Magnetic Resonance Spectroscopy is a Non-Invasive Technique to Evaluate Urinary Chemical Composition in Fetal Urinary Tract Obstruction
Michael P. Kurtz, MD, Caleb P. Nelson, MD, MPH, Robert V. Mulkern, PhD, Mukund Balasubramanian, PhD, Judy A. Estroff, MD, Carol E. Barnewolt, MD, Alan B. Retik, MD.
Boston Children's Hospital, Boston, MA, USA.
BACKGROUND: The standard of care in evaluation of fetal lower urinary tract obstruction (LUTO) prior to shunt placement is to sample urinary biochemistry by vesicocentesis. This is invasive and can result in fetal ascites. A standard 1.5T or 3T MRI scanner can obtain chemical composition data from tissue or fluid from a pre-selected region via magnetic resonance spectroscopy (MRS). Similar to B2-microglobulin, higher fetal urinary lactate is known to be associated with greater degree of dysplasia. As lactate has a unique spectroscopic signature we sought to apply MRS as a new method of fetal evaluation for this condition.
METHODS: Pregnant women presenting to a single center with fetal LUTO or Society of Fetal Urology Grade 3 hydronephrosis were prospectively enrolled and underwent proton MRS at 3T using a standard fetal proton imaging receive coil and a PRESS sequence (TE = 144 ms). Voxels of 12x12x12mm3 were placed within dilated urinary structures (bladder, kidney, urinoma) or amniotic fluid. Resulting spectra were analyzed, and clinical variables collected pre- and postnatally.
RESULTS: Six patients underwent MRS. Inverted lactated doublets were detectable in a total of three patients, two of which were in the most severe cases of renal dysplasia, one with dialysis-dependent posterior urethral valves and one in a kidney with 2% function after birth. A positive control in amniotic fluid was confirmatory. Spectra are shown from a phantom with 2mM lactate in urine (Fig 1) and from a case of PUV (Fig 2).
CONCLUSIONS: MRS of the fetal bladder in cases of LUTO or hydronephrosis is feasible, completely noninvasive, and may provide useful information regarding renal function.
Research was supported by The Richard A. and Susan F. Smith President's Innovation Fund Award
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