Jerzy Szumowski

Fat/water quantitation and differential relaxation time measurement using chemical shift imaging technique

The use of chemical shift imaging for fat and water quantitation and differential measurement of relaxation times for the fat and water component is demonstrated using a hybrid technique. The efficacy of the imaging technique for fat and water quantitation has been tested by comparing the results of imaging to the results of volumetric measurements in phantoms with oil and water homogeneously mixed, fat extraction in ground meat of different grades, and biopsy in preliminary clinical studies. Good correlation is found between the fat and water content measured by imaging and that measured by other means except for the inability to differentiate unsaturated fat protons from water protons. Longitudinal (T1) and transverse (T2) relaxation times for water and fat are also shown to be measurable independently when fat and water signal are suppressed accordingly. The independently measured relaxation times correspond closely to those of the pure samples except that unsaturated protons give decreased water relaxation estimates.

MR Fat Suppression Combined with Gd-DTPA Enhancement in Optic Neuritis and Perineuritis

A fat suppression MR technique used in combination with Gd-DTPA enhancement was investigated to determine its value in cases of inflammatory optic nerve lesions. This technique, the so-called hybrid method, is a derivative of the chopper fat suppression technique and provides water-only images without increasing the imaging or postprocessing time. The study group consisted of four patients with acute visual loss, all of whom received Gd-DTPA. Conventional T2-weighted and fat suppression post-Gd-DTPA T1-weighted images were obtained in all patients; in addition, in one patient a post-Gd-DTPA T1-weighted image without fat suppression was obtained. In three patients, the conventional T2-weighted images failed to reveal any abnormality. In contrast, the enhanced optic nerve and enhanced perineural inflammatory infiltrate were easily identified on T1-weighted images after administration of Gd-DTPA and application of fat suppression technique. The lesions in inflammatory optic neuritis or perineuritis were easily distinguished from the surrounding fat, which had been suppressed. This combined technique resulted in significantly improved definition of normal anatomic structures and made the enhancing lesions more conspicuous, especially in areas with large amounts of fat such as the retrobulbar orbit.

PROTON (FAT/WATER) CHEMICAL SHIFT IMAGING IN MEDICAL MAGNETIC RESONANCE IMAGING : CURRENT STATUS

Fat/water CSI has recently been transformed from an experimental method to a routine clinical MRI approach, particularly for evaluating paramagnetic contrast enhancement in fat-rich regions and as a piggyback method for decreasing MRI artifacts, such as in MR angiographic and echo-planar imaging. The full and appropriate use of CSI in medical MRI requires consideration of the factors and strategies outlined in this review. As the commercial implementation of fat/water CSI continues, we can expect further applications in clinical and experimental studies. For example, in imaging areas where MRI has been of limited efficacy, such as pancreas imaging, skin microimaging and vascular imaging, there are indications that these CSI methods may have practical importance. It seems reasonable to project that for high chemically specific detail, medical fat/water CSI will ultimately be supplanted by SI methods, and certainly by localized spectroscopy. The power of the fat/water CSI method remains its extremely high anatomic resolution, which cannot be achieved by current spectroscopy or SI methods. The fat/water CSI methods provide a means for clinically relevant MRI with more accurate and chemically specific information. Expansion of these methods into three-dimensional and fast imaging formats is already taking place at or near the commercial level. For example, the feasibility of combining echo-planar imaging and CSI methods has already been demonstrated. Methods based on the phase-contrast techniques, such as susceptibility mapping and interferometry, are additional implementations that can provide detailed and more specific information in a high anatomic detail format.

MR fat suppression technique in the evaluation of normal structures of the knee.

The chopper fat suppression (CFS) pulse sequence, which is a phase sensitive implementation of the Dixon fat suppression method and the spin echo (SE) pulse sequence, was used in the evaluation of anatomic structures of the normal knee using 48 sets of imaging sequences in six volunteers using a repetition time/echo time combination of 1,500/30, 60 ms. A demonstration of the CFS technique in 10 patients with suspected knee pathology is also presented. A semiquantitative grading scale was established to rate anatomic visualization and used to compare CFS and SE pulse sequence techniques. The results in normal subjects demonstrate that hyaline cartilage is significantly better visualized by fat suppression pulse sequence than by conventional SE pulse sequence in the coronal and sagittal planes of imaging (p < 0.001). The preliminary results from patient studies suggest that CFS imaging may be useful in the evaluation of meniscal tears, in the differentiation of hyaline cartilage from joint fluid, and in the detection of both soft tissue and bone injuries.

Elementary single turn solenoids used as the transmitter and receiver in magnetic resonance imaging

A single turn solenoid, also called a loop-gap resonator, is a device that is efficient for radio frequency spectroscopy on relatively large samples. Thus, the device provides an effective means for magnetic imaging where the single turn solenoid may serve both as the transmitter and receiver coil. The device is readily constructed and provides very efficient use of radio frequency (RF) power for imaging extremities such as breasts, arms, feet, and hands. The resulting magnetic images are acquired in short times with good anatomical resolution and considerable reduction of the RF power delivered to the patient.

Lactate observation in vivo by spectral editing in real time

We have developed a novel in vivo proton MR spectroscopy magnetization transfer method for detection of lactate in ischemic tissue in the presence of interfering fat proton resonances. Pyruvate is magnetically labeled with a saturation pulse and, when converted to lactate, the lactate retains the label. Difference of spectra obtained with and without a saturation pulse contain no fat resonances. High-resolution spectra (determined with a GE 1.5 T Signa) of low lactate levels were obtained in vivo by water suppression using a 2662 composite RF pulse and slice-selective gradients. Spectral subtraction was performed in real time allowing the monitoring of a buildup of the intensity of the lactate peak. Pyruvate-lactate saturation transfer techniques should find wide applicability in the study of ischemia.

A Chemical Shift Imaging Strategy for Paramagnetic Contrast-Enhanced MRI

Administration of paramagnetic contrast agents provides for increased contrast and improvement in the detection and staging of a variety of lesions on T1-weighted spin-echo sequences. The underlying mechanism consists of shortening of the spin-lattice relaxation time of lesions which become highlighted on post-contrast T1-weighted images (McNamara 1987). This approach, however, may be suboptimal in lipid-rich regions and may fail when a lesion becomes isointense as a result of the overlapping relaxation times of enhanced lesion and lipid. For example, enhanced tumor within bone marrow may be undetectable using conventional T1-weighted spin-echo technique (Traill and Sartoris 1989).