Effects of Iodinated Contrast Agent on Diffusion Weighted Magnetic Resonance Imaging

Rationale and Objectives

To evaluate the effects of iodine contrast agent on diffusion signal intensity and apparent diffusion coefficient (ADC) in diffusion-weighted imaging (DWI) studies in magnetic resonance imaging (MRI) examination just after computed tomography (CT) contrast imaging.

Materials and Methods

On a 1.5 T MRI scanner, ADC was calculated from the signal intensity of DWI (b = 0 and 1000) using phantoms filled with contrast agent (0, 4.5, 6.0, 9.0, 30, and 60 mgI/mL). We evaluated the signal intensities of DWI and ADC in 10 patients (3 women, 7 men, 35–68 years old) examined by MRI study less than 40 minutes after injection of 100 mL of iopamidol (300 mgI/mL) for CT study.

Results

The DWI signal increased until a CT value of 190 HU, but showed no changes above this value. The ADC decreased with increases in CT value. Less than 40 minutes after injection of iopamidol (300 mgI/mL) for CT scan, the signal intensity of DWI was significantly increased and ADC was significantly decreased.

Conclusions

It is necessary to recognize the rate of decrease of ADC, because it is dependent on the density of iodine contrast agents.

Various examination modalities are often used in the same patient for diagnosis, and both computed tomography (CT) and magnetic resonance imaging (MRI) examinations may be performed consecutively on the same day.

Several studies have indicated that contrast agents used for CT and MRI may adversely influence the results of the other imaging modality . In these reports, it was suggested that iodinated contrast agents shorten T1 and T2 on MRI examination, and cause high signal intensity on T1-weighted imaging and low signal intensity on T2-weighted imaging .

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Materials and methods

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Relativetissueratio=Signalvalueofkidney/Signalvalueoffat(1) Relative

tissue

ratio

=

Signal

value

of

kidney

/

Signal

value

of

fat

(

1

)

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Results

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Table 1

Average Computed Tomography Values and Standard Deviation of Brain Meningiomas and Kidney Cortex and of the Bladder 2 and 15 Minutes after Injection of Contrast Agent, Respectively, in 20 Patients

Averaged CT Value (HU) SD Meningioma after injected two minutes 204.2 15.2 Kidney cortex after injected 2 minutes 182.3 4.11 Bladder after injected 15 minutes 488.2 25.3

Computed tomography values ranged from 180 to 500 HU.

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Discussion

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Conclusions

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