Biomedical subjects
Publications and source records attributed to R E Hendrick.
This article describes the essential elements of an effective quality control program in mammography. Quality Control tests recently updated in the 1994 ACR Mammography Quality Control Manual, such as the darkroom fog and limiting spatial resolution tests, are described in detail. The article goes on to describe some common problems in mammography quality control, including processor sensitometry and image quality problems.
Not all sites performing mammography produce optimal images at acceptably low doses. To address this situation, a voluntary accreditation program was instituted through the American College of Radiology. Each site applying for accreditation completes a detailed questionnaire about facilities and equipment, personnel, and quality control. Each unit at each site is evaluated by a medical physicist for clinical and phantom image quality and for average glandular dose. Although a site is accredited for 3 years, the performance of each unit is audited annually. Of 11,162 units for which accreditation was sought, only 5,856 (68%) passed at the first attempt, with another 18% passing after reapplication. The major reason for failure was inadequate clinical images, followed by inadequate phantom images, both inadequate clinical and phantom images, and inadequate quality control records. In a performance audit of 20 new units, an average of 5.8 problems were encountered per unit, the majority of which adversely affected image quality. These results support the requirement of equipment performance audits and raise the question of whether similar problems exist in other areas of medical imaging.
This article provides an introduction to the basic physical principles of magnetic resonance (MR) imaging. Essential basic concepts such as nuclear magnetism, tissue magnetization, precession, excitation, and tissue relaxation properties are presented. Hydrogen spin density and tissue relaxation times T1, T2, and T2* are explained. The basic elements of a planar MR pulse sequence are described: section selection during tissue excitation, phase encoding, and frequency encoding during signal measurement.
Some of the issues being addressed in mammography quality assurance are 1) that image quality is the most important technical aspect of mammography; 2) that image quality has improved steadily over the past two decades and will continue to improve at most mammography sites in the United States; 3) that the American College of Radiology's Mammography Accreditation Program is the best way to ensure high quality mammogram; 4) that access to high quality mammography is not geographically restricted, with over half the mammography sites in the United States now ACR accredited and another 30% participating in the accreditation process; 5) that regular and effective quality assurance, as described in the ACR Mammography Quality Control Manuals and as required of ACR accredited sites, is the only way to ensure that superior mammography image quality is maintained; and 6) that sites with higher mammography volume have better quality assurance practices and lower failure rates than others within the ACR Mammography Accreditation Program. Two bills passed by the United States Congress, the Medicare Coverage of Screening Mammography (1990) and the Mammography Quality Standards Act (1992), contain mammography quality assurance provisions. As a result of the 1990 Medicare bill, on-site inspections of Medicare screening sites began in the fall of 1992. The Mammography Quality Standards Act is scheduled to go into effect on October 1, 1994. The current challenges to mammography are to improve and maintain high image quality at every mammography site, to improve imaging of the dense breast, to implement patient-tracking and follow-up mechanisms to improve compliance and assess the efficacy of screening, and to ensure that federal mammography quality standards are effectively and appropriately implemented.
Despite recent improvements in mammography equipment and technique, the radiographically dense breast remains difficult to image. The problems in imaging the dense breast account for a large percentage of the cases of mammographically "missed" carcinomas. Other imaging modalities--such as ultrasonography, transillumination, thermography, computed tomography, magnetic resonance imaging, and radionuclide imaging--have been investigated for use in breast cancer detection. This overview discusses the current problems associated with imaging of the radiographically dense breast and suggests some avenues for investigation to develop solutions to these problems.
OBJECTIVE: The purpose of this study was to determine to what extent radiology residents are being trained in quality assurance procedures for mammography. MATERIALS AND METHODS: A telephone survey was conducted with 189 chief residents and 10 other senior residents from 199 of the 209 residency training programs in diagnostic radiology. RESULTS: Time spent on mammography rotations averaged 8 weeks. Only 10 residents (5%) were "very familiar" with the American College of Radiology (ACR) Mammography Accreditation Program; 72 (36%) were "not at all familiar" with it. Ninety-six (48%) knew that one technologist should be assigned quality control procedures. The majority did not know the recommended frequency for performing any of the five routine quality control procedures; only one knew the recommended frequencies for all five. Only twenty-seven (14%) knew the recommended maximum dose for a mammogram. Regarding biopsy yields and false-negative results: 92 residents (46%) sat in on outcome evaluation sessions; 54 (27%) played active roles, looking up and tabulating results; and 53 (27%) did not participate at all. CONCLUSION: Although time spent on mammography rotations has increased substantially, quality assurance issues are still largely neglected. It may not be reasonable for radiology residents to have detailed instruction in quality assurance procedures for mammography, but they should be more familiar with the general issues involved and the procedures intended to correct the problem of the variable quality of mammography in this country.
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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.
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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.
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.
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.
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.
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.
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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.
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.