Thomas Krohn

Automatic, three-segment, MR-based attenuation correction for whole-body PET/MR data

PurposeThe combination of positron emission tomography (PET) and magnetic resonance (MR) tomography in a single device is anticipated to be the next step following PET/CT for future molecular imaging application. Compared to CT, the main advantages of MR are versatile soft tissue contrast and its capability to acquire functional information without ionizing radiation. However, MR is not capable of measuring a physical quantity that would allow a direct derivation of the attenuation values for high-energy photons.MethodsTo overcome this problem, we propose a fully automated approach that uses a dedicated T1-weighted MR sequence in combination with a customized image processing technique to derive attenuation maps for whole-body PET. The algorithm automatically identifies the outer contour of the body and the lungs using region-growing techniques in combination with an intensity analysis for automatic threshold estimation. No user interaction is required to generate the attenuation map.ResultsThe accuracy of the proposed MR-based attenuation correction (AC) approach was evaluated in a clinical study using whole-body PET/CT and MR images of the same patients (n = 15). The segmentation of the body and lung contour (L-R directions) was evaluated via a four-point scale in comparison to the original MR image (mean values >3.8). PET images were reconstructed using elastically registered MR-based and CT-based (segmented and non-segmented) attenuation maps. The MR-based AC showed similar behaviour as CT-based AC and similar accuracy as offered by segmented CT-based AC. Standardized uptake value (SUV) comparisons with reference to CT-based AC using predefined attenuation coefficients showed the largest difference for bone lesions (mean value ± standard variation of SUVmax: −3.0% ± 3.9% for MR; −6.5% ± 4.1% for segmented CT). A blind comparison of PET images corrected with segmented MR-based, CT-based and segmented CT-based AC afforded identical lesion detectability, but slight differences in image quality were found.ConclusionOur MR‐based attenuation correction method offers similar correction accuracy as offered by segmented CT. According to the specialists involved in the blind study, these differences do not affect the diagnostic value of the PET images.

Dose-escalation using intensity-modulated radiotherapy for prostate cancer - evaluation of quality of life with and without 18 F-choline PET-CT detected simultaneous integrated boost

BackgroundIn comparison to the conventional whole-prostate dose escalation, an integrated boost to the macroscopic malignant lesion might potentially improve tumor control rates without increasing toxicity. Quality of life after radiotherapy (RT) with vs. without 18F-choline PET-CT detected simultaneous integrated boost (SIB) was prospectively evaluated in this study.MethodsWhole body image acquisition in supine patient position followed 1 h after injection of 178-355MBq 18F-choline. SIB was defined by a tumor-to-background uptake value ratio > 2 (GTVPET). A dose of 76Gy was prescribed to the prostate (PTVprostate) in 2Gy fractions, with or without SIB up to 80Gy. Patients treated with (n = 46) vs. without (n = 21) SIB were surveyed prospectively before (A), at the last day of RT (B) and a median time of two (C) and 19 month (D) after RT to compare QoL changes applying a validated questionnaire (EPIC - expanded prostate cancer index composite).ResultsWith a median cut-off standard uptake value (SUV) of 3, a median GTVPET of 4.0 cm3 and PTVboost (GTVPET with margins) of 17.3 cm3 was defined. No significant differences were found for patients treated with vs. without SIB regarding urinary and bowel QoL changes at times B, C and D (mean differences ≤3 points for all comparisons). Significantly decreasing acute urinary and bowel score changes (mean changes > 5 points in comparison to baseline level at time A) were found for patients with and without SIB. However, long-term urinary and bowel QoL (time D) did not differ relative to baseline levels - with mean urinary and bowel function score changes < 3 points in both groups (median changes = 0 points). Only sexual function scores decreased significantly (> 5 points) at time D.ConclusionsTreatment planning with 18F-choline PET-CT allows a dose escalation to a macroscopic intraprostatic lesion without significantly increasing toxicity.

First evidence of PSMA expression in differentiated thyroid cancer using [68Ga]PSMA-HBED-CC PET/CT

The prostate-specific membrane antigen (PSMA) has recently emerged as a target for radionuclide imaging and therapy of prostate cancer [1, 2]. However, PSMA expression was also shown on the cell membrane of endothelial cells of tumour neovasculature in a number of other cancers such as renal cell carcinoma [3, 4], colon carcinoma, neuroendocrine tumours, melanoma or breast cancer [3]. However, to our knowledge no study has yet investigated

Intensity-modulated radiotherapy for prostate cancer implementing molecular imaging with 18F-choline PET-CT to define a simultaneous integrated boost.

Purpose:To report the own experience with 66 patients who received 18F-choline PET-CT (positron emission tomography-computed tomography) for treatment planning.Patients and Methods:Image acquisition followed 1 h after injection of 178–355 MBq 18F-choline. An intraprostatic lesion (GTVPET [gross tumor volume]) was defined by a tumor-to-background SUV (standard uptake value) ratio > 2. A dose of 76 Gy was prescribed to the prostate in 2-Gy fractions, with a simultaneous integrated boost up to 80 Gy.Results:A boost volume could not be defined for a single patient. One, two and three or more lesions were found for 36 (55%), 22 (33%) and seven patients (11%). The lobe(s) with a positive biopsy correlated with a GTVPET in the same lobe in 63 cases (97%). GTVPET was additionally defined in 33 of 41 prostate lobes (80%) with only negative biopsies. GTVPET, SUVmean and SUVmax were found to be dependent on well-known prognostic risk factors, particularly T-stage and Gleason Score. In multivariate analysis, Gleason Score > 7 resulted as an independent factor for GTVPET > 8 cm3 (hazard ratio 5.5; p = 0.02) and SUVmax > 5 (hazard ratio 4.4; p = 0.04). Neoadjuvant hormonal treatment (NHT) did not affect SUV levels. The mean EUDs (equivalent uniform doses) to the rectum and bladder (55.9 Gy and 54.8 Gy) were comparable to patients (n = 18) who were treated in the same period without a boost (54.3 Gy and 55.6 Gy).Conclusion:Treatment planning with 18F-choline PET-CT allows the definition of an integrated boost in nearly all prostate cancer patients – including patients after NHT – without considerably affecting EUDs for the organs at risk. GTVPET and SUV levels were found to be dependent on prognostic risk factors, particularly Gleason Score.ZusammenfassungZiel:Erfahrungsbericht mit 66 Patienten nach 18F-Cholin-PET-CT (Positronenemissionstompgraphie-Computertomographie) zur Bestrahlungsplanung.Patienten und Methodik:Die Bildakquisition erfolgte 1 h nach Injektion von 178–355 MBq 18F-Cholin. Ein intraprostatischer Herd (GTVPET [makroskopisches Tumorvolumen]) wurde ab einem Tumor-zu-Hintergrund-SUV-(„standard uptake value“-)Quotienten > 2 definiert. Die Verschreibungsdosis für die Prostata betrug 76 Gy in 2-Gy-Einzeldosen mit simultanem integrierten Boost bis 80 Gy.Ergebnisse:Ein Boostvolumen konnte bei einem Patienten nicht definiert werden. Ein, zwei und drei oder mehr Herde wurden bei 36 (55 %), 22 (33 %) und sieben Patienten (11 %) gefunden. Der/die Lappen mit positiver Biopsie korrelierte/n in 63 Fallen (97 %)mit dem GTVPET im gleichen Lappen. Zusätzlich wurde ein GTVPET in 33 von 41 Lappen (80 %) mit nur negativen Biopsien definiert. GTVPET, SUVmean und SUVmax zeigten eine Abhängigkeit von bekannten Risikofaktoren, insbesondere T-Stadium und Gleason-Score. In multivariater Analyse resultierte ein Gleason-Score > 7 als ein unabhängiger Faktor für GTVPET > 8 cm3 (relatives Risiko 5,5; p = 0,02) und SUVmax > 5 (relatives Risiko 4,4; p = 0,04). Eine neoadjuvante Hormontherapie (NHT) war ohne Einfluss auf SUV-Werte. Die mittleren EUDs („equivalent uniform doses“) für Rektum und Blase (55,9 Gy und 54,8 Gy) waren vergleichbar zu Patienten (n = 18), die in der gleichen Periode ohne Boost bestrahlt wurden (54,3 Gy und 55,6 Gy).Schlussfolgerung:Die Bestrahlungsplanung nach 18F-Cholin-PET-CT ermöglicht die Definition eines integrierten Boostvolumens bei nahezu allen Patienten mit Prostatakarzinom – einschließlich Patienten nach NHT – ohne einen relevanten Einfluss auf die EUDs für die Risikoorgane. GTVPET- und SUV-Werte zeigten eine Abhängigkeit von prognostischen Risikofaktoren, insbesondere dem Gleason-Score.

Relationship between positive thyroglobulin doubling time and 18F-FDG PET/CT-positive, 131I-negative lesions.

AimIn patients with differentiated thyroid carcinoma (DTC), metastases can either show iodine-131 (131I) uptake on whole-body scintigraphy or 18F-2-fluoro-2-deoxy-D-glucose (18F-FDG) uptake on combined PET and X-ray computed tomography (PET/CT), or a mix of both. The present study investigates the relationship between uptake patterns and prognosis in DTC patients, using thyroglobulin doubling time (TgDT) as a surrogate marker of prognosis. Materials and methodsWe retrospectively examined 18F-FDG PET/CT and 131I WBS in 65 DTC patients who were referred to our department of nuclear medicine for 18F-FDG PET/CT between May 2007 and June 2011. ResultsEight patients were excluded from analysis because of other diseases that caused intense 18F-FDG uptake or because of failure to show 131I WBS uptake. 18F-FDG uptake was seen in 30 out of 57 (53%) patients, of whom 14 showed some degree of 131I uptake. In these 30 positive scans, we identified a total of 181 18F-FDG-positive lesions. Of these, 60 lesions (33%) showed concurrent 131I uptake on whole-body scintigraphy. Of the nine patients with a positive TgDT in the patient group eight had 18F-FDG-positive, 131I-negative lesions, indicating poorer prognosis for this group. ConclusionIn this initial exploratory retrospective study there appears to be an association between a positive TgDT and 18F-FDG-positive, 131I-negative metastases, which should encourage further studies in order to establish whether 18F-FDG PET-CT is the preferred primary imaging modality in patients with a positive TgDT. Roughly two-thirds of patients with a negative TgDT will show at least some degree of 131I positivity, potentially enabling further 131I therapy.

Negative 18F-2-fluorodeoxyglucose PET/CT predicts good cancer specific survival in patients with a suspicion of recurrent ovarian cancer

AIM The aim of the present study was to investigate the diagnostic and prognostic value of combined (18)F-2-fluorodeoxyglucose positron emission tomography and contrast enhanced X-ray computed tomography (FDG-PET/CT) in women with a suspicion of recurrent ovarian cancer. PATIENTS AND METHODS We retrospectively reviewed 48 patients with a suspicion of recurrent ovarian cancer who were referred to our department for combined FDG-PET/CT. RESULTS Median follow-up was 25 months. 38/48 (79%) patients showed pathological findings on PET/CT. 17/48 (35%) of patients died of ovarian cancer. One FDG-PET/CT was false positive and one was false negative, leading to a sensitivity and positive predictive value of 97% and a specificity and negative predictive value of 90%. 33/48 (69%) underwent a change in therapy following FDG-PET/CT. There was a significantly better survival in FDG-PET/CT negative than in positive patients (p=0.04). In the FDG-PET/CT negative group no patients had died of ovarian cancer during follow-up. Remarkably, there was no difference in survival between patients who only had peritoneal metastases on FDG-PET/CT and those who also had extraperitoneal metastases (p=0.71). CONCLUSION A negative FDG-PET/CT has a high negative predictive value for the presence of disease and, more importantly, is associated with a very good disease-specific survival rate.

Different intravenous contrast media concentrations do not affect clinical assessment of 18F-fluorodeoxyglucose positron emission tomography/computed tomography scans in an intraindividual comparison.

ObjectiveThe purpose of this study was to perform an intraindividual comparison of the influences of different iodine contrast media on tracer uptake, contrast enhancement, and image quality in combined positron emission tomography (PET)/computed tomography (CT). Materials and MethodsFifty-one patients underwent baseline and follow-up combined PET/CT consisting of low-dose unenhanced and venous contrast-enhanced CT with contrast media containing a high concentration of iodine (iopromide, 370 mg/mL) and a standard iodine concentration (iopromide, 300 mg/mL). The total iodine load (44.4 g) and the iodine delivery rate (1.29 g/s) were identical for the 2 protocols. The mean and maximum standard uptake values, as measures of tracer uptake and contrast enhancement for unenhanced and contrast-enhanced PET/CT, were quantified at 10 different anatomical sites, and images were analyzed for clinically relevant differences. ResultsThe mean and maximum standard uptake values were significantly increased in contrast-enhanced PET/CT compared with unenhanced PET/CT at each anatomical site (P < 0.05). Comparison of tracer uptake between the 300- and 370-mg iodine contrast media showed no significant differences (all P > 0.05). Comparison of contrast enhancement between the 300- and 370-mg iodine contrast media showed no significant difference at any anatomical site (all P > 0.05). Analysis of image quality revealed no clinically relevant differences between the 2 different iodine contrast media (P = 0.739). ConclusionThe use of contrast-enhanced CT scans for attenuation correction in PET/CT does not cause clinically relevant artifacts in PET scan reconstruction, regardless of the iodine concentration used. Standard- and high-iodine contrast media can be used equivalently.

Multiphase CT scanning and different intravenous contrast media concentrations in combined F-18-FDG PET/CT: Effect on quantitative and clinical assessment

PURPOSE To evaluate the influence of multiphase CT scanning and different intravenous contrast media on contrast enhancement, attenuation correction and image quality in combined PET/CT. MATERIAL AND METHODS 140 patients were prospectively enrolled for F-18-FDG-PET/CT including a low-dose unenhanced, arterial and venous contrast enhanced CT. The first (second) 70 patients, received contrast medium with 370 (300) mg iodine/ml. The iodine delivery rate (1.3mg/s) and total iodine load (44.4g) were identical for both groups. Contrast enhancement and maximum and mean standardized FDG uptake values (SUVmax and SUVmean) were determined for the un-enhanced, arterial and venous PET/CT at multiple anatomic sites and PET reconstructions were visually evaluated. RESULTS Arterial contrast enhancement was significantly higher for the 300mg/ml contrast medium compared to 370mgI/ml at all anatomic sites. Venous enhancement was not different between the two contrast media. SUVmean and SUVmax were significantly higher for the contrast enhanced compared to the non-enhanced PET/CT at all anatomic sites (all P<0.001). Tracer uptake was significantly higher in the arterial than in the venous PET/CT in the arteries using both contrast media (all P<0.001). No differences in tracer uptake were found between the contrast media (all P>0.05). Visual assessment revealed no relevant differences between the different PET reconstructions. CONCLUSIONS There is no relevant qualitative influence on the PET scan from the use of different intravenous contrast media in its various phases in combined multiphase PET/CT. For quantitative analysis of tracer uptake it is required to use an identical PET/CT protocol.

Gated Myocardial Perfusion SPECT: Algorithm-Specific Influence of Reorientation on Calculation of Left Ventricular Volumes and Ejection Fraction

Gated myocardial perfusion SPECT allows calculation of end-diastolic and end-systolic volumes (EDV and ESV, respectively) and left ventricular ejection fraction (LVEF). The quantification algorithms QGS (quantitative gated SPECT), 4D-MSPECT, and CARE heart show a good correlation with cardiac MRI. Nevertheless, differences in contour finding suggest algorithm-specific effects if heart axes vary. The effect of tilting heart axes on gated SPECT was quantified as a possible source of error. Methods: Sixty men underwent gated SPECT (450 MBq of 99mTc-tetrofosmin or sestamibi, 8 gates/cycle). After correct reorientation (R0), datasets were tilted by 5°, 10°, 15°, 20°, 30°, and 45° along both long axes (R5, R10, R15, R20, R30, and R45, respectively). EDV, ESV, and LVEF were calculated using QGS, 4D-MSPECT, and CARE heart. Because a 15° tilt could be a maximum possible misreorientation in routine, R0 and R15 results were analyzed in detail. Absolute-difference values between results of tilted and correctly reoriented datasets were calculated for all tilts and algorithms. Results: QGS and CARE heart succeeded for R0 and R15 in all cases, whereas 4D-MSPECT failed to find the basal plane in 1 case (patient B). R2 values between paired R15/R0 results were 0.992 (QGS), 0.796 (4D-MSPECT; R2 = 0.919 in n = 59 after exclusion of the failed case), and 0.916 (CARE heart) for EDV; 0.994 (QGS), 0.852 (4D-MSPECT; R2 = 0.906 in n = 59), and 0.899 (CARE heart) for ESV; and 0.988 (QGS), 0.814 (4D-MSPECT; R2 = 0.810 in n = 59), and 0.746 (CARE heart) for LVEF. Concerning all levels of misreorientation, 1 patient was excluded for all algorithms because of multiple problems in contour finding; additionally for 4D-MSPECT patient B was excluded. In the 45° group, QGS succeeded in 58 of 59 cases, 4D-MSPECT in 58 of 58, and CARE heart in 33 of 59. Mean absolute differences for EDV ranged from 5.1 ± 4.1 to 12.8 ± 10.5 mL for QGS, from 6.7 ± 6.3 to 34.2 ± 20.7 mL for 4D-MSPECT, and from 5.4 ± 5.6 to 25.2 ± 16.1 mL for CARE heart (tilts between 5° and 45°). Mean absolute differences for ESV ranged from 4.1 ± 3.7 to 8.0 ± 9.4 mL for QGS, from 5.6 ± 8.0 to 10.0 ± 10.5 mL for 4D-MSPECT, and from 5.4 ± 5.6 to 25.5 ± 16.1 mL for CARE heart. Mean absolute differences for LVEF ranged from 1.1% ± 1.0% to 2.2% ± 1.8% for QGS, from 4.0% ± 3.5% to 8.0% ± 7.1% for 4D-MSPECT, and from 3.4% ± 2.9% to 9.2% ± 6.0% for CARE heart. Conclusion: Despite tilted heart axes, QGS showed stable results even when using tilts up to 45°. 4D-MSPECT and CARE heart results varied with reorientation of the heart axis, implying that published validation results apply to correctly reoriented data only.

PET/CT in lung cancer: Influence of contrast medium on quantitative and clinical assessment.

AbstractObjectivesTo evaluate the influence of intravenous contrast medium and different contrast medium phases on attenuation correction, PET image quality and clinical staging in combined PET/CT in patients with a suspicion of lung cancer.MethodsSixty patients with a suspicion of lung cancer were prospectively enrolled for combined 18F-FDG-PET/CT examination. PET images were reconstructed with non-enhanced and arterial and venous phase contrast CT. Maximum and mean standardised uptake values (SUVmax and SUVmean) and contrast enhancement (HU) were determined in the subclavian vein, ascending aorta, abdominal aorta, inferior vena cava, portal vein, liver and kidney and lung tumour. PET data were evaluated visually for clinical staging and image quality.ResultsSUVmax was significantly increased between contrast and non-contrast PET/CT at all anatomic sites (all P < 0.001). SUVmax was significantly increased for arterial PET/CT compared to venous PET/CT in the arteries (all P < 0.001). Venous PET/CT resulted in significantly higher SUVmax values compared to arterial PET/CT in the parenchymatous organs (all P < 0.05). Visual clinical evaluation of malignant lesions showed no differences between contrast and non-contrast PET/CT (P = 1.0).ConclusionsContrast enhanced CT is suitable for attenuation correction in combined PET/CT in lung cancer; it affects neither the clinical assessment nor image quality of the PET images.Key Points• Positron emission tomography combined with computed tomography is now a mainstream investigation • There has been debate about whether CT contrast agents affect PET results • Contrast-enhanced CT is satisfactory for attenuation correction in lung cancer PET/CT • Multiphase CT does not affect PET; additional unenhanced CT is unnecessary • For quantitative follow-up PET analysis, an identical PET/CT protocol is required