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MRI yields cross-sectional image acquisition in multiple planes with very high contrast resolution. Additionally, in MRI of the breast, evaluation of the entire implant is possible. Not only is MRI very sensitive to loss of implant integrity and rupture, but also MRI can evaluate and characterize adjacent fluid collections or soft-tissue masses. Anatomic relationships of abnormalities and normal structures are well seen. In some situations, MRI may offer clinically relevant information not adequately addressed by other imaging modalities.

Background Recent studies indicate that medication resistant depressed patients can be successfully treated by a series of sessions of High Frequency repetitive Transcranial Magnetic Stimulation (HF-rTMS), delivered on the left dorsolateral prefrontal cortex (DLPFC). However, changes in subjectively experienced mood give only limited insight into the underlying physiological responses. Previous studies in depressed patients, as well as in healthy volunteers, have reported a possible impact of HF-rTMS on the hypothalamic-pituitary-adrenal (HPA) axis. Objective We wanted to evaluate the emotional and neurobiological impact of one session of HF-rTMS applied on the left DLPFC in a sample of unipolar treatment resistant depressed patients of the melancholic subtype. Methods 20 right-handed antidepressant-free depressed patients were studied using a sham-controlled, ‘single’ blind, crossover design. We examined subjective mood changes with Visual Analogue Scales (VAS). To examine HF-rTMS effects on the HPA-axis, we analyzed salivary cortisol levels. Mood assessment and salivary cortisol levels were assessed before and immediately after stimulation. To detect any delayed effects, all measurements were also re-assessed 30 min post HF-rTMS. The left DLPFC was determined under MRI guidance. Results One session of HF-rTMS did not result in any subjectively experienced mood changes. However, salivary cortisol concentrations decreased significantly immediately and 30 min after active HF-rTMS. Conclusions Although one session of HF-rTMS on the left DLPFC did not influence mood subjectively in melancholic unipolar depressed patients, we found support for the hypothesis that a single session has a significant impact on the HPA-axis, as measured by salivary cortisol. Our results may provide more insight into the underlying working mechanisms of HF-rTMS in unipolar melancholic depression, and could add further information about endocrinological functioning in affective disorders.

Magnetic resonance (MR) imaging has proved beneficial in the evaluation of internal derangements of the knee. A limitation to general acceptance of MR imaging of the knee has been availability and cost. The recent introduction of low-field-strength MR imaging has shown promise in decreasing the cost and increasing the availability of this modality. High-resolution (pixel size, 0.7 mm2), three-dimensional Fourier transform (3DFT), thin-section (3.5 mm) imaging performed on a 0.064-T permanent magnet was used to evaluate 117 knees in 114 consecutive patients. The appearance of normal anatomy and internal derangements of the knee at low-field-strength imaging is described. Arthroscopic correlation was available for 28 knees. Findings from low-field-strength MR imaging and arthroscopy agreed in 79% of cases in the determination of meniscal tears. Partial-flip-angle techniques with 3DFT produced thin-section images of the knee of diagnostic quality. The authors conclude that in patients with internal derangements of the knee, low-field-strength (0.064-T) MR imaging may provide useful information.

Previous studies in healthy volunteers reported a possible impact of high frequency repetitive transcranial magnetic stimulation (HF-rTMS) on stress hormones, like cortisol. In this sham-controlled, "single blind", crossover study, we examined whether HF-rTMS had an effect on the hypothalamic-pituitary-adrenal (HPA) axis, by analysing salivary cortisol levels. Two studies were conducted. First, HF-rTMS on the left dorsolateral prefrontal cortex (DLPFC) was performed in 28 young healthy female volunteers. Second, in a comparable, but different group of 26 healthy females, HF-rTMS was performed on the right DLPFC. Salivary cortisol levels were assessed before, immediately after and 30 min after real and sham HF-rTMS. We found no support for the hypothesis that one single session of HF-rTMS on the left or the right DLPFC has an immediate or delayed impact on the HPA-axis, as measured by salivary cortisol. Although we controlled for several methodological problems in HF-rTMS research, the hypothesis that one single session of HF-rTMS on the left or on the right DLPFC can influence the HPA-axis in healthy volunteers was not supported.

OBJECTIVE. We introduce stratification data for three methods (Agatston, volume, mass) obtained from one single patient population.MATERIALS AND METHODS. Measurements in 11,490 individuals scanned from 1999 to 2002 with electron-beam CT were used for this study.RESULTS. Our Agatston score ranges agree reasonably well with the Kondos values except for measurements in patients at the extreme ages, at which we sampled a wider age range and consequently had different biases of averages. Neither method is preferable because except for a small percentage of individuals near the dividing lines, stratification is the same for the three methods. When we matched them against a known “lesion” phantom, the Agatston and volume scores behave nonlinearly, and the latter grossly overestimates volume. The mass method is linear except for lesions near the edge of detectability and matches known volumes to within a small percentage.CONCLUSION. We provide validated risk stratification data for use with mass scoring methods.

With the introduction of direct digital radiography into clinical practice, there are opportunities to provide faster and more reliable ways of performing traditional radiological tasks. A technique was developed for evaluating and measuring scoliosis, which involves the computerized stitching of a radiograph of the thoracic spine with a radiograph of the lumbar spine. A technique is provided for real-time, graphic feedback during the stitching process, as well as during calculation and display of the Cobb angle to ensure accuracy. Initial data indicates an accuracy within 1 to 2 degrees. The time required to stitch the two images and measure the Cobb angle is on the average of 5 minutes per case. Using computerized techniques of image stitching and angle calculation, with real-time graphical feedback, the task of scoliosis evaluation is more accurate, less time consuming, and prone to fewer human errors. The requirement for special film cassettes is also eliminated.

One-hundred and nineteen implants were imaged in an open-sided low-field magnetic resonance imaging system. Thirty-four of these implants were removed, and postoperative reports were made available. We found a variety of signs associated with the implants, including internal structures, loss of saline in double-lumen implants, intracapsular and extracapsular fluid accumulations, signal dropout regions most likely associated with calcifications, and debris and fluid in the silicone, as well as degradation of the silicone, disruptions of the capsule and bulging, and extracapsular silicone. Conclusions of intact versus ruptured were made on the basis of these findings and found to be confirmed in 32 of 34 cases, with 1 false-positive and 1 false-negative result. Based on MRI criteria for a broad sample of the population, 27 percent of the implants were considered ruptured.

In principle, tomographic imaging of breast implants provides the information needed to compute implant volume. We have investigated the reliability of this measurement as a means of diagnosing the loss of gel from the implant. We find that measurement errors, postimplantation changes of the implant, uncertainties in the patients' records, and lack of knowledge of the implant temperature in the body can lead to significant discrepancies, making this measurement unreliable as a diagnostic tool.

Magnetic resonance imaging (MRI) offers a unique and extraordinary window into the body. Since 1983 the growth and acceptance of this modality as a diagnostic tool has been prodigious, and the enthusiasm with which it is received still grows. The original uses were centered on head imaging, and have since expanded to spine and extremities. Some acceptance is now being seen for body imaging, more for central portions of the chest and in the pelvis than in the abdomen. The routine use of MRI for cardiovascular work is generally limited to large centers. Because of the patient demand for MRI, and because of the desire to obtain revenue from the units, MRI has not been fully exploited in areas where the primary payoff is a contribution towards understanding disease processes. For this latter purpose, one of the most important characteristics of MRI is that it is non-invasive, and therefore ideally suited for both cross-sectional and longitudinal studies. There is an obvious match between MRI and the needs of those who aim to understand the evolution of the human atherosclerotic plaque.

Nuclear magnetic resonance (NMR) images of live rats with sterile and pyogenic abscesses, hematomas, and various implanted and spontaneous neoplasms demonstrated good contrast differentiation between pathologic and surrounding normal tissues. This differentiation was maximal when both the T1 and T2 tissue relaxation times were used as criteria. Neoplasms have a broad range of T1 and T2 values and may be confused with abscesses or hematomas. Tissue rate constants (1/T1 and 1/T2) are mainly dependent on total water content, the exception being fat, which has a 1/T2 value much shorter than that expected on the basis of water content alone.

Advances in technology make it possible to extend the range of physical and chemical tissue parameters used for formation of images. This in turn adds to the capabilities to diagnose disease and assess its extent. Quantitative improvements in instrumentation augment the fidelity with which the imaging is performed, and at a certain point provide a quantum jump in diagnostic capability. We discuss recent technological advances in digital radiography, NMR and nuclear medicine imaging that demonstrate these effects.

The Fab fragments of antibodies against cell-type-specific surface antigens of mouse mammary epithelial cells (MME-antigens) were used to localize mammary tumors successfully. The radioiodine-labeled anti-MME (Fab) was injected into mice carrying simulated mammary metastases, and after 24 hours the amount of label per gram of excised tissue was several times greater in the tumor than in liver, brain, lung, or muscle. Kidney showed considerable accumulation of label but this appeared to be nonspecific. Kinetic studies revealed a rapid elimination of labeled Fab in the urine with only 1% of the injected dose remaining in the entire blood pool after 24 hours. Wit a high-purity germanium camera, mammary tumors were clearly located ty the /sup 131/I-labeled anti-MME (Fab), and normalization to /sup 99m/Tc-pertechnetate distribution in the animal increased the specificity. The density of /sup 131/I-label was fourfold greater over the mammary tumor than over comparable areas of the mouse. No accumulation of /sup 131/I-anti-MME (Fab) was observed in nonmammary tumors nor in mammary tumors when labeled nonspecific Fab was used. An analogous system using an antihuman mammary epithelial antiserum is being developed for localization of breast metastases in humans.

A study of 24 rats implanted in the hind leg with mammary adenocarcinomas and five sham-implanted rats, followed from the second to the eight week postimplantation, showed nuclear magnetic resonance imaging capable of detecting all the tumors without yielding any false-positives in the control rats. The T1 relaxation time of tumors overlapped that of muscle, and the T2 times overlapped fat, but the combination was unique when comparing tumors to muscle and fat. Necrotic regions of the tumor and the bladder contents tended to have very long T1 and T2 relaxation times. The difference in relaxation time between tumors and muscle could be accounted for in terms of water content, which was approximately 8% higher for the tumors. The study corroborates data from previous studies indicating that NMR imaging is a highly sensitive modality, although T1 and T2 times are not exclusive indicators of malignancy.

Fibrosarcoma tumor cells were implanted in the hind legs of 25 rats and studied from the first to the sixth week postimplantation. Nuclear magnetic resonance imaging detected all tumors and did not yield any false-positives in five control rats. The T1 relaxation values of tumors overlapped those of muscle, and the T2 values overlapped those of fat, but the combination of the two values allowed discrimination of each of the three tissues with no overlap. The difference in relaxation time between tumor and muscle could be accounted for on the basis of water content, which was approximately 14% higher in the tumors. This study confirms data from previous studies suggesting that nuclear magnetic resonance imaging is a highly sensitive modality, but that T1 and T2 values are not specific for individual pathologic conditions.

A multiwire proportional chamber positron camera consisting of four 48 × 48 cm2 detectors linked to a small digital computer has been designed, constructed, and characterized. Initial clinical application to brain imaging using 68Ga DTPA in 10 patients with brain tumors is described. Tomographic image reconstruction is accomplished by an algorithm determining the intersection of the annihilation photon paths in planes of interest. Final image processing utilizes uniformity correction, simple thresholding, and smoothing. The positron brain images were compared to conventional scintillation brain scans and x-ray computerized axial tomograms (CAT) in each case. The positron studies have shown significant mitigation of confusing superficial activity resulting from craniotomy in comparison to conventional brain scans. Central necrosis of lesions observed in the positron images, but not in the conventional scans, has been confirmed in CAT. Modifications of the camera are being implemented to improve image quality, and these changes combined with the tomography inherent in the positron scans are anticipated to result in images superior in information content to conventional brain scans.

Gated magnetic resonance (MR) imaging was used to evaluate central cardiovascular anatomy in 172 subjects, 31 of whom were healthy volunteers. Using the spin-echo technique, images of diagnostic quality were obtained in 93% of cases with TE = 28 msec and in 65% of cases with TE = 56 msec. Transverse multisection sequences encompassing most of the left ventricle required approximately 6-8 minutes. Corroborative studies were available in 134 of 141 patients who had cardiovascular disease; two dimensional echocardiograms and angiography in 133 and 100 patients, respectively. Gated MR demonstrated the wall thinning and complications caused by prior myocardial infarctions and high signal intensity of the myocardium at the site of acute myocardial infarctions. MR accurately demonstrated anatomic abnormalities owing to hypertrophic and congestive cardiomyopathies, congenital abnormalities of the heart and great vessels, rheumatic heart disease, pulmonary hypertension, and cardiac and paracardiac masses. Depiction of cardiovascular anatomy and pathoanatomy was attained without the use of any contrast media. Consequently, gated MR is an effective technique for cardiac diagnosis. The short time required for tomographic examination of the entire heart using the multisection technique renders this a practical cardiac imaging modality.

Principal component analysis (PCA), a common tool from multivariate statistical analysis, has been implemented into the computer display system of a MR imaging device. PCA allows the calculation of images in which the information in a defined region of interest inherent in the basic acquired images is condensed. PCA image calculation has been applied to acquired MR studies of 13 patients with brain lesions. The appearance of the brain lesions on the resultant PCA images was scored in comparison to the acquired images before and after administration of Gd-DTPA as well as to other calculated images including T1, T2, hydrogen density, and contrast-optimized images. The conspicuity of a lesion and the number of distinguishable components within a lesion were slightly superior on PCA than on the acquired images. PCA is an analytical tool for MR imaging that should be helpful in revealing information that is inherent in, but not readily visible on, standard acquired MR images.

Whole body nuclear magnetic resonance (NMR) imaging of the cardiovascular system was carried out in early clinical trials in 244 volunteers and patients using a 3.5 KGauss (0.35 T) unit. The spin echo technique with multiple imaging parameters was used. Blood vessels were clearly discriminated from solid organs and lesions because little or no intraluminal signal is seen with laminar blood flow at normal velocities, whereas a more intense image is generated by solid organs. Characteristic flow signals were observed in normal patients and were accentuated by varying the imaging parameters. Cardiac chambers were well delineated in some patients on nongated images. In one case, internal topography of the ventricles was exquisitely displayed on a gated image. Intraluminal pathology, such as dissection of the aorta, aneurysms of the aorta and left ventricle, and aortic atheroma, was clearly demonstrated. Patency of coronary arterial bypass grafts was shown. Abnormal flow patterns due to slow or turbulent flow were accentuated on images using the second spin echo. This preliminary experience indicates the considerable potential of NMR imaging in the evaluation of cardiovascular diseases.

The availability of semiconductor detectors, principally High Purity Germanium, permits consideration of new generations of nuclear medicine imaging devices. These are characterized by excellent spatial resolution and by simultaneous multiple radioisotope imaging capabilities. The technology and some of its resultant benefits are presented here.

A programme was written to detect flow in a sequence of MR images and to construct 3-D vessel maps from the detected flow regions. Reduction in first echo intensity and prolongation of calculated T2 value were used as flow-detection criteria. The programme was used to image the aorta in 6 patients with abdominal aortic aneurysm and 5 patients with aortic dissection. Results were compared with contrast angiography in 9 cases and X-ray CT in 2. The images obtained by the two techniques were comparable in 9 cases. In 2 cases of aortic dissection, where flow in the false lumen was slow, the false lumen could not be demonstrated by angiography, but was clearly seen in the reconstructed MR images.

The unique properties of magnetic resonance imaging result in the potential to differentiate various components of the diseased arterial wall. In this article four cases are presented in which magnetic resonance imaging showed mural aortic thrombus and its anatomic relationship to the visceral and renal arteries. Once thrombus is identified and localized specific operative strategies can be undertaken to prevent recurrent embolic events and/or avoid perioperative thromboembolic complications. (J Vasc Surg 1989;9:801–5.)

MRI is a powerful diagnostic modality of expanding availability. Equipment and installation amount to nearly $2M per site. An important component of diagnostic efficacy is not just equipment costs but also replacement costs, which for x-ray CT amount to 14-20% of the purchase cost per year; and in the early years of that technology reached 30-50%. We show how design choices made during the R&D stages of MRI development have allowed us to improve system performance parameters such as data reconstruction, archiving and display speeds, computational capabilities, operator interfaces, imaging sequence flexibility and signal-to-noise levels. Over the last four years these improvements have been made at a retrofit cost well below our target of 6-7% of the purchase price per year.

The capability of magnetic resonance (MR) imaging for detecting aortic, iliac, and femoral stenoses and occlusions was evaluated. Multisection spin-echo studies at 0.35 tesla were obtained of the infrarenal aorta to the femoral bifurcation in 24 patients, all of whom had undergone intraarterial angiography within 14 days of imaging. Transaxial MR images were compared with the angiograms. Arterial stenoses and occlusions in these vessels detected by MR imaging correlated with angiographic findings in 91% of the instances. Protrusional atherosclerotic plaques and occlusions and stenoses in the aortoiliac region were demonstrated accurately on MR images; complications of previous vascular surgery, such as aneurysms at sites of previous anastomoses or endarterectomy, were also identified. Due to the limited spatial resolution, MR images failed to demonstrate some femoral stenoses. MR imaging may be used for evaluation of aortoiliac vascular disease and for follow-up study after surgical revascularization. However, the limited spatial resolution, noncomposite display of the aortoiliofemoral circulation, and lack of evaluation of peripheral runoff provided by current MR imaging techniques militate against its replacing angiography prior to vascular intervention.

From forty-four cases in the world's literature and one case of our own, diagnostic criteria have been adduced for the stiff-man syndrome in the original sense of Moersch and Woltman [1]. A unique pattern of tonic muscle rigidity emerges, based on clinical and electromyographic findings and objective effects of neuromuscular blocking agents monitored by the electromyograph. These criteria are utilized to establish the validity or probable validity of thirty-four of the forty-five cases and to reject eleven which appear to represent neuraxis disease, myopathy, chronic recurrent tetanus, fibrosis replacement of muscle of obscure origin and other conditions. A tentative hypothesis is formulated to account for the state of tonic muscle rigidity of stiff-man syndrome. Persistent extrafusal (α-neurone) muscle contractility is probably maintained by abnormal activity of the γ-motor system, itself possibly subjected to a drive from suprasegmental regions. Painful spasm is due to further intensification of muscle contraction triggered by new trains of enteroceptive, exteroceptive and emotional stimuli directly or indirectly influencing the hyperexcitable α-neurone system. Metabolic factors may also be implicated, as suggested by the presence of a nonglucose reducing substance in the urine and a rise in inorganic serum phosphorus during glycogen deposition. These metabolic deviations and the heightened drive of the γ-motor system need further clarification.

The replacement of conventional clinical techniques and the development of new techniques using solid state detectors are discussed. Work presented here includes a simplified (geometry and counting-time independent) method for in-vitro iodine and bromine determinations, in-vivo iodine measurements through a tissue absorption correction based on the ratio of. K? to Ks radiation, cardiac output studies, and evaluation of absorptive characteristics of cerebral ventricles.

The excessive induction of hepatic delta-aminolevulinic acid synthetase in rats after the administration of porphyria-inducing compounds is prevented by prior treatment with phenobarbital. Studies in vivo and in vitro indicate that phenobarbital prevents the induction of chemical porphyria by increasing the rate of detoxification of inducers by way of drug-metabolizing enzymes of the hepatic endoplasmic reticulum.

Twenty normal subjects and ten patients with pericardial abnormalities underwent ECG-gated magnetic resonance (MR) imaging of the thorax using a 0.35-tesla superconducting system. The patients with pericardial abnormalities were also evaluated with serial chest radiographs, ultrasound, computed tomography, and/or angiography. ECG gating was necessary to identify the normal pericardium, which was visualized as a 1- to 2-mm-wide curvilinear structure of low signal intensity. Pericardial thickening in constrictive pericarditis was clearly delineated on gated MR images. Pericardial inflammation caused a marked increase in signal intensity as well as thickening of the pericardium. Pericardial effusions and pericardial adhesions were also demonstrated. A simple pericardial cyst and a complex pericardial mass were identified and differentiated from pericardial fat and diaphragmatic eventration. MR appears to be an important modality for the evaluation of pericardial disease.

A preliminary study of the relation between food intake and intensity of gallbladder bile on nuclear magnetic resonance (NMR) images was made. Twelve subjects (seven volunteers, five patients) were imaged following a minimum of 14 hours of fasting. Six of seven volunteers were reimaged one hour after stimulation by either a fatty meal or an alcoholic beverage. An additional seven patients were imaged two hours after a hospital breakfast. It was found that concentrated bile emits a high-intensity spin echo signal (SE), while hepatic bile in the gallbladder produces a low-intensity SE signal. Following ingestion of cholecystogogue, dilute hepatic bile settles on top of the concentrated bile, each emitting SE signals of different intensity. The average T1 value of concentrated bile was 594 msec, while the T1 value of dilute hepatic bile was 2,646 msec. The average T2 values were 104 msec for concentrated bile and 126 msec for dilute bile. The most likely cause for the different SE intensities of bile is the higher water content, and therefore longer T1 and T2 relaxation times, of hepatic bile. It is suggested that NMR imaging has the ability to provide physiological information about the gallbladder and that it may prove to be a simple and safe clinical test of gallbladder function.

Longitudinal vascular structures are difficult to observe on the standard abdominal transaxial magnetic resonance (MR) image sections. To display the information in a three-dimensional reconstruction, an algorithm was written to identify blood flow in a series of transaxial MR sections and was applied to reconstructing images of the aorta and iliac arteries in 12 patients with aortic aneurysm, dissection, or aortoiliac atherosclerosis. Results were validated by angiography. In all patients, the outline of the flow channel in the reconstructed image followed closely the outline of the lumen on angiograms. In aortic dissection, the MR images showed the two lumens more completely than did the angiograms, and in atherosclerosis, sites of vascular stenosis were correctly identified on MR images. The technique is valuable in providing anatomic information as well as functional information on cross-sectional areas and relative flow velocities.

A mouse monoclonal antibody (BLMRL-HMFG-Mc5) prepared against a defined cell surface antigen of human mammary epithelial cells, non-penetrating glycoprotein (NPGP), was used in imaging and distribution studies in athymic nude mice grafted with human breast tumors. For in vivo tissue distribution studies, 125I-labeled monoclonal antibody was injected into nude mice carrying simulated metastases of human tumors (breast and colon carcinomas). After 22-24 hr the amount of radioactivity per gram of tissue was 3-4 times higher in the breast tumor than in liver, brain, lung, muscle, or spleen. In contrast, colon carcinoma tissue, grafted and treated likewise, did not show higher accumulation of radioactivity relative to other tissues. At 4 days, the incorporation in breast tumors remained almost as high, while the circulating radioactive tracer and the incorporation in tissues other than breast had fallen significantly. In tumor imaging studies, breast tumor masses as small as 4 mm in diameter were clearly localized on a whole body scan using 131I-labeled BLMRL-HMFG-Mc5 antibodies with a High-Purity germanium gamma camera. Normalization of 131I-distribution to that of 99mTc-pertechnetate increased the specificity of this imaging methodology. The quantitative density of 131I-label was 2-3 fold higher over the breast tumor than over comparable areas of the mouse. No positive localization images were obtained for similar implants of colon and lung carcinomas or melanomas after injections of 131I-labeled BLMRL-HMFG-Mc5. Localization of human breast tumors in this model can be achieved with 131I-labeled anti-breast epithelial monoclonal antibodies.

The noninvasive quantification of pulmonary edema could be of importance in patient management. We have developed a portable Compton-scatter densitometer capable of measuring density in the range of 0.1-1 g/cm3 independently of the chest wall. Change in lung density was investigated in 19 dogs with pulmonary edema induced by a combination of raised left atrial pressure and hemodilution. The increase in lung density correlated with the postmortem assessment of lung water (r = 0.862, p less than 0.01) and with hemodynamic indicators of pulmonary edema (r = 0.749, p less than 0.01). Subtracting the intravascular component of lung density did not improve the correlation with postmortem lung water (r = 0.850, p less than 0.01). The measurement of absolute lung density by a Compton-scatter technique may be a potentially useful method of quantifying pulmonary edema.

Nuclear magnetic resonance (NMR) images of the thorax were obtained in ten normal volunteers, nine patients with advanced bronchogenic carcinoma, and three patients with benign thoracic abnormalities. In normal volunteers, mediastinal and hilar structures were seen with equal frequency on NMR images and computed tomographic scans. The hila were especially well displayed on spin-echo images. Spin-echo images showed mediastinal invasion by tumor, vascular and bronchial compression and invasion, and hilar and mediastinal adenopathy. Tumor and benign abnormalities could be separated from mediastinal and hilar fat because of their longer T1 times. Lung masses and nodules as small as 1.5 cm could be seen on the spin-echo images. NMR imaging shows promise for assessment of benign and malignant mediastinal, hilar, and lung abnormalities.

Technology is providing exciting new ways to diagnose and characterize disease in a non-invasive manner. The decrease in morbidity and mortality that is realized by substituting pneumoencephalography and cerebral angiography by x-ray computed tomography (CT) and brain radionuclide imaging, or coronary angiography by radionuclide ventriculography and perfusion studies, cannot be easily quantitated by costeffectiveness studies. The dollar value of peace of mind, patient dignity and comfort, avoidance of blindness or loss of limb, stroke, etc., cannot be derived from system analysis.

Magnetic resonance imaging (MRI) generates a series of cross-sections, or slices, of the human body. The advantage of tomographic images over planar images such as those of standard x-rays is that overlap is avoided. The disadvantage is that the planar view is unfamiliar to most people, and to make use of the information in the images it is often necessary to study many slices and to visualize mentally features in three dimensions.

A low-cost portable non-invasive densitometer is described. While the present system is optimized for lung densitometry, similar configurations can be used for bone densitometry and in industrial applications.

Cardiac anatomy was defined by gated nuclear magnetic resonance (NMR) imaging at a magnetic field strength of 3.5 kGauss in eight normal subjects and 10 patients with chronic myocardial infarctions. Multisectional imaging was performed with the spin-echo technique and encompassed most of the left ventricle in an imaging time of 5 to 12 min. In all subjects internal cardiac structure was well delineated without the use of any type of contrast medium. The myocardial wall-blood interface was sharply defined, resulting in visualization of trabeculations, papillary muscle, and chordal structures in both ventricles. In patients with ischemic heart disease, the extent of postinfarctional wall thinning, aneurysms, and mural thrombi were depicted on NMR images. Images obtained with the second spin-echo (delay time = 56 msec) demonstrated high signal intensity in regions of the left ventricular chamber adjacent to the site of aneurysms or infarctions; this finding suggested stasis of blood in a region of akinesis or dyskinesis. The results of this study show that gated NMR is feasible as a technique for imaging the human heart and is capable of demonstrating a variety of left ventricular abnormalities associated with chronic myocardial infarction. NMR is a completely noninvasive technique for clinical imaging of the cardiovascular system.

In a patient with hereditary coproporphyria, increased enzymatic synthesis of δ-aminolevulinic acid (ALA) in the liver contributed to the increased excretion of porphyrins and their precursors. A similar enzymatic abnormality has been found in acute intermittent porphyria. By contrast, in a patient with porphyria cutanea tarda, despite massive porphyrinuria, hepatic ALA synthetase was not detectably elevated. Additional experimental data indicate that heme participates in the feedback regulation of ALA synthetase. Three possible hypotheses describe the defective site of porphyrin biosynthesis in the hepatic porphyrias: a primary increase in ALA synthetase activity; partial blocks in heme biosynthesis; or diversion of heme from its role in the feedback regulation of ALA synthetase.