E. Russell Ritenour

Medical imaging physics

Preface.Preface to the First Edition.Acknowledgments.Imaging in Medicine. Structure of Matter. Radioactive Decay. Interactions of Radiation. Production of X Rays. Radiation Quantity and Quality. Interaction of X and y Rays in the Body. Radiation Detectors for Quantitative Measurement. Accumulation and Analysis of Nuclear Data. Computers and Image Networking. Probability and Statistics. Instrumentation for Nuclear Imaging. Radiography. Fluoroscopy. Computed Tomography. Influences of Image Quality. Analytic Description of Image Quality. Visual Perception. Ultrasound Waves. Ultrasound Transducers. Ultrasound Instrumentation. Doppler Effect. Fundamentals of Magnetic Resonance. Magnetic Resonance Imaging and Spectroscopy. Magnetic Resonance Imaging Instrumentation, Bioeffects, and Site Planning. Experimental Radiobiology. Human Radiobiology. Protection from External Sources of Radiation. Protection from Internal Sources of Radiation. Future Developments in Medical Imaging. Appendix I: Review of Mathematics. Appendix II: Fourier Transform. Appendix III: Multiples and Prefixes. Appendix IV: Masses in Atomic Mass Units for Neutral Atoms of Stable Nuclides and a Few Unstable Nuclides. Answers to Selected Problems. Index.

MRI compatibility and visibility assessment of implantable medical devices

We have developed a protocol to evaluate the magnetic resonance (MR) compatibility of implantable medical devices. The testing protocol consists of the evaluation of magnetic field‐induced movement, electric current, heating, image distortion, and device operation. In addition, current induction is evaluated with a finite element analysis simulation technique that models the effect of radiofrequency fields on each device. The protocol has been applied to several implantable infusion pumps and neurostimulators with associated attachments. Experiments were performed using a 1.5‐T whole‐body MR system with parameters selected to approximate the intended clinical and worst case configuration. The devices exhibited moderate magnetic field‐induced deflection and torque but had significant image artifacts. No heating was detected for any of the devices. Pump operation was halted in the magnetic field, but resumed after removed. Exposure to the magnetic field activated some of the neurostimulators.J. Magn. Reson. Imaging 1999;9:596–603.

Dosimetric characterization of a cone-beam O-arm™ imaging system

This study compared patient dose and image quality of a mobile O-arm cone beam imaging system in the 3D scan acquisition mode to those of a 64 slice Computed Tomography (CT) imaging system. The investigation included patient dose, scattered radiation, and image quality measurements. The patient dose was measured using a 0.6 cc Farmer ion chamber and 30 cm long Computed Tomography (CT) head and body polymethylmethacrylate (PMMA) phantoms. The results show that under identical radiographic techniques (kVp, mAs, etc.) and with the same scan length, the O-arm in 3D scan acquisition mode delivers approximately half the radiation dose of a 64 slice CT scanner. Scattered radiation was measured at several locations around the O-arm, at 1 m, 2 m and 3 m distances in 3D CT scan acquisition mode with a RadCal 10 x 5-180 pancake ion chamber using a 30 cm long CT body phantom as the source of scatter. Similar measurements were made in a 64 slice CT scanner. The data demonstrate that scattered radiation from the O-arm to personnel involved in a clinical procedure is comparable to that from a 64 slice CT scanner. Image quality was compared by exposing a CATPHAN phantom to comparable doses in both the O-arm and the CT scanner. The resultant images were then evaluated for modulation transfer function (MTF), high-contrast spatial resolution, and low contrast sensitivity for clinical application purpose. The O-arm shows comparable high contrast to the CT (7 lp/cm vs. 8 lp/cm). The low contrast in the O-arm is not visible due to fixed pattern noise. For image guided surgery applications where the location of a structure is emphasized over a survey of all image details, the O-arm has some advantages due to wide radiation beam coverage and lower patient dose. The image quality of the O-arm needs significant improvement for other clinical applications where high image quality is desired.

The potential for radiation‐induced skin damage in interventional neuroradiological procedures: A review of 522 cases using automated dosimetry

The Food and Drug Administration (FDA) has recommended the monitoring of radiation skin dose to patients during procedures having the potential for radiation damage. Radiologists need information about typical radiation doses during interventional procedures. The skin doses to patients during 522 interventional neuroradiological procedures have been monitored using an automated dosimetry system. Estimated entrance skin doses (ESD) were binned into 0.5 Gy increments and compared to FDA recommended thresholds for inclusion in the patient record. Percentages of procedures exceeding the above mentioned thresholds are presented. In addition, the percentage of dose in each view and the percentage of dose in fluoroscopic and digital angiographic modes are shown. Six percent of embolization procedures and one percent of cerebral angiograms are estimated to have potential for main erythema (ESD>6 Gy). All types of procedures have potential for temporary erythema and exceed the threshold for inclusion in the patient record (ESD> 1 Gy) at the 95% percentile. The types of procedures with most potential for skin damage also have significant percentages of dose in the digital angiographic mode. Thus, monitoring fluoroscopic time alone underestimates the potential for skin injury. On the other hand, combining the doses in the posterior-anterior and lateral views, tends to overestimate the potential for radiation injury.

Health effects of low level radiation: carcinogenesis, teratogenesis, and mutagenesis.

The carcinogenic effects of radiation have been demonstrated at high dose levels. At low dose levels, such as those encountered in medical diagnosis, the magnitude of the effect is more difficult to quantify. Three reasons for this difficulty are (1) the effects in human populations are small compared with the natural incidence of cancer in the populations; (2) it is difficult to transfer results obtained in animal studies to the human experience; and (3) the effects of latency period and plateau increase the complexity of population studies. In spite of these difficulties, epidemiologic studies of human populations exposed to low levels of radiation still play a valuable role in the determination of radiation carcinogenecity. They serve to provide upper estimates of risk and to rule out the appearance of new effects that may be masked by the effects of high doses. While there is evidence for mutagenic effects of radiation in experimental animals, no conclusive human data exist at the present. It is not possible to rule out the presence of genetic effects of radiation in humans, however, because many problems exist with regard to the epidemiologic detection of small effects when the natural incidence is relatively large. In animals, subtle effects (eg, a decrease in the probability of survival from egg to adult) may occur with greater frequency than more dramatic disorders in irradiated populations. However, these types of genetic abnormalities are difficult to quantitate. Current risk estimates are based primarily upon data pertaining to dominant mutations in rodents. Some specific locus studies also permit identification of recessive mutation rates. The embryo and fetus are considered to be at greater risk for adverse effects of radiation than is the adult. This sensitivity was predicted in 1906 by the law of Bergonie and Tribondeau and has been demonstrated in human and animal populations. At high dose levels (above 15 rem), the effects of radiation depend upon the gestational stage at which irradiation occurs. Prior to the second week, the predominant effect is preimplantation death, while during the period of major organogenesis (second to sixth week), growth retardation and CNS abnormalities may be produced. These effects have not been demonstrated with a high degree of statistical significance at low dose levels (below 15 rem) and are not considered to present a serious hazard for patients undergoing radiologic exams.

Building future medical education environments over ATM networks

The educational requirements of our society are changing. It is no longer sufficient to obtain an education at a single point in time and be done; rather, education must be a lifelong process to allow people, particularly those in technical diciplines, to keep up with their constantly changing fields. This is especially true with medical education, as exemplified by the continued training of radiology residents. It has been difficult to provide this training to physicians and other health care practitioners who are spread over a wide geographical area and who cannot travel away from their communities for lenghty training sessions. To meet the needs of this expanding base of students, it is necessary to go beyond the traditional campus setting and bring education to the students.

Radiation dosimetry of intraoperative cone-beam compared with conventional CT for radiofrequency ablation of osteoid osteoma.

BACKGROUND Radiofrequency (RF) ablation is the standard of care for the surgical treatment of non-spinal osteoid osteoma and has greatly reduced morbidity associated with surgical excision. Precise placement of the RF ablation probe is necessary to avoid incomplete ablation. Limiting radiation exposure is especially advantageous in the pediatric population in whom osteoid osteoma frequently occurs. The aim of this study was to compare the radiation dosimetry and clinical outcomes among patients treated with RF ablation using three different localization techniques. METHODS Case-control methods were used to analyze sixty-six cases. Patients were categorized into three treatment groups: (1) intraoperative three-dimensional cone-beam CT (computed tomography) imaging (O-Arm) with surgical navigation (StealthStation S7), (2) intraoperative three-dimensional imaging (O-Arm) only, and (3) radiology suite-based diagnostic CT imaging. Radiation dosimetry and clinical outcome were analyzed with use of the dose-length product and local-relapse-free survival, respectively. RESULTS Mean age was nineteen years for the twenty-three patients in group 1, twenty years for the seven patients in group 2, and nineteen years for the thirty-six patients in group 3. Mean follow-up was fifty-three months. The mean radiation dose for groups 1, 2, and 3 was 446.62, 379.78, and 1058.83 mGy-cm, respectively. Significant (p < 0.05) differences in the radiation dose existed between groups 1 and 3 and between groups 2 and 3, whereas no difference was found between groups 1 and 2. Local-remission-free survival at three years for groups 1, 2, and 3 was 84.7% (95% confidence interval [CI], 64.5% to 100%), 100% (95% CI, 100% to 100%), and 90.7% (95% CI, 80.7% to 100%), respectively. Fifty-eight (92%) of the sixty-three followed patients were asymptomatic at the latest follow-up visit. CONCLUSIONS RF ablation using intraoperative cone-beam CT imaging, with or without surgical navigation, was associated with a significantly lower radiation dose compared with ablation using a radiology suite-based CT technique. Ablation using each of the three imaging techniques was equally effective in treating osteoid osteomas with a similar risk of relapse.

Axial and lateral resolution of rotational intravascular ultrasound: in vitro observations and diagnostic implications

AbstractPurpose: To determine the axial and lateral resolution of a rotating intravascular ultrasound system and the diagnostic implications for the diagnosis of early artherosclerosis. Methods: The resolution of a 20 MHz rotating transducer was tested in a specially designed high-resolution phantom and in five aortic autopsy specimens with varying degrees of early atherosclerosis. Results: The best lateral resolution is at the minimal distance between transducer and object. Measurements in the wire phantom showed this to be better than 0.43 mm. This is less than the axial resolution which is better than 0.13 mm. Decreasing lateral resolution with increasing distance between transducer and object is manifested by arcing and overestimation of the extent of focal atherosclerotic lesions. Conclusion: Axial resolution is significantly better than lateral resolution. Rapid deterioration of lateral resolution affects the diagnostic ability to characterize the extent of early atherosclerosis. Eccentric positioning of the transducer tip, particularly in larger vessels, will therefore influence diagnostic accuracy in vivo.

Radiation exposure risk to the surgeon during operative angiography

Intraoperative angiography has become an essential adjunct to reconstructive vascular surgery. Therefore, radiation exposure and its potential risks to the performing surgeon need to be known. To study this, we designed experimental and clinical tests quantifying the radiation exposure to the surgeon during different intraoperative angiograms. Radiation exposure to various parts of the surgeons body was quantified by thermoluminescence dosimetry. During each exposure a surgeon standing one foot from the x-ray tube received an absorbed dose equivalent to 0.24 to 1.4 millirems, which is about half that of an intraoperative cholangiogram. With 5 000 millirems considered the maximum permissible dose, this would imply that an upper limit of about 3 500 intraoperative angiograms each year (68 each week) could be performed safely. Comparatively, abdominal angiography carried the most significant risk (p = 0.01) and peripheral angiography was the least hazardous. Fluoroscopy increased radiation exposure more than four times that of nonfluoroscopic procedures (p = 0.05). The surgeons extremities received the greatest dose, followed by the eyes and neck, suggesting the need for individual monitoring devices for those parts to be worn by surgeons who perform operative angiograms more frequently than average. Our study indicates that the radiation dose received by the surgeon during operative angiography, especially that of peripheral vessels, is minimal. Operative arteriography is not only a simple and readily available diagnostic tool, but it is quite a safe procedure if applied correctly.

Lossy compression should not be used in certain imaging applications such as chest radiography

Computational techniques are frequently used to compress image data so that transmission and storage requirements are reduced. If the computational techniques result in no loss in image resolution, the technique is referred to as lossless compression. Greater compression of data may yield some loss in spatial or temporal resolution, and is referred to as lossy compression. In some radiologic examinations [e.g., gastrointestinal (GI) studies], some resolution loss may be tolerable, whereas in others (chest examinations and mammography) it conceivably could result in missed pathology. Without lossy compression, however, data requirements can be overwhelming for transmission, storage and retrieval of images such as chest films. The unanswered question, addressed in this Point/Counterpoint issue, is whether some degree of lossy compression can be tolerated in chest radiography.