Dual-Energy CT Colonography for Preoperative “One-Stop” Staging in Patients with Colonic Neoplasia

Rationale and Objectives

To evaluate the benefits of dual-energy computed tomography (CT) colonography (DECTC) as a preoperative staging tool in patients with clinically suspected colorectal cancer (CRC).

Materials and Methods

Twenty-two patients with colorectal neoplasia underwent preoperative abdominal DECTC on a dual-source scanner (SOMATOM Definition Flash; Siemens) operated at tube potentials of Sn140/100 kVp. Scans were evaluated for local tumor stage and the presence of synchronous intracolonic and extracolonic findings using dual-energy color-coded images. An enhancement ≥25 Hounsfield units (HU) was defined to indicate malignancy. Patients’ effective doses were calculated.

Results

Preoperative DECTC allowed for complete bowel evaluation in all patients, including subjects with stenosing CRC. DECTC revealed 22 carcinomas (mean enhancement, 47 ± 12 HU). In total, 22 synchronous intracolonic lesions were detected, including 19 adenomas (mean enhancement, 51 ± 19 HU). Benign structures showed enhancement <25 HU. Comparing DECTC to histopathology, 95% carcinomas and 71% synchronous lesions proximal to stenosing CRC could be verified. Mean estimated effective dose was 13.0 ± 5.2 mSv.

Conclusions

Preoperative DECTC can be used as an accurate and dose-efficient primary-staging examination. Especially after incomplete optical colonoscopy, virtual colonoscopy enables full preoperative colonic assessment on the same day. Dual-energy CT enables distinction between neoplasia and non-neoplastic findings within and outside the colon. Therefore, DECTC can be regarded as a promising “one-stop” staging examination in patients with clinically suspected CRC.

Colorectal cancer (CRC) ranks second in women and third in men on the list of the most commonly diagnosed cancers in the economically developed world and develops from benign precursor lesions with malignant potential (colorectal adenomas) following the adenoma–carcinoma sequence . For detection of these lesions, optical colonoscopy (OC) is considered standard of care. Noninvasive alternatives are computed tomographic colonography (CTC, also known as virtual colonoscopy) and magnetic resonance (MR) colonography . Exact cancer staging is mandatory to determine the patient’s individual prognosis and treatment strategy.

Recently, numerous clinical applications for dual-energy (DE) CT have emerged, predominantly developed on dual-source CT scanners operating two x-ray tubes at different tube potentials. The two data sets acquired show differences in photon attenuation. Based on three material decomposition algorithms, virtual nonenhanced (VNE) images and color-coded iodine maps can be generated ( Fig 1 ) .

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Figure 1

Dual-energy (DE) computed tomography colonography in a 62-year-old male patient with clinically suspected colorectal cancer (CRC). Virtual nonenhanced image ( upper left ) and iodine-only image ( upper right ) can be fused to a color-coded DE image ( lower right ). Images show a stenosing CRC ( arrow ) and a synchronous adenoma ( arrowhead ). Asterisk denotes normal enhancement of left kidney. Polypoid lesion detected proximal to colonic stenosis on three-dimensional endoluminal images ( lower left ) can be verified on two-dimensional color-coded DE images ( lower right ), in which colonic neoplasia shows significant iodine uptake. (Color version of figure is available online.)

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Materials and methods

Patient Population

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Bowel Preparation

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Image Acquisition and Interpretation

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Table 1

Scan Parameters of Dual-Source CT Scanner SOMATOM Definition Flash ∗

Tube potential A/B (kVp) Sn140/100 Slices 2 × 128 Slice collimation (mm) 32 × 0.6 Rotation time (seconds) 0.5 Pitch 0.6 Reference milliampere seconds value of tube A/B 300/232 Intravenous contrast agent (containing iodine) Imeron 400; flow rate, 2.5 mL/s; delay, 70 seconds Fecal tagging None Online dose modulation CARE Dose4D ∗ Iterative reconstruction (in conjunction with dual-energy mode) Sinogram-Affirmed Iterative Reconstruction ∗

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Results

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Table 2

Study Population Overview ( N = 22)

Females/males 9/13 Median age (years) 71 (age range, 50–90) Mean BMI (kg/m 2 ) 25.3 ± 4.8 (range, 18.7–36.1) Volume of contrast agent applied (mL) 76 ± 28 Mean estimated effective dose (mSv)E DE supine = 11.4 ± 4.6 (9.2 ± 3.2)

E prone = 1.7 ± 0.8 (1.4 ± 0.7)

E DE supine + prone = 13.0 ± 5.2 (10.6 ± 3.6)

Mean estimated effective dose ( E ) was calculated for supine dual-energy computed tomography colonography (DECTC) acquisitions ( E DE supine ), prone single-energy low-dose CTC acquisitions ( E prone ), and both positions ( E DE supine + prone ), respectively.

Note: E for body mass index (BMI) < 25 kg/m 2 in brackets.

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DECTC Findings

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Table 3

Overview of DECTC and Histopathologic Findings

DECTC Findings_n_ CT Attenuation (HU) VNE Enhancement Carcinomas 2228 ± 8__47 ± 12 T1/T2/T3/T4 0/6/14/1 Tx 1 ∗ N+ 14 M+ 5 Adenomas 1925 ± 8__51 ± 19 Location of lesions Cecum 1 Descending colon 4 Ascending colon 3 Sigmoid colon 13 Hepatic flexure 1 Rectosigmoid junction 5 Transverse colon 9 Rectum 8 Splenic flexure 1 Morphology of lesions Sessile 12 Mass 23 Pedunculated 8 Flat 2 Size of lesions Small (6–9 mm) 6 Large (10–29 mm) 14 Mass (≥30 mm) 25

Histopathologic Findings_n_ Carcinomas 22 T1/T2/T3/T4 2/2/12/2 Tx 3 † yT0 1 ‡ N+ 9 Adenomas 12 Tubular adenoma 7 Tubulovillous adenoma 5

DECTC, dual-energy computed tomography colonography.

The presence of regional lymph node (N) or distant (M) metastasis is indicated by “+.” The computed tomography (CT) attenuation of the virtual nonenhanced (VNE) image and enhancement were recorded in Hounsfield units (HU; in italics).“ n ” Indicates number of lesions.

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Histopathologic Findings

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Comparing DECTC to Histopathologic Findings

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Table 4

T and N Status of Colorectal Cancers

T Status T1/T2 T3/T4 ∑ Staged correctly 2 11 13 Overstaged/understaged 2 3 5 ∑ 4 14 18 N Status N0 N+ ∑ Staged correctly 5 7 12 Overstaged/understaged 4 2 6 ∑ 9 9 18

“N+” indicates positive regional lymph nodes, “∑” means sum.

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Table 5

Comparing Synchronous DECTC Findings to Histopathology

Classified as neoplasia on DECTC images Histopathologic Findings Neoplastic Non-neoplastic ∑ Yes 11 1 12 No 1 0 1 ∑ 12 1 13

One lesion classified as an adenoma on dual-energy computed tomography colonography (DECTC) images was histopathologically verified as a third cancer (T1N0), both neoplastic lesions. “∑” means sum.

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Prone Data Set and Estimated Effective Doses

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Discussion

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References

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Dual-Energy CT Colonography for Preoperative “One-Stop” Staging in Patients with Colonic Neoplasia

Rationale and Objectives

Materials and Methods

Results

Conclusions

Materials and methods

Patient Population

Bowel Preparation

Image Acquisition and Interpretation

Results

DECTC Findings

Histopathologic Findings

Comparing DECTC to Histopathologic Findings

Prone Data Set and Estimated Effective Doses

Discussion

References

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