pattern of mediastinal cysts on T2-weighted MR imaging: phantom and clinical study.

PURPOSE: To evaluate the intracystic MRI (magnetic resonance imaging) signal intensity of mediastinal cystic masses on T2-weighted images. MATERIALS AND METHODS: A phantom study was performed to evaluate the signal intensity of a mediastinal cystic mass phantom (rubber balloon containing water) adjacent to a cardiac phantom pulsing at the rate of 60/min. T2-weighted images (sequence, fast spin echo [FSE] and single shot fast spin echo [SSFSE]) were acquired for the mediastinal cystic mass phantom. Further, a clinical study was performed in 33 patients (16 men, 17 women; age range, 19-85 years; mean, 65 years) with thymic cysts or pericardial cysts. In all patients, T2-weighted images (FSE and SSFSE) were acquired. The signal intensity of cystic lesion was evaluated and was compared with that of muscle. A region of interest (ROI) was positioned on the standard MR console, and signal intensity of the cystic mass (cSI), that of the muscle (mSI), and the rate of absolute value of cSI-mSI to standard deviation (SD) of background noise (|cSI-mSI|/SD=CNR [contrast-to-noise ratio]) were measured. RESULTS: The phantom study demonstrated that the rate phantom-ROI/saline-ROI was higher in SSFSE (0.36) than in FSE (0.19). In clinical cases, the degree of the signal intensity was higher in SSFSE than in FSE. The CNR was significantly higher in SSFSE (mean ± standard deviation, 111.0 ± 47.6) than in FSE (72.8 ± 36.6) (p<0.001, Wilcoxon signed-rank test). CONCLUSIONS: Anterior mediastinal cysts often show lower signal intensity than the original signal intensity of water on T2-weighted images. SSFSE sequence reduces this paradoxical signal pattern on T2-weighted images, which may otherwise cause misinterpretation when assessing cystic lesions.

[Perceptual image dissimilarity--a novel metric for objective assessment of image quality in computed tomography with iterative reconstruction].

An iterative reconstruction (IR) technique in computed tomography (CT) is expected to play an important role in reducing the radiation dose while preserving both spatial resolution and contrast-to-noise ratio. However, images obtained by using the IR technique are known to have different visual appearances from those obtained by using the traditional filtered back-projection (FBP) reconstruction. This appearance is often figuratively described as "blocky," but it has not been objectively characterized further. In this paper, we propose a novel image quality metric, called "perceptual image dissimilarity" (PID), to characterize the visual dissimilarity between FBP and IR images. The PID was formulated as a grayscale transformation and subsequent structural similarity (SSIM)-based image quality measurement. The PID metric was validated using phantom images with three different modules. Sixty datasets, each consisting of an IR image and its corresponding noise-level-equivalent FBP image, were visually assigned "subjective dissimilarity scores" on a five level scale by six observers. The data sets were then quantitatively analyzed using both the PID and the traditional mean squared error (MSE) metrics. Our results show that the PID is highly consistent with the subjective dissimilarity score and thus delivers superior performance, whereas the MSE fails to quantify the observers' visual perception.

Gemstone spectral imaging: determination of CT to ED conversion curves for radiotherapy treatment planning.

The monochromatic images acquired by Gemstone spectral imaging (GSI) mode on the GE CT750 HD theoretically determines the computed tomography (CT) number more accurately than that of conventional scanner. Using the former, the CT number is calculated from (synthesized) monoenergetic X-ray data. We reasoned that the monochromatic image might be applied to radiotherapy treatment planning (RTP) to calculate dose distribution more accurately. Our goal here was to provide CT to electron density (ED) conversion curves with monochromatic images for RTP. Therefore, we assessed the reproducibility of CT numbers, an important factor on quality assurance, over short and long time periods for different substances at varying energy. CT number difference between measured and theoretical value was investigated. The scanner provided sufficient reproducibility of CT numbers for dose calculation over short and long time periods. The CT numbers of monochromatic images produced by this scanner had reasonable values for dose calculation. The CT to ED conversion curve becomes linear with respect to the relationship between CT numbers and EDs as the energy increases. We conclude that monochromatic imaging from a fast switching system can be applied for the dose calculation, keeping Hounsfield units (HU) stability.

Feasibility and accuracy of relative electron density determined by virtual monochromatic CT value subtraction at two different energies using the gemstone spectral imaging.

BACKGROUND: Recent work by Saito (2012) has demonstrated a simple conversion from energy-subtracted computed tomography (CT) values (ΔHU) obtained using dual-energy CT to relative electron density (RED) via a single linear relationship. The purpose of this study was to investigate the feasibility of this method to obtain RED from virtual monochromatic CT images obtained by the gemstone spectral imaging (GSI) mode with fast-kVp switching. METHODS: A tissue characterization phantom with 13 inserts made of different materials was scanned using the GSI mode on a Discovery CT750 HD. Four sets of virtual monochromatic CT images (60, 77, 100 and 140 keV) were obtained from a single GSI acquisition. When we define Δ HU in terms of the weighting factor for the subtraction α, Δ HU ≡ (1 + α)H - αL (H and L represent the CT values for high and low energy respectively), the relationship between Δ HU and RED is approximated as a linear function, a × Δ HU/1000 + b (a, b = unity). We evaluated the agreement between the determined and nominal RED. We also have investigated reproducibility over short and long time periods. RESULTS: For the 13 insert materials, the RED determined by monochromatic CT images agreed with the nominal values within 1.1% and the coefficient of determination for this calculation formula was greater than 0.999. The observed reproducibility (1 standard deviation) of calculation error was within 0.5% for all materials. CONCLUSIONS: These findings indicate that virtual monochromatic CT scans at two different energies using GSI mode can provide an accurate method for estimating RED.

Endometrial cancer: preoperative staging using three-dimensional T2-weighted turbo spin-echo and diffusion-weighted MR imaging at 3.0 T: a prospective comparative study.

OBJECTIVES: To prospectively assess the efficacy of 3-T magnetic resonance (MR) imaging using the three-dimensional turbo spin-echo T2-weighted and diffusion-weighted technique (3D-TSE/DW) compared with that of conventional imaging using the two-dimensional turbo spin-echo T2-weighted and dynamic contrast-enhanced technique (2D-TSE/DCE) for the preoperative staging of endometrial cancer, with pathological analysis as the reference standard. METHODS: Seventy-one women with endometrial cancer underwent MR imaging using 3D-TSE/DW (b = 1,000 s/mm(2)) and 2D-TSE/DCE. Two radiologists independently assessed the two imaging sets. Accuracy, sensitivity, and specificity for staging were analysed with the McNemar test; the areas under the receiver operating characteristic curve (Az) were compared with a univariate z-score test. RESULTS: The results for assessing deep myometrial invasion, accuracy, sensitivity, specificity and Az, respectively, were as follows: 3D-TSE/DW-observer 1, 87 %, 95 %, 85 % and 0.96; observer 2, 92 %, 84 %, 94 % and 0.95; 2D-TSE/DCE-observer 1, 80 %, 79 %, 81 % and 0.89; observer 2, 86 %, 84 %, 87 % and 0.86. Most of the values were higher with 3D-TSE/DW without significant differences (P > 0.12). For assessing cervical stromal invasion, there were no significant differences in those values for both observers (P > 0.6). CONCLUSIONS: Accuracy of 3D-TSE/DW was at least equivalent to that of the conventional technique for the preoperative assessment of endometrial cancer. KEY POINTS: • New techniques in MR imaging help assess patients with endometrial cancer. • A 3D T2-weighted TSE sequence seems equally as accurate as conventional techniques. • Three-dimensional TSE/DW imaging does not require intravenous contrast material and is relatively quick. • Tumour extent of endometrial cancer can be clearly shown on diffusion-weighted images. • Junctional zone can be visualised well on 3D-TSE T2-weighted images.

[Impact of preventive administration of antiemetic drugs on risk of acute nausea and vomiting induced by transcatheter arterial chemoembolization in patients with hepatocellular carcinomas - a retrospective study].

This study aimed to evaluate the impact of the preventive administration of antiemetic drugs on the risk of acute nausea and vomiting induced by transcatheter arterial chemoembolization(TACE)in patients with hepatocellular carcinomas(HCCs). From January 2007 to June 2009, a total of 536 patients with HCCs who underwent TACE with a mixture of iodized oil, epirubicin, and porous gelatin particles were included in this retrospective study. Of those patients, 23 out of 357(6.4% ) who had received the 5-HT(3) receptor antagonist before TACE, and 18 out of 179(10.1% )without the medication, experienced vomiting. The multivariate logistic regression model with a predictive success of 92. 4% for vomiting identified significant associations between female gender(odds ratio: 3.73, p<0.001 ), the number of tumors(1.29, p<0.01 ), and administration of pentazocine(11.70, p<0.05)with the risk of vomiting. In contrast, the preventive administration of antiemetic drugs was not included in the model as a significant predictive variable. We therefore conclude from this retrospective study that the 5-HT(3) receptor antagonist did not significantly contribute to preventing the TACE-induced emesis.

Quantitative evaluation of cerebral blood flow and oxygen metabolism in normal anesthetized rats: 15O-labeled gas inhalation PET with MRI Fusion.

UNLABELLED: PET with (15)O gas has been used for the quantitative measurement of cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO(2)), oxygen extraction fraction (OEF), and cerebral blood volume (CBV) in humans. However, several technical difficulties limit its use in experiments on small animals. Herein, we describe the application of the (15)O gas steady-state inhalation method for normal anesthetized rats. METHODS: Eight normal male Sprague-Dawley rats (mean body weight ± SD, 268 ± 14 g) under anesthesia were investigated by (15)O-labeled gas PET. After tracheotomy, an airway tube was placed in the trachea, and the animals were connected to a ventilator (tidal volume, 3 cm(3); frequency, 60/min). The CBF and OEF were measured according to the original steady-state inhalation technique under artificial ventilation with (15)O-CO(2) and (15)O-O(2) gases delivered through the radioactive gas stabilizer. CBV was measured by (15)O-CO gas inhalation and corrected for the intravascular hemoglobin-bound (15)O-O(2). Arterial blood sampling was performed during each study to measure the radioactivity of the whole blood and plasma. MR image was performed with the same acrylic animal holder immediately after the PET. Regions of interest were placed on the whole brain of the PET images with reference to the semiautomatically coregistered PET/MR fused images. RESULTS: The data acquisition time for the whole PET experiment in each rat was 73.3 ± 5.8 (range, 68-85) min. In both the (15)O-CO(2) and the (15)O-O(2) studies, the radioactivity count of the brain reached a steady state by approximately 10 min after the start of continuous inhalation of the gas. The quantitative PET data of the whole brain were as follows: CBF, 32.3 ± 4.5 mL/100 mL/min; CMRO(2), 3.23 ± 0.42 mL/100 mL/min; OEF, 64.6% ± 9.1%; and CBV, 5.05 ± 0.45 mL/100 mL. CONCLUSION: Although further technical improvements may be needed, this study demonstrated the feasibility of quantitative PET measurement of CBF, OEF, and CMRO(2) using the original steady-state inhalation method of (15)O-CO(2) and (15)O-O(2) gases and measurement of CBV using the (15)O-CO gas inhalation method in the brain of normal anesthetized rats.

[The potential of dual-energy virtual monochromatic imaging in reducing renal cyst pseudoenhancement: a phantom study].

Renal cyst pseudoenhancement, an artifactual increase of computed tomography (CT) attenuation for cysts with increased iodine concentrations in the renal parenchyma, complicates the classification of cysts and may thus lead to the mischaracterization of a benign non-enhancing lesion as an enhancing mass. The purpose of this study was to use a phantom model to assess the ability of dual-energy virtual monochromatic imaging to reduce renal pseudoenhancement. A water-filled cylindrical cyst model suspended in varying concentrations of iodine solution, to simulate varying levels of parenchymal enhancement, was scanned with a dual-energy CT scanner using the following three scanning protocols with different combinations of tube voltage: 80 and 140 kV; 80 and 140 kV with tin filter; and 100 and 140 kV with tin filter. Virtual monochromatic images were then synthesized for each dual-energy scan. Single-energy scan with a tube voltage of 120 kV was also performed to obtain polychromatic images as controls. Mean attenuation values (in Hounsfield units) of cyst proxies were measured on both polychromatic and virtual monochromatic images. Pseudoenhancement was considered to be present when the cyst attenuation level increased by more than 10 HU as the background iodine concentration increased from 0.0% to 0.4%, 1.5%, or 2.5%. Our results revealed that pseudoenhancement was not observed on any of the monochromatic images, but appeared on polychromatic images at a background iodine concentration of 2.5%. We thus conclude that dual-energy virtual monochromatic images have a potential to reduce renal pseudoenhancement.

Usefulness of contrast-enhanced three-dimensional MR angiography using time-resolved imaging of contrast kinetics applied to description of Extracranial Arteriovenous Malformations: initial experience.

PURPOSE: The purpose of this study was to evaluate the usefulness of contrast-enhanced three-dimensional MR angiography using time-resolved imaging of contrast kinetics (TRICKS-MRA) to demonstrate extracranial arteriovenous malformations (E-AVMs). MATERIALS AND METHODS: TRICKS-MRA was performed in 33 patients (adults; n = 30, children; n = 3) with E-AVMs. Four different scan protocols were arranged based on the size of E-AVM, and serial images were acquired from the start of contrast injection with a time frame ranging from 1.2 to 7.1s. Demonstration of feeding arteries and drainage veins, and the extent of nidus was qualitatively graded using a three-point scale. In sixteen patients who underwent DSA 3 days to 15 months after TRICKS-MRA, the comparability of TRICKS-MRA to DSA was evaluated using a three-point scale. In each category, score of 3 or excellent was defined as the positive result. RESULTS: Demonstration of the feeding arteries, the drainage veins, and the extent of nidus were graded as excellent in 68%, 65%, and 58% of the patients, respectively. Comparability of TRICKS-MRA to DSA was excellent in 75%, 88%, and 88% of the sixteen patients who underwent DSA. CONCLUSION: TRICKS-MRA is a feasible and useful vascular imaging technique to provide time-resolved analysis of angioarchitecture of E-AVMs.

Breast diffusion-weighted MRI: comparison of tetrahedral versus orthogonal diffusion sensitization for detection and localization of mass lesions.

PURPOSE: To evaluate the potential of tetrahedral diffusion-weighted imaging (DWI) compared to orthogonal DWI for detection and localization of early enhanced breast mass lesions at 1.5T. MATERIALS AND METHODS: Sixty-seven consecutive patients (mean age 51.7 years, range 14-84 years) with 68 solitary early enhanced breast lesions suspicious for cancer on dynamic contrast-enhanced magnetic resonance imaging (MRI) were enrolled in this retrospective study. Two radiologists independently observed maximum intensity projection images of orthogonal and tetrahedral DWI and the diagnostic accuracy and background tissue visibility between two DWI techniques were compared. Contrast-enhanced MRI was used as the reference standard. Background tissue visibility was assessed based on whether the "breast quadrant" and "skin line" were determined. A phantom validation study for apparent diffusion coefficient (ADC) values was also conducted. RESULTS: Sensitivity (93%) and specificity (96%) on tetrahedral DWI were equivalent to those on orthogonal DWI (sensitivity, 88%; specificity, 95%). Background tissue was more easily determined with tetrahedral DWI (breast quadrant, 90%; skin lines, 95%) than with orthogonal DWI (breast quadrant, 61%; skin lines, 16%). ADC values of tetrahedral DWI were highly correlated with those of orthogonal DWI. CONCLUSION: Tetrahedral DWI provided equivalent detectability of mass lesions with improved visibility of surrounding anatomical structure.

[Noninvasive assessment of coronary artery with substantial contrast volume reduction using 320-detector row computed tomography: a feasibility study].

The recently introduced 320-detector row computed tomography (320-row CT) allows very fast volumetric acquisition of the entire heart. Because the total amount of contrast agent required for CT coronary angiography (CTCA) depends directly on the acquisition time, 320-row CTCA would substantially reduce the contrast agent dose. The objective of this retrospective study was to evaluate the feasibility of contrast volume reduction on 320-row CTCA compared with 64-detector row CTCA (64-row CTCA). We retrospectively reviewed consecutive 320- and 64-row CTCA data (16 eligible cases for each; administrated contrast volume, 20-24 ml for the former and 50-65 ml for latter) from a homogeneous patient population (age ≤ 81, body weight ≤ 67 kg, and heart rate ≤ 69 bpm). The two types of CTCA data were compared with respect to the successful rate of adequate intravascular contrast enhancement defined as the number of segments with attenuations of more than 250 HU divided by total number of coronary segments evaluated. Our dataset provided mean intravascular attenuation values of 320 and 404 HU on the 320- and 64-row CTCA, respectively. Although the attenuation values were statistically lower for the 320-row CTCA (P < 0.001), there was no significant difference in the successful rates of adequate intravascular contrast enhancement (rate of 0.98 for each; P > 0.05). We therefore conclude that 320-row CTCA is a feasible method of diagnostic imaging and is superior to 64-row CTCA because it uses less of the contrast medium.

Uterine tumors: comparison of 3D versus 2D T2-weighted turbo spin-echo MR imaging at 3.0 T--initial experience.

PURPOSE: To compare a three-dimensional (3D) T2-weighted turbo spin-echo (TSE) magnetic resonance (MR) sequence (VISTA; Philips Medical Systems, Best, the Netherlands) with a two-dimensional (2D) T2-weighted TSE sequence in terms of image quality, signal intensity (SI) difference ratios, conspicuity, and staging of uterine tumors. MATERIALS AND METHODS: This retrospective study was approved by the institutional review board, and informed consent was waived. Sixty-one women (mean age, 53.0 years ± 13.7 [standard deviation]; range, 30-87 years) with cervical carcinoma (n = 28), endometrial carcinoma (n = 21), or leiomyoma (n = 30) of the uterus were included. Patients underwent T2-weighted MR imaging at 3 T with both 1-mm-thick 3D and 5-mm-thick 2D T2-weighted TSE sequences. Three-dimensional T2-weighted TSE images were reconstructed at 5-mm thickness with the aid of a workstation. Quantitative analyses of signal-to-noise ratio (SNR) and SI difference ratios between tumors and other tissues and qualitative analyses of image quality and tissue conspicuity were performed. Two radiologists independently assessed local-regional staging for carcinomas. Quantitative values, qualitative scores, and tumor staging were analyzed by using the paired t test, Wilcoxon signed rank test, and McNemar test, respectively. RESULTS: Mean myometrial SNR was higher on 3D than 2D images (14.3 vs 9.8; P < .0001). Mean SI difference ratios between cervical (0.45 vs 0.34; P < .0001) or endometrial (0.46 vs 0.40; P = .044) carcinomas and gluteal muscle were higher on 3D images, but those between leiomyoma and myometrium (0.33 vs 0.43; P < .0001) were lower than those on 2D images. Image quality (P = .0004) and carcinoma conspicuity (P < .0005) were superior with the 3D T2-weighted TSE sequence. Although multiplanar reconstruction of 3D T2-weighted TSE images was useful for staging in one case, there were no significant differences between 3D and 2D T2-weighted TSE imaging in accuracy of staging for the two readers for cervical or endometrial carcinoma. CONCLUSION: The 3D T2-weighted TSE sequence showed certain advantages over the 2D T2-weighted TSE sequence, and it has the potential to improve the performance of MR imaging for the evaluation of uterine carcinoma.

Phase-contrast MR studies of CSF flow rate in the cerebral aqueduct and cervical subarachnoid space with correlation-based segmentation.

PURPOSE: Accurate measurement of cerebrospinal fluid (CSF) flow rate elucidates pathophysiological changes in the intracranial environment and is thus clinically useful. We investigated the feasibility of correlation coefficient (CC) analysis for extracting CSF lumens in the cerebral aqueduct and cervical subarachnoid space (SAS) to quantify CSF flow rate and net flow from data acquired by phase-contrast magnetic resonance imaging (PC-MRI). METHODS: First, in phantom studies on pulsatile flow using a 1.5-tesla MR imaging system, we investigated the accuracy of CC analysis and used a statistical approach to determine an optimal threshold value for extracting the CSF lumens (CC(min)). Second, we performed phantom studies on constant flow with various flow rates to estimate the accuracy of low flow measurement by PC-MRI. Finally, in 6 healthy male volunteers aged 24 +/- 2 years, we estimated the CSF lumen areas, net flows, and peak flow rates in the cerebral aqueduct and cervical SAS using CC analysis with the optimal CC(min) value determined in phantom studies. Three observers analyzed results to compare reproducibility of CC analysis with that of manual segmentation. RESULTS: The optimal CC(min) value for CC analysis was 0.41 for a matrix measuring 256 x 256. The CSF lumen area extracted by CC analysis was 6.15 +/- 2.52 mm(2), and the net flow in the cerebral aqueduct was 0.74 +/- 0.38 mL/min; in the cervical SAS, lumen area was 135.60 +/- 17.94 mm(2) and net flow, 12.55 +/- 12.67 mL/min. The reproducibility of CSF lumen extraction was better by CC analysis than manual segmentation. CONCLUSION: CC analysis offers a quick and reproducible method for segmenting CSF lumens and calculating CSF flow rate.

[Observer performance of PACS-oriented digitized mammography in the detection of fibrils, microcalcifications, and masses: a phantom study].

The film digitizer plays an important transitory role as an analog-to-digital bridge for the implementation of PACS on screen-film mammography. The objective of this phantom study was to compare the observer performance of a digitized mammogram on liquid crystal displays (LCDs) with that of the original film mammogram, and to clarify which matrix size of LCDs is adequate for the interpretation of digitized mammography. The American College of Radiology mammographic accreditation phantom containing variously sized fibrils, simulated microcalcifications, and tumor-like masses was radiographed with a screen-film mammographic system. The original film was digitized with a sampling pitch of 50 mum and a density depth of 12 bit. Six observers who were trained in mammography individually viewed digitized images on LCDs and original film. Observer performance of a digitized mammogram with a 2-megapixel LCD was compared with that of original film. The observers were asked to rate the detectability of each test object according to a three-point scale (obviously visible=2, barely detectable=1, undetectable=0). The difference in the mean score between two systems at each object was evaluated by the Wilcoxon's test. In addition, the dependence of observer performance on the matrix size of LCDs ranging from 1-to 5-megapixel was tested with Scheffé's multiple comparison. The observers also judged the detectability according to the three-point scale. The results show that the digitized mammogram provides acceptable but slightly inferior detectability than original film. There was no dependence of matrix size in observer performance with more than 2-megapixel LCDs.

Development of a noninvasive method to measure intravascular and intracardiac pressure differences using magnetic resonance imaging.

PURPOSE: We developed a noninvasive method using magnetic resonance (MR) imaging to measure differences in intravascular and intracardiac pressure, and we investigated the feasibility of the method's use in a pulsatile flow phantom and human studies. METHODS: We measured 3 velocity components using phase contrast MR imaging on a 1.5T MR scanner, used velocity data in Navier-Stokes equations to obtain pressure gradients, and directly integrated the in-plane pressure gradients to calculate pressure differences. To validate our method, we compared the pressure differences obtained by our method with the theoretical values obtained from an axisymmetric model of arterial stenosis. We also estimated the pressure differences in glass-tube phantoms simulating various vascular pathologies and in the left ventricle and aortic arch of a normal volunteer as clinical application. RESULTS: The pressure differences obtained by our method agreed well with theoretical values obtained using the straight-tube phantom with stenosis of 45%, but we observed some differences when stenosis was 65%. We clearly observed variations in pressure differences at specific locations at various phases of a cardiac cycle in both phantom and human studies. CONCLUSION: This method appears useful for measuring intravascular and intracardiac pressure differences.