MR imaging of the colon: "technique, indications, results and limitations"

Clinical issues and challenges in imaging of gastrointestinal diseases: A minireview and our experience

Imaging techniques play a crucial role in the modern era of medicine, particularly in gastroenterology. Nowadays, various non-invasive and invasive imaging modalities are being routinely employed to evaluate different gastrointestinal (GI) diseases. However, many instrumental as well as clinical issues are arising in the area of modern GI imaging. This minireview article aims to briefly overview the clinical issues and challenges encountered in imaging GI diseases while highlighting our experience in the field. We also summarize the advances in clinically available diagnostic methods for evaluating different diseases of the GI tract and demonstrate our experience in the area. In conclusion, almost all imaging techniques used in imaging GI diseases can also raise many challenges that necessitate careful consideration and profound expertise in this field.

Virtual gastrointestinal colonoscopy in combination with large bowel endoscopy: Clinical application

Although colorectal cancer (CRC) has no longer been the leading cancer killer worldwide for years with the exponential development in computed tomography (CT) or magnetic resonance imaging, and positron emission tomography/CT as well as virtual colonoscopy for early detection, the CRC related mortality is still high. The objective of CRC screening is to reduce the burden of CRC and thereby the morbidity and mortality rates of the disease. It is believed that this goal can be achieved by regularly screening the average-risk population, enabling the detection of cancer at early, curable stages, and polyps before they become cancerous. Large-scale screening with multimodality imaging approaches plays an important role in reaching that goal to detect polyps, Crohn’s disease, ulcerative colitis and CRC in early stage. This article reviews kinds of presentative imaging procedures for various screening options and updates detecting, staging and re-staging of CRC patients for determining the optimal therapeutic method and forecasting the risk of CRC recurrence and the overall prognosis. The combination use of virtual colonoscopy and conventional endoscopy, advantages and limitations of these modalities are also discussed.

MR imaging techniques of the bowel

Due to advances in technology, magnetic resonance is an increasingly popular method for evaluating the small bowel and colon because of the lack of radiation, wealth of information provided by the images, and growing demand from gastroenterologists, surgeons, and oncologists. Careful attention to proper technique, however, is necessary to obtain high-quality images. Factors that need to be considered for successful magnetic resonance of the bowel include method for administration of oral or rectal contrast, patient positioning, need for antiperistaltic medication, and imaging sequences and planes.

Intravenous, contrast-enhanced MR colonography using air as endoluminal contrast agent: impact on colorectal polyp detection

PURPOSE

To compare diagnostic accuracy and patient tolerance of MR colonography with intravenous contrast and luminal air (MRC) to conventional colonoscopy (CC).

MATERIALS AND METHODS

IRB approval and written informed consent were obtained. Forty-six patients, both screening and symptomatic, underwent MRC followed by CC. The MRC technique employed 3D T1W spoiled gradient echo sequences performed after the administration of gadopenetate dimeglumine, with parallel imaging. The diagnostic accuracy and tolerance of patients for MRC was compared to CC.

RESULTS

Twenty-four polyps were detected in eighteen patients with CC (5 polyps ≥ 10 mm, 4 polyps 6-9 mm, 15 polyps ≤ 5 mm). MRC was 66.7% (12/18) sensitive and 96.4% (27/28) specific for polyp detection on a per-patient basis. When analyzed by polyp size, sensitivity and specificity of MRC was 100% (5/5) and 100% (19/19), respectively, for lesions greater than 10mm, 100% (4/4) and 100% (20/20) for lesions 6-9 mm, and sensitivity of 20% (3/15) lesions less than 5mm. The sensitivity and specificity of MRC for detecting significant lesions (>6mm) was 100% (9/9) and 100% (15/15), respectively. Regarding tolerance of the exams, there were no significant differences between MRC and CC. Thirty-five percent (n=16) of patients preferred MRC as a future screening test compared to 33% (n=15) for CC.

CONCLUSION

MRC using air as an intraluminal contrast agent is a feasible and well-tolerated technique for detecting colonic polyps ≥ 6 mm in size. Further studies are warranted.

Derivation of a T2-weighted MRI total colonic inflammation score (TCIS) for assessment of patients with severe acute inflammatory colitis-a preliminary study

OBJECTIVE

To derive an MRI score for assessing severity, therapeutic response and prognosis in acute severe inflammatory colitis.

METHODS

Twenty-one patients with acute severe colitis underwent colonic MRI after admission and again (n = 16) after median 5 days of treatment. Using T2-weighted images, two radiologists in consensus graded segmental haustral loss, mesenteric and mural oedema, mural thickness, and small bowel and colonic dilatation producing a total colonic inflammatory score (TCIS, range 6-95). Pre- and post-treatment TCIS were compared, and correlated with CRP, stool frequency, and number of inpatient days (therapeutic response marker). Questionnaire assessment of patient worry, satisfaction and discomfort graded 1 (bad) to 7 (good) was administered

RESULTS

Admission TCIS correlated significantly with CRP (Kendall's tau=0.45, 95% confidence interval [CI] 0.11-0.79, p = 0.006), and stool frequency (Kendall's tau 0.39, 95% CI 0.14-0.64, p = 0.02). TCIS fell after treatment (median [22 range 15-31]) to median 20 [range 8-25], p = 0.01. Admission TCIS but not CRP or stool frequency was correlated with length of inpatient stay (Kendall's tau 0.40, 95% CI 0.11-0.69, p = 0.02). Patients reported some discomfort (median score 4) during MRI.

CONCLUSIONS

MRI TCIS falls after therapy, correlates with existing markers of disease severity, and in comparison may better predict therapeutic response.

Role of 3.0-T MR colonography in the evaluation of inflammatory bowel disease

Conventional colonoscopy combined with histologic analysis represents the standard of reference for the evaluation of colorectal disease and is usually the initial examination in patients with a suspected or established diagnosis of inflammatory bowel disease (IBD). However, it is increasingly being recognized that colonoscopy is limited to providing information regarding mucosal alterations. Colonoscopy cannot help estimate the depth of involvement of colonic lesions and does not provide information regarding the presence of extraluminal complications such as abscesses or fistulas. Recent technologic advances in magnetic resonance (MR) imaging, with its high spatial and tissue resolution, have raised expectations as to the potential role of this modality in the evaluation of colonic lesions in patients with IBD, as either a complement or an alternative to colonoscopy. MR colonography allows the characterization of colonic changes in acute and chronic IBD and can depict a wide spectrum of related lesions, including ulcers, edema, wall thickening, hyperemia, and fistulas, as well as potential extraluminal complications. The bulk of available evidence indicates that MR colonography can be useful as a problem-solving tool in the evaluation of IBD, as an alternative to colonoscopy whenever tissue sampling is not required, and for the assessment of the entire colon in cases of incomplete colonoscopy.

Imaging of the gastrointestinal tract-novel technologies

Imaging of the gastrointestinal tract is very useful for research and clinical studies of patients with symptoms arising from the gastrointestinal tract and in visualising anatomy and pathology. Traditional radiological techniques played a leading role in such studies for a long time. However, advances in non-invasive modalities including ultrasound (US), computed tomography (CT), positron emission tomography (PET), magnetic resonance imaging (MRI), etc, have in the last decades revolutionised the way in which the gastrointestinal tract is studied. The resolution of imaging data is constantly being improved and 3D acquisition, tools for filtering, enhancement, segmentation and tissue classification are continually being developed. Additional co-registration techniques allow multimodal data acquisition with improved classification of tissue pathology. Furthermore, new functional imaging techniques have become available. Altogether, the future of gastrointestinal imaging looks very promising which will be of great benefit in clinical and research studies of gastrointestinal diseases. The purpose of this review is to highlight the capabilities of the newest techniques to explore the detailed morphology, biomechanical properties, function and pathology of the gastrointestinal tract.

New technologies for human cancer imaging

Despite technical advances in many areas of diagnostic radiology, the detection and imaging of human cancer remains poor. A meaningful impact on cancer screening, staging, and treatment is unlikely to occur until the tumor-to-background ratio improves by three to four orders of magnitude (ie, 10(3)- to 10(4)-fold), which in turn will require proportional improvements in sensitivity and contrast agent targeting. This review analyzes the physics and chemistry of cancer imaging and highlights the fundamental principles underlying the detection of malignant cells within a background of normal cells. The use of various contrast agents and radiotracers for cancer imaging is reviewed, as are the current limitations of ultrasound, x-ray imaging, magnetic resonance imaging (MRI), single-photon emission computed tomography, positron emission tomography (PET), and optical imaging. Innovative technologies are emerging that hold great promise for patients, such as positron emission mammography of the breast and spectroscopy-enhanced colonoscopy for cancer screening, hyperpolarization MRI and time-of-flight PET for staging, and ion beam-induced PET scanning and near-infrared fluorescence-guided surgery for cancer treatment. This review explores these emerging technologies and considers their potential impact on clinical care. Finally, those cancers that are currently difficult to image and quantify, such as ovarian cancer and acute leukemia, are discussed.

MR imaging of the gastro-intestinal tract in children

MR imaging (MRI) is an established method for the evaluation of particularly inflammatory bowel disease in adults, as well as for acute abdominal pain in pregnant women. Despite the fact that MRI is ideally suited for the evaluation of children the method is still not established in these patients. The value of MRI in Crohn's disease, ulcerative colitis and appendicitis as well as intestinal tumors and malformations has been documented in children. There will be more indications in the future depending on the development of new imaging techniques, faster sequences, stronger gradients and increasing availability. Furthermore, the radiologist's attention must be drawn to decrease the radiation burden in children and to replace ionizing techniques especially in chronic disease with the need for repeated follow-up studies and in younger children. This review will discuss some general considerations for the use of MRI in evaluating the paediatric gastro-intestinal tract.

Colonography by CT, MRI and PET/CT combined with conventional colonoscopy in colorectal cancer screening and staging

Colorectal cancer (CRC) remains a leading cancer killer worldwide. But the disease is both curable and preventable at an early stage. Regular CRC cancer screening has been shown to reduce the risk of dying from CRC. However, the importance of large-scale screening is only now starting to be appreciated. This article reviews a variety of imaging procedures available for detecting ulcerative colitis (UC) and Crohn’s disease (CD), polyps and CRC in their early stage and also presents details on various screening options. Detecting, staging and re-staging of patients with CRC also require multimodality, multistep imaging approaches. Staging and re-staging with conventional colonoscopy (CC), computer tomography colonography (CTC), magnetic resonance colonography (MRC) and positron emission tomography/computer tomography colonography (PET/CTC) are of paramount importance in determining the most appropriate therapeutic method and in predicting the risk of tumor recurrence and overall prognosis. The advantages and limitations of these modalities are also discussed.