Effective dose and radiation risk under 640-slice abdominal computed tomography examination without contrast medium injection.

BACKGROUND: Medical imaging plays a crucial role in modern medicine. In order to provide fast and accurate medical diagnosis, computed tomography (CT) is a commonly used tool in radiological examinations, and 640-slice CT is the most advanced CT imaging modality. OBJECTIVE: To evaluate the radiation dose and the risk under 640-slice abdominal CT examination. METHODS: Examinations were performed using a 640-slice CT scanner on an Alderson-Rando anthropomorphic phantom. The used scanning acquisition parameters were the same as those used on abdominal examination without contrast medium injection in clinical practice. To measure the absorbed doses, optically stimulated luminescence dosimeters (OSLDs) were put into liver, stomach, bladder, gonads, colon, small intestine, bone marrow, and skin. RESULTS: According to the 1990 Recommendations of the International Commission on Radiological Protection (ICRP Publication 60), the calculated effective doses received from this examination were 0.90 mSv in males and 0.89 mSv in females. According to the 2007 Recommendations of the International Commission on Radiological Protection (ICRP Publication 103), the calculated effective dose received from this examination was 0.83 mSv in both sexes. CONCLUSIONS: Radiation doses obtained from the abdominal 640-slice CT examination are lower than the yearly cumulative doses received from natural radiation, revealing there is no deterministic effect and radiation risk is relatively low; therefore, this CT examination is considered safe.

Assessment of image quality and dose in contrast-enhanced head and neck CT angiography of New Zealand rabbit.

BACKGROUND: Although computed tomography (CT) is a powerful diagnostic imaging modality for diagnosing vascular diseases, it is some what risky to human health due to the high radiation dosage. Thus, CT vendors have developed low dose computed tomography (LDCT) aiming to solve this problem. Nowadays, LDCT has gradually become a main stream of CT examination. OBJECTIVE: This study aimed to assess the feasibility of LDCTAin an animal model and compare the imaging features and doses in two clinical scanners. METHODS: Twenty-two New Zealand rabbit head and neck CTA images pre- and post-contrast agent injection were performed using256-sliceand 64-slice CT scanners. The tube voltages used in the 256-slice and the 64-slice CTA were 70 kVp and 80 kVp, respectively. Quantitative images indices and radiation doses obtained from CTA in these two scanners were compared. RESULTS: More neck arterial vessels could be visualized in multi-planar reconstruction (MPR) CTA on the 256-slice CT scanner than on the 64-slice CT scanner. After contrast agent injection, all observed neck arterial vessels had higher CT numbers in 256-slice CTA than in 64-slice CTA. There was no significant difference in contrast-to-noise (CNR) of CTA images between these two scanners. CT dose index (CTDI) and dose length product (DLP) for the 256-slice CTA were lower than those for the 64-slice CTA. CONCLUSIONS: Low dose CTA of rabbits with 70 or 80 kVp is feasible in a 256-slice or a 64-slice CT scanner. The radiation dose from the 256-slice CTA was much lower than that from the 64-slice CTA with comparable SNR and CNR. The technique can be further applied in longitudinal monitoring of an animal stroke model in the future.

Evaluation of the effectiveness of student learning and teacher instruction on team-based learning during quality control of diagnostic imaging.

Background: Team-Based Learning (TBL), which is a student-centered instructional approach, has been applied in various health-related courses, but research on the effectiveness of TBL in radiologic technology is limited. More research is needed to examine the effectiveness of TBL within the field of radiologic technology as well as to study teachers' reflective practices for instructional development in TBL.Objectives: This study examines the effectiveness of TBL on students' learning and course instructors' instructional development during quality control activities in diagnostic imaging.Design: This study employed an action research approach with mixed-methods. The study was categorized using four TBL modules as the topics: film/screen receptors and processors, radiography, mammography, and computed tomography. Quantitative data included pre-test scores on individual readiness assurance tests (IRAT-pre), group readiness assurance tests (GRAT), and post-test scores on individual readiness assurance tests (IRAT-post). Qualitative data included students' responses to open-ended questions about their experience with TBL and transcripts of instructors' interviews.Results: Forty junior college students participated in the study. A non-parametric test was conducted to compare the scores. The results showed that the GRAT score was significantly higher than the IRAT-pre-score, and the IRAT-post score was significantly higher than the IRAT-pre-score. The IRAT-post score was significantly higher than the GRAT score for the first and fourth modules, but IRAT-post score was significantly lower than the GRAT score on the second and third modules. Using direct content analysis, five themes were coded around instructional development, while 15 themes were coded to understand students' experiences with TBL.Conclusions: TBL can be an effective instructional approach to improve students' understanding of radiologic technology content. The results of this research can help instructors decide what action plan to implement to increase the effectiveness of TBL when further employing it for radiologic technology courses.

Longitudinal investigation of ischemic stroke using magnetic resonance imaging: Animal model.

BACKGROUND: Arterial embolism is a major cause of ischemic stroke. Currently, digital subtraction angiography (DSA) is the gold standard in clinical arterial embolization examinations. However, it is invasive and risky. OBJECTIVE: This study aims to longitudinally assess the progression of carotid artery embolism in middle cerebral artery occlusion animal model (MCAO) using magnetic resonance imaging (MRI) techniques. METHODS: Turbo spin echo (TSE), time of flight magnetic resonance angiography (TOF-MRA) and diffusion weighted magnetic resonance imaging (DWI) were used to evaluate the image characteristics of cerebral tissues at 1, 2, 3, 7, 14, 21 and 28 days after MCAO microsurgery on Sprague-Dawley (SD) rats. Quantitative analysis was performed and compared in MCAO hemisphere and contralateral normal hemisphere. Furthermore, pathologic section using triphenyl tetrazolium chloride (TTC) stain was performed as well. RESULTS: TOF-MRA showed carotid signal void in the embolism side, which is evidence of artery occlusion. The used MRI techniques showed that edema gradually dissipated within one week, but there was no significant change afterwards. The time-varying signal intensity of MRI techniques in MCAO hemisphere changed significantly, but there were no significant changes in contralateral normal hemisphere. Cerebral injury was also confirmed by analysis of pathology images. CONCLUSIONS: The MCAO animal model was successfully established on SD rats using the microsurgery to assess arterial embolization of intracranial tissue injury.

Dynamic magnetic resonance imaging of carbogen challenge on awake rabbit brain at 1.5T.

BACKGROUND: Anesthesia may alter the cellular components contributing to the magnetic resonance imaging (MRI) signal intensities. Developing awake animal models to evaluate cerebral function has grown in importance. OBJECTIVE: To investigate a noninvasive strategy for dynamic MRI (dMRI) of awake rabbits during carbogen challenge. METHODS: A nonmetallic assistive device with a self-adhering wrap secure procedure was developed for the head fixation of awake rabbits. Multi-shot gradient echo echo-planar imaging sequence was applied for the dMRI on a 1.5 T clinical MRI scanner with a quadrature head coil. The carbogen challenge pattern was applied in a sequence of air - carbogen - air - carbogen - air. Twelve scans were performed for each block of carbogen challenge. T2-weighted fast-spin echo and T1-weighted gradient echo sequences were performed before and after dMRI to evaluate the head position shifts. The whole dMRI scan time was about 30 minutes. RESULTS: The position shift of 8 rabbits in the x-and y-direction was less than 3%. The average MRI signal intensities (SI) from the 8 rabbits during carbogen challenge was fitted well using exponential growth and decay functions. The average MRI SI increase due to carbogen inhaling was 1.51%. CONCLUSIONS: The proposed strategy for head dMRI on an awake rabbit during carbogen challenge is feasible.

Optimal dosage and early intervention of L-ascorbic acid inhibiting K2Cr2O7-induced renal tubular cell damage.

Chromium poisoning can cause renal failure and death. Chromium intoxication may be managed using L-ascorbic acid (vitamin C) therapy. However, the evidence supporting the effectiveness of this treatment is insufficient, and the mechanism of action has not been clarified in renal cells. In this study, our results showed that the optimal regimen of L-ascorbic acid therapy in human epithelial renal proximal tubule cells, HK-2 cells, was 30 µg/mL. Supplementation of L-ascorbic acid with 30 µg/mL and within 8 h of chromium intoxication (K2Cr2O7, Cr6+) was effective to inhibit renal tubular cell damage by blocking generation of free radicals, cell apoptosis, and autophagy. Intracellular chromium concentrations were estimated using electrothermal atomic absorption spectrometry. Treatment of L-ascorbic acid within 8 h of chromium intoxication significantly decreased the entry of chromium into the cells. Moreover, concomitant administration of L-ascorbic acid with repeatedly dosing at 8-hourly intervals had a better protective effect at lower concentration of L-ascorbic acid when compared to single dosing of L-ascorbic acid at an early time point of chromium intoxication. These findings might help physicians develop effective therapy strategies in renal failure.

Noninvasive Shock Wave Treatment for Capsular Contractures After Breast Augmentation: A Rabbit Study.

BACKGROUND: Capsular contracture is the most common complication of breast augmentation. Although numerous procedures are intended to prevent capsular contracture, their efficacy does not satisfy surgeons or patients. In the present study, we used shock waves to develop innovative protocols to treat capsular contracture in rabbits. METHODS: We used shock waves to treat capsular contracture in a rabbit model. Six clinical parameters were evaluated to determine the treatment efficacy of shock waves on the pathological histology of capsular contracture. Dual-flip-angle T1-mapping magnetic resonance imaging was used to confirm the pathological findings. RESULTS: Among the parameters, myxoid change, vascular proliferation, and lymphoplasma cell infiltration around the capsule increased more after treatment than they did in a control group. Capsular thickness, inner thinner collagen layer, and capsule wall collagen deposition decreased after shock wave treatment; only the inner thinner collagen layer and capsule wall collagen deposition changed significantly. The MRI findings for both scar thickness and water content were consistent with pathological biology findings. CONCLUSION: This was the first pilot study and trial to treat capsular contractures using shock waves. We found that shock waves can cause changes in the structure or the composition of capsular contracture. We conclude that the treatment could decrease water content, loosen structure, decrease collagen deposition, and might alleviate scar formation from capsular contracture. We believe that the treatment could be a viable remedy for capsular contractures. NO LEVEL ASSIGNED: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

The Impact of Flip Angle and TR on the Enhancement Ratio of Dynamic Gadobutrol-enhanced MR Imaging: In Vivo VX2 Tumor Model and Computer Simulation.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is widely used to diagnose cancer and monitor therapy. The maximum enhancement ratio (ERmax) obtained from the curve of signal intensity over time could be a biomarker to distinguish cancer from normal tissue or benign tumors. We evaluated the impact of flip angle (FA) and repetition time (TR) on the ERmax values of dynamic gadobutrol-enhanced MR imaging, obtaining T1-weighted (T1W) MR imaging of VX2 tumors using 2-dimensional fast spoiled gradient echo (2D FSPGR) with various FAs (30°, 60° and 90°) at 1.5 tesla before and after injection of 0.1 mmol/kg gadobutrol. In vivo study indicated significant differences between ERmax values and area under the ER-time curve (AUC100) of VX2 tumors and muscle tissue, with the highest ERmax and AUC100 at FA 90°. Computer simulation also demonstrated the ER as a strictly increasing monotonic function in the closed interval [0°, 90°] for a given TR when using T1W FSPGR, and the highest ER value always occurred at FA 90°. The FA for the highest ER differed from that for the highest signal-to-noise or contrast-to-noise ratio. For long TR, the ER value increases gradually. However, for short TR, the ER value increases rapidly and plateaus so that the ER value changes little beyond a certain FA value. Therefore, we suggest use of a higher FA, near 90°, to obtain a higher ERmax for long TR in 2D SPGR or FSPGR and a smaller FA, much less than 90°, to reach an appropriate ERmax for short TR in 3D SPGR or FSPGR. This information could be helpful in setting the optimal parameters for DCE-MRI.

Inorganic arsenic trioxide induces gap junction loss in association with the downregulation of connexin43 and E-cadherin in rat hepatic "stem-like" cells.

Chronic exposure to inorganic arsenic trioxide causes tumors of the skin, urinary bladder, lung, and liver. Several cancer initiators and promoters have been shown to alter cell-cell signaling by interference with gap junction intercellular communication (GJIC) and/or modulation of cell adhesion molecules, such as connexin43 (Cx43), E-cadherin, and ß-catenin. The aim of this study was to determine whether the disruption of cell-cell interactions occurs in liver epithelial cells after exposure to arsenic trioxide. WB-F344 cells were treated with arsenic trioxide (6.25-50 µM) for up to 8 hours, and gap junction function was analyzed using the scrape-load/dye transfer assay. In addition, the changes in mRNA and protein levels of Cx43, E-cadherin, and ß-catenin were determined. A significant dose- and time-dependent decrease in GJIC was observed when WB-F344 cells were exposed to arsenic trioxide (p < 0.05). Consistent with the inhibition of GJIC, cells' exposure to arsenic trioxide resulted in dose- and time-dependent decreases in Cx43 and E-cadherin mRNA expression and protein levels. However, arsenic trioxide did not alter the mRNA or protein levels of ß-catenin. In an immunofluorescence study, nuclei were heavily stained with anti-ß-catenin antibody, indicating significant nuclear translocation. In this study, we also demonstrated that arsenic trioxide-induced GJIC loss was a reversible process. Taken together, these data support the hypothesis that disruption of cell-cell communication may contribute to the tumor-promoting effect of inorganic arsenic trioxide.

Preliminary study of non-invasive shock wave treatment of capsular contracture after breast implant: animal model.

The incidence rate of capsular contracture after breast implant is about 8% to 12%. Patients would feel extremely uncomfortable after scar formation. Administering oral medications (such as vitamin E and Zafirlukast tablets, etc.) or invasive breast capsulectomy surgery was commonly used for capsular contracture repair in clinical therapy. However, the therapeutic effect is still under investigation. Shock waves can be used to remove soft connective tissue in clinical applications. It has been widely used in orthopedics and rehabilitation. No related research paper about shock wave treatment of capsular contracture has been published yet. It might provide another choice for capsular contracture repair. In order to simulate breast implantation, two silica-gel bags filled with normal saline were implanted into New Zealand rabbit's thighs bilaterally as an animal model. Six weeks later, daily shock wave treatment on the right thigh was performed for six weeks after capsular contractures were formed, while the other thigh was used as a control. Then, magnetic resonance imaging (MRI) was used to compare the difference between treated and un-treated thighs. Afterwards, pathological sections were analyzed to confirm the findings. It has been demonstrated that shock wave treatments are capable of changing the structure and composition of capsular contractures. The structure of scar became myxoid changed or collagen deposition of scar decreased after shock wave treatment, hence, the formation of scars decreased. Increased myxoid and decreased collagen deposition has also been found.

Quantifying liver cirrhosis by extracting significant features from MRI T2 image.

Most patients with liver cirrhosis must undergo a series of clinical examinations, including ultrasound imaging, liver biopsy, and blood tests. However, the quantification of liver cirrhosis by extracting significant features from a T2-weighted magnetic resonance image (MRI) provides useful diagnostic information in clinical tests. Sixty-two subjects were randomly selected to participate in this retrospective analysis with assigned to experimental and control groups. The T2-weighted MRI was obtained and to them dynamic adjusted gray levels. The extracted features of the image were standard deviation (SD), mean, and entropy of pixel intensity in the region of interest (ROI). The receiver operator characteristic (ROC) curve, 95% confidence intervals, and kappa statistics were used to test the significance and agreement. The analysis of area under ROC shows that SD, mean, and entropy in the ROI were significant between the experimental group and the control group. Smaller values of SD, mean, and entropy were associated with a higher probability of liver cirrhosis. The agreements between the extracted features and diagnostic results were shown significantly (P < 0.001). In this investigation, quantitative features of SD, mean, and entropy in the ROI were successfully computed by the dynamic gray level scaling of T2-weighted MRI with high accuracy.

Early response of hepatocellular carcinoma to transcatheter arterial chemoembolization: choline levels and MR diffusion constants--initial experience.

PURPOSE: To prospectively investigate the apparent diffusion coefficient (ADC) and choline levels measured at hydrogen 1 ((1)H) magnetic resonance (MR) spectroscopy, to monitor therapeutic responses of hepatocellular carcinoma (HCC) to transcatheter arterial chemoembolization (TACE). MATERIALS AND METHODS: Institutional review board approval was obtained, and all patients and control subjects provided informed consent. Histologically proved large HCCs (>3 cm in diameter) were evaluated in 20 patients (16 men and four women; mean age, 59 years; range, 34-80 years) before TACE and 2-3 days after TACE. A control group of eight adults (five men and three women; mean age, 43 years; range, 24-76 years) with normal livers was examined by using the same protocol. Hepatic choline levels were measured by means of an external phantom replacement method, quantifying the peak at 3.2 ppm at (1)H MR spectroscopy. ADCs were measured for all lesions. A Wilcoxon rank sum test was used to compare absolute choline concentrations and ADCs at baseline between HCCs and normal liver parenchyma. Changes in choline levels and ADCs in the tumors before and after TACE were analyzed by using the Wilcoxon signed rank test. RESULTS: The median preoperative choline level in patients with HCC (measured in 18 of the 20 patients) was 4.0 mmol/L (range, 0.0-17.2 mmol/L), which was significantly higher than that in patients with normal livers (n = 8) (median, 1.6 mmol/L; range, 0.0-2.1 mmol/L; P < .01). Among 18 patients with HCC, choline levels decreased significantly from before TACE to after TACE (P < .01). A significant increase in ADC from before TACE to after TACE in the 20 patients with HCC was also found (P < .01). CONCLUSION: Hepatic choline levels and ADCs may allow monitoring of therapeutic responses of HCC to TACE although larger, more definitive and quantitative studies with clinical end points are needed.

Effect of intravenous gadolinium-DTPA on diffusion-weighted magnetic resonance images for evaluation of focal hepatic lesions.

OBJECTIVE: Diffusion-weighted imaging (DWI) is usually performed before administration of intravenous contrast agents. Repetition of DWI is occasionally necessary after contrast administration, but the effects of contrast material on DWI and apparent diffusion coefficient (ADC) values in the abdomen have not yet been fully examined. The purpose of this work is to assess whether administration of gadolinium-based contrast material significantly affects DWI and ADC values at the focal hepatic lesions. METHODS: The results of DWI at 3.0 T (Signa VH3; GE Medical Systems, Milwaukee, WI) were examined in 20 patients (age range: 33-86 years, mean age = 68 years) who were evaluated by means of a hepatic protocol at our hospital. Among the 20 patients studied, a total of 57 lesions were detected. Diffusion-weighted imaging was obtained using single-shot echo planar imaging with a b value of 500 s/mm. Patients were injected with 0.1 mmol/kg gadopentetate dimeglumine. The signal-to-noise ratio (SNR) of the liver and the hepatic lesions was examined, and the contrast-to-noise ratio (CNR) of each lesion was evaluated. In addition, the ADC values calculated from the DWI were compared before and after administration of contrast agent. The statistical significance of differences between precontrast and postcontrast administration was determined by use of a paired t test. RESULTS: The SNR and CNR of the DWI were not significantly different before and after administration of contrast agent. The ADC values tended to decrease after administration of contrast agent for each focal hepatic lesion and the liver, although they did not reach statistical significance. CONCLUSION: There was no significant difference before and after administration of contrast agent in the SNR or CNR of DWI. This indicates the feasibility of postcontrast DWI as a substitute for an unsuccessful precontrast-enhanced study in clinical practice.

The Characterization and Imaging Behavior of a New Developed Paramagnetic Contrast Agent NMG2[Gd(TTDA-BOM)].

[Gd(TTDA-BOM)]2-is a newly developed paramagnetic contrast agent.The ligand,TTDA-BOM,bears a benzyloxymethyl group so that the lipophilicity is increased. The water exchange rate for [Gd(TTDA-BOM)]2-is significantly higher than that of [Gd(DTPA)]2-and [Gd(BOPTA)]2-.In addition, the bound relaxivity of this Gd (III) complex has a remarkably high value with HSA. Therefore,it has potential to be used as a blood pool contrast agent for MRI. The aim of this study is to investigate the characterization and imaging behavior of NMG2[Gd(TTDA-BOM)] in normal rat livers and hearts using a 3T high field whole-body MR scanner.The high field MR scanner is expected to have a higher signal to noise ratio. The relaxivities r1and r2for [Gd(TTDA-BOM)]2-at 3T are 5.97 mM-1s-1and 7.99 mM-1s-1respectively, which are higher than those for [Gd(DTPA)]2(r1=4.64 mM-1s-1and r2= 5.08 mM-1s-1). The dynamic MRI studies show that there is marked enhancement in livers and hearts right after the bolus injection and the enhancement ratios keep high until two hours. In conclusion, [Gd(TTDA-BOM)]2-might have a good potential in both cardiovascular and hepatobiliary applications.

Evaluation of [Gd(Bz-TTDA)]2- as a potential contrast agent in MR imaging of the hepatobiliary system: an animal study.

PURPOSE: To evaluate the potential of a new lipophilic paramagnetic complex [Gd(Bz-TTDA)]2- [(4s)-4-benzyl-3,6,10-tri(carboxymethyl)-3,6,10-triazadodecandioic acid]2- designed for use as a hepatobiliary MR contrast agent. MATERIALS AND METHODS: MR imaging studies for normal and hepatocellular carcinoma (HCC) rat models were performed using a 1.5-T scanner. Sequential multislice T1-weighted turbo field echo (TFE) (TR/TE/flip angle: 15 msec/6.1 msec/25 degrees) coronal images of normal rats were obtained before and after intravenous injections of 0.1 mmol/kg [Gd(Bz-TTDA)]2- in study groups (N = 12) or 0.1 mmol/kg gadopentate dimeglumine (Gd-DTPA)2- in control groups (N = 12). Similar protocols of MR imaging with additional T2-weighted images were used for the rats with implanted HCC in both study and control groups (N = 12, in each group). MR images were analyzed to evaluate the time-enhancement change (% increase of signal-to-noise ratio [SI/N]) in normal liver, renal cortex, renal medulla, and tumors. The liver-lesion contrast-to-noise ratios (CNR) were also evaluated in study and control groups. The rats were killed immediately after the last MR scan to undergo autopsy and histopathologic observation. The acute toxicity test (medial lethal dose, LD50) in mice was also done. RESULTS: The liver enhancement in normal rats reached a plateau 5-50 minutes after injection of [Gd(Bz-TTDA)]2-, maintained for three hours, then gradually declined. Intensity of enhancement in liver, renal cortex, and medulla after injection of [Gd(Bz-TTDA)]2- was significantly higher than with Gd-DTPA. The efficacy of tumor characterization with injection of [Gd(Bz-TTDA)]2- was similar to that of Gd-DTPA at the early dynamic phase of the contrast study. However, the liver-lesion CNRs were significantly higher in the study group in the later phase, when tumor enhancement decreased and liver enhancement persisted. The dose of LD50 in acute toxicity test of [Gd(Bz-TTDA)]2- in mice was 7.5 mmol/kg. CONCLUSION: The preliminary results in this animal study indicated that [Gd(Bz-TTDA)]2- has the potential of becoming a reliable liver MR contrast agent.