Objective—To construct and optimize a fiducial marker suitable for both CT and MRI.
Sample—Fiducial markers containing serial dilutions of iopamidol mixed with water.
Procedures—IV tubing sets were infused with serial dilutions (0% to 100%; increments of 10%) of iopamidol. Tubing ends were sealed; additional seals were added to create an equilateral triangle. A reference point was created by placing a crimp in 1 side. Markers were fixed to a gelatin soft tissue–attenuating phantom and evaluated by use of CT and MRI. For CT, simple linear regression analysis was used to assess the relationship between the percentage of marker contrast medium and quantitative variables, including marker attenuation, attenuation changes in the phantom, and beam-hardening artifact length. A subjective grading scheme for artifact creation on CT images and marker visibility on MRI images was used. Measurements were obtained by investigators who were unaware of the contents of each marker.
Results—Percentage of contrast medium in each marker was strongly correlated with marker attenuation (r2 = 0.96), artifact length (r2 = 0.765), and mean attenuation changes within the phantom (r2 = 0.826) for CT. Subjective CT scores indicated that concentrations of contrast medium > 50% resulted in excessive artifacts. Markers with concentrations of iopamidol > 50% had poor subjective MRI visibility scores. No artifacts were seen on MRI.
Conclusions and Clinical Relevance—A marker containing a 10% solution of iodinated contrast medium mixed with water provided ideal contrast for both CT and MRI.
OBJECTIVE To evaluate changes in the dimension and volume of feline injection-site sarcomas (FISSs) before (in vivo) and after surgical excision and formalin fixation (ex vivo) as determined by measurements obtained from 2-D and 3-D CT images.
SAMPLE 10 excised FISSs.
PROCEDURES The maximum length, width, and depth of each FISS were measured on contrast-enhanced 2-D CT images of the tumor obtained in vivo and ex vivo. Those measurements were used to estimate tumor volume with the standard ellipsoid formula. Tumor volume was also calculated from 3-D CT images with software that used a volume-rendering algorithm. Student paired t tests were used for comparisons between the in vivo and ex vivo assessments.
RESULTS Small decreases were detected in maximum tumor length, width, and depth between the in vivo and ex vivo assessments; however, tumor length was the only dimension that decreased significantly between the 2 assessments. Median tumor volume decreased significantly between the in vivo and ex vivo assessments regardless of the method used to estimate it. Tumor volume estimated by the ellipsoid formula was significantly lower than that estimated by the 3-D CT software at both assessments.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that shrinkage of FISSs following excision and formalin fixation was small and may be less than that of grossly normal tissue. Tumor volume estimated by the ellipsoid formula was consistently less than that estimated by 3-D CT software and should not be used when accuracy of tumor volume is of particular concern and advanced CT imaging is available.