Bias in research studies.

Bias is a form of systematic error that can affect scientific investigations and distort the measurement process. A biased study loses validity in relation to the degree of the bias. While some study designs are more prone to bias, its presence is universal. It is difficult or even impossible to completely eliminate bias. In the process of attempting to do so, new bias may be introduced or a study may be rendered less generalizable. Therefore, the goals are to minimize bias and for both investigators and readers to comprehend its residual effects, limiting misinterpretation and misuse of data. Numerous forms of bias have been described, and the terminology can be confusing, overlapping, and specific to a medical specialty. Much of the terminology is drawn from the epidemiology literature and may not be common parlance for radiologists. In this review, various types of bias are discussed, with emphasis on the radiology literature, and common study designs in which bias occurs are presented.

Imaging of cystic diseases of the pancreas.

Although the majority of cystic lesions of the pancreas seen in clinical practice represent postinflammatory pseudocysts, it is important for the radiologist to be knowledgeable of the wide spectrum of cystic masses of the pancreas and the variable prognoses they possess. As a result of similarities in the imaging features of these lesions, a definitive diagnosis is often not possible. By combining imaging features with clinical history, a reasonable differential diagnosis can be offered to the referring physician. In some cases, biopsy or fluid aspiration may be required prior to surgery. In a patient without the appropriate history of pancreatitis and the presence of a cystic pancreatic mass, it is incumbent upon the radiologist to offer alternative diagnoses of cystic neoplasms of the pancreas.

Is severity of necrotizing pancreatitis increased in extended necrosis and infected necrosis?

INTRODUCTION: We previously reported that organ failure occurs in 50% of patients with necrotizing pancreatitis, that extended pancreatic necrosis (greater than 50% necrosis) is not associated with an increased prevalence of organ failure or infected necrosis, and that the prevalence of organ failure is similar in sterile necrosis and infected necrosis. AIMS To analyze these relations in a larger group of patients and to evaluate other factors that might have prognostic significance. METHODOLOGY: We reviewed 1,110 consecutive cases of acute pancreatitis between January 1, 1995, and January 1, 2000. Necrosis was documented by contrast-enhanced CT. A value less than 0.05 was considered significant. RESULTS: Ninety-nine patients (9%) had necrotizing pancreatitis; 52% had organ failure. Patients with extended pancreatic necrosis did not have increased prevalence of organ failure or infected necrosis but did have an increased need for intubation and an increased mortality rate associated with multiple organ failure. Patients with infected necrosis did not have an increased prevalence of organ failure but did have a marginally increased prevalence of multiple organ failure and increased need for intubation. Overall mortality was 14% and was markedly increased among patients with organ failure at admission (47%) and among patients who had multiple organ failure during the hospitalization (49%). CONCLUSION: Although severity of necrotizing pancreatitis was somewhat increased in extended pancreatic necrosis and infected necrosis, mortality was more strongly linked to organ failure at admission and multiple organ failure during hospitalization.

Computed tomography and magnetic resonance imaging of hepatic metastases.

The detection and characterization of liver metastases is well performed with either computed tomography or magnetic resonance imaging. The administration of intravenous contrast is essential for almost all indications, with multiphasic imaging aiding in lesion characterization and detection. The use of multidetected CT (MDCT) provides the ability for optimized vascular and multiplanar imaging, but has also resulted in increased examination complexity. Tissue-specific MR contrast agents can yield the highest rate of lesion detection and thus may be useful in presurgical planning.

Multimodality diagnosis of liver tumors: feature analysis with CT, liver-specific and contrast-enhanced MR, and a computer model.

RATIONALE AND OBJECTIVES: The purpose of this study was to measure and to clarify the diagnostic contributions of image-based features in differentiating benign from malignant and hepatocyte-containing from non-hepatocyte-containing liver lesions. MATERIALS AND METHODS: Six experienced abdominal radiologists each read images from 146 cases (including a contrast material-enhanced computed tomographic [CT] scan and contrast-enhanced and unenhanced magnetic resonance [MR] images) following a checklist-questionnaire requiring them to rate quantitatively each of as many as 131 image features and then reported on each of the two differentiations. The diagnostic value of each feature was assessed, and linear discriminant analysis was used to develop statistical prediction rules (SPRs) for merging feature data into computerized "second opinions." For the two differentiations, accuracy (area under the receiver operating characteristic curve [Az]) was then determined for the radiologists' readings by themselves and for each of three SPRs. RESULTS: Thirty-seven candidate features had diagnostic value for each of the two differentiations (a slightly different feature set for each). Radiologists' performance at both differentiations was excellent (Az = 0.929 [benign vs malignant] and 0.926 [hepatocyte-containing vs non-hepatocyte-containing]). Performance of the SPR that operated on the features from all modalities together was better than that of radiologists (Az = 0.936 [benign vs malignant] and 0.951 [hepatocyte-containing vs non-hepatocyte-containing]), but this difference was of marginal statistical significance (P = .11). Contrast-enhanced MR imaging and contrast-enhanced CT each made significant adjunctive contributions to accuracy compared with unenhanced MR imaging alone. CONCLUSION: Many CT- and MR imaging-based features have diagnostic value in differentiating benign from malignant and hepatocyte-containing from non-hepatocyte-containing liver lesions. Radiologists could also benefit from the fully informed SPR's "second opinions."

Magnetic resonance imaging in patients with pancreatitis: evaluation of signal intensity and enhancement changes.

PURPOSE: To evaluate the utility of unenhanced and enhanced T1-weighted fat-suppressed (T1-FS) magnetic resonance imaging (MRI) in detecting pancreatitis. MATERIALS AND METHODS: 1.5-T MRI was performed in 25 patients with acute and 23 patients with chronic pancreatitis and in 20 control subjects without known pancreatic disease. T1-FS spin-echo and contrast-enhanced arterial-predominant (DYN1) and portal-predominant (DYN2) fast multiplanar spoiled gradient-echo (FMPSPGR) sequences were evaluated. These three sets of images were evaluated both subjectively for decreased or heterogeneous signal intensity (rating scale, 0-3) and objectively (region of interest (ROI)) in the head, body, and tail of the pancreas, in each patient. RESULTS: Good correlation between subjective assessment and objective data was demonstrated. The T1-FS sequence showed an abnormality with greater frequency (T1-FS > DYN1, 81/144 scores; T1-FS = DYN1, 63/144 scores; T1-FS < DYN1, 0/144 scores) and magnitude (average subjective score, 2.48 vs. 1.74; P < 0.0003) than that of the contrast-enhanced FMPSPGR (decreased or heterogeneous enhancement). The overall sensitivity and specificity of MRI was 92% and 50%, respectively. On the basis of signal intensity and enhancement, MRI was not able to differentiate acute from chronic pancreatitis. CONCLUSION: MRI was highly sensitive for disease detection, particularly using the T1-FS sequence, but using the sequences described, was not able to differentiate acute from chronic pancreatitis.