The use of personal computers in nuclear medicine.

Consolidating personal computers (PCs) with nuclear medicine technology can create high computational power comparable with that produced by vendor-specific computer equipment, and at more affordable prices. The integration of a standard platform and operating system with a large installed base has enabled our department to maintain itself at the cutting edge of technology with minimal expense. Along with the savings from the purchase of PC software and hardware come the added advantage of rapid training of staff with minimal in-house effort, especially given the vast educational support in the general community. The integration of a standard platform and operating system with a large installed base has provided the nuclear medicine department with computational resources once unheard of because of economies of scale. The acceptance and integration of a pervasive, flexible technology into nuclear medicine have shown that state-of-the-art studies can be performed at low cost.

Relationship between lactate and ammonia thresholds in heart transplant patients.

The purpose of this investigation was to study the relationship between both blood ammonia thresholds (AmT) and lactate thresholds (LT) during dynamic exercise in cardiac transplant patients (CTPs). Eleven male patients who had undergone orthotopic cardiac transplantation (age: 54 +/- 11 years, mean +/- SD; height: 165.1 +/- 6.6 cm; body mass: 78.3 +/- 16.1 kg) participated in this study. Each of them performed a bicycle ergometer test (ramp protocol) until volitional fatigue. During each test, gas exchange parameters and ECG responses were determined continuously. In addition, blood lactate and ammonia concentrations were measured every 2 min for determination of both LT and AmT, respectively. Peak values of oxygen uptake (Vo2), respiratory exchange ratio, ventilation, and heart rate averaged 15.9 +/- 3.03 mL.Kg-1.min-1, 1.02 +/- 0.06, 46.69 +/- 5.69 L.min-1, and 124 +/- 16 beats per minute, respectively. However, blood concentrations of lactate and ammonia at peak exercise were 3.7 +/- 0.4 mmol.L-1 and 85.6 +/- 31.7 micrograms.dL-1, respectively. LT and AmT were detected in 8 (72.7% of total) and 9 (81.8% of total) of 11 subjects, respectively. No significant differences were found between mean values of LT and AmT, when both were expressed either as Vo2 (10.01 +/- 1.19 vs 10.5 +/- 2.38 mL.kg-1.min-1, respectively) or as percent Vo2 peak (64.62 +/- 11.362 vs 66.48 +/- 9.19%, respectively). In addition, LT and AmT were significantly correlated (p < 0.05) when both were expressed either as Vo2 (mL.kg-1.min-1) or as percent Vo2 peak (r = 0.70 and r = 0.68, respectively). Our findings suggest that in CTPs, both LT and AmT occur at similar workloads, probably as a result of skeletal muscle alterations associated with chronic deconditioning and immunosuppressive therapy.

Flow determination using computed tomography: application to aortic dissection. Part I.

The CT method of flow determination evaluated in this study was based on the application of contrast enhancement dynamics. In order to characterize flow, such parameters as mean transit time, rise time, peak CT value, curve width and variance, and others were derived from the venoarterial indicator dilution curves using a perfect mixers-in-series model of curve fitting analysis and a bolus injection of contrast medium. The technique was first validated in a steady state phantom model that simulated in vivo conditions of right-sided mixing closely by the introduction of a number of mixers. A series of flows through small tubes was measured. Good correlation was obtained (r = .85). For a fixed number of mixers, the central second moment of the primary peak of the indicator dilution curve or variance decreased with increasing flow and peak CT value increased. Applied to the clinical situation, this method would allow characterization of blood flow using an intravenous bolus of contrast.

Dynamic gadolinium DTPA-enhanced magnetic resonance of intravascular stents.

RATIONALE AND OBJECTIVES: Magnetic resonance contrast enhancement depends on the timing of image acquisition. Human trials have demonstrated efficacy of renal artery stents on salvage of renal function. This study assessed the ability of dynamic gadolinium (Gd)-DTPA administration to demonstrate renal and iliac artery stent patency compared to conventional angiography as the gold standard. METHODS: Seven subjects with eight stents referred for angiography underwent dynamic magnetic resonance studies, all with renal artery stenting. All were examined with conventional angiography and after dynamic Gd-DTPA infusion. Coronal magnetic resonance images were acquired using a GE Signa 1.5 T magnet (fast spoiled gradient echo; echo time = 4.2 ms; repetition time = 68-150 ms; flip angle = 75 degrees) 0 to 600 seconds after 0.1 mmol/Kg Gd-DTPA intravenous bolus injection during sequential breath-hold acquisitions 13 to 32 seconds each. RESULTS: All eight stents were visualized with 100% accurate patency documentation. CONCLUSIONS: Fast spoiled gradient echo magnetic resonance imaging with bolus Gd-DTPA administration can provide adequate time and spatial resolution to demonstrate arterial stent patency.

First-pass evaluation of myocardial output during dipyridamole stress using turbo-FLASH magnetic resonance imaging.

RATIONALE AND OBJECTIVES: This study evaluated the value of dynamically enhanced fast low-angle shot (FLASH) magnetic resonance (MR) imaging in measuring cardiac output with and without dipyridamole pharmacological stress. METHODS: Ten subjects underwent rest and stress MR imaging. Rest images were acquired using electrocardiogram gated MR (turbo-FLASH: repetition time = 6 mseconds; echo time = 12 mseconds; flip angle = 12 degrees, inversion time = 100) 10 to 45 seconds after intravenous bolus of 0.04 mmol/kg gadolinium (Gd)-DTPA using a Siemens 1.0-tesla Magnetom SP. Stress was induced within the MR imaging scanner with 0.56 mg/kg dipyridamole over 4 minutes with stress MR images obtained after a second bolus of Gd-DTPA in exactly the same position and time intervals. Cardiac output was calculated with a least squares error analysis before and after dipyridamole stress for the left and right ventricles in all 10 patients, and comparison was made with cardiac output by Fick dilution technique during cardiac catheterization in seven patients. RESULTS: This MR analysis methodology shows reasonable correlation (r = 0.953) between left ventricular and right ventricular cardiac output with no effect on cardiac output during immediate dipyridamole stress. Fick dilution studies demonstrated a correlation of 0.96. CONCLUSIONS: Turbo-FLASH MR can demonstrate time-activity curves and cardiac output calculations consistent with theoretical predictions.

Incidence of adrenal masses in patients referred for renal artery stenosis screening MR.

RATIONALE AND OBJECTIVES: Prior work has shown the efficacy of magnetic resonance (MR) in renal artery stenosis evaluation. The increasing role of renal artery stenosis in the differential diagnostic evaluation of hypertension raises the question of whether MR should be used as a screening modality. This project evaluated the additional potential benefits of MR by determining the incidence of adrenal masses in this selected population. METHODS: A 2-year retrospective study analysis of patients who failed to respond to antihypertensive medical management and were referred for renal MR for hypertension amassed 77 subjects ranging in age from 18 to 88 years. A masked analysis for adrenal masses was performed on this data set. Magnetic resonance techniques included T2-weighted turbo spin-echo (repetition time [TR] 2000-4000 ms, echo time [TE] 80-100 ms, turbo factor 2-16), T1-weighted spin-echo (TR 200-500 ms, TE 10-30 ms), gradient-echo time-of-flight (TR 26 ms, TE 6.9 ms, 40 degrees flip angle, 2 excitations), and dynamic gadopentetate dimeglumine-enhanced MR angiography (three-dimensional gradient recalled echo, TR 10 ms, TE 3 ms, 40 degrees flip angle, 1 excitation). RESULTS: Thirty-three patients had renal artery disease, 44 had normal renal arteries, and 7 had adrenal masses. Forty-three percent of patients who underwent renal MR had disease of the renal arteries detected, and 9% of patients referred for MR had adrenal masses that would have been missed with scintigraphy and/or angiography, of which 57% were responsible for hypertension. CONCLUSIONS: The ability to evaluate renal artery and adrenal anatomy globally can be useful, as exemplified in the current series, and the adrenals should be examined carefully in any renal MR in a hypertensive patient.

Impact of mild pulmonary hypertension on mortality and pulmonary artery pressure profile after heart transplantation.

BACKGROUND: Pulmonary hypertension is a risk factor for early mortality after transplantation, but the risk threshold is debated. Also, little is known about the evolution of pulmonary circulation after transplantation. The aim of this study was to determine the influence of current risk pulmonary pressure parameters on early post-operative mortality and to assess the time-related changes in pulmonary pressure after surgery. METHODS: One hundred twelve consecutive transplanted patients were studied retrospectively to determine the influence of trans-pulmonary gradient of >12 mm Hg and pulmonary vascular resistance of >2.5 Wood units, at baseline or after vasodilator test, on early mortality. A multivariate analysis was used to study the hemodynamic parameters associated with early mortality. The pulmonary pressures of all surviving patients were studied for up to 3 years after surgery. RESULTS: Early mortality in the groups with and without pulmonary hypertension were 24.4% and 5.6%, respectively (p =.009). The only variable that was independently associated with early mortality was the pulmonary vascular resistance index (odds ratio = 1.459). Mild pulmonary hypertension disappeared 1 year after heart transplantation. CONCLUSIONS: Mild pulmonary hypertension is a risk factor for early postoperative mortality. The hemodynamic parameter most closely associated with early mortality is pulmonary vascular resistance index. The hemodynamic profile of pulmonary circulation after heart transplantation is partially dependent on the level of pulmonary hypertension before transplantation, at least during the first year after surgery.

Strongyloides stercoralis hyperinfection associated with human T cell lymphotropic virus type-1 infection in Peru.

A study was conducted in Lima, Peru to determine if patients with Strongyloides hyperinfection had human T cell lymphotropic virus type-1 (HTLV-I) infection. The study included patients with Strongyloides hyperinfection and a control group consisted of sex- and age-matched asymptomatic healthy individuals whose stools were negative for Strongyloides. A third group included patients with intestinal strongyloidiasis. Sera from each study subject were tested for HTLV-1/2I by an ELISA and Western blot. The HLTV-1 infection rates (85.7%, 18 of 21) were significantly (P < 0.001) associated with Strongyloides hyperinfection compared with the control group (4.7%, 1 of 21). The HTLV-1 rate (10%, 6 of 62) for patients with intestinal strongyloidiasis was significantly (P < 0.001) lower than patients with Strongyloides hyperinfection, but did not differ significantly (P > 0.05) from the control group. The association of HTLV-1 infection was observed among 17 of 19 patients more than 20 years of age and one of two younger patients. None had HTLV-2 infection. In conclusion, Strongyloides hyperinfection among Peruvian patients was highly associated with HTLV-1 infection.

Use of three-dimensional MR angiography for tracking a contrast bolus in the carotid artery.

Contrast-bolus tracking in the carotid bifurcation was accomplished using an MR angiographic technique with a 3D turbo field-echo readout (TR/TE = 6/3, flip angle = 50 degrees) modified by a keyhole scheme. Optimal visibility of the contrast bolus was achieved by digital subtraction from a reference volume. This technique reliably time-resolves the carotid arteries from the jugular veins.

World Wide Web program for optimizing and assessing medical student performance during the radiology clerkship.

RATIONALE AND OBJECTIVES: The purpose of this study was to adapt the technology of the World Wide Web to the teaching and evaluation of medical students participating in the radiology clerkship at our institution. MATERIALS AND METHODS: Teaching modules were placed on a local intranet site. One hundred two student evaluations were conducted online as a standardized, written- and image-based test that was administered both before and after the clerkship. The computer-delivered test consisted of 40 standardized questions that were sorted by category (based on American College of Radiology code criteria) and randomly administered from a pool of 200 potential questions. Scores from before and after the clerkship were analyzed statistically to evaluate the effectiveness of the educational program and the student performance. Student case presentation scoring and clerkship administration tasks were also evaluated both before and after implementation of the modules during the first 12 months of this project (July 1997 to July 1998). RESULTS: A statistically significant (P < .001) improvement in test performance was found in 102 consecutive students, and all 102 students (100%) preferred the digital-testing format. The amount of time needed to tabulate the teacher evaluation, grade the test, and score the oral presentations decreased substantially with the digital system. CONCLUSION: An intranet-based method of evaluating students in an ongoing fashion allows for additional growth in content and ease of use during the radiology clerkship.

Meta analysis of the relationship between tuberous sclerosis complex and renal cell carcinoma.

The association of angiomyolipoma with tuberous sclerosis complex (TSC) patients is well recognised. Some literature has suggested that patients with TSC are at increased risk of renal neoplasm, particularly since angiomyolipomas can be locally invasive and demonstrate tumor like neovascularity on angiography. In an attempt to place in context one case of metastatic renal cell carcinoma in a patient with TSC a meta analysis of the literature was performed. One pediatric patient with TSC and metastatic renal cell carcinoma was evaluated. Reviews and case reports of TSC and renal cell carcinoma and related imaging findings were identified by searching the MEDLINE database, the 'bibliography of reviews' in Index Medicus, personal files and the reference lists from all identified reviews. Individual cases suitable for review in the available literature from 1922 through 1993 comprised the data base. The data base was analysed with the method of proportions and unpaired two-tailed Student's t-test for different populations. A cumulative summary of the literature amassed 107 additional cases from 62 reports over 71 years. Our case is the 17th case, to our knowledge, of renal cell carcinoma in TSC. Analysis of the distribution of characteristics and incidence of; renal cysts, renal cell carcinoma, and lymph node involvement demonstrate no increased risk of renal cell carcinoma in patients with TSC (P = NS). Though anecdotal evidence has suggested a relationship between TSC and renal cell carcinoma, meta analysis of cases of coincident TSC renal complex, cystic changes, angiomyolipoma and renal cell carcinoma implies an identical, though small, risk of malignancy in TSC patients as compared with the normal population.

Chronic cyclosporine-induced nephrotoxiciy in heart transplant patients: long-term benefits of treatment with mycophenolate mofetil and low-dose cyclosporine.

BACKGROUND: Cyclosporine-induced nephropathy is a major limitation in heart transplant patients. Cyclosporine dose reduction may lead to substantial early improvement in renal function. Our aim was to study the long-term benefits of therapy with low doses of cyclosporine plus mycophenolate mofetil in heart transplant patients with drug-induced nephrotoxicity. METHODS: Twenty-five adult heart transplant patients with cyclosporine-related nephrotoxicity (mean posttransplant = 41.7 +/- 25.7 months) were included in the retrospective analysis (22 men, mean age = 58.8 +/- 7.9 years.). Patients were switched from azathioprine to mycophenolate mofetil (1 to 3 g/d), followed by a stepwise reduction in cyclosporine dosage (trough cyclosporine level maintained around 100 ng/mL). Renal function was determined by serial measurements of serum creatinine and glomerular filtration rate at 3-month intervals. RESULTS: With a mean follow-up of 30 +/- 13 months, the baseline creatinine of 2.37 +/- 0.5 mg/dL decreased to 1.59 +/- 0.40 mg/dL (P < .0001). The baseline glomerular filtration rate of 36.77 +/- 10.10 mL/min improved to 54.98 +/- 13.80 mL/min (P < .0001). The cyclosporine level was the unique independent variable associated with renal functional improvement (partial R(2) = 0.4). Within the first 3 months, renal function displayed a rapid improvement after conversion to mycophenolate mofetil (P < .001), reaching a plateau, without further significant improvement over the course of time. CONCLUSIONS: Cyclosporine-induced nephrotoxicity is not a progressive, irreversible disease. Reduction in cyclosporine exposure by addition of mycophenolate mofetil is useful to achieve long-term renal functional improvement, thereby avoiding chronic renal failure. A unique, significant factor associated with this improvement was the reduction in cyclosporine level.

In vivo three-dimensional evaluation of the tracheobronchial tree.

Traditionally computed axial tomography has had limitations in evaluating diseases that affect the tracheobronchial tree because of respiratory-induced artifacts, with the likelihood of missing lesions as a result of misregistration. Spiral computed tomography (CT) differs from conventional CT in that the entire thorax can be rapidly imaged in the axial plane after a single breath-hold. Five patients underwent non-contrast-enhanced volumetric CT, with emphasis on three-dimensional reconstruction, and endoscopic evaluation with pathologic confirmation. In all cases, there was complete corroboration between volumetric CT and endoscopic evaluation. The use of selective thresholds allowed the air within the tracheobronchial tree to be used as a negative contrast agent. Thus with the integration of selective windowing, detailed three-dimensional tracheobronchial anatomy may be elucidated. The absence of respiratory registration artifact due to the single breath-hold technique raises the confidence that three-dimensional and multiplanar images generated from such studies are accurate representations of the pathologic conditions at hand. By the integration of volumetric CT techniques and rapid three-dimensional display of tracheobronchial structures, volumetric CT bronchography becomes practical.

Biliary tree necrosis in transplanted liver detected by spiral CT with three-dimensional reconstruction.

We present a case where spiral computed tomography (CT) with three dimensional reconstruction was able to generate cholangiographic images demonstrating biliary tree necrosis in a transplanted liver. Volumetric CT as a one step diagnostic solution to establish a diagnosis in patients after liver transplantation can expedite appropriate therapy and reduce the number of invasive studies. By the integration of volumetric CT techniques and rapid three-dimensional display of biliary structures, volumetric cholangiography may become practical. Though spatial resolution may prove to be a limiting factor in replacing cholangiography for subtle mural disease, volumetric CT can yield clinically useful information.

MRI isolation of infected renal cyst in autosomal dominant polycystic kidney disease.

The use of gadolinium-enhanced magnetic resonance (MR) to isolate an infected renal cyst in the setting of autosomal dominant polycystic kidney disease (ADPKD) has not been previously described. A case in which T1- and T2-weighted and gadolinium-enhanced MR images were used to identify a single purulent cyst in a patient with ADPKD is herein presented. We suggest that gadolinium-enhanced MR be considered useful in the evaluation of ADPKD patients with suspected infected cyst.

Comparison of spiral CT and conventional CT in 3D visualization of facial trauma: work in progress.

Spiral computed tomography (SCT) differs from conventional CT (CCT) in that regions of the body can be rapidly imaged via continuous scanning. This is accompanied by simultaneous advancement of the patient, thus allowing volumetric data acquisition of up to 60 cm in less than a minute. Thus motion is minimized and slice misregistration is minimized when multiplanar and three dimensional reconstructions are performed. This paper compares the utility of SCT and CCT in facial trauma. A total of six patients were studied with either CCT or SCT of the face after trauma. SCT scans were obtained using a Siemens Somatom Plus-S CT scanner (2 mm thick collimation and 3 mm/sec table feed for 32 s). Three-dimensional (3D) and multiplanar reconstruction images of the facial bones were generated after appropriate thresholds were selected by the radiologist; similar images generated with a CCT (GE quick 9800) were compared using a three point scale with kappa analysis. SCT is able to generate axial and reformatted images of comparable quality to CCT (k = 0.47-0.89) in less than half the time to perform an examination (26 min vs 63 min). SCT can rapidly produce (3D) and multiplanar reformatted images of facial trauma with minimal motion, or misregistration artifact when compared to CCT.

Case report: legionella infected thoracic aortic graft.

A case of a thoracic aortic graft in a patient with Marfan's syndrome infected with legionella is presented. The pathogenesis of graft infection and aspects of examination with aortography, gallium scanning, magnetic resonance imaging (MRI), and spiral volumetric computed tomography (CT) are presented, and the pathophysiology and management of thoracic aortic graft infections is briefly discussed.

Value of spiral CT in hemodynamically stable patients following blunt chest trauma.

INTRODUCTION: Features of spiral CT (SCT)-fast scanning, dynamic injection of contrast allowing optimal vessel opacification, and supplemental multiplanar imaging-promises to provide increased accuracy in the diagnosis of acute and non acute thoracic vascular disease. Recent work demonstrating the cost effective triage of hemodynamically stable patients after blunt chest trauma for angiography based on dynamic CT findings has prompted an investigation into the accuracy of SCT in this clinical setting. METHODS: A retrospective review of all patients seen in the emergency department over the period of one year for aortic, thoracic, or blunt chest trauma evaluation was performed (74 patients) and all SCT scans available were reviewed and data reformatted for optimal delineation of pathology using maximum intensity projection and multiplanar reformation. The accuracy and predictive positive and negative values of SCT were calculated with respect to angiography, surgical, and/or clinical follow up evaluation. RESULTS: Twenty three (31%) patients went directly to angiography owing to mediastinal widening on chest film and hemodynamic instability, of which four were positive and required emergent surgery. Seven hemodynamically stable patients (9%) had noncontrast SCT owing to mediastinal widening on chest film, all of which had angiography with none having great vessel trauma. Fourty four hemodynamically stable patients (60%) had contrast enhanced SCT (ceSCT), of which five (11%) were abnormal and underwent angiography, four of these were positive for aortic damage, one for a subclavian artery laceration. Of the remaining 39 patients who had normal ceSCT; five had angiography, all of which were normal. Of the remaining 34 patients that had normal ceSCT none had adverse outcome on clinical follow-up, minimum of 12 months. CONCLUSION: The predictive positive value for aortic trauma of ceSCT in blunt trauma is 80%, with a predictive negative value of 100%, indicating that it is feasible for SCT to be a first line exam in blunt chest trauma in the future.

MR hysterography using axial long TR imaging with three-dimensional projections of the uterus.

A rapid screening technique for the presentation of uterine cavity anatomy obtained with MR is described. MR hysterographic (MRHG) images were generated and evaluated for uterine cavity abnormalities. Six patients referred for MRI evaluation of the uterus for infertility had an MRI using a pelvic phased array coil with axial 3 mm interleaved fast spin echo images (TR 9000 ms, TE 288 ms with fat saturation) processed using maximum intensity projection algorithms to construct MRHG images. Using the conventional MR sequence as the gold standard the MRHG images were evaluated by two reviewers and accuracy calculated. MRHG took less than 3 min, demonstrated the correct diagnosis in all with a quality score of diagnostic to optimal, and with excellent interobserver agreement (kappa 0.9).

A system for automated procedure documentation.

Quantitative information regarding competency in performing procedures is invaluable in attesting to a house officer's abilities when assessments need to be made. Thus, the means by which procedures, proficiency, and experience can be recorded and organized in an automated fashion need not be any further away than the nearest micro-computer. The procedure documenting system (PDS) automates the documenting of procedures and quantitative information pertaining to these procedures, and shortens the time demanded of the house officer to document procedures from a mean of 5.5 to 1.9 min. This paper is a description of the work done to automate the recording of procedures performed by housestaff at a teaching hospital and the acceptance by housestaff. This computer program takes the specific information and places it into a specialized database so that house officers can have detailed documentation attesting to their proficiency in various procedures. In addition, the program director can access the database to document the quantity of procedures to which an individual house officer has attained competence.