[CT colonography: patient preparation and examination technique]

[CT colonography : Technique and indications]

BACKGROUND

Dedicated radiological expertise and a high-quality examination, performed according to current technical standards and for accepted indications, are prerequisite to achieve excellent results with CT colonography (CTC).

OBJECTIVES

The aim of this article is to review current standards of the examination technique as well as indications and contraindications for CTC based on recent recommendations and guidelines.

MATERIALS AND METHODS

Based on extensive literature research, current knowledge about the examination technique and the indications and contraindications is summarized.

RESULTS

CTC is the radiological examination of choice for the detection of colorectal neoplasia. Beside incomplete or refused colonoscopy and contraindications to colonoscopy, CTC is also a noninvasive option for opportunistic colorectal cancer screening. The examination technique is based on a CTC-specific patient preparation scheme that includes fecal tagging, colonic distension, low-dose CT scans in two patient positions and a combined 2D and 3D data evaluation.

CONCLUSIONS

Performing CTC according to current technical standards is prerequisite for high-quality examinations and is, thus, also a key factor to obtain a correct diagnosis. CTC is a noninvasive examination, capable of providing clinically relevant diagnoses for a wide range of indications.

Imaging of colorectal cancer - the clue to individualized treatment

Colorectal cancer (CRC) is the most common gastrointestinal neoplasm and the second most common cause for cancer-related death in Europe. Imaging plays an important role both in the primary diagnosis, treatment evaluation, follow-up, and, to some extent, also in prevention. Like in the clinical setting, colon and rectal cancer have to be distinguished as two quite separate entities with different goals of imaging and, consequently, also different technical requirements. Over the past decade, there have been improvements in both more robust imaging techniques and new data and guidelines that help to use the optimal imaging modality for each scenario. For colon cancer, the continued research on computed tomography (CT) colonography (CTC) has led to high-level evidence that puts this technique on eye height to optical colonoscopy in terms of detection of cancer and polyps ≥10 mm. However, also for smaller polyps and thus for screening purposes, CTC seems to be an optimal tool. In rectal cancer, the technical requirements to perform state-of-the art imaging have recently been defined. Evaluation of T-stage, mesorectal fascia infiltration and extramural vascular invasion are the most important prognostic factors that can be identified on MRI. With this information, risk stratification both for local and distal failure is possible, enabling the clinician to tailor the optimal therapeutic approach in non-metastatic rectal cancer. Imaging of metastatic CRC is also covered, although the complex ramifications of treatment options in the metastatic setting are beyond the scope of this article. In this review, the most important recent developments in the imaging of colon and rectal cancer will be highlighted. If used in an interdisciplinary setting, this can lead to an individualized treatment concept for each patient.

[CT colonography as routine method]

CLINICAL/METHODICAL ISSUE

Colorectal cancer is a major public health challenge in Austria and Germany. As the participation in dedicated colonoscopy screening programs is rather low, the question of alternative methods is raised again and computed tomography (CT) colonography seems to be a gentle alternative with a very high patient acceptance.

STANDARD RADIOLOGICAL METHODS

In recent years CT colonography (CTC) has been established besides conventional colonoscopy as a radiological method for the investigation of the entire colon. From axial two-dimensional images three-dimensional images can be generated, allowing a virtual flight through the colon which is why this technique is also known as virtual colonoscopy.

METHODICAL INNOVATIONS

The technique of CTC has been improved continuously during recent years. On the one hand the steady decrease in the layer thickness (currently ≤ 1 mm) has improved the resolution of volume data sets and on the other hand there has been significant progress in postprocessing.

PERFORMANCE

Numerous studies have recently shown that the significance of CTC in the detection of advanced adenomas is similar to conventional colonoscopy.

ACHIEVEMENTS

Meanwhile CT colonography is now a routine investigation method established in both symptomatic and asymptomatic patients (screening).

PRACTICAL RECOMMENDATIONS

Study data now clearly show that CTC, as an alternative to conventional colonoscopy, is a powerful method for investigation of colorectal cancer. To achieve good results adequate preparation including fecal tagging, standardized technical procedures during the investigation and expertise in both 2D and 3D reading are essential.