ADVANCED IMAGING CENTER PHYSICIAN NEWS

May 1, 2002

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VALUE OF IN-PHASE & OUT-OF-PHASE MR IMAGING
in Diagnosing ADRENAL ADENOMAS, FOCAL FATTY INFILTARATION, etc.

CASE #1:  The patient in Fig. 1a-b presented with a left adrenal mass on a CT scan.  The question was whether or not this represented a benign adenoma or other solid adrenal tumors including a malignancy.

CASE #2:  The patient in Fig. 2a-b presented with a possible right lobe liver mass on a CT.  The question was whether or not this represented a benign focal fatty infiltration (FFI) or a solid hepatic tumor including a malignancy.

IMAGING FINDINGS: 

PATIENT #1:  CT images (not shown) demonstrated a low density left adrenal mass on patient #1 with some enhancement.  The CT density on precontrast images was around 0 HU (near water density), which is typically seen with adenomas.  The MR image (Fig. 1a) shows the mass to be of intermediate signal intensity on in-phase T1W images (red arrow), which is nonspecific.  However, on out-of-phase images (Fig. 1b), the mass became darker, indicating the presence of fatty metamorphism typically seen with a non-functioning adenoma.  Diagnosis of an adenoma can be comfortably made with this technique.

PATIENT #2:  CT images (not shown) demonstrated an ill-defined low density are in the right lobe of the liver.  A mass could not be excluded.  The MR image (Fig. 2a) shows the area to be barely visible and of subtle low-to-intermediate signal intensity on in-phase T1W images (yellow arrow), which is nonspecific.  However, on out-of-phase images (Fig. 2b), the area became darker, indicating the presence of fatty component typically seen with focal fatty infiltration (FFI).

DISCUSSION:  Out-of-phase MR imaging relies on the fact that the protons in water and fat resonate at a slightly different frequency (220 Hz at 1.5 Tesla to be exact).  This difference is exploited to cause the fat and water protons to be exactly “out-of-phase”, thus canceling each other out and causing a darker image.  This is accomplished by varying the so-called echo-time (TE).  At 1.5 Tesla, fat and water protons are “in-phase” at TE’s of about 0, 4.4, 8.8 msec, etc. and “out-of-phase” at TE’s of about 2.2, 6.6 msec, etc *.  Out-of-phase MR images typically have a dark border around the organs (“boundary effect”) such as seen in Fig. 1b, 2b.  Other fat-containing lesions can be diagnosed in the same manner.  All the above MR images were obtained on AIC’s high-field Siemens Symphony utilizing ultrafast breath-hold scanning.

For more information, you may call me at personally (661) 949-8111.

Ray Hashemi, MD, PhD
Director