P. Rogalla

Coronary magnetic resonance angiography: Experimental evaluation of the new rapid clearance blood pool contrast medium P792

The signal‐enhancing characteristics of a new monodisperse monogadolinated macromolecular MR contrast medium (P792) were evaluated for magnetic resonance angiography (MRA) of the coronary arteries. A total of 15 cardiac examinations were performed in pigs at 1.5 T using a 3D gradient‐echo sequence. Images were acquired during breath‐hold before and up to 35 min after IV injection of Gd‐DTPA (0.3 mmol Gd/kg), Gd‐BOPTA (0.2 mmol Gd/kg), and P792 (13 μmol Gd/kg). An increase in the signal‐to‐noise ratio (SNR) of 97% ± 17%, 108% ± 37%, and 109% ± 31% in coronary arteries and of 82% ± 19%, 82% ± 24%, and 28% ± 18% in myocardium, respectively, was measured during the first postcontrast acquisition. The blood‐to‐myocardium signal‐difference‐to‐noise ratio (SDNR) was significantly higher for P792 than for the other Gd compounds (P < .05) for up to 15 min after injection. Qualitative assessment showed that visualization of the coronary arteries and their branches was significantly better for P792 compared to the low‐molecular Gd compounds (P < .05). The blood pool contrast medium P792 is well suited for MRA of the coronary arteries. Magn Reson Med 46:932–938, 2001.

Virtual endoscopy of the nose and paranasal sinuses.

Abstract. The purpose of this study was to evaluate the applicability of virtual endoscopy (VE) in the region of the nose and paranasal sinuses on the basis of volume-rendered spiral CT data. Forty-five patients underwent a low-dose spiral CT of the sinuses. The data were transferred to a workstation running software for volume rendering (EasyVision, Philips Medical Systems, Eindhoven, The Netherlands). Six orthogonal views of the maxillary sinuses and the nasopharynx and a fly-through movie of the nose were calculated. Two radiologists evaluated the coronal reconstructions and virtual endoscopy with respect to detectability of pathology using a checklist comprising 10 points. In 30 patients who underwent subsequent endoscopic surgery, surgeons were asked to rank the degree of assistance of the preoperative virtual endoscopy. In general, virtual endoscopy was possible in all 45 patients. The mean time required for path definition and movie calculation for virtual endoscopy were 8 ( ± 2) min and 3 ( ± 1) min, respectively. Overall, more anatomical details were depicted on coronal reconstructions; however, a high degree of similarity between virtual endoscopy and the intraoperative impression was reported by the surgeons. We conclude that virtual endoscopy of the nose and paranasal sinuses may develop into a standard means to guide surgeons during endoscopic interventions.

Colonography using multislice CT

Computed tomography (CT) represents the preferred imaging modality for imaging the large bowel when virtual endoscopic reconstructions are desired. Using the spiral acquisition technique, it has become possible to scan the entire abdomen within a single breathhold, however, slice thicknesses of 5 mm or more are necessary should the breathhold not last longer than 30-40 s. With the advent of multislice CT, contiguous 1-mm slices can be obtained through the entire abdomen while even shortening the breathhold to 25-30 s. The improved speed and spatial resolution of multislice CT results in remarkably sharp virtual reconstructions allowing detection of polyps with sizes less than 3 mm. The disadvantages must still be considered including a dataset consisting of up to 800 images representing a new challenge for postprocessing hard- and software.

Linear and volume measurements of pulmonary nodules at different CT dose levels - intrascan and interscan analysis.

PURPOSE To compare the interobserver variability of the unidimensional diameter and volume measurements of pulmonary nodules in an intrascan and interscan analysis using semi-automated segmentation software on ultra-low-dose computed tomography (ULD-CT) and standard dose CT (SD-CT) data. MATERIALS AND METHODS In 33 patients with pulmonary nodules, two chest multi-slice CT (MSCT) datasets (1 mm slice thickness; 20 % reconstruction overlap) had been consecutively acquired with an ultra-low dose (120 kV, 5 mAs) and standard dose technique (120 kV, 75 mAs). MSCT data was retrospectively analyzed using the segmentation software OncoTREAT (MeVis, Bremen, Germany, version 1.3). The volume of 229 solid pulmonary nodules included in the analysis as well as the largest diameter according to RECIST (Response Evaluation Criteria for Solid Tumors) were measured by two radiologists. Interobserver variability was calculated and SD-CT and ULD-CT data compared in an intrascan and interscan analysis. RESULTS The median nodule diameter (n = 229 nodules) was registered with 8.2 mm (range: 2.8 to 43.6 mm, mean: 10.8 mm). The nodule volume ranged between 0.01 and 49.1 ml (median 0.1 ml, mean 1.5 ml). With respect to interobserver variability, the intrascan analysis did not reveal statistically significant differences (p > 0.05) between ULD-CT and SD-CT with broader limits of agreement for relative differences of RECIST measurements (-31.0 % + 27.0 % mean -2.0 % for SD-CT; -27.0 % + 38.6 %, mean 5.8 % for ULD-CT) than for volume measurements (-9.4 %, 8.0 %, mean 0.7 % for SD-CT; -13 %, 13 %, mean 0.0 % for ULD-CT). The interscan analysis showed broadened 95 % confidence intervals for volume measurements (-26.5 % 29.1 % mean 1.3 %, and -25.2 %, 29.6 %, mean 2.2 %) but yielded comparable limits of agreement for RECIST measurements. CONCLUSION The variability of nodule volumetry assessed by semi-automated segmentation software as well as nodule size determination by RECIST appears to be independent of the acquisition dose in the CT source dataset. This is particularly important regarding size determination of pulmonary nodules in screening trials using low-dose CT data for follow-up imaging.

Safe and easy power injection of contrast material through a central line

Abstract. Power-assisted injection of contrast material into an antecubital vein is commonly used in CT and has been proven superior to manual injection. Power-assisted injection through a central line bares the risk of rupturing the line because manual control over the pressure applied by the power injector is lacking. We present a simple safety device which allows manual control of the pressure by means of an interposed three-way stopcock combined with a small syringe for pressure equalization.

Computer-aided pulmonary nodule detection - performance of two CAD systems at different CT dose levels.

PURPOSE To evaluate the impact of dose reduction on the performance of computer-aided lung nodule detection systems (CAD) of two manufacturers by comparing respective CAD results on ultra-low-dose computed tomography (ULD-CT) and standard dose CT (SD-CT). MATERIALS AND METHODS Multi-slice computed tomography (MSCT) data sets of 26 patients (13 male and 13 female, patients 31 - 74 years old) were retrospectively selected for CAD analysis. Indication for CT examination was staging of a known primary malignancy or suspected pulmonary malignancy. CT images were consecutively acquired at 5 mAs (ULD-CT) and 75 mAs (SD-CT) with 120 kV tube voltage (1 mm slice thickness). The standard of reference was determined by three experienced readers in consensus. CAD reading algorithms (pre-commercial CAD system, Philips, Netherlands: CAD-1; LungCARE, Siemens, Germany: CAD-2) were applied to the CT data sets. RESULTS Consensus reading identified 253 nodules on SD-CT and ULD-CT. Nodules ranged in diameter between 2 and 41 mm (mean diameter 4.8 mm). Detection rates were recorded with 72 % and 62 % (CAD-1 vs. CAD-2) for SD-CT and with 73 % and 56 % for ULD-CT. Median false positive rates per patient were calculated with 6 and 5 (CAD-1 vs. CAD-2) for SD-CT and with 8 and 3 for ULD-CT. After separate statistical analysis of nodules with diameters of 5 mm and greater, the detection rates increased to 83 % and 61 % for SD-CT and to 89 % and 67 % for ULD-CT (CAD-1 vs. CAD-2). For both CAD systems there were no significant differences between the detection rates for standard and ultra-low-dose data sets (p > 0.05). CONCLUSION Dose reduction of the underlying CT scan did not significantly influence nodule detection performance of the tested CAD systems.

Tissue transition projection (TTP) of the intestines.

Abstract. Tissue transition projection (TTP) represents a three-dimensional reconstruction technique for volumetric image data sets. To demonstrate the principle characteristics of TTP, a simple phantom consisting of two pipes with a simulated, wall-adherent polyp was scanned with spiral CT, and images were reconstructed by means of volume rendering for both opaque surface reconstructions and TTP. Tissue transition projection was used in 7 patients for reconstruction of the small intestine or the colon. Unlike three-dimensional reconstructions with opaque surfaces, TTP enhances surface transitions while suppressing homogeneous areas, allowing delineation of the bowel wall similar to conventional double-contrast studies.

CT colonography: Data acquisition and patient preparation techniques

The success of a virtual endoscopy is essentially dependent on the image quality of the corresponding 3-dimensional reconstructions. Before loading image data on a post-processing computer, certain prerequisites concerning the source data must be met. To carry out a CT colonography, the source data must be of good quality. High spatial resolution in all geometrical directions, continuous data acquisition without gaps, and artefact-free images are pivotal factors influencing source data. A generally applicable rule is that the size of the smallest detectable polyp is limited by the nominal slice thickness, emphasizing the ultimate importance of the initially chosen primary slice collimation. Furthermore, calculation of an endoluminal view is impossible without sufficient distension of the bowels. Thorough patient preparation that accommodates the technical circumstances for post-processing is also required for attaining a high sensitivity in polyp detection.

Assessment of left ventricular volumes and function: intraindividual comparison of multi-slice spiral CT and electron beam CT in an animal model.

Purpose: To evaluate multi-slice spiral computed tomography (MSCT) for measurements of left ventricular volumes, ejection fraction (EF), and myocardial mass in comparison with electron beam CT (EBCT) as a reference method. Material and Methods: Six minipigs underwent both standardized contrast-enhanced MSCT (effective acquisition time per cardiac cycle 125.7±30.1 ms, reconstructed slice thickness 8 mm) and EBCT (acquisition time 50 ms, collimated slice thickness 8 mm). The contrast-to-noise ratio of the left ventricle was measured in each animal, and the contour sharpness of the myocardium was analyzed. Volumes (EDV, ESV, SV) ejection fraction (EF), and muscle mass were calculated by MSCT and by EBCT using the slice summation method. Results: MSCT had a higher contrast-to-noise ratio and delineated the myocardial contours more sharply than EBCT. There was a close linear correlation between both modalities for all parameters (EDV: rP=0.88, ESV: rP=0.91, SV: rP=0.85, EF: rP=0.93; mass: rP=0.90; P<0.05 each). MSCT slightly overestimated ESV and slightly underestimated SV and EF compared with EBCT (P<0.05 each). Conclusions: Image quality in MSCT is superior to that of EBCT. Functional parameters correlate well between both modalities, but the accuracy of MSCT is limited by its lower temporal resolution.

Toward computer-aided emphysema quantification on ultralow-dose CT: reproducibility of ventrodorsal gravity effect measurement and correction

Computer aided quantification of emphysema in high resolution CT data is based on identifying low attenuation areas below clinically determined Hounsfield thresholds. However, the emphysema quantification is prone to error since a gravity effect can influence the mean attenuation of healthy lung parenchyma up to ± 50 HU between ventral and dorsal lung areas. Comparing ultra-low-dose (7 mAs) and standard-dose (70 mAs) CT scans of each patient we show that measurement of the ventrodorsal gravity effect is patient specific but reproducible. It can be measured and corrected in an unsupervised way using robust fitting of a linear function.