Materials and Methods: Lumbar vertebral osteomyelitis was induced in 10 rabbits with intradiscal injection of bacteria in a vertebral disk (test level) versus saline injection in another disk (control level). After a mean interval of 12 days, rabbits were imaged prior to and 24 hours after administration of USPIO. The MR imaging protocol included T1-weighted spin-echo, T2-weighted fast spin-echo, and T2*-weighted gradient-echo sequences. MR findings were compared with histologic findings (macrophage immunostaining and Perls Prussian blue staining). A Wilcoxon signed rank test was used to compare signal-to-noise ratio (SNR) results before and after USPIO administration.
Results: T1-weighted MR images of infected vertebral test levels obtained 24 hours after USPIO administration showed a significant increase in SNR (P = .005), whereas T2- and T2*-weighted images showed no significant changes in SNR (P = .14 and P = .87, respectively). Histologic examination results of infected areas demonstrated complete replacement of hematopoietic bone marrow by macrophage infiltration. Perls Prussian blue staining showed that some macrophages were iron loaded. T1- (P = .02), T2- (P = .04), and T2*-weighted (P = .04) images of control vertebrae showed a significant decrease in SNR. Histologic examination results confirmed the persistence of normal hematopoietic bone marrow without macrophage infiltration, which was reflected by more intensive Perls Prussian blue staining compared with that in infected areas.
Conclusion: MR imaging can depict USPIO-loaded macrophage infiltration present in infected areas in an experimental rabbit model of vertebral osteomyelitis.
© RSNA, 2008
]]>Materials and Methods: Four coronary stents (2, 3, 4, and 5 mm) were examined at 64-section dual-energy multidetector CT by using a dual-detector "double-decker" imager with stacked high- and low-energy detector arrays, 0.67-mm section thickness, and 32 x 0.625-mm collimation. Simultaneous high- and low-energy data sets were acquired at 80 and 140 kVp and at 400 mAs. Cardiac motion was simulated in a moving anthropomorphic heart phantom. Stents were imaged longitudinally and axially with the phantom at rest and with it in motion. Use of an enhancement algorithm based on high- and low-energy absorption profiles was proposed. Stent lumen depiction and stent mesh delineation were quantified in terms of contrast-to-noise ratio (CNR) and kurtosis (), respectively. Image quality was analyzed at univariate general linear model analysis in which peak voltage and data enhancement algorithm were dependent factors and stent orientation and cardiac motion were independent factors.
Results: Analysis of CNR and revealed an interdependency between CNR and and stent diameter: The CNR and of smaller stents increased significantly when these stents were imaged at lower peak voltages in the axial plane and with the enhancement algorithm applied to the 80-kVp data sets (P < .001). The CNR and of larger stents increased significantly when these stents were imaged at higher peak voltages in the longitudinal plane, and imaging of these stents benefited from the enhancement algorithm being applied to the 140-kVp data sets (P < .001).
Conclusion: Dual-energy multidetector CT performed with optimized acquisition parameters and alternative image postprocessing led to enhanced coronary stent lumen depiction to an extent beyond that achieved with single-energy multidetector CT.
© RSNA, 2008
Supplemental material:
Materials and Methods: The animal research protocol was approved by the Institutional Animal Care and Use Committee. Fifty-two rats (38 treated, 14 control) were included. A CCl4 mixture was injected three times per week for 2–16 weeks. Fat-to-water ratios (FWRs) were calculated. Images were obtained with 12 saturation offset frequencies; magnetization transfer ratios (MTRs) were calculated. Distribution volume (DV), mean transit time (MTT), and portal fraction (PF) of blood inflow were calculated. For pairwise group comparisons, an unequal two-tailed Student t test was used. For pairwise correlations between variables, Pearson correlation coefficients were calculated. For multiple pairwise comparisons, Bonferroni correction was performed by adjusting the significance level ().
Results: FWR and DV were correlated with CCl4 treatment duration from 0 through 8 weeks (r = 0.658, P < .001 and r = –0.664, P < .001, respectively; = .010). PF and MTT were correlated with CCl4 treatment duration from 0 through 16 weeks (r = –0.483, P = .002 and r = 0.414, P = .008, respectively; = .010). DV was inversely correlated with FWR over the same period (r = –0.581, P < .001; = .007). Fibrotic rats without cirrhosis had a higher FWR and lower DV and PF (P < .001, P < .001, and P = .004, respectively; = .017) than control rats, and lower MTR, DV, and MTT (P = .014, .001, and .010, respectively; = .017) than cirrhotic rats. Cirrhotic rats had a higher FWR and a lower PF (P < .001, = .017) than control rats.
Conclusion: Magnetization transfer contrast is not a specific indicator of increased fibrosis in diseased liver; steatosis may influence some perfusion parameters.
© RSNA, 2008
]]>Materials and Methods: In an in vitro study, T1 and T2 relaxation times of three dilution series of gadopentetate dimeglumine (concentration, 0–20.0 mmol gadolinium per liter) at ioversol concentrations with iodine concentration of 0, 236.4, and 1182 mmol iodine per liter (corresponding to 0, 30, and 150 mg of iodine per milliliter) were measured at 1.5 and 3.0 T. The relaxation rate dependence on concentrations of gadolinium and iodine was analytically modeled, and continuous profiles of signal versus gadolinium concentration were calculated for 10 pulse sequences used in current musculoskeletal imaging. After fitting to experimental discrete profiles, maximum signal-to-noise ratio (SNR), gadolinium concentration with maximum SNR, and range of gadolinium concentration with 90% of maximum SNR were derived. The overall influence of field strength and iodine concentration on these parameters was assessed by using t tests. The deviation of simulated from experimental signal-response profiles was assessed with the autocorrelation of the residuals.
Results: The model reproduced relaxation rates of 0.37–38.24 sec–1, with a mean error of 4.5%. Calculated SNR profiles matched the discrete experimental profiles, with autocorrelation of the residuals divided by the mean of less than 5.0. Admixture of ioversol consistently reduced T1 and T2, narrowed optimum gadolinium concentration ranges (P = .004–.006), and reduced maximum SNR (P < .001 to not significant). Optimum gadolinium concentration was 0.7–3.4 mmol/L at both field strengths. At 3.0 T, maximum SNR was up to 75% higher than at 1.5 T.
Conclusion: Admixture of ioversol to gadopentetate dimeglumine solutions results in a consistent additional relaxation enhancement, which can be analytically modeled to allow a near-quantitative a priori optimized match of contrast media concentrations and imaging protocol for a broad variety of pulse sequences.
© RSNA, 2008
]]>Materials and Methods: After approval by the institutional animal use and care committee, an RF electrode was used to ablate the entire prostate in 15 dogs. During ablation, pulse-inversion harmonic US was performed by using an endocavitary probe after an intravenous bolus injection (0.04 mL/kg) and infusion (0.015 µL/kg/min) of a US contrast agent. In group 1 (n = 4), no cooling protection was used during ablation. In group 2 (n = 5), urethral and bladder protection was provided by inserting a 12-F catheter infused with cold saline (8°C ± 4 [standard deviation]) at a rate of 100 mL/min. In group 3 (n = 6), further protection of the neurovascular bundles (NVBs) was provided by infusing cold saline (8°C ± 4) into the iliac arteries at a rate of 50 mL/min by means of catheterization of the femoral artery. Pathologic findings among the three groups were compared by using the Wilcoxon rank sum test.
Results: The average volumes of prostate ablation achieved in the three groups were 96.6%, 91.9%, and 92%. Contrast-enhanced pulse-inversion harmonic US allowed visualization and monitoring of urethral and NVB blood flow during the ablation. Without protection, damage to the urethra and the NVB was demonstrated at both US and pathologic examination. There was highly significant difference in urethral damage between groups with and the group without urethral cooling (P = .002), while intraarterial cooling demonstrated a nonsignificant trend toward a decreased NVB damage (P = .069).
Conclusion: Contrast-enhanced US can guide RF ablation of the entire prostate. Infusion of cold saline provides effective protection for the urethra during such procedures. The application of intraarterial cooling did not provide a significant improvement in the protection of the NVB in this small study.
© RSNA, 2008
]]>Materials and Methods: The institutional animal care and use committee approved the animal studies. In vivo and ex vivo studies were performed. In the in vivo study, 20 lumbar vertebrae from six swine were locally heated by using 1- or 2-cm active-tip internally cooled electrodes. In the ex vivo study, 12 fresh pig cadaver lumbar vertebrae were extracted from four swine, and spinal tumor models with or without cortical bone defect were created by stuffing a cavity with muscle tissue and locally heated by using a 1-cm active-tip internally cooled electrode. The temperature was monitored in the spinal canal and around the vertebral body during ablation. Mann-Whitney U test was used to indicate a significant difference between groups by using 1- and 2-cm active tip in the in vivo study and between groups with and without cortical defect in the ex vivo study.
Results: In the in vivo study in which 1- and 2-cm active-tip needles were used, the temperature in the spinal canal rose to 38.2°C ± 2.7 (standard deviation) and 45.5°C ± 6.2, respectively. The latter was significantly higher than the former (P < .001). In the ex vivo study in which tumor models with or without a cortical bone defect were used, the temperature in the spinal canal rose to 48.4°C ± 6.2 and 31.3°C ± 3.4, respectively. The former was significantly higher than the latter (P < .001).
Conclusion: For in vivo cases with a 2-cm active tip and ex vivo cases with a vertebral posterior bone defect, the temperature rose to over 45°C, potentially injuring the spinal cord and peripheral nerves.
© RSNA, 2008
]]>Materials and Methods: This study was granted exempt status by the institutional review board and the animal care and use committee. Fractures simulating the CML were produced in distal femurs of 20 deceased fetal pigs. Twenty normal femurs served as control femurs. Femurs were imaged with a standard single-side–read 100-µm pixel sampling imaging plate (IP), a high-resolution dual-side–read 50-µm pixel sampling IP, and a high-detail screen-film imaging system. Eight tube current–time product settings (0.5–10.0 mAs) and two tube voltage selections (56 and 70 kVp) were employed. Two pediatric radiologists evaluated 920 images for fracture by using a five-point Likert scale. Area under the receiver operating characteristic curve (Az) values for the imaging systems were compared by using nonparametric 2 tests (all P < .05).
Results: For pooled rater data, performance of computed radiography was comparable to that of screen-film imaging, and superior performance (P = .04) was achieved with the more experienced rater. The Az value tended to increase as the tube current–time product setting was increased. Within each system, there was no significant difference in Az values for all images obtained at 56 and 70 kVp (dual-side–read IP, P = .63; single-side–read IP, P = .25; screen-film imaging system, P = .5). At 56 kVp, a dose reduction of up to 69% was achieved, and accuracy of computed radiography was comparable to that of screen-film imaging.
Conclusion: Findings in this study suggest that computed radiography can replace screen-film imaging in the detection of CMLs and may permit dose reduction.
© RSNA, 2008
]]>Materials and Methods: Institutional animal care and use committee approval was obtained. Seventeen female rats with implanted human breast cancers underwent dynamic albumin-(Gd-DTPA)30–enhanced MR imaging followed by an initial dose of bevacizumab or saline (as a control). Treatment was continued every 3rd day, for a total of four doses at five possible dose levels: 0 mg bevacizumab (n = 4 [control rats]), 0.1 mg bevacizumab (n = 3), 0.25 mg bevacizumab (n = 2), 0.5 mg bevacizumab (n = 5), and 1.0 mg bevacizumab (n = 3). A second MR imaging examination was performed 24 hours after the initial dose to enable calculation of the acute change in MR imaging–assayed leakiness, or KPS. This acute change in KPS at MR imaging was correlated with tumor growth response for each cancer at the completion of the 11-day treatment course. For statistical analyses, an unpaired two-tailed t test, analysis of variance, and linear regression analyses were used.
Results: The MR imaging–assayed change in tumor microvascular leakiness, tested as a potential biomarker, correlated strongly with tumor growth rate (R2 = 0.74, P < .001). KPS and tumor growth decreased significantly in all bevacizumab-treated cancers compared with these values in control group cancers (P < .05).
Conclusion: The MR imaging–assayed acute change in vascular leakiness after a single dose of bevacizumab was an early, measurable predictive biomarker of tumor angiogenesis treatment response.
© RSNA, 2008
]]>Materials and Methods: Spherical and lobulated pulmonary nodules 3–15 mm in diameter were placed in a commercially available lung phantom and scanned by using a 16-section computed tomographic (CT) scanner. Nodule volume (V) was determined by using the diameters of 27 spherical nodules and the mass and density values of 29 lobulated nodules measured by using the formulas V = (4/3)r3 (spherical nodules) and V = 1000 · (M/D) (lobulated nodules) as reference standards, where r is nodule radius; M, nodule mass; and D, wax density. Experiments were performed to evaluate seven reconstruction kernels and the independent effects of FOV and section thickness. Automated nodule volume measurements were performed by using computer-assisted volume measurement software. General linear regression models were used to examine the independent effects of each parameter, with percentage overestimation of volume as the dependent variable of interest.
Results: There was no substantial difference in the accuracy of volume estimations across the seven reconstruction kernels. The bone reconstruction kernel was deemed optimal on the basis of the results of a series of statistical analyses and other qualitative findings. Overall, volume accuracy was significantly associated (P < .0001) with larger reference standard–measured nodule diameter. There was substantial overestimation of the volumes of the 3–5-mm nodules measured by using the volume measurement software. Decreasing the FOV facilitated no significant improvement in the precision of lobulated nodule volume measurements. The accuracy of volume estimations—particularly those for small nodules—was significantly (P < .0001) affected by section thickness.
Conclusion: Substantial, highly variable overestimation of volume occurs with decreasing nodule diameter. A section thickness that enables the acquisition of at least three measurements along the z-axis should be used to measure the volumes of larger pulmonary nodules.
© RSNA, 2008
]]>Materials and Methods: Institutional animal use and care committee approval was obtained. Thirty male rats made up four groups of rats with an injured left posterior tibial nerve (irreversible neurotmesis, reversible neurotmesis, severe axonotmesis, or moderate axonotmesis) and one control group. There were six rats in each group. Signal intensity changes were seen in the gastrocnemius muscle on the T2-weighted MR images. T2 values were also measured in vivo with the Carr-Purcell-Meiboom-Gill method. Gait function was assessed by calculating the print length factor (PLF). T2 ratios and PLFs on the injured side were compared with those on the unaffected side. Ratios of specific acquisition points within groups were compared by using repeated-measures analysis of variance. Comparisons across the five groups at each acquisition point were performed by using one-way analysis of variance with Scheffe post hoc testing. P < .05 indicated a significant difference.
Results: The more severe the nerve damage, the higher the signal intensity on T2-weighted MR images. There were significant differences in T2 ratios between the nerve injury groups and the control group (P < .05). Changes in T2 values and ratios depended on the degree of nerve injury. In the reversible neurotmesis group, T2 values and ratios began to decrease 28 days after surgery. In the severe and moderate axonotmesis groups, T2 values and ratios began to decrease 14 days after surgery. The starting point of functional recovery also depended on the degree of nerve injury.
Conclusion: The degree and prognosis of nerve injury can be evaluated by observing changes in signal intensity on T2-weighted images and the time course of T2 values and ratios.
© RSNA, 2008
]]>Materials and Methods: The study was approved by the research animal care and use committee, and all husbandry and experimental studies were compliant with the National Research Council's Guide for the Care and Use of Laboratory Animals. Twenty-four coagulation zones (three per animal) were created at thoracotomy in eight female domestic swine (mean weight, 55 kg) by using a microwave ablation system with 17-gauge lung-tuned triaxial antennas. Ablations were performed for 10 minutes each by using (a) a single antenna, (b) a single antenna with bronchial occlusion, and (c) an array of three antennas powered simultaneously. The animals were sacrificed immediately after ablation. The coagulation zones were excised en bloc and sectioned into approximately 4-mm slices for measurement of size, shape, and circularity. Analysis of variance and two-sample t tests were used to identify differences between the three ablation groups.
Results: The overall mean diameters of coagulation achieved with a single antenna and bronchial occlusion (4.11 cm ± 1.09 [standard deviation]) and with multiple-antenna arrays (4.05 cm ± 0.69) were significantly greater than the overall mean diameter achieved with a single antenna alone (3.09 cm ± 0.83) (P = .016 for comparison with multiple antennas, P = .032 for comparison with bronchial occlusion). No significant differences in size were seen between the coagulation zones created with bronchial occlusion and those created with multiple antennas (P = .68). The coagulation zones in all groups were very circular (isoperimetric ratio > 0.80) at cross-sectional analysis.
Conclusion: A 17-gauge triaxial microwave ablation system tuned for lung tissue yielded large circular zones of coagulation in vivo in porcine lungs. The coagulation zones created with bronchial occlusion and multiple antennas were significantly larger than those created with one antenna.
© RSNA, 2008
]]>Materials and Methods: The local animal care committee approved this study. The following contrast media were used: (a) iodixanol (150 mg of iodine per milliliter and 320 mg I/mL, 0.29 osm/kg H2O), (b) iopromide (150 mg I/mL, 0.34 osm/kg), (c) 0.5 mol/L gadodiamide (0.78 osm/kg), and (d) 1.0 mol/L gadobutrol (1.6 osm/kg). After left-sided nephrectomy, contrast media (3 mL per kilogram of body weight) were injected (20 mL/min) in a noncrossover design into the right renal artery of pigs during a 10-minute ischemic period. There were eight pigs in each group and one group for each contrast medium. We compared histomorphology, radiographic contrast medium excretion, subjective radiodensity of nephrograms (70 kVp) at the end of injection, and contrast medium plasma half-life elimination times 1–3 hours after injection. Longer elimination times resulted in lower glomerular filtration rates.
Results: Gadobutrol caused extensive tubular necrosis and moderate glomerular necrosis; gadodiamide and iopromide, minimal to mild tubular necrosis; and iodixanol, no necrosis. Gadobutrol was the only contrast medium to show no sign of excretion, and its plasma half-life elimination time (median, 1103 minutes; P < .001) was significantly longer than that of other contrast agents. Gadodiamide had a significantly longer plasma half-life elimination time (median, 209 minutes; P = .01) than did iodine-based contrast media (median, 136–142 minutes). The 320 mg I/mL dose of iodixanol had the highest radiodensity, whereas gadodiamide had the lowest radiodensity. The radiodensity of the 320 mg I/mL dose of iodixanol was greater than that of the 150 mg I/mL dose of iodixanol, which was equal to the radiodensities of the 150 mg I/mL dose of iopromide and 1.0 mol/L gadobutrol, which in turn were greater than that of 0.5 mol/L gadodiamide.
Conclusion: Plasma iso-osmotic iodine-based contrast media used at commercially available concentrations have superior attenuation and nephrotoxic profiles compared with equal volumes of hyperosmotic nonionic 0.5–1.0 mol/L gadolinium-based contrast media when performing renal arteriographic procedures.
© RSNA, 2008
]]>Materials and Methods: By using the Geant4 Monte Carlo tool kit, the Cristy anthropomorphic phantom and the geometry of a dedicated breast CT prototype were simulated. The simulation was used to track x-rays emitted from the source until their complete absorption or exit from the simulation limits. The interactions of the x-rays with the 65 different volumes representing organs, bones, and other tissues of the phantom that resulted in energy deposition were recorded. These data were used to compute the radiation dose to the organs and tissues during a complete dedicated breast CT scan relative to the average glandular dose to the imaged breast (relative organ dose [ROD]), by using the x-ray spectra proposed for dedicated breast CT imaging. The effectiveness of a lead shield for reducing the dose to the organs was investigated.
Results: The maximum ROD among the organs was for the ipsilateral lung with a maximum ROD of 3.25%, followed by ROD for the heart and the thymus. Of the skeletal tissues, the sternum received the highest dose with a maximum ROD to the bone marrow of 2.24% and to the bone surface of 7.74%. The maximum ROD to the uterus, representative of that of an early-stage fetus, was 0.026%. These maxima occurred for the highest-energy x-ray spectrum (80 kVp) that was analyzed. A lead shield does not substantially protect the organs that receive the highest dose from dedicated breast CT.
Conclusion: Although the dose to the organs from dedicated breast CT is substantially higher than that from planar mammography, it is comparable to or considerably lower than that reached by other radiographic procedures and much lower than that of other CT examinations.
© RSNA, 2008
]]>Materials and Methods: This study was approved by the Institutional Animal Care and Use Committee; 21 canines were imaged with one standard and two subsecond DE MR techniques in four conditions: condition 1, breath holding and steady gating; 2, non–breath holding and steady gating; 3, breath holding and irregular heart rhythm; and 4, non–breath holding and irregular heart rhythm. Images were randomized and scored for diagnostic accuracy, image quality, and observer confidence. Sensitivity, specificity, and diagnostic accuracy for MI detection were calculated for each technique and clinical condition separately. The 2, paired t, and McNemar tests were used for comparisons.
Results: Fifteen dogs had MIs. Among conditions 2–4, differences were not significant (P > .05); data were pooled and referred to as group B. Condition 1 was group A. Accuracy, image quality, and observer confidence, respectively, for standard DE MR imaging were 96%, 3.7 ± 0.8, and 2.7 ± 0.6 in group A but only 74%, 2.4 ± 0.8, and 1.8 ± 0.7 in group B (P ≤ .004 for each). Corresponding scores for subsecond techniques were unaffected by respiratory motion and/or arrhythmia. Subsecond techniques had higher accuracy (82% and 86% vs 74%), better image quality (3.9 ± 0.7 and 3.2 ± 0.8 vs 2.4 ± 0.8), and greater confidence (2.4 ± 0.7 and 2.1 ± 0.7 vs 1.8 ± 0.7) (P ≤ .0002 for each) than standard DE MR imaging. In group A, standard performed better than subsecond DE MR imaging.
Conclusion: Standard DE MR imaging is appropriate for MI detection with breath holding and regular heart rhythm, while subsecond techniques are appropriate with an irregular heart rhythm and when breath holding is not possible.
© RSNA, 2008
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