Radiologist evaluation of a multispectral image compression algorithm for magnetic resonance images.

With the advent of teleradiology and picture archiving and communication systems (PACS), the expense and time required for image transmission and long term image archiving become important. The use of validated image compression algorithms can greatly reduce these costs. A lossy, multispectral image compression scheme at compression ratios (CR) of 25:1 and 32:1 was used for a set of 26 different patient MR exams. The original and compressed/decompressed (CD) images sets were evaluated in a blinded fashion by four radiologists in two phases. The main objective was to determine whether radiologic interpretation would vary between the two types of CD image sets and the corresponding originals. In general, the compression algorithm caused a slight decrease in image quality; however, the interpretation of pathology did not change between the original and CD image sets. In only one case at the maximum CR = 32 did one of four radiologists change the interpretation of pathology after CD. In this study, lossy multispectral image compression of MR images at CR = 25 maintained diagnostic integrity. This could play a significant role in image storage and communications.

A canine model of acute hydrocephalus with MR correlation.

Within 3 hours of induction of acute hydrocephalus in a canine model, lateral ventricular CSF pressure increased from an initial average of 14.6 +/- 2.8 cm H2O to 40.2 +/- 5.7 cm H2O. Ventricular volumes, as measured from MR images, increased 1.45 +/- 0.94 cm3, 1.92 +/- 0.82 cm3, and 2.24 +/- 0.60 cm3 after 6, 24, and 48 hours, of hydrocephalus, respectively. This canine model was reliable and consistent with clinical conditions.

Oligosaccharides interfere with the establishment and progression of experimental pneumococcal pneumonia.

Oligosaccharides that block the adherence of bacteria to epithelial cells in vitro--lacto-N-neotetraose (LNnT) and its alpha2-3- and alpha2-6-sialylated derivatives--were tested for their abilities to attenuate the course of pneumococcal pneumonia and to prevent colonization of the nasopharynx in animal models. Intratracheal administration of these agents concurrently with bacteria dramatically decreased pneumococcal load in the lungs of rabbits and conferred protection from bacteremia. The oligosaccharides ameliorated pneumonia and bacteremia when given therapeutically 24 h after infection was established. When administered intranasally, neoglycoconjugates of the active oligosaccharides prevented colonization of the nasopharynx of infant rats. In addition to in vitro anti-adherence properties, LNnT acted directly on cultured lung epithelial cell lines to induce changes such that pneumococcal adherence was prevented for prolonged periods. These activities encourage continued development of oligosaccharides as a class of potentially preventive and therapeutic agents for infectious diseases.

Diagnosis of cerebral ventriculomegaly in normal adult beagles using quantitative MRI.

The brain of 17 asymptomatic normal adult beagles was evaluated with magnetic resonance imaging. Lateral ventricular size was quantified using computer algorithms. In beagles with large ventricles, contrast medium was introduced into the cerebellomedullary cistern to determine whether obstructive hydrocephalus was present. Total lateral ventricular volume ranged from 77 mm3 to 11,726 mm3. Based on Gd-DTPA diffusion, the CSF flow pattern was considered normal and normal neural morphology was seen using electron microscopy. Results suggest a high incidence of clinically asymptomatic ventriculomegaly in normal adult beagles.

Quantitation of normal canine hippocampus formation volume: correlation of MRI with gross histology.

The hippocampal formation possesses an important role in the development and maintenance of short-term memory. In this study, magnetic resonance imaging (MRI) and gross histology were used to quantify the volume of the hippocampal formation in canines. High resolution MRI, using 1 mm thick slices and an intraplanar resolution of 0.35 mm was performed at 2.0 T both in vivo and in vitro following in situ fixation. The volumes of the hippocampal formations were determined from MR images and compared to those obtained from one mm thick gross histologic sections. The average volume of the canine hippocampal formation, measured from in vivo and in vitro MR images was 476.0 +/- 79.5 and 467.3 +/- 53.7 mm3, respectively. Determined from gross histology, the volume of the hippocampal formation was 463.6 +/- 24.1 mm3. Quantitation of the canine hippocampal formation using in vivo MRI showed good correlation with in vitro MRI and histology, verifying the reliability and reproducibility of in vivo MRI measurements. High resolution MRI using 1 mm thick slices through the whole canine hippocampal formation is necessary for accurate volume determination of a structure of this size.

MRI evaluation of dexamethasone acetate therapy for osteoarthritis in the hand.

A patient with clinically diagnosed Stage I primary idiopathic osteoarthritis of the first metacarpal trapezium joint of the left hand received intra-articular administration of dexamethasone acetate. Compared to pretreatment T2- weighted MR images, greatly decreased MR signal intensity was observed in the affected joint space and adjacent soft tissues 2 days after dexamethasone acetate therapy. This was representative of reduced edema in the metacarpal trapezium joint and demonstrated the ability of MRI to follow pharmacological treatment for arthritis.

Direct in vivo observation of transventricular absorption in the hydrocephalic dog using magnetic resonance imaging.

RATIONALE AND OBJECTIVES: A model of chronic noncommunicating hydrocephalus in canines was developed, and gadolinium-DTPA (Gd-DTPA)-enhanced magnetic resonance imaging, physiologic and morphologic studies were performed to investigate transventricular absorption of cerebrospinal fluid. METHODS: Chronic hydrocephalus was induced in 12 mongrel dogs by injection of a silastic mixture into the prepontine cisterns. Ventricular pressure was measured during the development of hydrocephalus, and lateral ventriculo-ventricular perfusions with Gd-DTPA were performed under controlled conditions during serial magnetic resonance imaging studies. RESULTS: Hydrocephalus developed over an average of 129 +/- 24 days after induction, and the intraventricular pressure increased from an initial level of 14 +/- 4 cm H2O to a stabilized plateau of 25 +/- 5 cm H2O. Increased signal intensity in the brain matter, as seen on magnetic resonance images of chronic hydrocephalic dogs perfused with Gd-DTPA in the lateral ventricles, was consistent with the presence of the contrast agent in the periventricular extracellular space. This increased signal intensity was not observed in control animals. CONCLUSIONS: These results provide direct evidence of transventricular absorption in chronic hydrocephalus.

Transmission line analysis of noncylindrical birdcage resonators.

Transmission line theory, validated for the standard cylindrical birdcage coil, has been employed for the analysis of a rectangular birdcage resonator which is useful for MR imaging of the hand. Due to lack of cylindrical symmetry in the rectangular coil, RF field uniformity was evaluated and found to be critically dependent upon the choice of column from which the coil was linearly driven. Effective L1 and L2 inductance elements were determined using known formulas for self and mutual inductance contributions, and compensation of the different inductance elements of the hand coil was performed to produce cylindrically symmetric birdcage current patterns. RF field mapping using the Biot-Savart law demonstrated a rectangular coil sensitivity 22% greater than a comparable cylindrical version. MR hand and wrist images were acquired using the rectangular birdcage coil. In addition, transmission line analysis was extended to other noncylindrical birdcage geometries.

Use of transmission line analysis for multi-tuning of birdcage resonators.

A general analysis for double- and higher order tuning of birdcage resonators is presented based on a lumped element transmission line model. Expressions were developed for the determination of the resonant frequencies of bandstop and bandpass birdcage coils and, with specific restrictions, for capacitor values required to obtain any two desired mode one resonant frequencies. Experimental measurements on three variants each of an eight-column bandstop and an eight-column bandpass were in excellent agreement with theory; the average absolute frequency difference and percent deviation were 1.51 +/- 1.57 MHz and 2.61 +/- 2.36%, respectively. In addition, 31P and 1H phantom images were obtained at 2.0 T using a representative bandstop coil.

Experimental design and fabrication of birdcage resonators for magnetic resonance imaging.

Although the birdcage resonator has been theoretically described for single- and multinuclear operation, this study provides the basic experimental guidelines needed for the fabrication and testing of such coils for various geometries and resonant frequencies from 10 to 95 MHz. The correlation of coil dimensions and resonant frequencies with individual inductance elements, L1 and L2, is also shown. Experimentally derived algorithms are presented for the determination of the capacitance needed for low-pass resonators based on measurements of the coil's "global" inductance. Ten low-pass birdcage coils with eight legs were evaluated and their four resonant frequencies were within 4% of theoretical predictions.

Explicit treatment of mutual inductance in eight-column birdcage resonators.

A formulation has been developed for the determination of self and mutual inductances in unloaded, eight-column symmetric birdcage coils using their expected resonant mode current patterns and well-known inductance formulas. The average frequency differences between theory and experiment for mode one resonances for nine low-pass coils were 0.66 (+/- 0.57) MHz and 2.14 (+/- 2.08) MHz using effective (self plus mutual) and self inductances, respectively, and similarly, for three high-pass coils, 1.19 (+/- 0.56) MHz and 2.79 (+/- 2.20) MHz. These frequency differences were more pronounced for the higher modes; for mode four, the differences neglecting mutual inductance were 14.30 (+/- 11.10) MHz and 10.42 (+/- 4.60) MHz for the low- and high-pass coils, respectively. This analysis provides the first explicit evaluation of the total end-ring and column inductances L1 and L2 within each birdcage section at resonance with resulting excellent agreement in resonant frequencies between theory and experiment.

Generalized electrical analysis of low-pass and high-pass birdcage resonators.

The radio-frequency 'birdcage resonator' has found wide use in MRI/MRS for its field homogeneity and signal-noise characteristics. This paper presents a general analysis, derived from lumped element transmission line theory, of the electrical behavior of unloaded, N-column birdcage resonators applicable to several versions of the basic design including low-pass and high-pass coils. Analytic expressions and computer results are presented for both types of coil describing resonant frequencies, input and characteristic impedances, dispersion relations, pass-bands, resonant peak bandwidth and Q. Theoretical expressions for normalized resonant frequency difference ratios independent of element values and resonator geometry have been developed for generic low- and high-pass coils. Experimental measurements of resonant frequencies were made for six coils, and the average agreement with theoretical predictions was approximately 4%.