Objective To explore the susceptibility weighted imaging (SWI) appearance of paramagnetic and diamagnetic materials, its imaging theory, and its value of differential diagnosis from their appearance. Methods The diamagnetic and paramagnetic phantom were made and the X-Y axial SWI phase image of phantom then was obtained. Twenty-eight cases of intracerebral calcium and 21 cases of hemorrhage examined with MRI scan and CT scan were retrospectively investigated. The appearance of calcium and hemorrhage on SWI were analyzed and compared with their appearance on CT and conventional MRI. Results Phantom experiment indicated that the equator plane scan of diamagnetic sphere showed high signal in centre surrounded by low signal ring and high signal in two poles of sphere along Z axis of main magnetic field. The paramagnetic sphere appeared the opposite appearance of diamagnetic sphere with centre low signal surrounded by high signal ring in equator plane and low signal in two poles of sphere along Z axis of main magnetic field. The SWI manifestations of 4 cases of intracerebral sphere or sphere-like calcification ( chorioidal calcification) and 9 cases of sphere or sphere-like hemorrhage(2 cases of traumatic hemorrhage, 1 case of hypertension related basal ganglion hemorrhage, 4 cases of metastasis hemorrhage and 2 cases of cavernous hemangioma hemorrhage)were consistent with diamagnetic and paramagnetic sphere phantom respectively. Four cases of calcification in basal ganglion showed the mixed high and low signal. Seven cases of irregular calcification ( neoplastic calcification) aside from basal ganglion appeared complex appearance, though mainly in high signal. Other sphere or sphere-like calcification aside from basal ganglion ( 14 cases of pineal calcification, 4 cases of chorioidal calcification, 2 cases of cerebral cysticercosis calcification and 1 case of neoplastic calcification ) showed markedly high signal. Nine cases of intracerebral iobular hemorrhage (2 cases of hypertension related basal ganglion hemorrhage, 4 cases of unknown casual hemmorrhge and 3 cases of cavernous hemangioma hemorrhage) displayed a multiple concentric circle appearance, other 3 hemorrhage showed complex appearance, though mainly in low signal. Ten cases of calcification had no specific appearance on T1 WI and T2WI. Conclusion Phase image of SWI is helpful in differentiating intracerebral diamagnetic from paramagnetic materials and it has some advantage in detecting calcification over T WI and T2 WI.

PURPOSE: Most hepatic metastases are hypovascular, and CT scanning during peak hepatic enhancement is thusimportant for the detection of hepatic lesions. The purpose of this study was to determine whether images obtainedby bolus tracking show greater hepatic enhancement. MATERIALS AND METHODS: We prospectively evaluated 101 patientswho underwent helical CT of the abdomen, using either a fixed 60-sec delay(n=50) or bolus tracking (n=51). For thelatter, we used a hepatic enhancement threshold of 50HU over baseline on monitor phase to determine a 6-sec delaybetween the monitor and diagnostic scanning phase. For all patients, three region-of-interest measurements wererecorded, one at each of the upper, middle, and lower levels of the liver; the measurements were averaged andsubtracted from the baseline density that measured CT values in three different hepatic segments at the mid-levelof the liver. We compared mean enhancement above the baseline of the liver between fixed 60-sec delay and bolustracking. RESULTS: A statistically significant difference in the enhancement level of the liver (upper, p=.001;middle, p=.001; lower, p=.003) was noted between fixed 60-sec delay (upper, 65.3+/-16HU; middle, 67.4+/-16.5HU;lower, 68.5(19.4HU) and bolus tracking (upper, 75.2+/-15.5HU; middle, 74.4+/-13.7HU;lower, 75.6+/-13.6HU). With fixeddelay, 86% of patients reached 50HU of enhancement, but with bolus tracking, 98% reached this level. For onenhancement value of 60HU, the corresponding figures were 64% and 86%. Mean delay for the transition betweenmonitoring scans and diagnostic scan initiation was 63.8+/-7.9(range, 48-79)secs. For two patients in whom theenhancement curve did not reach threshold (50HU), the default time was 70 sec; one subsequently failed to reachthis same threshold. CONCLUSION: Using the same amounts of contrast material, bolus tracking provides a greaterlevel of hepatic enhancement than a fixed 60-ses delay, and is thus helpful for the detection of hypovascularmasses such as metastatic lesions.
Abdomen ; Humans ; Liver ; Neoplasm Metastasis ; Prospective Studies ; Tomography, Spiral Computed ; Tomography, X-Ray Computed