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Biomedical subjects

R E Hendrick

Publications and source records attributed to R E Hendrick.

At least 19 recordsLinked to original sources
PubMed1992

Quality assurance in mammography. Accreditation, legislation, and compliance with quality assurance standards.

The status of mammography quality assurance in the United States has been reviewed briefly. The history, goals, current status, and possible future directions of the ACR Mammography Accreditation Program have been described, and other ACR activities in mammography quality assurance have been discussed, including ACR Standards of Practice in Mammography, ACR Mammography Quality Control Manuals, and the ACR/CDC Cooperative Agreement on Quality Assurance in Mammography. The quality assurance provisions of recently adopted federal legislation on mammography have been reviewed, including the Medicare legislation on screening mammography, along with the proposed Women's Health Equity Act mammography quality assurance provisions. Finally, a simple plan has been proposed to fuse these activities into a coherent program for ensuring consistently high quality mammography at every site in the United States.

Accreditation↗
PubMed1991

The American College of Radiology Mammography Accreditation Program.

This article discusses the background, goals, criteria, current results, impact, and future directions of the American College of Radiology's (ACR's) Mammography Accreditation Program. To date, approximately one half of the mammographic units in the United States have voluntarily applied for accreditation through the ACR program, with approximately one quarter of the units in the United States now accredited. Application rates have increased steadily since the start of the program in August 1987. The equipment performance criteria and professional criteria defined and employed in the ACR Mammography Accreditation Program have been adopted as standards for the performance of screening mammography by the ACR and have served as a basis for quality assurance standards in state and federal legislation on mammography.

Accreditation↗
PubMed1991

Advances in magnetic resonance imaging and spectroscopy.

Over the past decade, MR imaging and MR spectroscopy have provided a classic example of the rapid progress that can be accomplished by closely coupled technological advancement and clinical application. This article reviews some of the technical and clinical advances in MR imaging and MR spectroscopy that have occurred over the past year.

Fluoroscopy↗
PubMed1990

Evaluation of the double-quantum filter for the measurement of intracellular sodium concentration.

Evaluation of the double-quantum filter for sodium was performed on several sample series of bovine serum albumin in water. Both single-quantum (1Q) and double-quantum (2Q) measurements were obtained. The quality of the 2Q filter was found to be quite sensitive to pulse width setting. Ordinary 1Q measurements of sodium in albumin-containing solutions show 100% visibility. At high ionic strengths, the 2Q albumin results confirm earlier conclusions demonstrating the tendency for the albumin molecule to unfold under a variety of influences. At physiological sodium concentrations, the magnitude of the 2Q/1Q ratio is controlled not only by the concentration of albumin, but also by the solution pH. Non-zero, double-quantum signals were observed in physiological samples consisting of essentially intracellular material (packed red blood cells) as well as in extracellular material (plasma and urine). Measurements in human urine showed no 2Q signal. However, high-concentration NaCl solutions did produce real, measurable 2Q signals. Therefore, the 2Q filter does not measure intracellular sodium exclusively. Although packed red blood cells gave the highest 2Q/1Q ratio (8.5 x 10(-3), plasma gave a very considerable 2Q/1Q ratio (2.3 x 10(-3). Because of its relatively high extracellular concentration, extracellular sodium may give a greater absolute 2Q signal than intracellular sodium in unmodified tissue samples. Based on these data, we conclude that a 2Q filter will not provide a useful measurement of intracellular sodium in in vivo tissue samples.

Erythrocytes↗
PubMed1990

Standardization of image quality and radiation dose in mammography.

Image quality is the cornerstone to the practice of high-quality mammography. To ensure high quality in the practice of mammography, the American College of Radiology has established a voluntary program for the accreditation of mammographic screening sites. Between August 15, 1987, and February 1, 1989, 647 mammography units completed the accreditation program. Data collected from those units are presented, demonstrating that broad ranges of image quality and dose currently exist among mammographic screening sites. Reasons are discussed for the wide ranges observed, and steps are proposed to narrow the ranges of image quality and dose in the practice of mammography.

Accreditation↗
PubMed1990

Liver-lesion tissue contrast on MR images: effect of iron oxide concentration and magnetic field strength.

This study assessed the enhancement of liver-lesion contrast by using low levels of iron oxide contrast agent at four common magnetic resonance (MR) imaging field strengths: 0.15, 0.35, 0.5, and 1.5 T. Adenocarcinomas were percutaneously inserted into the livers of 15 rats. Iron oxide was given intravenously in concentrations of 0 (control group), 2.5, 5, 10, and 20 mumol/kg to three rats in each concentration group. All images were acquired between 1 and 24 hours after injection. Liver-lesion contrast ratios and contrast-to-noise ratios (C/Ns) were calculated. Results showed increased liver-lesion contrast and C/Ns with increased iron oxide concentration up to 10-20 mumol/kg at all four magnetic field strengths. At 0.15 T, iron oxide produced lower gains in tumor-liver contrast. At middle and high magnetic field strengths, liver-lesion contrast was similar for each level of iron oxide concentration, but C/Ns were markedly higher at 1.5 T than at middle field strength. Low levels of iron oxide contrast agent are effective at magnetic field strengths of 0.35 T and above, producing the greatest increase in C/N at middle field strengths.

Animals↗
PubMed1989

White matter lesions: role of spin density in MR imaging.

To study the effect of hydrogen spin density (N[H]) on magnetic resonance (MR) image contrast in white matter disease of the brain, T1, T2, and N[H] values were determined for normal white matter and idiopathic white matter lesions (IWMLs) in 21 patients by using multiple spin-echo (SE) sequences. T1 values of IWMLs were significantly greater than those of normal white matter in all patients studied, and T2 values of IWMLs were significantly greater in 20 of 21 patients. N[H] values of IWMLs were greater in 20 of 21 patients, with statistically significant differences from those of normal white matter in 17 of those 20 patients. Averaged over all 21 patients studied, N[H] values of IWMLs were 20% higher than N[H] values of normal white matter. The effect of unequal N[H] values on contrast between IWMLs and normal tissues is to reduce contrast on short SE sequences with a short repetition time (TR) and a short echo time (TE), while enhancing contrast between IWMLs and normal tissues on long TR/TE SE sequences. Elevated N[H] values in IWMLs have a minimal effect on contrast in conventional inversion-recovery (IR) sequences but substantially enhance contrast between IWMLs and normal brain tissues in short inversion time IR sequences.

Brain↗
PubMed1989

Short TI inversion-recovery imaging of the liver: pulse-sequence optimization and comparison with spin-echo imaging.

Magnitude-reconstructed short inversion-time (TI) inversion-recovery (IR) sequences have the advantage of reducing the signal of fat while providing additive T1 and T2 contrast. A double-echo short TI IR sequence was implemented to offer different degrees of T1- and T2-dependent image contrast. In 50 consecutive patients with proved liver tumors (30 metastases, 13 hemangiomas, seven other primary liver tumors), images obtained with a double-echo IR sequence at a repetition time (TR) of 1,500 msec, echo time (TE) of 30 and 60 msec, and TI of 80 msec (TR/TE/TI = 1,500/30, 60/80) were compared with those obtained with spin-echo (SE) sequences at a TR of 275 msec and a TE of 14 msec (TR/TE = 275/14) and 2,350/60, 120, 180. Metastases-liver contrast-to-noise ratios were highest at SE 275/14, followed by IR 1,500/30/80 and SE 2,350/180. IR 1,500/30/80 and SE 275/14 sequences consistently showed higher sensitivity for the detection of metastases than T2-weighted SE sequences. Differential diagnosis of benign and malignant lesions was more reliable with T2-weighted SE sequences than T2-weighted short TI IR sequences.

Adult↗
PubMed1987

Maximizing signal-to-noise and contrast-to-noise ratios in FLASH imaging.

This paper presents an analysis of signal-to-noise and contrast-to-noise ratios from small tip angle, gradient reversal (FLASH) imaging. Analytic and numerical techniques are used to determine the delay times and tip angles that maximize signal-to-noise per unit time from a single tissue. Similar procedures are used to determine the delay times and tip angles that maximize both T1-induced and T-2*-induced contrast-to-noise per unit time for a pair of tissues as a function of tissue characteristics and pulse sequence sampling times. The advantage of optimized FLASH imaging over optimized spin-echo imaging is quantitated by comparing signal-to-noise and contrast-to-noise ratios per unit time from the two sequences. Images are used to confirm these numerical results, to compare noise levels resulting from gradient reversals versus 180 degrees rephasing pulses and to assess the possible adverse effects of static magnetic field inhomogeneities on FLASH imaging.

Humans↗
PubMed1987

Sampling time effects on signal-to-noise and contrast-to-noise ratios in spin-echo MRI.

This work discusses the effect of sampling time on noise, signal-to-noise and contrast-to-noise ratios in magnetic resonance imaging. A simple imaging experiment is performed to demonstrate the effect of sampling time on noise, confirming theoretical expectations that doubling the sampling time while decreasing the read gradient strength by a factor of two reduces statistical noise to 1/square root 2 of its original level. This result suggests that sampling time should be maximized within the constraints of the pulse sequence: namely, that sampling time should be increased and read gradient strength decreased as TE is increased. Revised expressions for signal-to-noise and contrast-to-noise ratios are presented based on the assumption that sampling time increases linearly with echo delay time above a certain minimum TE value. The revised expressions are then used to derive new predictions of the interpulse delay times that maximize signal-to-noise and contrast-to-noise ratios in spin-echo imaging. It is demonstrated that sampling times are critical in determining whether T1-weighted or T2-weighted sequences produce superior tissue contrast in spin-echo imaging.

Image Enhancement↗
PubMed1987

Motion artifact reduction with fast spin-echo imaging.

The influence of signal averaging (n), repetition time (TR), and echo delay (TE) on systematic noise (cardiac, vascular, respiratory, and peristaltic ghost artifacts) and statistical noise (thermal effects) was determined in eight healthy volunteers and 57 patients. Systematic noise was the dominant factor degrading abdominal magnetic resonance (MR) images. Signal averaging was the primary determinant of both statistical and systematic image noise, fitting a power function (n)b with b = 0.44 and -0.42, respectively, close to the expected b = -0.5 power function. All types of ghosting showed the same sensitivity to signal averaging. Normalized systematic noise increased slightly with TR (b = 0.16) and increased markedly with TE (b = 0.40). These data indicate that the short TR, short TE technique is a powerful method for reducing motion artifacts on breathhold images and can be combined with signal averaging to further suppress artifacts, improve signal-to-noise ratio, and maximize anatomic resolution.

Abdomen↗
PubMed1987

Contrast optimization for the detection of focal hepatic lesions by MR imaging at 1.5 T.

The relative efficacies of different spin-echo pulse sequences at 1.5 T were evaluated in the detection of focal hepatic disease. Pulse sequences compared were spin-echo with a repetition time (TR) of 200 msec and echo time (TE) of 20 msec, with six excitations; TR = 300 msec, TE = 20 msec, with 16 excitations (T1-weighted sequences); and a double spin-echo with TR = 2500 and TE = 25 and 70, with two excitations (proton-density-weighted and T2-weighted pulse sequences, respectively). Respiratory-motion compensation, which involved a recording of the phase-encoding gradients (Exorcist), was used for the last two sequences. Spin-echo with TR = 2500 msec and TE = 70 msec was superior in lesion detection and contrast-to-noise ratio. The proton-density-weighted and T2-weighted sequences with respiratory compensation produced better artifact suppression than did the short TR, short TE T1-weighted sequence with temporal averaging. In contradistinction to prior results at 0.6 T, T2-weighted pulse sequences appear superior to T1-weighted pulse sequences with multiple excitations for both lesion detection and artifact suppression at 1.5 T.

Cysts↗
PubMed1985

MR imaging technology: maximizing the signal-to-noise ratio from a single tissue.

The pulse-sequence equations for spin-echo magnetic resonance imaging were used to determine interpulse delay times that give the highest signal-to-noise ratio from a single tissue. This theoretical result was then verified experimentally using 1-, 2-, and 5-mM/l copper sulfate solutions imaged on a 0.15-T resistive system. Theoretical analysis determined the spin-echo interpulse delay times that maximize the signal-to-noise ratio from a single tissue as TEopt = TEmin, the minimum echo delay time permitted by the system, and, to a good approximation, TRopt = 1.27 T1 + 1.90 TEmin, with T1 the longitudinal magnetic relaxation time of the tissue. Phantom measurements of the signal-to-noise ratio in a typical imaging system confirmed the theoretically determined TRopt values to within 7%.

Humans↗
PubMed1984

Optimizing tissue contrast in magnetic resonance imaging.

Magnetic resonance imaging demands that tissue contrast and signal-to-noise advantages be sought in each component of the imaging system. One component of magnetic resonance imaging in which contrast and signal-to-noise ratios are easily manipulated is in the choice of pulse sequences and interpulse delay times. This article provides a general method for determining the best choices of interpulse delay times in pulse sequences and applies that method to saturation recovery, inversion recovery, and spin-echo sequences. Saturation recovery and inversion recovery sequences with rephasing pulses, and tissues with unequal hydrogen densities are considered. Optimization of pulse sequences is carried out for the two distinct cases of (a) a fixed number of sequence repetitions and (b) a fixed total imaging time. Analytic expressions are derived or approximate expressions are provided for the interpulse delay times that optimize contrast-to-noise ratios in each pulse sequence. The acceptable range of interpulse delay times to obtain reasonable contrast using each pulse sequence is discussed.

Animals↗