Understanding ADC variation by fat content effect using a dual-function MRI phantom.

BACKGROUND: A dual-function phantom designed to quantify the apparent diffusion coefficient (ADC) in different fat contents (FCs) and glass bead densities (GBDs) to simulate the human tissues has not been documented yet. We propose a dual-function phantom to quantify the FC and to measure the ADC at different FCs and different GBDs. METHODS: A fat-containing diffusion phantom comprised by 30 glass-bead-containing fat-water emulsions consisting of six different FCs (0, 10, 20, 30, 40, and 50%) multiplied by five different GBDs (0, 0.1, 0.25, 0.5, and 1.0 g/50 mL). The FC and ADC were measured by the "iterative decomposition of water and fat with echo asymmetry and least squares estimation-IQ," IDEAL-IQ, and single-shot echo-planar diffusion-weighted imaging, SS-EP-DWI, sequences, respectively. Linear regression analysis was used to evaluate the relationship among the fat fraction (FF) measured by IDEAL-IQ, GBD, and ADC. RESULTS: The ADC was significantly, negatively, and linearly associated with the FF (the linear slope ranged from -0.005 to -0.017, R2 = 0.925 to 0.986, all p < 0.001). The slope of the linear relationship between the ADC and the FF, however, varied among different GBDs (the higher the GBD, the lower the slope). ADCs among emulsions across different GBDs and FFs were overlapped. Emulsions with low GBDs plus high FFs shared a same lower ADC range with those with median or high GBDs plus median or lower FFs. CONCLUSIONS: A novel dual-function phantom simulating the human tissues allowed to quantify the influence of FC and GBD on ADC. RELEVANCE STATEMENT: The study developed an innovative dual-function MRI phantom to explore the impact of FC on ADC variation that can affect clinical results. The results revealed the superimposed effect on FF and GBD density on ADC measurements. KEY POINTS: • A dual-function phantom made of glass bead density (GBD) and fat fraction (FF) emulsion has been developed. • Apparent diffusion coefficient (ADC) values are determined by GBD and FF. • The dual-function phantom showed the mutual ADC addition between FF and GBD.

Value of CT in the diagnosis and management of gallstone ileus.

AIM: To retrospectively establish the diagnostic criteria of gallstone ileus on CT, and to prospectively apply these criteria to determine the diagnostic accuracy of CT to confirm or exclude gallstone ileus in patients who presented with acute small bowel obstruction (SBO). Another purpose was to ascertain whether the size of ectopic gallstones would affect treatment strategy. METHODS: Fourteen CT scans in cases of proved gallstone ileus were evaluated retrospectively by two radiologists for the presence or absence of previously reported CT findings to establish the diagnostic criteria. These criteria were applied in a prospective contrast enhanced CT study of 165 patients with acute SBO, which included those 14 cases of gallstone ileus. The hard copy images of 165 CT studies were reviewed by a different group of two radiologists but without previous knowledge of the patient's final diagnosis. All CT data were further analyzed to determine the diagnostic accuracy of gallstone ileus when using CT in prospective evaluation of acute SBO. The size of ectopic gallstone on CT was correlated with the clinical course. RESULTS: The diagnostic criteria of gallstone ileus on CT were established retrospectively, which included: (1) SBO; (2) ectopic gallstone; either rim-calcified or total-calcified; (3) abnormal gall bladder with complete air collection, presence of air-fluid level, or fluid accumulation with irregular wall. Prospectively, CT confirmed the diagnosis in 13 cases of gallstone ileus with these three criteria. Only one false negative case could be identified. The remaining 151 patients are true negative cases and no false positive case could be disclosed. The overall sensitivity, specificity and accuracy of CT in diagnosing gallstone ileus were 93%, 100%; and 99%, respectively. Surgical exploration was performed in 13 patients of gallstone ileus with ectopic stones sized larger than 3 cm. One patient recovered uneventfully following conservative treatment with an ectopic stone sized 2 cm in the long axis. CONCLUSION: Contrast enhanced CT imaging offered crucial evidence not only for the diagnosis of gallstone ileus but also for decision making in management strategy.

CT diagnosis of small bowel obstruction due to phytobezoar.

BACKGROUND AND PURPOSE: Small bowel obstruction (SBO) is a commonly encountered abdominal problem in the emergency ward. Phytobezoar is an uncommon cause of SBO which has specific radiographic findings on computed tomography (CT). This study evaluated the CT appearance of small bowel phytobezoar. METHODS: Eighty two patients with SBO who underwent CT examination and surgical treatment over a 6-year period were included. The presence of fecal ball sign, defined as a clearly distinguishable, ovoid or round intraluminal mass with mottled gas pattern outlined by fluid or oral contrast material in the dilated small bowel at the site of obstruction, and abruptly collapsed lumen beyond the lesion on CT was evaluated in all cases. The CT findings of the patients with SBO and the patients with fecal ball sign on CT were reviewed. The diagnosis was established based on surgical findings. RESULTS: Fecal ball sign was identified in 9 of the 82 patients. Operative findings revealed that SBO was secondary to phytobezoar in 7 of these patients. The specificity and sensitivity of fecal ball sign in the diagnosis of SBO secondary to phytobezoar were 97% and 100%, respectively. CONCLUSIONS: Fecal ball sign is accurate in the preoperative diagnosis of phytobezoar as the underlying cause of SBO. Early recognition of fecal ball sign in the CT study is of paramount importance in precise preoperative diagnosis in patients with SBO.

Eosinophilic fasciitis in a military recruit: MRI evaluation with clinical correlation.

Eosinophilic fasciitis (EF) is an uncommon connective tissue disease. We report a patient with EF who presented with episodic swelling and stiffness of his legs and forearms in combination with peripheral eosinophilia. Imaging studies of the legs and forearms, including computed tomography (CT) and magnetic resonance imaging (MRI), clearly demonstrated the characteristic finding of fascial thickening. The complete clinical imaging and pathological findings are described in this report. Cross-sectional imaging is useful in diagnosing EF and in the appropriate clinical scenario may be helpful in differentiating EF from other connective tissue diseases.