Friedrich D. Knollmann

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 unenhanced (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-weighted and unenhanced and contrast-enhanced fat-suppression scans. 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.

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.

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.

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.

Coronary artery calcium scoring: diagnostic accuracy of different software implementations.

Purpose:To compare the diagnostic power of different software implementations for the quantification of coronary artery calcium. Materials and Methods:Electron beam computed tomography was performed in 109 heart transplant recipients at the same time as catheter coronary angiography and intracoronary ultrasound. Electron beam computed tomography images were analyzed by 3 software packages marketed for the quantification of coronary calcifications using the same software settings, and the resultant calcium scores correlated with the invasive reference methods by Bland-Altman plots and analysis of the receiver operating characteristics. Results:Although all scoring systems displayed close correlations upon regression analysis (r2 = 0.94–0.99), their ability to detect disease as per the invasive reference method varied significantly in some instances. The area under the ROC curve varied between Az = 0.78 and 0.85 for the detection of coronary artery stenosis upon coronary angiography (P = 0.05–0.13), and between Az = 0.75 and 0.83 for the detection of accelerated intimal proliferation (P = 0.03–0.18). Conclusions:Different software implementations for the quantification of coronary artery calcium load may display diagnostically relevant differences in spite of close direct correlation.

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.

Therapieevaluation von Lebermetastasen in der 16– Zeilen – CT – Vergleich einer Metastasenvolumetrie mit dem Vorgehen nach RECIST

Ziele: Vergleich einer Tumorvolumetrie mit dem Vorgehen nach RECIST bei der Verlaufsbeurteilung von Lebermetastasen gastrointestinaler Primartumoren unter systemischer Therapie. Methode: In einer retrospektiven Studie wurden die Lebermetastasen gastrointestinaler Tumoren von insgesamt 30 Patienten (20Manner, 10 Frauen) im Verlauf beobachtet. Pro Patient wurden zwischen 2 und 3 Metastasen evaluiert. Das Intervall der Verlaufsbeobachtung lag zwischen 1 und 10 Monaten (Median: 3,5 Monate). Die Beurteilung des Krankheitsverlaufes wurde zum einen anhand des Diameters nach RECIST durchgefuhrt, zu anderen durch die Bestimmung des Metastasenvolumens. Zur Quantifizierung des Tumorvolumens wurden drei in ihren methodischen Ansatzen unterschiedliche Segmentationsverfahren verwendet: eine saatpixelbasierte Methode, die manuelle Schichtsegmentierung und eine schwellenwertbasierte Methode. Die Untersuchungen wurden in einem fur das abdominelle Staging ublichen Standardprotokoll mit einem 16-Zeilen-CT (GE LightSpeed 16) durchgefuhrt. Scan – Parameter: 320 mA Rohrenstrom, 120kV Rohrenspannung, 0,7s Rotationszeit, 0,9 Pitch. Ergebnis: Insgesamt wurden 80 Lebermetastasen mit einem mittleren Diameter von 26,5mm und mittleren Volumina zwischen 8,29cm3 und 8,66cm3 evaluiert. Die Bewertung eines Krankheitsprogresses divergierte anhand einer Metastasenvolumetrie zwischen 23% (saatpixelbasierten Methode), 20% (Schichtsegmentierung) und 17% (schwellenwertbasierte Methode) der Patienten von der Klassifikation nach RECIST. Die Ergebnisse der Verlaufbeurteilung unterschieden sich zwischen dem Vorgehen nach RECIST und dem saatpixelbasierten Verfahren (p=0,016) sowie der manuellen Schichtsegmentierung (p=0,031) signifikant. Die Ergebnisse der schwellenwertbasierten Methode zeigten keinen signifikanten Unterschied bei der Bewertung der Therapie im Vergleich zu einer Anwendung der RECIST – Kriterien. Schlussfolgerung: Die Evaluation des Metastasenvolumens fuhrte im Vergleich zur Betrachtung des maximalen Diameters haufiger zur Detektion eines Krankheitsprogresses. Eine fruhzeitige Detektion eines Krankheitsprogresses kann potentiell das klinische Vorgehen bei der Durchfuhrung einer systemischen Therapie beeinflussen. Korrespondierender Autor: Rothe JH Charite Centrum 6 fur diagnostische und interventionelle Radiologie und Nuklearmedizin, Campus Virch, Klinik fur Strahlenheilkunde, Augustenburger Platz 1, 13353 Berlin, Berlin E-Mail: jan-holger.rothe@charite.de

Diagnostik der Herzfunktion im 16-Zeilen-Multidetektor-CT

Zusammenfassung Mit der Einführung der Mehrzeilen-Detektor-Computertomographie findet die computertomographische Diagnostik auch Zugang zu Fragen der Ventrikelfunktion. Obwohl für die meisten Fälle echokadiographische Untersuchungen die Methode der Wahl bleiben, besteht in ausgesuchten Fällen ein Zusatznutzen für dieses moderne CT-Verfahren.Summary With the introduction of multirow-detector computed tomography, cardiac function can be assessed with CT. Although the assessment of cardiac function remains the domain of echocardiography, an incremental benefit of using the modern CT techniques can be demonstrated in carefully selected cases.

Magnetresonanztomographie bei Trägern künstlicher Herzklappen

Zusammenfassung Die Indikationen zur Magnetresonanztomographie (MRT) bei Trägern künstlicher Herzklappen sind kritisch. Eine generelle Kontraindikation gegen die MRT ist zweifelhaft. Einige diagnostische Fragestellungen wie Prozesse in der hinteren Schädelgrube, Spinalabszesse und bei Beschwerden im Inneren des Knies lassen sich durch die MRT besser untersuchen als mit anderen radiologischen Verfahren. Die MRT kann Träger künstlicher Herzklappen auf dreierlei Weise direkt beeinträchtigen: 1) Bewegung und Dislozierung der Klappenprothese, 2) Erwärmung und 3) Induktion von Arrhythmien durch elektrische Ströme, und indirekt durch eine Verzerrung des MRT-Bildes mit der Gefahr einer diagnostischen Fehlinterpretation. Die gegenwärtige Literatur über Sicherheitsaspekte der MRT bei Trägern künstlicher Herzklappen erscheint nicht ausreichend.    Deshalb wurde 1998 eine Umfrage unter fünfundzwanzig Herstellern künstlicher Herzklappen durchgeführt bezüglich der Kompatibilität, Sicherheit, oder der Kontraindikation der MRT ihrer jeweiligen Klappenprothese. Die in Europa führenden Klappen-Hersteller bescheinigten eine MRT-Sicherheit. Einige Firmen stützten ihre Aussagen auf nicht einzusehende Untersuchungen, oder übertrugen die Verantwortung auf den Arzt, der die MRT durchführt. Andere Firmen gaben keine MRT-Sicherheitsgarantie oder antworteten nicht. Zwei Klappenhersteller warnten explizit vor der MRT bei bestimmten Prothesentypen. Aufbauend auf unsere Umfrage wird ein Überblick über die technischen Aspekte, die klinischen Umstände und die Voraussetzungen für MRT-Sicherheitsstandards bei Trägern künstlicher Herzklappen gegeben.Summary The indications for magnetic resonance imaging (MRI) on prosthetic heart valve recipients remain critical. A generalized contraindication for MRI is doubtful. Some diagnostic questions such as interests in pathologies of the posterior cranial fossa, spinal abscesses, and internal derangements for the knee, strongly recommend the advantages of MRI versus all other radiological diagnostic techniques. MRI can directly affect patients with prosthetic valves in three ways by: 1) movement or dislodgment of the prosthesis, 2) heating, and 3) arrhythmias induced by electric currents, and indirectly by distortion of the image and its subsequent misinterpretation. Present literature that concerns the safety considerations of current values appears to be incomplete.    Therefore, a survey of twenty-five valve manufacturers with regard to compatibility, safety or contraindication for MRI on their respective prosthetic heart valves was performed in 1998. Those manufacturers who distribute most of the valves in Europe confirmed the safety of MRI. However, some gave their assurances based on inadequate data, or assigned all responsibility to the physician. Some companies did not give any assurance for MRI safety or failed to respond to our enquiry. Two valve manufacturers warned against performing MRI on certain prostheses. Based on our 1998 questionnaire, the technical issues, the clinical circumstances, the prerequisites and criteria for and the definition of safety standards for MRI on prosthetic heart valve recipients are presented in this paper.