Virtual mono-energetic images and iterative image reconstruction: abdominal vessel imaging in the era of spectral detector CT.

AIM: To compare the quality of virtual mono-energetic (VMI) and polychromatic images reconstructed with hybrid iterative (PCIHIR) or model-based reconstruction (PCIMBR) derived from dual-layer spectral detector computed tomography (SDCT) in arterial phase images to visualise the aorta and abdominal main branches. MATERIAL AND METHODS: A retrospective review of 50 patients with abdominal arterial phase scans was undertaken. Attenuation, intraluminal noise, and signal-/contrast-to-noise ratio (S-/CNR) were assessed in the PCIHIR, PCIMBR and VMI40keV, VMI70keV, and VMI100keV images. Contrast, noise, and visualization of soft-plaque, and macro-/micro-calcifications were scored in a blinded reading by two radiologists. RESULTS: VMI40keV yielded highest S-/CNR (p≤0.001). VMI70keV and PCIMBR showed comparable SNR (p≥0.999) and yielded higher SNR than PCIHIR. VMI70keV yielded higher CNR than PCIHIR (p<0.001) and PCIMBR (p<0.045). VMI100keV yielded lowest CNR (p≤0.001) and SNR (p≥0.104). In the subjective analysis, VMI40keV outperformed PCIMBR for contrast and noise, PCIMBR scored better than VMI70keV, and the latter scored better than PCIHIR for these categories (all p<0.001). PCIMBR was superior for depiction of soft-plaque and micro-calcifications (p<0.001). VMI100keV visualized micro-calcifications second best (p<0.001) and matched PCIMBR for the depiction of macro-calcifications (p>0.999), while VMI40keV scored second best for depiction of soft-plaque (p<0.020). CONCLUSIONS: VMI40keV and VMI70keV yield better S-/CNR than PCIHIR and PCIMBR; however, PCIMBR visualized arteriosclerotic plaques best, followed by VMI40keV for depiction of soft-plaque and VMI100keV for macro- and micro-calcification. Based on the present findings, PCIMBR on conventional CT and VMI40keV supplemented by VMI100keV on SDCT are recommended for the diagnostic assessment of abdominal arteries.

[Lower leg, ankle and foot]. / Distaler Unterschenkel, Sprunggelenk und Fuß.

CLINICAL/METHODICAL ISSUE: Bipedal locomotion means high mechanical stress on the lower extremities and susceptibility to fractures. On the one hand, these can be the result of a one-time traumatic stress in the context of high speed traumas or falls, but can also result from repetitive microtraumas with subsequent stress fractures. STANDARD RADIOLOGICAL METHODS: For all fracture entities and localizations, X­ray diagnostics is the basic modality. METHODICAL INNOVATIONS: For optimal surgical reconstruction of intra-articular fractures or in complex fracture configurations, computed tomography should be generously used to improve postoperative outcome. PERFORMANCE: The classification of the individual fractures should enable standardised further therapy planning, especially with regard to conventional or surgical treatment. ACHIEVEMENTS: The combination of X­ray, magnetic resonance imaging and computed tomography makes a reliable diagnosis regarding foot fractures possible. PRACTICAL RECOMMENDATIONS: Important for the use of individual classification systems is always, in addition to clinical relevance, the safe and equal understanding of the individual types and degrees by the radiologist and the referring colleague.

Virtual monoenergetic images from spectral detector CT as a surrogate for conventional CT images: Unaltered attenuation characteristics with reduced image noise.

OBJECTIVE: This study aimed to identify the energy level of virtual monoenergetic images (VMI) that closest represents conventional images (CI) in order to demonstrate that these images provide improved image quality in terms of noise and Signal-to-noise ratio (SD/SNR) while attenuation values (HU) remain unaltered as compared to CI. METHODS: 60 and 30 patients with contrast-enhanced (CE) and non-enhanced (NCE) spectral detector CT (SDCT) of the abdomen were included in this retrospective, IRB-approved study. CI and VMI of 66-74 keV as well as quantitative iodine maps were reconstructed (Q-IodMap). Two regions of interest were placed in each: pulmonary trunk, abdominal aorta, portal vein, liver, pancreas, renal cortex left/right, psoas muscle, (filled) bladder and subcutaneous fat. For each reconstruction, HU and SD were averaged. ΔHU and SNR (SNR = HU/SD) were calculated. Q-IodMap were considered as confounder for ΔHU. In addition, two radiologists compared VMI of 72 keV and CI in a forced-choice approach regarding image quality. RESULTS: In NCE studies, no significant differences for any region was found. In CE studies, VMI72keV images showed lowest ΔHU (HUliver CI/VMI72keV: 104 ±â€¯18/103 ±â€¯17, p ≥ 0.05). Iodine containing voxels as indicated by Q-IodMap resulted in an over- and underestimation of attenuation in lower and higher VMI energies, respectively. Image noise was lower in VMI images (e.g. muscle: CI/ VMI72keV: 15.3 ±â€¯3.3/12.3 ±â€¯2.9 HU, p ≤ 0.05). Hence, SNR was significantly higher in VMI72keV compared to CI (e.g. liver 3.8 ±â€¯0.6 vs 3.0 ±â€¯0.8, p ≤ 0.05). In visual analysis, VMI72keV were preferred over CI at all times. CONCLUSIONS: VMI72keV show improved SD/SNR characteristics while the attenuation remains unaltered as compared to CI.

Improved visualization of hypodense liver lesions in virtual monoenergetic images from spectral detector CT: Proof of concept in a 3D-printed phantom and evaluation in 74 patients.

OBJECTIVES: The well-known boost of iodine associated-attenuation in low-keV virtual monoenergetic images (VMI_low) is frequently used to improve visualization of lesions and structures taking up contrast media. This study aimed to evaluate this concept in reverse. Hence to investigate if increased attenuation within the liver allows for improved visualization of little or not-enhancing lesions. METHODS: A 3D-printed phantom mimicking the shape of a human liver exhibiting a lesion in its center was designed and printed. Both, parenchyma- and lesion-mimic were filled with different solutions exhibiting 80/100/120HU and 0/15/40/60HU, respectively. Further, a total of 74 contrast-enhanced studies performed on a spectral detector CT scanner (SDCT) were included in this retrospective study. Patients had MRI or follow-up proven cysts and/or hypodense metastases. VMI of 40-200 keV as well as conventional images (CI) were reconstructed. ROI were placed in lesion and parenchyma(-mimics) on CI and transferred to VMI. Signal- and contrast-to-noise ratio were calculated (S-/CNR). Further, two radiologists independently evaluated image quality. Data was statistically assessed using ANOVA or Wilcoxon-test. RESULTS: In phantoms, S/CNR was significantly higher in VMI_low. The cyst-mimic in highly attenuating parenchyma-mimic on CI yielded a CNR of 6.4 ± 0.8; using VMI_40 keV, mildly hypodense lesion-mimic in poorly attenuating parenchyma-mimic exhibited a similar CNR (5.8 ± 0.9; p ≤ 0.05). The same tendency was observed in patients (cyst in CI/metastasis in VMI_40 keV: 4.4 ± 1.2/3.9 ± 1.8; p ≤ 0.05). Qualitative analysis indicated a benefit of VMI_40 keV (p ≤ 0.05). CONCLUSIONS: VMI_low from SDCT allow for an improved visualization of hypodense focal liver lesions exploiting the concept of contrast blooming in reverse.

[Which typical foot fractures should the radiologist know?] / Welche typischen Fußfrakturen sollte der Radiologe kennen?

CLINICAL/METHODICAL ISSUE: Due to mechanical loading and the number of joints involved, fractures of the foot are among the most common fractures. STANDARD RADIOLOGICAL METHODS: X-ray is basis for diagnostic workup of all foot fractures. METHODICAL INNOVATIONS: For stress fractures, the additional use of magnetic resonance imaging (MRI) is indicated. Computed tomography (CT) can be used for preoperative imaging of intraarticular tarsal fractures. PERFORMANCE: Simple traumatic fractures can be reliably diagnosed by X­ray. On the other hand, there is a poor sensitivity for stress fractures. ACHIEVEMENTS: Using a combination of X­ray, MRI, and CT, it is possible to reliably diagnosis and classify foot fractures. PRACTICAL RECOMMENDATIONS: The first step to diagnose a foot fracture should be the X­ray. CT and MRI can also be used to detect intra-articular fractures and MRI can be used for stress fractures.

Assessment of arterially hyper-enhancing liver lesions using virtual monoenergetic images from spectral detector CT: phantom and patient experience.

PURPOSE: To investigate a benefit from virtual monoenergetic reconstructions (VMIs) for assessment of arterially hyper-enhancing liver lesions in phantom and patients and to compare hybrid-iterative and spectral image reconstructions of conventional images (CI-IR and CI-SR). METHODS: All imaging was performed on a SDCT (Philips Healthcare, Best, The Netherlands). Images of a non-anthropomorphic phantom with a lesion-mimicking insert (containing iodine in water solution) and arterial-phase images from contrast-enhanced patient examinations were evaluated. VMIs (40-200 keV, 10 keV increment), CI-IR, and CI-SR were reconstructed using different strengths of image denoising. ROIs were placed in lesions, liver/matrix, muscle; signal-to-noise, contrast-to-noise, and lesion-to-liver ratios (SNR, CNR, and LLR) were calculated. Qualitatively, 40, 70, and 110 keV and CI images were assessed by two radiologists on five-point Likert scales regarding overall image quality, lesion assessment, and noise. RESULTS: In phantoms, SNR was increased threefold by VMI40keV compared with CI-IR/SR (5.8 ± 1.1 vs. 18.8 ± 2.2, p ≤ 0.001), while no difference was found between CI-IR and CI-SR (p = 1). Denoising was capable of noise reduction by 40%. In total, 20 patients exhibiting 51 liver lesions were assessed. Attenuation was the highest in VMI40keV, while image noise was comparable to CI-IR resulting in a threefold increase of CNR/LLR (CI-IR 1.3 ± 0.8/4.4 ± 2.0, VMI40keV: 3.8 ± 2.7/14.2 ± 7.5, p ≤ 0.001). Subjective lesion delineation was the best in VMI40keV image (p ≤ 0.01), which also provided the lowest perceptible noise and the best overall image quality. CONCLUSIONS: VMIs improve assessment of arterially hyper-enhancing liver lesions since they increase lesion contrast while maintaining low image noise throughout the entire keV spectrum. These data suggest that to consider VMI screening after arterially hyper-enhancing liver lesions.

[Functional MRI 2.0. ²³Na and CEST imaging]. / Funktionelle MRT 2.0. ²³Na- und CEST-Bildgebung.

In recent years the purely morphological magnetic resonance imaging (MRI) has been increasingly flanked by so-called functional imaging methods, such as diffusion-weighted imaging (DWI), to obtain additional information about tissue or pathological processes. This review article presents two MR techniques that can detect physiological processes in the human body. In contrast to all other functional MR imaging techniques, which are based on hydrogen protons, the first technique presented (X-nuclei imaging) uses the spin of other nuclei for imaging and consequently allows a completely different insight into the human body. In this article X-nuclei imaging is focused on sodium ((23)Na) MRI because it currently represents the main focus of research in this field due to the favorable MR properties of sodium. The second MR technique presented is the relatively novel chemical exchange saturation transfer (CEST) imaging that can detect exchange processes between protons in metabolites and protons in free water. The first part of this article introduces the basic technical principles, problems, advantages and disadvantages of these two MR techniques, whereas the second part highlights the potential clinical applications. Examples illustrate several potential applications in neuroimaging (e. g. stroke and tumors), musculoskeletal imaging (e. g. osteoarthritis and degenerative processes) and abdominal imaging (e. g. kidneys and hypertension). Both techniques inherently contain an incredible potential for future imaging but are still on the threshold of clinical use and are currently under evaluation in many university centers.

[Infectious diseases and injuries of bladder and urinary tract]. / Infektionskrankheiten und Verletzungen der Harnblase und der ableitenden Harnwege.

Urinary tract infections are the most common infectious diseases in Germany. In most cases clarification does not rely on imaging techniques other than sonography and is made mostly based on clinical symptoms. Computed tomography (CT) and magnetic resonance imaging (MRI) can be used in selected cases to find the cause and detection or exclusion of complications, e.g. recurrent or atypical and complicated courses. The method of choice for clarification of urolithiasis is CT. Using low-dose techniques, detection or exclusion of urinary stones can be achieved with a high sensitivity and specificity as well as an acceptable level of radiation exposure. Native stone CT supplies additional fundamental information that can substantially influence further therapy planning. The diagnosis of ureteral injuries is clinically and radiologically not trivial and clarification is aided by urographic contrast media. The method of CT cystography has an important role in the diagnostics of urinary bladder injuries.

[Oncological diseases and postoperative alterations of the bladder and urinary tract]. / Onkologische Erkrankungen und postoperative Veränderungen der Harnblase und der ableitenden Harnwege.

In the challenging evaluation of upper urinary tract malignancies multidetector computed tomography (CT) has become the standard imaging method. Cross sectional imaging not only allows the detection and visualization of the tumor itself but also provides nodal and metastasis staging in one examination (one-stop-shop). The majority of urothelial carcinomas are located in the urinary bladder. In this case, CT and more recently magnetic resonance imaging (MRI) can also deliver decisive information regarding TNM classification. A combination of clinical, histological, morphological and functional parameters allows both risk stratification and a targeted therapy based on the individual tumor stage.

Adjuvant IMRT/XELOX radiochemotherapy improves long-term overall- and disease-free survival in advanced gastric cancer.

PURPOSE: In a retrospective analysis, adjuvant intensity-modulated radiation therapy (IMRT) combined with modern chemotherapy improved advanced gastric cancer survival rates compared to a combination of three-dimensional conformal radiation therapy (3D-CRT) and conventional chemotherapy. We report on the long-term outcomes of two consecutive patient cohorts that were treated with either IMRT and intensive chemotherapy, or 3D-CRT and conventional chemotherapy. PATIENTS AND METHODS: Between 2001 and 2008, 65 consecutive gastric cancer patients received either 3D-CRT (n = 27) or IMRT (n = 38) following tumor resection. Chemotherapy comprised predominantly 5-fluorouracil/folinic acid (5-FU/FA) in the earlier cohort and capecitabine plus oxaliplatin (XELOX) in the latter. The primary endpoints were overall survival (OS) and disease-free survival (DFS). RESULTS: Median OS times were 18 and 43 months in the 3D-CRT and IMRT groups, respectively (p = 0.0602). Actuarial 5-year OS rates were 26 and 47 %, respectively. Within the IMRT group, XELOX gave better results than 5-FU/FA in terms of OS, but this difference was not statistically significant. The primary cause of death in both groups was distant metastasis. Median DFS times were 14 and 35 months in the 3D-CRT and IMRT groups, respectively (p = 0.0693). Actuarial 5-year DFS rates were 22 and 44 %, respectively. Among patients receiving 5-FU/FA, DFS tended to be better in the IMRT group, but this was not statistically significant. A similar analysis for the XELOX group was not possible as 3D-CRT was almost never used to treat these patients. No late toxicity exceeding grade 3 or secondary tumors were observed. CONCLUSION: After a median follow-up period of over 5 years, OS and DFS were improved in the IMRT/XELOX treated patients compared to the 3D-CRT/5-FU/FA group. Long-term observation revealed no clinical indications of therapy-induced secondary tumors or renal toxicity.

Assessment of renal function after conformal radiotherapy and intensity-modulated radiotherapy by functional 1H-MRI and 23Na-MRI.

PURPOSE: Adjuvant radiochemotherapy (RCHT) improves survival of patients with locally advanced gastric cancer. Conventional three-dimensional conformal radiotherapy (3D-CRT) results in ablative doses to a significant amount of the left kidney, while image-guided intensity-modulated radiotherapy (IG-IMRT) provides excellent target coverage with improved kidney sparing. Few long-term results on IMRT for gastric cancer, however, have been published. Functional magnetic resonance imaging (fMRI) at 3.0 T including blood oxygenation-level dependent (BOLD) imaging, diffusion-weighted imaging (DWI) and, for the first time, (23)Na imaging was used to evaluate renal status after radiotherapy with 3D-CRT or IG-IMRT. PATIENTS AND METHODS: Four disease-free patients (2 after 3D-CRT and 2 after IMRT; FU for all patients > 5 years) were included in this feasibility study. Morphological sequences, axial DWI images, 2D-gradient echo (GRE)-BOLD images, and (23)Na images were acquired. Mean values/standard deviations for ((23)Na), the apparent diffusion coefficient (ADC), and R2* values were calculated for the upper/middle/lower parts of both kidneys. Corticomedullary (23)Na-concentration gradients were determined. RESULTS: Surprisingly, IG-IMRT patients showed no morphological alterations and no statistically significant differences of ADC and R2* values in all renal parts. Values for mean corticomedullary (23)Na-concentration matched those for healthy volunteers. Results were similar in 3D-CRT patients, except for the cranial part of the left kidney. This was atrophic and presented significantly reduced functional parameters (p = 0.001-p = 0.033). Reduced ADC values indicated reduced cell density and reduced extracellular space. Cortical and medullary R2* values of the left cranial kidney in the 3D-CRT group were higher, indicating more deoxygenated hemoglobin due to reduced blood flow/oxygenation. ((23)Na) of the renal cranial parts in the 3D-CRT group was significantly reduced, while the expected corticomedullary (23)Na-concentration gradient was partially conserved. CONCLUSIONS: Functional MRI can assess postradiotherapeutic renal changes. As expected, marked morphological/functional effects were observed in high-dose areas (3D-CRT), while, unexpectedly, no alteration in kidney function was observed in IG-IMRT patients, supporting the hypothesis that reducing total/fractional dose to the renal parenchyma by IMRT is clinically beneficial.

[Functional magnetic resonance imaging for evaluation of radiation-induced renal damage]. / Funktionelle MRT der Niere zur Erfassung strahleninduzierter Nierenschädigungen.

The diagnosis of radiation-induced (especially chronic) renal alterations/damage is difficult and currently relies primarily on clinical evaluation. The importance of renal diagnostic evaluation will increase continuously due to the increasing number of long-term survivors after radiotherapy. This article evaluates the potentia diagnostic contribution of magnetic resonance (MR) imaging with a focus on functional MRI. The following functional MRI approaches are briefly presented and evaluated: blood oxygenation level-dependent imaging (BOLD), diffusion-weighted imaging (DWI) or diffusion tensor imaging (DTI), MR perfusion measurements and (23)Na imaging. In summary, only DWI and contrast-enhanced MR perfusion currently seem to be suitable approaches for a broader, clinical implementation. However, up to now valid data from larger patient studies are lacking for both techniques in regard to radiation-induced renal alterations. The BOLD and (23)Na imaging procedures have a huge potential but are currently neither sufficiently evaluated with regard to radiation-induced renal alterations nor technically simple and reliable for implementation into the clinical routine.

Imaging of tumor viability in lung cancer: initial results using 23Na-MRI.

PURPOSE: 23Na-MRI has been proposed as a potential imaging biomarker for the assessment of tumor viability and the evaluation of therapy response but has not yet been evaluated in patients with lung cancer. We aimed to assess the feasibility of 23Na-MRI in patients with lung cancer. MATERIALS AND METHODS: Three patients with stage IV adenocarcinoma of the lung were examined on a clinical 3 Tesla MRI system (Magnetom TimTrio, Siemens Healthcare, Erlangen, Germany). Feasibility of 23Na-MRI images was proven by comparison and fusion of 23Na-MRI with 1H-MR, CT and FDG-PET-CT images. 23Na signal intensities (SI) of tumor and cerebrospinal fluid (CSF) of the spinal canal were measured and the SI ratio in tumor and CSF was calculated. One chemonaive patient was examined before and after the initiation of combination therapy (Carboplatin, Gemcitabin, Cetuximab). RESULTS: All 23Na-MRI examinations were successfully completed and were of diagnostic quality. Fusion of 23Na-MRI images with 1H-MRI, CT and FDG-PET-CT was feasible in all patients and showed differences in solid and necrotic tumor areas. The mean tumor SI and the tumor/CSF SI ratio were 13.3 ± 1.8 × 103 and 0.83 ± 0.14, respectively. In necrotic tumors, as suggested by central non-FDG-avid areas, the mean tumor SI and the tumor/CSF ratio were 19.4 × 103 and 1.10, respectively. CONCLUSION: 23Na-MRI is feasible in patients with lung cancer and could provide valuable functional molecular information regarding tumor viability, and potentially treatment response.

"Number needed to read"--how to facilitate clinical trials in MR-angiography.

PURPOSE: To evaluate the effect of the number of readers on the statistical results in peripheral MRA. MATERIALS AND METHODS: 40 patients with peripheral arterial occlusive disease were included as a sample dataset in this study, randomly separated into two matched groups with n = 20 patients (group 1--gadobutrol, group 2--gadoterate meglumine) who underwent a continuous table movement MRA of the peripheral vessels at 3 T. Image quality (IQ) of 17 vessel segments was evaluated by 5 independent readers. The effect of the number of readers on significance and statistical power was statistically analyzed. RESULTS: Image quality in group 1 (gadobutrol) ranks significantly higher compared to group 2 (gadoterade meglumine) with a diagnostic IQ in 97% vs. 78% (p < 0.0001). For the diagnostic/non-diagnostic IQ assessment significance was reached with one reader 1/5 times (20%), with two readers in 4/10 (40%), with three readers in 6/10 (60%), with four readers in 4/5 (80%), with five readers in 1/1 (100%). Power considerations showed considerable gain when increasing the number of readers. CONCLUSION: Increasing the number of readers in a diagnostic MRA-study can be used to achieve a higher power or to decrease the number of subjects included with maintained statistical validity.

Image quality of T2w-TSE of the abdomen and pelvis with Cartesian or BLADE-type k-space sampling: a retrospective interindividual comparison study.

PURPOSE: The purpose of this study was to evaluate the image quality of T2-weighted (T2w) imaging of the abdomen and pelvis based on the acquisition of rotating rectangular stripes of k-space data after successive radiofrequency excitation (BLADE technique) in comparison to T2w turbo-spin-echo (TSE) sequences with Cartesian k-space sampling. MATERIALS AND METHODS: A total number of 107 patients with MR imaging of the abdomen or the pelvis were included in this retrospective interindividual study. All exams were performed in the clinical routine at 1.5T. The T2w images were randomly performed in BLADE technique or as TSE sequences. Two blinded radiologists assessed the images, presented in a random order, concerning the delineation of the abdominal and the musculoskeletal structures, the artifacts of these structures, and the overall image qualities. RESULTS: For the abdomen the mean overall image quality of the T2w-BLADE was rated 3.2 vs. 3.1 for T2w-TSE (p=0.871). The mean musculoskeletal/visceral artifacts of the T2w-BLADE were scored as 2.9/3.0 vs. 3.2/2.6 for the T2w-TSE (p=0.101/p=0.051). The delineation of the musculoskeletal, respectively of the visceral structures was assessed for the T2w-BLADE as 3.0/3.4 vs. 3.2/3.1 for the T2w-TSE (p=0.263; p=0.185). For the pelvis the mean overall image quality of the T2w-BLADE was 3.4 vs. 2.9 for the T2w-TSE (p=0.005). Furthermore the musculoskeletal/visceral artifacts were assessed with a mean of 3.6/3.3 for the T2w-BLADE vs. 3.0/2.8 for the T2w-TSE (p=0.005; p=0.011). The musculoskeletal/visceral delineation of the T2w-BLADE was rated 3.6/3.4 vs. 3.0/2.8 for the T2w-TSE sequence (p<0.001; p=0.008). CONCLUSION: In imaging of the pelvis the overall quality of T2w sequences with k-space sampling in BLADE technique was rated significantly superior compared with the standard Cartesian sampling. Similar results were assessed for the reduction of the amount of artifacts and blurring. By contrast, no significant benefit could be demonstrated for the T2w-BLADE in the abdomen.