British Journal of Radiology 75 (2002),401-408 © 2002 The British Institute of Radiology
Optimization of scanning parameters for CT colonography
N P Power, MRCPI, FRCR
1
M D Pryor, MSc
2
A Martin, DCR, PgDip
1
J Horrocks, MSc, PhD
2
A M McLean, FRCP, FRCR
1 and
R H Reznek, FRCP, FRCR
1
Departments of 1 Radiology and 2 Clinical Physics, St. Bartholomew's Hospital, West Smithfield, London EC1A 7EB, UK
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Abstract
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To determine the optimal collimation, pitch and reconstruction interval for CT colonography, 10 spherical polyps between 1 mm and 10 mm diameter and made of tissue equivalent material with a CT number of 40 Hounsfield units (HU) were placed in the colon of an anthropomorphic phantom. The phantom was scanned at slice thicknesses of 3 mm, 5 mm and 7 mm and pitches of 1.0, 1.3, 1.5, 1.7 and 2.0 on an IGE Hispeed advantage system. Images were reconstructed for each scanning parameter at the minimum intervals allowed along the z-axis. The optimum scanning protocol was assessed by measuring maximum contrast between the polyp and air, sensitivity for detection of each polyp along the z-axis, and relative radiation dose. In addition, images were reviewed separately by two radiologists who graded polyp conspicuity as: 0, not seen; 1, faintly seen; 2, well seen. It was found that varying the scanning parameters caused a marked alteration in the maximum contrast between each polyp and air. For example, for the 5 mm polyp, the range of contrasts from best to worst case was 910–490 HU. It was noted that with contrasts of less than 500 HU, polyps were only faintly seen. A slice thickness of 3 mm with a pitch of 2 offers optimal polyp conspicuity with a relatively low radiation dose, we conclude that scanning parameters can be optimized for threshold contrast, radiation dose and subjective conspicuity. We propose an optimal parameter of 3 mm slice thickness and pitch 2.
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Introduction
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Barium enema and colonoscopy have been the traditional methods of evaluation of the large bowel. However, owing to well documented drawbacks of these procedures [1, 2], recent years have seen the increased use of CT, which is more acceptable to patients than barium enema [3] and allows visualization both within and without the colon, thus representing a viable alternative when either barium enema or colonoscopy cannot be completed. Terminology such as spiral CT pneumocolon [4], CT colography [5–7] and virtual colonoscopy have now been replaced by CT colonography, a multi component exam comprising axial section review with potential two-dimensional (2D) and three-dimensional (3D) display. Axial CT lacks the ability to provide contiguous colon display, and there is a risk of partial voluming of small adenomas [8]. Hara et al [7] have demonstrated an improvement in the detection of small colonic polyps using 2D reformatting techniques. Thus, most recent work has concentrated on the efficacy of 2D and 3D display [2, 5, 6, 8]. However, the data processing involved in the generation of these more sophisticated images can be time consuming and the hardware required expensive. Dachman et al [5] used axial images with 3D reconstructions for problem solving, while Hara et al [6] and Royster et al [2] found the two techniques to be complementary. As virtual endoscopic review of the colon is limited by the quality of the original image data [9], optimization of scanning parameters will maximize the accuracy of the study as a whole.
Current technique for CT colonography entails adequate bowel preparation, air insufflation per rectum and the use of an iv muscle relaxant, either glucagon or buscopan (hyoscine-n-butylbromide), although these requirements may change in the future. While different scanning parameters have been suggested by different workers for the acquisition of axial images, (summarized in Appendix), consensus on optimal parameters has not been obtained. The aim of our study was to determine optimal collimation, pitch and reconstruction interval for CT colonography by subjectively and objectively assessing the effects of a range of such parameters on the conspicuity of phantom polyps of varying sizes, and by comparing relative dose from each parameter.
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Materials and methods
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Phantom and scanning technique
10 spherical phantom polyps of 1–10 mm diameter were made in-house of epoxy resin based tissue equivalent material [10] with a CT number of +40 Hounsfield units (HU). These were all fixed at the same level inside the lumen of an anthropomorphic phantom using adhesive tape. The anthropomorphic phantom (Figure 1
) is similiarly made of tissue equivalent material and constitutes the equivalent of a 5.5 cm thick section of abdomen. 10 cm Perspex blocks were also placed each side of the phantom in the z-axis to simulate scatter within the patient. The phantom was then scanned at a range of slice thicknesses and pitches on an IGE Hispeed advantage system (General Electric, Milwaulkee, WI), using 120 kV and SmartScan (General Electric, Milwaukee, WI) (a dose reduction programme that varies mAs depending on the thickness of tissue being scanned) to optimize mAs per scan, and with a field of view of 32 cm x 32 cm. Data was then reconstructed at the minimum intervals allowed for each slice thickness and pitch setting. The different slice thicknesses, pitches, mAs and reconstruction intervals used are shown in Table 1.
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Figure 1. Anthropomorphic phantom with polyps along the inner colonic wall on (a) lung windows and (b) soft tissue windows.
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Dose assessment
Assessment of the relative radiation dose for each scanning technique was made using the CT dose index (CTDI) for the 3 mm, 5 mm and 7 mm slice widths. Measurements were made using a 10 cm CT pencil ionization chamber and electrometer (Radcal Corporation, Monrovia, CA). The measured dose was then corrected for pitch and expressed relative to the dose for the 7 mm slice thickness, pitch 2 scan, i.e. the largest slice thickness and pitch, giving the lowest dose.
Contrast and conspicuity assessment
For each scan protocol, images were viewed to determine the slice at which the 10 mm polyp was best observed. A region of interest (ROI) was drawn over the 10 mm polyp, with an area equal to 
r2, where r was taken to equal (polyp diameter-3 mm)/2, i.e. for the 10 mm polyp the area of the ROI used was 
[(10-3)/2]2=38 mm2. This was to ensure that the ROI was well within the polyp region, and to avoid partial voluming effects. Where a polyp could not be seen, contrast was not measured. The average CT number within the ROI was then taken in the same position for every reconstructed slice and plotted against the z-axis position. The transition between widely separated attenuation values has been shown to occur over several voxels [11].
A 4th order polynomial fit was made through the data set (Figure 2). This procedure was repeated for each polyp size and scan parameter. For each scan protocol and polyp size the following CT values were taken from the fitted curve.
- Maximum CT number, corresponding to optimum alignment of the polyp within the slice.
- CT number at half the slice thickness from the peak of the curve, corresponding to the worst alignment of the polyp with the slice.
All CT numbers were converted into a contrast value relative to air to indicate their difference to the surrounding area.
Subjective assessment involved two radiologists reviewing all images separately. While reviewing images the radiologists were blinded to the scanning parameter under review to reduce bias. Images were reviewed on the workstation on lung window settings (window level -550, width 1500). Lung windows are an accepted setting for review of CT colonography images [2, 6]. Polyp conspicuity was graded separately by each radiologist using a grading method introduced by Dachman et al [8]: 0, not seen; 1, faintly seen; 2, well seen. Where disparity between assessments occurred, the conspicuity score was assigned as the mean of the score from the two radiologists, e.g. polyp faintly seen by radiologist A and not seen by radiologist B produces an assigned observer score of 0.5. Finally, the number of images produced of the 5.5 cm thick phantom using each scanning parameter was noted.
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Results
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Scanning parameter optimization
All polyps of 7 mm or more in size were well seen by both radiologists (conspicuity score 2) and generated high contrast (>579 HU) regardless of the scanning parameter used. Conversely, the 1 mm polyp was not seen on any scan. Similiarly, the 2 mm and 3 mm polyps were only faintly seen (conspicuity scores 0.5–1) on scans of narrow collimation and low pitch (up to 5 mm collimation, 1.5 pitch for the 3 mm polyp, and 3 mm collimation, 2 pitch for the 2 mm polyp). Maximum contrast obtained was 558 HU for the 3 mm polyp and 403 HU for the 2 mm polyp, both with a 3 mm collimation and pitch 1. Given that all polyps 7 mm or more in size were well seen and those of 3 mm or less in size were faintly seen, regardless of scanning parameter it is clear that assessment of the conspicuity of the 4–6 mm polyps across different scanning parameters, and the relative dose to the patient from these different parameters, is important to permit use of parameter optimization. Figure 3 plots maximum contrast and relative dose for different scanning parameters for the 5 mm polyp. With 3 mm slice thickness contrast was high, i.e. from 911 HU (pitch 1.0) to 848 HU (pitch 2.0). When slice thickness was increased to 5 mm, maximum contrast fell to a range of 773 HU (pitch 1.0) to 603 HU (pitch 2.0). Further increasing the slice thickness to 7 mm caused a drop in contrast to 593 HU (pitch 1.0) and 480 HU (pitch 2.0). Figure 4 compares optimal contrasts, and Figure 5 conspicuity scores, with relative doses from each scanning parameter for the 4 mm, 5 mm, and 6 mm polyps. It can be seen that 3 mm slice thickness with a pitch of 2 combined high contrast (926 HU for the 6 mm polyp, 848 HU for the 5 mm polyp and 674 HU for the 4 mm polyp) and high conspicuity score (2 for 6 mm and 5 mm polyps, 1.5 for the 4 mm polyp) with low relative dose (1.51). The nearest comparable relative dose (1.50, from slice thickness 5 mm, pitch 1.7) gave lower contrasts (6 mm polyp; 711 HU; 5 mm polyp, 625 HU; 4 mm polyp, 561 HU) and lower conspicuity scores (6 mm polyp, 2; 5 mm polyp, 1.5; 4 mm polyp, 1).
Scanning parameters, measured contrast and conspicuity score
The results of changing collimation and pitch were considered separately in terms of their effects on both measured contrast and subjective conspicuity in an attempt to determine whether either was more significant. For the 5 mm polyp, measured contrast at 3 mm collimation, pitch 1.5 was 862 HU and the conspicuity score was 2. When slice thickness was increased to 5 mm (an increase of a factor of 1.66) and pitch kept the same, i.e. 1.5, the measured contrast was 705 HU, a difference of 157 HU, and the conspicuity score was again 2. When pitch was increased by a similar factor, i.e. from 1.0 to 1.7, at 5 mm collimation for the 5 mm polyp, the difference between measured contrasts was 148 HU (773 HU for 5 mm collimation, pitch 1.0, and 625 HU for 5 mm collimation, pitch 1.7), while there was a slight fall in conspicuity score from 2 to 1.5. This would suggest that collimation and pitch are of similar significance in determining polyp contrast and conspicuity. However, as slice thickness increases, it appears to be of greater significance. For example, at 5 mm collimation, pitch 1.5, measured contrast for the 5 mm polyp was 705 HU and the conspicuity score was 2. When slice thickness was increased to 7 mm, i.e. a factor of 1.4, and pitch kept at 1.5, measured contrast fell to 517 HU, a difference of 188 HU, and the conspicuity score fell to 1. Increasing pitch by a similar factor did not appear to effect either measured contrast or conspicuity as much. For example, at 5 mm collimation, pitch 1.0, measured contrast for the 5 mm polyp was 773 HU and the conspicuity score was 2. At 5 mm collimation, pitch 1.3, contrast for the same polyp was 740 HU, a difference of 33 HU, and the conspicuity score was 2, while at pitch 1.5, as previously seen, contrast was 705 HU, a difference of 68 HU, and the conspicuity score was again 2. These results suggest that at narrow collimation, collimation and pitch are equally significant in determining polyp contrast and conspicuity, whereas at wider collimation, a change in collimation is more significant.
Scanning parameters and relative dose
Table 2 compares the different scanning parameters with respect to the relative dose from each. Not surprisingly, the scanning parameter with the widest collimation and largest pitch, i.e. 7 mm collimation and pitch 2, gave the lowest relative dose and the doses from the other parameters have been expressed relative to this. Assessing collimation and pitch separately suggests that altering the pitch makes a more significant contribution to dose. For example, the relative dose from the 3 mm collimation, pitch 1.0 parameter was 3.02. Increasing collimation to 5 mm (a factor of 1.66) with the same pitch reduced relative dose to 2.55. However, increasing pitch by an almost identical factor, i.e. to 1.7, caused a larger reduction in relative dose, to 1.78 mSv. This trend was also found when collimation was increased; at 5 mm collimation, pitch 1.0, relative dose, as mentioned above, was 2.55, while at 7 mm collimation (an increase in collimation by a factor of 1.4) with the same pitch, relative dose was 2.00. Increasing pitch by a similar factor caused an increased reduction in dose; at 5 mm collimation, pitch 1.3, relative dose was 1.96 while at pitch 1.5 it was 1.70. Thus an alteration in pitch appeared to effect a greater reduction in relative dose than an alteration in collimation by a similar factor.
Slice/polyp alignment and measured contrast
There was little difference in measured contrast between the best slice/polyp alignment, i.e. maximum contrast and the worst slice/polyp alignment. For example, for the 5 mm polyp scanned at 3 mm collimation and pitch 1.5, measured contrast at best alignment was 862 HU and 858 HU at worst alignment, a difference of 4 HU. However, at wider collimation the differences increased; at 7 mm collimation and pitch 1.5, measured contrast for the 5 mm polyp at best alignment was 517 HU and 489 HU at worst, a difference of 28 HU. The increase in difference in contrast between the alignments applied to polyps of all sizes.
Scanning parameters and number of images obtained
The anthropomorphic phantom is 5.5 cm thick and the number of images obtained from each scanning parameter (reconstructed at minimum intervals) is shown in Table 2
. As would be expected the number of images decreased as collimation and pitch increased. Comparison of collimation and pitch suggests that pitch was slightly more significant in terms of the number of images produced. For example, at 5 mm collimation and pitch 1.0, 51 images were produced, while increasing the collimation to 7 mm (a factor of 1.4) with the same pitch, reduced the number of images to 43. Increasing pitch by a similar factor produced slightly fewer images; 39 for 5 mm collimation and pitch 1.3, and 31 for pitch 1.5. 3 mm collimation and pitch 2, which as shown in Figures 3–5 gave low relative dose (1.51) and good contrast and conspicuity for the mid-sized polyps, also gave a relatively small number of images (33).
Measured contrast and conspicuity score
All polyps 7 mm or more in size had conspicuity scores of 2 on all scans. For the 6 mm polyp, conspicuity score was 2 until the 7 mm collimation, pitch 1.5 scan. The measured contrast for the 6 mm polyp at 7 mm collimation and pitch 1.3 was 609 HU, and at pitch 1.5, 575 HU. For the 5 mm polyp, conspicuity score fell from 2 to 1.5 at the 5 mm collimation and pitch 1.7 scan, and coincided with a drop in measured contrast from 705 HU (5 mm collimation, pitch 1.5) to 625 HU (pitch 1.7). A fall in conspicuity score from 2 to 1.5 for the 4 mm polyp coincided with a fall in measured contrast from 762 HU (collimation 3 mm, pitch 1.7) to 674 HU (pitch 2.0). Thus, a measured contrast of 600–700 HU is necessary for mid-sized polyps to be clearly seen.
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Discussion
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The term "adenoma–carcinoma sequence" was first used in 1951 by Jackman and Mayo [12] and the concept advanced by Morson in 1966 [13]. There is now widespread acceptance of the fact that most colorectal neoplasms arise from pre-existing adenomas. The size of an adenoma is relevant with regard to its malignant potential. The risk of neoplastic transformation in polyps of less than 5 mm diameter is felt to be very small (less than 0.1%) [7]. Nonetheless, the goal of any imaging modality in the large bowel must be the detection of polyps as small as possible. The advent of various CT techniques has led to increased interest in its possible use as a screening tool for large bowel neoplasia. Dependent on age and sex distribution, the incidence of adenomatous polyps in a screening population is between 3% and 10% [3]. If CT is to gain acceptance for screening of colon cancer, it must be efficient at clearly depicting small polyps. CT is a trade-off between the amount of coverage to be obtained in a single breath hold, spatial resolution and patient dose, the latter being of special relevance if CT based screening is to be considered. In our study, the effective dose for CT was calculated using the measured CTDI values and published organ dose sets [14], assuming that patients are scanned from the top of the liver to the base of the pelvis. The effective dose for scanning with a 3 mm slice thickness, pitch 2 was calculated as 5.4 mSv. This compares favourably with the mean effective dose from a barium enema of 7.2 mSv, as reviewed by Hart et al [15]. While most of the literature concentrates on 2D and 3D reformatted images, their cost, both financial and in terms of radiologist input, renders them impractical for everyday use in most centres. In addition, the necessity for optimal scanning parameters for the acquisition of axial images prior to post processing is well documented [16], as such parameters can affect the development of stairstep (interpolation) artefacts in 2D displays and rippling artefacts in 3D displays [17]. To our knowledge, our study is the first to assess optimal contrast of each polyp, obtained with each scanning parameter as an objective means of parameter comparison. The contrast value of 40 HU for each polyp meant that an approximation to the attenuation of polyps in vivo, and therefore the contrast between polyp and air, could be obtained. In addition, comparison of relative dose from each scanning parameter using a pencil ionization chamber allowed us to further compare the parameters objectively. Separate review of each scan by two radiologists for polyp conspicuity, a method previously used for 2D [18] and 3D reformatting methods [16], allowed subjective comparison of the different parameters.
In our study, both an anthropomorphic phantom and phantom polyps were used. Clearly, phantoms are not a true simulation of clinical practice. In our 5.5 cm section of colon phantom, there was no faecal or fluid residue, a situation which, even with optimal bowel preparation, is difficult to recreate clinically. Neither was there any patient movement or bowel peristalsis. In addition no haustral folds were present in our short segment of colonic lumen. Haustral folds have been a cause of false positive detection of colonic polyps in previous studies [6, 19]. We readily acknowledge discrepancies between our study and an in vivo situation as drawbacks. The in vitro data presented here may be helpful to define a more limited range of parameter sets to be tested in vivo.
All scanning in this study was performed on a spiral CT scanner. The advent of multislice CT scanning will have a great impact on examinations of this nature owing to the different scanning parameters that can be used and reduction of dose to the patient that will result. However, multislice CT scanners are not universally available and thus we feel that this study remains relevant.
An additional criticism that could be levelled at this study is the fact that the reviewing radiologists were aware of the presence and location of the colonic polyps. However, we regarded this study as being a comparison of the efficacy of different scanning parameters with regard to polyp contrast, conspicuity and relative dose rather than an experiment in polyp detection. In addition, reviewing radiologists were blinded as to the scanning parameter under review to reduce bias.
Furthermore, all our polyps were spherical and we did not examine the detection of flat lesions in the colon, which has previously been found to be troublesome [18]. Further studies of either an in vitro or in vivo nature will be necessary to advance the detection of such easily missed lesions by CT. Owing to the spherical nature of our polyps, we did not examine the effects of gantry angle on polyp conspicuity or contrast. Dachman et al [18] have previously found gantry angle to be a relatively insignificant factor in the detection of spherical polyps at a given slice thickness and pitch. Gantry angle is felt to be a more important factor in the detection of flat or pedunculated lesions.
In summary, we have compared different scanning parameters for CT colonography with respect to polyp contrast, objective conspicuity and relative dose and suggest that a slice thickness of 3 mm at a pitch of 2 combines optimal contrast and conspicuity with a relatively low dose. We therefore recommend this scanning parameter. However, further work in this area is needed, particularly with regard to the extrapolation of scanning parameters to 2D and 3D reformatting, their use in vivo, the potential impact of multislice CT scanners on these examinations, and with respect to the detection of flat colonic lesions.
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Appendix
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Received for publication October 24, 2001.
Revision received January 11, 2002.
Accepted for publication January 23, 2002.
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References
|
|---|
-
Day JJ, Freeman AH, Coni NK, Dixon AK. Barium enema or computed tomography for the frail elderly patient? Clin Radiol 1993;48:48–51.[Medline]
-
Royster AP, Fenlon HM, Clarke PD, Nunes DP, Ferrucci JT. CT colonoscopy of colorectal neoplasms: two-dimensional and three-dimensional virtual-reality techniques with colonoscopic correlation. AJR 1997;169:1237–42.[Abstract/Free Full Text]
-
Rex DK. CT and MR colography (virtual colonoscopy)—status report. J Clin Gastroenterol 1998;27:199–203.[Medline]
-
Amin Z, Boulos PB, Lees WR. Technical report: spiral CT pneumocolon for suspected colonic neoplasms. Clin Radiol 1996;51:56–61.[Medline]
-
Dachman AH, Kuniyoshi JK, Boyle CM, Samara Y, Hoffmann KR, Rubin DT, et al. CT colonography with three dimensional problem solving for detection of colonic polyps. AJR 1998;171:989–95.[Abstract/Free Full Text]
-
Hara AK, Johnson CD, Reed JE, Ehman RL, Ilstrup DM. Colorectal polyp detection with CT colography: two- versus three-dimensional techniques (work in progress). Radiology 1996;200:49–54.[Abstract/Free Full Text]
-
Hara AK, Johnson CD, Reed JE, Ahlquist DA, Nelson H, Ehman RL, et al. Detection of colorectal polyps by computed tomographic colography: feasibility of a novel technique. Gastroenterology 1996;110:284–90.[Medline]
-
Hara AK, Johnson CD, Reed JE, Ahlquist DA, Nelson H, MacCarthy RL, et al. Detection of colorectal polyps with CT colography: initial assessment of sensitivity and specificity. Radiology 1997;205:59–65.[Abstract/Free Full Text]
-
Jolesz FA, Lorensen WE, Shinmoto H, Atsumi H, Nakajima S, Kavanaugh P, et al. Interactive virtual endoscopy. AJR 1997;169:1229–35.[Free Full Text]
-
White DR, Martin RJ, Darlison R. Epoxy based resin tissue substances. Br J Radiol 1997;50:814–21.[Abstract/Free Full Text]
-
Hopper KD, Iyriboz TA, Mahraj RP, Wise SW, Kasales CJ, TenHave TR, et al. CT bronchoscopy: optimisation of imaging parameters. Radiology 1998;209:872–7.[Abstract/Free Full Text]
-
Jackman RJ, Mayo CW. The adenoma-carcinoma sequence in cancer of the colon. Surg Gynecol Obstet 1951;93:327–30.
-
Morson BC. Factors influencing the prognosis of early cancer of the rectum. Proc R Soc Med 1966;59:607–8.[Medline]
-
Jones DG, Shrimpton PC. Normalised organ doses for X-ray computed tomography calculated using Monte Carlo techniques. NRPB-SR250. Chilton, UK: National Radiological Protection Board, 1996.
-
Hart D, Hillier MC, Wall BF, et al. Doses to patients from medical X-ray examinations in the UK—1995 review. NRPB-R289. Chilton, UK: National Radiological Protection Board, 1996.
-
Beaulieu CF, Napel S, Daniel BL, Ch'en IY, Rubin GD, Johnstone IM, et al. Detection of colonic polyps in a phantom model: implications for virtual colonoscopy data acquisition. J Comput Assist Tomogr 1998;22:656–63.[Medline]
-
McFarland EG, Brink JA. Helical CT colonography (virtual colonoscopy): the challenge that exists between advancing technology and generalizability. AJR 1999;173:549–59.[Free Full Text]
-
Dachman AH, Lieberman J, Osnis RB, Chen S-YJ, Hoffmann KR, Chen C-T, et al. Small simulated polyps in pig colon: sensitivity of CT virtual colography. Radiology 1997;203:427–30.[Abstract/Free Full Text]
-
Chen SC, Lu DS, Hecht JR, Kadell BM. CT colonography: value of scanning in both the prone and supine positions. AJR 1999;172:595–9.[Abstract/Free Full Text]
-
Fenlon HM, Nunes DP, Clarke PD, Ferrucci JT. Colorectal neoplasm detection using virtual colonoscopy: a feasibility study. Gut 1998;43:806–11.[Abstract/Free Full Text]
-
McFarland EG, Brink JA, Loh J, Wang G, Argiro V, Balfe DM, et al. Visualisation of colorectal polyps with spiral CT colography: evaluation of processing parameters with prospective volume rendering. Radiology 1997;205:701–7.[Abstract/Free Full Text]
-
Harvey CJ, Amin Z, Hare CMB, Gillams AR, Novelli MR, Boulos PB, et al. Helical CT Pneumocolon to assess colonic tumours: radiologic-pathologic correlation. AJR 1998;170:1439–43.[Abstract/Free Full Text]
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Abstract
Introduction
–) vs scan parameters for 5 mm polyp (–
–).
–), 5 mm (–
–) polyps.