The aim of the present study was to determine whether alterations in hepatic energy expenditure following partial hepatectomy (PHx), as documented by in vivo hepatic 31 P-MRS, correlate with standard parameters of hepatic regeneration and/or liver function. In addition, we sought to determine whether changes in hepatic energy levels are proportional to the extent of hepatic resection. Adult male Sprague-Dawley rats (4-7 per group) underwent a 40%, 70%, or 90% PHx or sham surgeries. Magnetic resonance spectroscopy (MRS) examinations were performed on each animal 24 or 48 hours thereafter. After MRS examinations, [ 3 H]thymidine incorporation into hepatic DNA, proliferating cell nuclear antigen (PCNA) protein expression, and serum bilirubin determinations were performed on each rat. Twenty-four hours following surgery, rats that had undergone 70% PHx had unchanged adenosine triphosphate (ATP) levels but significantly lower ATP/inorganic phosphate (Pi) ratios (P < .05), whereas, at 48 hours post-PHx, both ATP and ATP/Pi levels were lower than in sham-and nonoperated controls (P < .05). Hepatic regeneration and liver dysfunction mirrored these changes; correlations existed between ATP/Pi ratios and [ 3 H]thymidine incorporation (r ‫؍‬ ؊0.61, P < .005), PCNA protein expression (r ‫؍‬ ؊0.62, P < .005), and serum bilirubin (r ‫؍‬ ؊0.49, P < .05). For rats that had undergone graded resections, depleted energy levels 48 hours post-PHx were proportional to the extent of resection, degree of enhanced regenerative activity, and liver dysfunction. In conclusion, 31 P-MRS-generated ATP/Pi index is a noninvasive, robust determination that correlates with standard parameters of hepatic regeneration and function. (HEPATOLOGY 2002;36:345-353.)

Although MRI offers highly diagnostic medical imagery, patient access to this modality worldwide is very limited when compared with X-ray or ultrasound. One reason for this is the expense and complexity of the equipment used to generate the switched magnetic fields necessary for MRI encoding. These field gradients are also responsible for intense acoustic noise and have the potential to induce nerve stimulation. We present results with a new MRI encoding principle which operates entirely without the use of conventional B0 field gradients. This new approach--'Transmit Array Spatial Encoding' (TRASE)--uses only the resonant radiofrequency (RF) field to produce Fourier spatial encoding equivalent to conventional MRI. k-space traversal (image encoding) is achieved by spin refocusing with phase gradient transmit fields in spin echo trains. A transmit coil array, driven by just a single transmitter channel, was constructed to produce four phase gradient fields, which allows the encoding of two orthogonal spatial axes. High-resolution two-dimensional-encoded in vivo MR images of hand and wrist were obtained at 0.2 T. TRASE exploits RF field phase gradients, and offers the possibility of very low-cost diagnostics and novel experiments exploiting unique capabilities, such as imaging without disturbance of the main B0 magnetic field. Lower field imaging (<1 T) and micro-imaging are favorable application domains as, in both cases, it is technically easier to achieve the short RF pulses desirable for long echo trains, and also to limit RF power deposition. As TRASE is simply an alternative mechanism (and technology) of moving through k space, there are many close analogies between it and conventional B0 -encoded techniques. TRASE is compatible with both B0 gradient encoding and parallel imaging, and so hybrid sequences containing all three spatial encoding approaches are possible.

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