Electron-beam computed tomography in the assessment of coronary artery disease after heart transplantation.

BACKGROUND: Our aim was to compare the electron-beam CT (EBCT) features of coronary arteries in heart transplant recipients with those of biplane coronary angiography and intracoronary ultrasound (ICUS). METHODS AND RESULTS: We examined 112 heart transplant recipients (25 female; age, 17 to 69 years; median, 52 years) 1 to 153 months (median, 46 months) after surgery by EBCT to detect coronary artery calcifications. Calcifications were quantified by the Agatston scoring system. EBCT scores were compared with coronary angiography in all patients and ICUS of the left anterior descending coronary artery (LAD) in 100 patients. Coronary artery calcifications were found in 84 patients (75%). Angiographically, 16 patients displayed >50% coronary artery stenoses, all of whom had some degree of coronary artery calcification and only 1 of whom had a score of <55 (P<0.0001). With this threshold, EBCT had a sensitivity of 94%, a specificity of 79%, a positive predictive value of 43%, and a negative predictive value of 99% for detecting stenosis. ICUS confirmed the presence of calcified plaques in all patients with an LAD score >9. EBCT total calcium score was associated with the degree of intimal proliferation in that patients without ICUS features of allograft vasculopathy had a median score of 0 (25th percentile, 0; 75th percentile, 0), whereas patients with Stanford class IV vasculopathy had a median score of 41 (9 to 98, P<0.0001). CONCLUSIONS: EBCT is a promising noninvasive test for the detection of coronary heart disease in cardiac transplant recipients.

[Potential advantages of the MRI for the radiofrequency ablation of liver tumors]. / Potenzial der MRT für die Radiofrequenzablation von Lebertumoren.

PURPOSE: To present first results of radiofrequency ablation of liver tumors using a new MR compatible applicator. MATERIALS AND METHODS: We performed 37 interventions in 20 patients (mean age 58.6 years) with primary intrahepatic malignancies or metastases: colorectal carcinoma n = 6, hepatocellular carcinoma n = 3, pancreatic carcinoma n = 4, sarcoma n = 2, cholangiocellular carcinoma n = 1, carcinoma of the tonsil n = 1, breast carcinoma n = 1, gastric carcinoma n = 1, and gastrointestinal stroma tumor n = 1. Interventions were performed under CT-guidance with CT fluoroscopy (n = 32) and under MR-guidance (n = 5) using fast T1-weighted sequences in breath-hold technique. RFA was performed with the RF-generator (150 W) under local anesthesia and sedation using MR compatible applicators (Starburst XL, Rita Medical Systems, USA) together with the appropriate Soft Tissue Introducer System. Intra-interventional control was performed with intrahepatically or intralesionally placed introducer system or applicator. MRI was performed with plain breath-triggered T2-weighted turbo spin echo sequences (TSE T2) with fat saturation. RESULTS: All interventions were performed without major events. The mean diameter of induced coagulation was 4.0 (+/- 0.7) cm. Repositioning was necessary in 8 interventions (21 %) after detection of residual tumor on an intra-interventional MRI. After a mean follow-up of 6.5 (+/- 1.2) months, the local tumor control rate was 92 %. CONCLUSION: MR-compatible RF applicators offer the opportunity for intra-interventional detection of residual tumor during RF ablations by use of sensitive MRI sequences. These procedures may lead to a higher confidence in tumour ablation and may reduce the number of re-interventions and local recurrences of intrahepatic tumors.

Role of high-resolution magnetic resonance imaging for differentiating melanin-containing skin tumors.

RATIONALE AND OBJECTIVES: The aim of the study was to evaluate the use of high resolution magnetic resonance imaging (MRI) for differentiation of melanin-containing skin tumors. METHODS: Twenty-seven melanocytic nevi and 18 malignant melanomas were examined by high resolution MRI. Signal intensities and signal-to-noise (SNR) and contrast-to-noise ratios (CNR) of the tumors were determined in enhanced (T1, T2, water-suppression, and fat-suppression sequences) and contrast-enhanced images (T1 and fat-suppression sequences). The differences were tested for significance by a Wilcoxon test. RESULTS: Malignant melanomas differed from melanocytic nevi in that they displayed a higher SNR in T2-weight and unenhanced and contrast-enhanced fat-suppression scan. Malignant melanomas exhibited a higher CNR than did benign lesions in unenhanced and contrast-enhanced fat-suppression sequences with dermis as reference tissue (P < 0.05) and in enhanced fat-suppression sequences with subcutis as reference tissue (P < 0.05). CONCLUSIONS: The usefulness of SNR and CNR analysis on MRI for the differentiation of malignant skin tumors from benign skin tumors of the melanin-containing system is limited. Clinical and histologic examinations are, further, the important step in evaluation of melanin-containing skin tumors.

Keratinization and necrosis. Morphologic aspects of lymphatic metastases in ultrasound.

RATIONALE AND OBJECTIVE: The authors performed a retrospective study in ultrasound to investigate new aspects in the sonomorphology of lymph node metastases of the neck. In this study, it could be demonstrated the first time that the histologic characteristics of the metastases determine the sonographic appearance. In addition to criteria such as the longitudinal/ transversal quotient, sonomorphology could support a more precise differential diagnosis of neck lymph nodes. METHODS: In 105 of 145 patients with histologically proved head and neck carcinomas, 187 lymph node metastases were detected by ultrasound. Sonomorphology was compared with the corresponding histology. RESULTS: Five sonomorphologic groups could be differentiated. (1) Thirty-one percent of the metastases were homogenous. (2) Concerning the more complex morphology of lymph node metastases in ultrasound, echolucent forms could be differentiated from echogenic textures: low- or nondifferentiated and nonkeratinizing metastases appeared echolucent and cyst-like, with dorsal signal amplification. (3) Nonkeratinizing lymphomas with necrosis showed single or multiple echolucent intranodal lesions. (4) In correlation with an increasing keratinization, the echogenecity of the lymph nodes increased and intranodal echogenic inclusions appeared. (5) An extended keratinization correlated with a central echogenecity. CONCLUSIONS: The morphologic assessment of lymph nodes in ultrasound allows for primary histologic and prognostic evaluation of lymph node metastases.

Fourier phase mapping of the human heart. The use of spatial modulation of magnetization cine magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Fourier phase mapping of cine cardiac magnetic resonance (MR) imaging offers noninvasive analysis of temporal cardiac activation patterns. The aim of our investigation was to extend this analysis to intramyocardial dynamics. METHODS: A fast-imaging with steady-state precision (FISP) two-dimensional gradient echo spatial modulation of magnetization (SPAMM) sequence and a segmented two-dimensional FISP-SPAMM sequence were applied to acquire cine MR images of the complete cardiac cycle on a 1.5-tesla imager. Signal intensity data were submitted to pixel-wise Fourier phase analysis. Color-encoded amplitude and phase maps were displayed for visual analysis. RESULTS: Using the unsegmented SPAMM two-dimensional FISP sequence, a more consistent tag-to-myocardium contrast and a higher number of cardiac phases was achieved than by using the segmented version of this sequence. The typical tag displacement reflected complex intramyocardial dynamics, including rotation. Phase mapping displayed a pattern of contraction consistent with electrophysiologic concepts of cardiac activation. In contrast, the segmented sequence did not reflect any differences in the onset of cardiac contraction, although tag displacement was apparent with this sequence as well. CONCLUSIONS. Fourier phase mapping of cardiac MR imaging tagging studies allows for noninvasive analysis of intramyocardial activation patterns. A temporal resolution of 50 mseconds per image at a heart rate of 75 beats per minute allows for an assessment of spatial differences in the onset of myocardial activation.

Hemodynamic tolerance of intravascular contrast agents for magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Intravascular contrast agents for magnetic resonance imaging (MRI) facilitate the quantification of tissue perfusion. The authors determined the hemodynamic tolerance of these agents. METHODS: Doses of 0.05, 0.15, and 0.45 mmol/kg of the polymeric intravascular contrast agent gadolinium-DTPA-polylysine, and di-nitrobenzyl-gadolinium-DTPA, a non-polymeric intravascular contrast agent with high protein binding, and gadolinium-DTPA dimeglumine, a paramagnetic contrast agent with extracellular distribution, were injected into 18 normal male rats as a peripheral intravenous bolus. Systolic, diastolic, and mean blood pressure, left ventricular end-diastolic and developed pressure, positive rate of pressure change (+dP/dt), dP/dt, the rate-pressure product, and heart rate were recorded during a period of 20 minutes. Hemodynamic effects were established by analysis of variance for repeated measurements. RESULTS: There was a transient increase of all blood pressure parameters and contractility for Gd-DTPA-polylysine at the dose of 0.45 mmol/kg only. Di-nitrobenzyl-Gd-DTPA increased blood pressure parameters at 0.45 mmol/kg only. At doses of 0.05 and 0.15 mmol/kg, no significant hemodynamic effects were observed. CONCLUSIONS: The authors conclude that Gd-DTPA-polylysine is hemodynamically safe at doses to 0.15 mmol/kg and acts like a plasma expander at higher doses after peripheral bolus injection in normal rats. Additional investigations are indicated to elucidate the mechanism of a nonsignificant and satiable transient hemodynamic depression after injection of 0.05 mmol/kg DNB-Gd-DTPA.

Differences in predominant enhancement mechanisms of superparamagnetic iron oxide and ultrasmall superparamagnetic iron oxide for contrast-enhanced portal magnetic resonance angiography. Preliminary results of an animal study original investigation.

RATIONALE AND OBJECTIVES: To determine the effect of particle size of superparamagnetic iron oxide (SPIO) contrast agents on magnetic resonance angiography of the portal venous system. METHODS: We studied eight beagle dogs by a T1-weighted 3D turbo-gradient echo magnetic resonance (MR) angiography sequence (TE 4 milliseconds, TR 11 milliseconds, flip angle 25 degrees, coronal imaging plane) before and after administration of either Resovist (SHU555A), a superparamagnetic iron oxide contrast agent with a mean particle size of 60 nm and a relaxivity ratio R2/R1 of approximately 7, or a new ultrasmall superparamagnetic iron oxide (USPIO) contrast agent with a mean particle size of approximately 20 nm and a R2/R1 ratio of approximately 2. Images were acquired on a 1.5-T MR body scanner. Both agents were injected as a peripheral bolus of 40 mumol Fe/kg body weight. Repeated scans were acquired before, immediately after, and 10, 20, 30, and 40 minutes after administration of the agent. RESULTS: After administration of Resovist, portal venous signal increased to 237% of control immediately after injection, while hepatic parenchymal signal intensity decreased to 86% of control. The maximal CNR increase to 177% was achieved immediately after injection of the agent. After USPIO, portal venous signal increased to 401% of the precontrast value immediately after injection, while hepatic parenchymal signal intensity also increased to 131% of control at this time. Hepatic signal then decreased progressively to 49% of control after 40 minutes. The maximal CNR increase to 326% was achieved 10 minutes after injection of the agent. CONCLUSIONS: It is concluded that superparamagnetic iron oxide particles of different sizes have different R2/R1 ratios and, consequently, different mechanisms of contrast improvement in T1-weighted portal MR angiograms.

Failure of gadopentetate dimeglumine-enhanced, high-resolution magnetic resonance imaging to differentiate among melanin-containing skin tumors.

RATIONALE AND OBJECTIVES: We evaluated the diagnostic potential of gadopentetate dimeglumine-enhanced, high-resolution magnetic resonance (MR) imaging to differentiate benign from malignant melanin-containing skin tumors. METHODS: Forty-five patients were prospectively examined using high-resolution MR imaging at 1.5 T using a 2.5-cm surface coil. For tumor assessment, T1-weighted and T2-weighted transverse spin-echo sequences were acquired. After intravenous administration of gadopentetate dimeglumine (0.1 mmol/kg), the T1-weighted transverse sequence was repeated. Contrast enhancement was quantitatively determined as the percentage increase of signal intensity. Histologic findings were correlated using the Wilcoxon signed-ranks test. The quality of contrast enhancement was assessed by three independent investigators who were unaware of the patients' history and histologic data. The signal-to-noise ratio (SNR) was calculated in the T2-weighted sequence. Significance was tested using the Wilcoxon signed-ranks test. RESULTS: In all tumors, contrast enhancement was visually discernible. Half of the cases were enhanced inhomogeneously. The percentage of contrast enhancement did not correlate with histologic findings. Malignant melanomas could not be differentiated from benign melanocytic nevi with the use of gadopentetate dimeglumine. Determination of the SNR in T2-weighted sequences revealed no significant difference for histologic subgroups or tumor type. CONCLUSION: Gadopentetate dimeglumine-enhanced MR imaging does not differentiate malignant melanomas from benign melanocytic nevi. Determination of the SNR in the T2-weighted sequences revealed no significant difference for histologic subgroups.

[Iron oxide contrast media improve the magnetic resonance imaging of the portal vein system--an animal experimental study]. / Eisenoxydkontrastmittel verbessern die kernspintomographische Darstellung des portalvenösen Systems--eine tierexperimentelle Untersuchung.

PURPOSE: The aim was to demonstrate that intravenous superparamagnetic iron oxide contrast agents improve the delineation of the portal venous system. MATERIAL AND METHODS: The portal venous system of 8 minipigs was demonstrated by a FLASH 2-D MRA-sequence. Scans were acquired before and after intravenous administration of 10 and 20 mumol/kg of a superparamagnetic iron oxide contrast agent (SHU 555 A). Signal intensities were measured in the portal vein and hepatic parenchyma and contrast-to-noise ratios were calculated. RESULTS: Following a cumulative dose of 10 mumol iron oxide, hepatic parenchymal signal intensity decreased to 67 +/- 6%, following 20 mumol to 29 +/- 4%, and following 40 mumol to 13 +/- 2% of control (p < 0.0001). These effects improved the contrast-to-noise ratio of the portal vein (469 +/- 114%, 858 +/- 243%, and 957 +/- 272% of control in the left portal vein main branch, p = 0.02). CONCLUSION: A decrease in hepatic parenchymal signal due to a magnetic susceptibility effect accounts for an improvement of portal venous conspicuity following intravenous administration of iron oxide contrast medium.

[Value of electron beam tomography (EBT)]. / Wertigkeit der Elektronenstrahl-Computertomographie (EBT) -- II. Nichtkardiale Anwendungen und Strahlenexposition.

Electron beam tomography (EBT) has been scientifically evaluated to a much lesser degree for non-cardiac indications than for cardiac purposes. Therefore, four groups of investigators in Berlin (2), Mannheim and Munchen, which were supported by the Deutsche Forschungsgemeinschaft (DFG), included applications outside the heart in their evaluation of EBT technology. EBT has proven useful to look for pulmonary embolism and to assess other vessels (aorta, aortic branches, and intracranial arteries). Imaging of the lung parenchyma benefits from its intrinsic high contrast and from the fast data acquisition of EBT. Limited photon efficiency, higher radiation exposure, increased noise levels and other artifacts, however, markedly reduce the value of EBT for imaging of low contrast objects compared to conventional spiral CT and multislice CT (MSCT), compromising, in particular, the morphologic depiction of parenchymal abdominal organs and the brain. Consequently, scientific studies to further evaluate EBT for scanning of the brain and parenchymal abdominal organs were not pursued. Radiation exposure for non-cardiac EBT studies is up to three times higher than that for respective spiral CT studies, and in children EBT can only be advocated in select cases. Radiation exposure for the various prospectively triggered cardiac examination protocols of EBT is lower than that for conventional coronary angiography. Radiation exposure in cardiac multislice CT exceeds severalfold that of EBT, but the dose efficiency of EBT and MSCT are similar due to higher spatial resolution and less image noise of MSCT. In addition, modifications of MSCT (ECG pulsing) can further reduce radiation exposure to the level of EBT. Technical improvements of the EBT successor scanner "e-Speed" enable faster data acquisition at higher spatial resolution. Within comparative studies, the "e-Speed" will have to prove its value and competitiveness, particularly in comparison with multislice CT. After profound scientific assessment in a multicenter evaluation supported by the Deutsche Forschungsgemeinschaft (DFG) and regardless of the specific suitability of electron beam tomography for various cardiac and some non-cardiac indications, the investigators unanimously find the electron beam tomograph Evolution C150 XP not suitable as a whole body CT scanner.

[Diagnostic value of electron-beam computed tomography (EBT). I. Cardiac applications]. / Diagnostische Wertigkeit der Elektronenstrahl-Computertomographie (EBT). I. Kardiale Anwendungen.

Electron beam tomography (EBT) directly competes with other non-invasive imaging modalities, such as multislice computed tomography, magnetic resonance imaging, and echocardiography, in the diagnostic assessment of cardiac diseases. EBT is the gold standard for the detection and quantification of coronary calcium as a preclinical sign of coronary artery disease (CAD). Its standardized examination protocols and the broad experience with this method favor EBT. First results with multislice CT indicate that this new technology may be equivalent to EBT for coronary calcium studies. The principal value of CT-based coronary calcium measurements continues to be an issue of controversy amongst radiologists and cardiologists due to lack of prospective randomized trials. Coronary angiography with EBT is characterized by a high negative predictive value and, in addition, may be indicated in some patients with manifest CAD. It remains to be shown whether coronary angiography with multislice CT is reliable and accurate enough to be introduced into the routine work-up, to replace some of the many strictly diagnostic coronary catheterizations in Germany and elsewhere. Assessment of coronary stent patency with EBT is associated with several problems and in our opinion cannot be advocated as a routine procedure. EBT may be recommended for the evaluation of coronary bypasses to look for bypass occlusions and significant stenoses, which, however, can be equally well achieved with multislice CT. Quantification of myocardial perfusion with EBT could not replace MRI or other modalities in this field. EBT has proven to be accurate, reliable and in some instances equivalent to MRI, which is the gold standard for the quantitative and qualitative evaluation of cardiac function. Some disadvantages, not the least of which is the limited distribution of electron beam scanners, favor MRI for functional assessment of the heart.

Thoracic computed tomography of patients infected with the human immunodeficiency virus: relevance for the course of disease.

To determine the diagnostic accuracy and prognostic implications of thoracic computed tomography (CT) in patients with human immunodeficiency virus infection (HIV), CT scans of 154 HIV-infected patients (mean age, 41 years; range 23-65 years; 18 female) with suspicion of pulmonary disease were retrospectively reviewed for signs of disease by two investigators blinded to clinical data other than positive HIV serology. Abnormal CT features were correlated with CD4-T lymphocyte count, histologic or microbiologic diagnosis, and survival. Computed tomography detected features of pulmonary disease in 133 patients. A recent chest film was available in 96 patients, and it was normal in 16. In 17 of 99 patients (17%) with histologic or microbiologic correlation, pathologic CT features could be demonstrated, though histologic and microbiological studies were unrevealing. Median survival was 649 days. Confluent pulmonary infiltrates and bilateral masses on CT indicated advanced disease with a median survival of 115 days (n = 11, p = 0.0005) and 174 days (n = 15, p < 0.0001), respectively. The authors concluded that thoracic CT detects pulmonary lesions in an appreciable portion of HIV-infected patients in whom chest radiographs, microbiologic methods, or histology failed to establish a diagnosis, and that CT findings allow for an estimation of patient survival in acquired immunodeficiency syndrome.

Radiologic anatomy of ventricular assist devices.

Ventricular assist devices (VAD) allow for long-term circulatory support of patients with end-stage heart failure. With the increasing duration of circulatory support, diagnostic imaging plays an important role in the management of patients on a VAD. The aim of our review was to analyze the radiologic features of different VADs. From 1987 to 1996, 319 patients (mean age 42 years, range 3 to 74 years) were treated with a VAD. A Berlin Heart VAD was implanted in 263 of the patients, the univentricular Baxtor Novacor was implanted in three patients, and the univentricular CI Heartmate was implanted in 19 patients. All patients were studied by serial chest radiographs. In addition, 70 patients underwent computed tomography (CT), and five patients underwent electron beam CT. The Berlin Heart VAD was used as a biventricular support system in 218 patients. In all cases, the position of the wire-directed cannulae was identified on the chest radiographs, while the exact position of the cannula tip could be visualized by CT only. The plastic cannulae of both the Novacor and the Heartmate were not discernible on radiographs, but required CT for evaluation. Computed tomography also resolved the metal components of the pumps. The titanium-made pump housing of the Heartmate caused beam-hardening artefacts that might conceal fluid accumulations in the pump pocket. Computed tomography is the standard of reference for examinations of cannula position, pump position, and pump components of ventricular assist devices.

[Use of patient-related contrast media protocols in cardiovascular computerized tomography]. / Nutzen patientenbezogener Kontrastmittelprotokolle für die kardiovaskuläre Computertomographie.

PURPOSE: To determine the temporal variability of the time to maximum aortic density after peripheral venous contrast injection in cardiovascular CT studies and to calculate potential contrast agent savings of selecting scan delay from test bolus kinetics. METHODS: A peripheral contrast bolus was administered intravenously in 138 consecutive patients to determine the time to maximum density in a left ventricular or aortic region of interest by electron beam CT. 20 EKG-triggered scans were acquired within 70 heartbeats. The deviation of the time to maximum density from a standard, fixed scan delay was determined. RESULTS: Mean time to maximum density was 22 s, and the average deviation from that mean was 5 s. At an injection rate of 4 cc/s, this deviation implies that determining the individual scan delay from a test bolus injection may potentially save 20 cc contrast per patient. This amount of contrast agent, in turn, is required for the test bolus. CONCLUSION: Deriving the individual scan delay from test bolus kinetics may improve image contrast in cardiovascular CT studies without additional contrast expense.

Use of semiflexible applicators for radiofrequency ablation of liver tumors.

PURPOSE: To evaluate the feasibility and potential advantages of the radiofrequency ablation of liver tumors using new MRI-compatible semiflexible applicators in a closed-bore high-field MRI scanner. METHODS: We treated 8 patients with 12 malignant liver tumors of different origin (5 colorectal carcinoma, 2 cholangiocellular carcinoma, 1 breast cancer) under MRI guidance. Radiofrequency ablation (RFA) was performed using 5 cm Rita Starburst Semi-Flex applicators (Rita Medical Systems, Milwaukee, WI, USA) which are suitable for MR- and CT-guided interventions and a 150 W RF generator. All interventions were performed in a closed-bore 1.5 T high-field MRI scanner for MRI-guided RFA using fast T1-weighted gradient echo sequences and T2-weighted ultra-turbo spin echo sequences. Control and follow-up MRI examinations were performed on the next day, at 6 weeks, and every 3 months after RFA. Control MRI were performed as double-contrast MRI examinations (enhancement with iron oxide and gadopentetate dimeglumine). All interventions were performed with the patient under local anesthesia and analgo-sedation. RESULTS: The mean diameter of the treated hepatic tumors was 2.4 cm (+/-0.6 cm, range 1.0-3.2 cm). The mean diameter of induced necrosis was 3.1 cm (+/-0.4 cm). We achieved complete ablation in all patients. Follow-up examinations over a duration of 7 months (+/-1.3 months, range 4-9 month) showed a local control rate of 100% in this group of patients. All interventions were performed without major complications; only 2 subcapsular hematomas were documented. CONCLUSION: RFA of liver tumors using semiflexible applicators in closed-bore 1.5 T scanner systems is feasible. These applicators might simplify the RFA of liver tumors under MRI control. The stiff distal part of the applicator facilitates its repositioning.

[New ways of imaging diagnosis of the heart with electron beam tomography]. / Neue Wege der bildgebenden Herzdiagnostik mit der Elektronenstrahltomographie.

Electron beam computed tomography is a noninvasive imaging tool for diagnosing heart disease. The method offers new insights into coronary heart disease, because the quantification of coronary artery calcification provides a fast, low-risk and cost efficient estimation of coronary risk with greater prognostic power than traditional risk estimates. With intravenous administration of an x-ray contrast agent, EBCT can detect coronary artery stenoses more accurately than other noninvasive methods. The quantification of myocardial blood flow by EBCT represents a realistic alternative to other methods of assessing myocardial perfusion. High temporal resolution allows for detailed analysis of cardiac dynamics. Other applications include the work-up of cardiac masses, pericardial disease, and investigations of the great vessels. As a dedicated cardiac imaging tool, EBCT provides new insights into cardiac physiology and disease, and offers a quantitative approach to many diagnostic problems. Limited availability, radiation exposure, and the need for a iodinated contrast agent still make EBCT an accessory modality at this time.