Thrombus imaging in acute ischaemic stroke using thin-slice unenhanced CT: comparison of conventional sequential CT and helical CT

Objectives

Thin-slice helical unenhanced CT can be used for thrombus imaging but increases radiation exposure. Conventional sequential images obtained by multidetector CT can be reconstructed into thin-slice images. The purpose of this study was to evaluate if conventional sequential unenhanced CT images can replace helical unenhanced CT for thrombus imaging.

Methods

Fifty consecutive patients with acute ischaemic stroke underwent both 5-mm conventional sequential unenhanced CT and helical unenhanced CT. Each of the sequential and helical unenhanced CT images was subsequently reconstructed into four 1.25-mm images. Thrombus volumes and HU were measured semi-automatically using both types of unenhanced CT. Thrombus HU ratio (rHU) was calculated using the HU of the contralateral segment. The intraclass correlation coefficient (ICC) and Bland–Altman plots were used to assess measurement agreement.

Results

The mean rHUs were 1.47?±?0.17 for sequential unenhanced CT and 1.47?±?0.18 helical unenhanced CT (P?=?0.542). The mean thrombus volumes were 124.25?±?125.65?mm³ and 117.84?±?124.32?mm³ on sequential and helical unenhanced CT images, respectively (P?=?0.063). Measurement agreement between thrombus volumes from the two unenhanced CT images was high (ICC?=?0.981).

Conclusions

Thin-slice unenhanced CT images reconstructed from 5-mm sequential images can replace helical unenhanced CT for thrombus imaging in acute ischaemic stroke.

Key Points

? Unenhanced CT is used to evaluate intra-arterial thrombus. ? Thrombus HU and volume measurements using sequential or helical CT are comparable. ? Conventional sequential images can replace helical CT for thrombus imaging. ? Radiation dose for thrombus imaging can be reduced using sequential CT.     

Preliminary report on virtual monochromatic spectral imaging with fast kVp switching dual energy head CT: comparable image quality to that of 120-kVp CT without increasing the radiation dose

Purpose

This study aimed to evaluate whether the image quality of virtual monochromatic spectral imaging with fast kVp switching dual-energy CT (DECT) can be comparable to that of 120-kVp single-energy CT (SECT) without increasing the radiation dose.

Materials and methods

We retrospectively identified 15 postoperative patients who had undergone both DECT and 120-kVp SECT within a short period of time for follow-up after brain surgery. Simulated 65 keV monochromatic images were reconstructed from DECT data. Subjective image noise, gray–white matter contrast, and overall image quality were rated using a four-point scale. Quantitative measurement of noise, contrast-to-noise ratio (CNR), and posterior fossa beam-hardening artifact were also performed. The figure of merit (FOM), calculated as CNR²/CTDI_vol, was used to quantify image quality improvement per exposure risk.

Results

The mean CTDI_vol was 70.2 ± 0.3 mGy for DECT, which was 11 % lower than SECT (78.9 ± 2.1 mGy). All images were graded above clinically acceptable. Quantitative and qualitative measures for simulated 65-keV images were comparable with SECT images, except for increase in subjective noise. FOM was significantly greater for simulated 65-keV images (P = .03).

Conclusion

Our results indicate that virtual monochromatic imaging possibly provides comparable image quality to that afforded by 120-kVp SECT without increasing the dose in routine head CT.     

Subtracted 3D CT angiography for the evaluation of intracranial aneurysms in 256-slice multidetector CT: usefulness of the 80-kVp plus compact contrast medium bolus protocol

Objectives

To evaluate the usefulness of an 80-kVp and compact contrast material protocol for arterial phase subtracted cerebral 3D-CTA using 256-slice multidetector CT.

Methods

Thirty-two patients underwent CT with 100 kVp and received a contrast dose of 370 mgI/kg body weight over 15 s (protocol A). Thirty-three patients underwent CT with 100 kVp and received a contrast dose of 296 mgI/kg body weight over 10 s (protocol B). Thirty-three other patients underwent CT with 80 kVp and received a contrast medium dose of 296 mgI/kg body weight over 10 s (protocol C). We compared the arterial attenuation and contrast noise ratio (CNR) of each protocol. Two independent readers assessed overall image quality.

Results

Arterial attenuation was significantly higher under protocols A (418.6?±?71.1 HU) and C (442.7?±?79.3 HU) than under protocol B (355.8?±?107.2 HU; P?<?0.05). The CNR of protocol C (26.1?±?6.1) was higher than that of protocol A (20.7?±?8.4; P?<?0.05). The overall image quality of protocol A was higher than that of protocol C (P?<?0.01).

Conclusion

The 80-kVp plus compact contrast protocol is well suited to arterial phase subtracted cerebral 3D-CTA without confounding venous enhancement.

Key Points

? Subtracted 3D CT angiography is useful in the evaluation of intracranial aneurysms. ? A compact contrast material protocol increased arterial attenuation without venous contamination. ? Low-kVp CT compensated for the decreased amount of contrast medium. ? An 80-kVp CT with a compact enhancement bolus provides good intracranial 3D-CT angiography.     

The role of dual energy CT in differentiating between brain haemorrhage and contrast medium after mechanical revascularisation in acute ischaemic stroke

Objectives

To assess the feasibility of dual energy computed tomography (DE-CT) in intra-arterially treated acute ischaemic stroke patients to discriminate between contrast extravasation and intracerebral haemorrhage.

Methods

Thirty consecutive acute ischaemic stroke patients following intra-arterial treatment were examined with DE-CT. Simultaneous imaging at 80 kV and 140 kV was employed with calculation of mixed images. Virtual unenhanced non-contrast (VNC) images and iodine overlay maps (IOM) were calculated using a dedicated brain haemorrhage algorithm. Mixed images alone, as “conventional CT”, and DE-CT interpretations were evaluated and compared with follow-up CT.

Results

Eight patients were excluded owing to a lack of follow-up or loss of data. Mixed images showed intracerebral hyperdense areas in 19/22 patients. Both haemorrhage and residual contrast material were present in 1/22. IOM suggested contrast extravasation in 18/22 patients; in 16/18 patients this was confirmed at follow-up. The positive predictive value (PPV) of mixed imaging alone was 25 %, with a negative predictive value (NPV) of 91 % and accuracy of 63 %. The PPV for detection of haemorrhage with DE-CT was 100 %, with an NPV of 89 % and accuracy improved to 89 %.

Conclusions

Dual energy computed tomography improves accuracy and diagnostic confidence in early differentiation between intracranial haemorrhage and contrast medium extravasation in acute stroke patients following intra-arterial revascularisation.

Key Points

? Contrast material and haemorrhage have similar density on conventional 120-kV CT. ? Contrast material hinders interpretation of CT in stroke patients after recanalisation. ? Iodine and haemorrhage have different attenuation at lower kVs. ? Dual energy CT improves accuracy in early differentiation of haemorrhage and contrast extravasation. ? Early differentiation between iodine and haemorrhage helps to initiate therapy promptly.     

Determination of optimal intravenous contrast agent iodine dose for the detection of liver metastasis at 80-kVp CT

Objectives

To determine the optimal iodine mass (IM) to achieve a 50-HU increase in hepatic attenuation for the detection of liver metastasis based on total body weight (TBW) or body surface area (BSA) at 80-kVp computed tomography (CT) imaging of the liver.

Methods

One-hundred and fifty patients who underwent contrast-enhanced CT at 80-kVp were randomised into three groups: 0.5 gI/kg, 0.4 gI/kg and 0.3 gI/kg. Portal venous phase images were evaluated for hepatic parenchymal enhancement (?HU) and visualisation of liver metastasis. Iodine mass per BSA (gI/m²) calculated in individual patients were evaluated.

Results

Mean ?HU for the 0.5 gI/kg group (84.2 HU) was higher than in the 0.4 gI/kg (66.1 HU) and 0.3 gI/kg (53.7 HU) groups (P?<?0.001). Linear correlation equations between ?HU and IM per TBW or BSA are ?HU?=?7.0?+?153.0?×?IM/TBW (r?=?0.73, P?<?0.001) and ?HU?=?11.4?+?4.0?×?IM/BSA (r?=?0.75, P?<?0.001), respectively. The three groups were comparable for the visualisation of hepatic metastases.

Conclusions

The iodine mass to achieve a 50-HU increase in hepatic attenuation at 80-kVp CT was estimated to be 0.28 gI/kg of body weight or 9.6 gI/m² of body surface area.

Key Points

? Hepatic enhancement is expressed as ?HU?=?7.0?+?153.0?×?IM [g]/TBW [kg]. ? Hepatic enhancement is expressed as ?HU?=?11.4?+?4.0?×?IM [g]/BSA [m ² ]. ? Essential iodine dose at 80-kVp CT was 0.28 gI/kg or 9.6 gI/m ² .     

Combining automated attenuation-based tube voltage selection and iterative reconstruction: a liver phantom study

Objectives

To determine the value of combined automated attenuation-based tube-potential selection and iterative reconstructions (IRs) for optimising computed tomography (CT) imaging of hypodense liver lesions.

Methods

A liver phantom containing hypodense lesions was imaged by CT with and without automated attenuation-based tube-potential selection (80, 100 and 120 kVp). Acquisitions were reconstructed with filtered back projection (FBP) and sinogram-affirmed IR. Image noise and contrast-to-noise ratio (CNR) were measured. Two readers marked lesion localisation and rated confidence, sharpness, noise and image quality on a five-point scale (1 = worst, 5 = best).

Results

Image noise was lower (31–52 %) and CNR higher (43–102 %) on IR than on FBP images at all tube voltages. On 100-kVp and 80-kVp IR images, confidence and sharpness were higher than on 120-kVp FBP images. Scores for image quality score and noise as well as sensitivity for 100-kVp IR were similar or higher than for 120-kVp FBP and lower for 80-kVp IR. Radiation dose was reduced by 26 % at 100 kVp and 56 % at 80 kVp.

Conclusions

Compared with 120-kVp FBP images, the combination of automated attenuation-based tube-potential selection at 100 kVp and IR provides higher image quality and improved sensitivity for detecting hypodense liver lesions in vitro at a dose reduced by 26 %.

Key Points

? Combining automated tube voltage selection/iterative CT reconstruction improves image quality. ? Attenuation values remain stable on IR compared with FBP images. ? Lesion detection was highest on 100-kVp IR images.     

Clinical evaluation of automatic tube voltage selection in chest CT angiography

Objective

To evaluate the clinical impact of automatic tube voltage selection on chest CT angiography (CTA).

Methods

Ninety-three patients were prospectively evaluated with a CT protocol aimed at comparing two successive CTAs acquired under similar technical conditions except for the kV selection: (1) the initial CTA was systematically obtained at 120 kVp and 90 ref mAs; (2) the follow-up CTA was obtained with an automatic selection of the kilovoltage (Care KV; Siemens Healthcare) for optimised CTA.

Results

At follow-up, 90 patients (97 %) underwent CTA with reduced tube voltage, 100 kV (n?=?26; 28 %) and 80 kV (n?=?64; 69 %), resulting in a significant dose-length-product reduction (follow-up: 87.27; initial: 141.88 mGy.cm; P?<?0.0001; mean dose reduction: 38.5 %) and a significant increase in the CNR at follow-up (follow-up: 11.5?±?3.5 HU; initial: 10.9?±?3.7 HU; P?=?0.03). The increase in objective image noise at follow-up (follow-up: 23.2?±?6.7 HU vs. 17.8?±?5.1 HU; P?<?0.0001) did not alter the diagnostic value of images.

Conclusion

Automatic tube voltage selection reduced the radiation dose delivered during chest CT angiograms by 38.5 % while improving the contrast-to-noise ratio of the examinations.

Key Points

? As low a dose as possible must be used for CT angiography. ? Automatic tube voltage selection permits reduced patient exposure. ? Lowering the kVp enables increased intravascular attenuation. ? Automatic tube voltage selection does not compromise the overall image quality.     

Initial experience with single-source dual-energy CT abdominal angiography and comparison with single-energy CT angiography: image quality, enhancement, diagnosis and radiation dose

Objectives

To assess image quality of virtual monochromatic spectral (VMS) images, compared to single-energy (SE) CT, and to evaluate the feasibility of material density imaging in abdominal aortic disease.

Methods

In this retrospective study, single-source (ss) dual-energy (DE) CT of the aorto-iliac system in 35 patients (32 male, mean age 76.5 years) was compared to SE-CT. By post-processing the data from ssDECT, VMS images at different energies and material density water (WD) images were generated. The image quality parameters were rated on 5-point scales. The aorto-iliac attenuation and contrast-to-noise ratio (CNR) were recorded. Quality of WD images was compared to true unenhanced (TNE) images. Radiation dose was recorded and statistical analysis was performed.

Results

Image quality and noise were better at 70 keV (P?<?0.01). Renal artery branch visualisation was better at 50 keV (P?<?0.005). Attenuation and CNR were higher at 50 and 70 keV (P?<?0.0001). The WD images had diagnostic quality but higher noise than TNE images (P?<?0.0001). Radiation dose was lower using single-phase ssDECT compared to dual-phase SE-CT (P?<?0.0001).

Conclusion

70-keV images from ssDECT provide higher contrast enhancement and improved image quality for aorto-iliac CT when compared to SE-CT at 120 kVp. WD images are an effective substitute for TNE images with a potential for dose reduction.

Key Points

? Multi-detector computed tomography (MDCT) angiography is now a routine procedure. ? Single-source dual-energy CT (ssDECT) can provide simultaneous data with different kilovoltages. ? 70 keV images showed better image quality than conventional single-energy (SE) CT. ? 70 keV images exhibited less image noise in comparison to SE-CT.     

Accuracy of early CT findings for predicting disease course in patients with acute pancreatitis

Purpose

To investigate whether computed tomography (CT)-based scoring systems obtained within 72 h of symptoms onset can predict disease course in acute pancreatitis.

Methods

Between October 2007 and December 2015, 189 patients (age range 21–93 years) who underwent abdominopelvic CT for the diagnosis of acute pancreatitis were included in the study. Balthazar grade and original and modified versions of CT severity index (CTSI) measurements were carried out for each patient.

Results

There were significant associations between each CT based scoring system and development of pancreatic and extrapancreatic complications (p < 0.001). A cutoff value of > 6 for CTSI and > 9 for the modified version of CTSI achieved a specificity of 98.7 and 99.2% for predicting pancreatic and extrapancreatic complications with areas under the curve (AUC) of 0.96 and 0.96, respectively. Balthazar grade of > C yielded a sensitivity of 98.4% for predicting pancreatic and extrapancreatic complications with an AUC of 0.95. The modified version of CTSI had the most significant association with pancreatic and extrapancreatic complications (HR: 3.22; p = 0.002, HR: 2.99, p = 0.003, respectively). Pancreatic necrosis was the only parameter significantly associated with mortality (HR: 5.83, p = 0.045).

Conclusion

Early CT scan has an important role in prediction of complications and the management of acute pancreatitis.

     

Urinary stone detection and characterisation with dual-energy CT urography after furosemide intravenous injection: preliminary results

Objectives

To investigate the added advantage of IV furosemide injection and the subsequent urine dilution in the detection of urinary calculi in the excretory phase of dual-source dual-energy (DE) computed tomography (CT) urography, and to investigate the feasibility of characterising the calculi through diluted urine.

Methods

Twenty-three urinary calculi were detected in 116 patients who underwent DECT urography for macroscopic haematuria with a split bolus two- or three-acquisition protocol, including a true unenhanced series and at least a mixed nephrographic excretory phase. Virtual unenhanced images were reconstructed from contrast-enhanced DE data. Calculi were recorded on all series and characterised based on their X-ray absorption characteristics at 100 kVp and 140 kVp in both true unenhanced and nephrographic excretory phase series.

Results

All calculi with a diameter more than 2 mm were detected in the virtual unenhanced phase and in the nephrographic excretory phase. Thirteen of these calculi could be characterised in the true unenhanced phase and in the mixed nephrographic excretory phase. The results were strictly identical for both phases, six of them being recognised as non-uric acid calculi and seven as uric acid calculi.

Conclusions

Mixed nephrographic excretory phase DECT after furosemide administration allows both detection and characterisation of clinically significant calculi, through the diluted urine.

Key points

? Urinary tract stones can be detected on excretory phase through diluted urine. ? Urinary tract stone characterisation with dual-energy CT (DECT) is possible through diluted urine. ? A dual energy split-bolus CT urography simultaneously enables urinary stone detection and characterisation.     

Value of CT angiography for the detection of intracranial vascular lesions in patients with acute severe headache

Objectives

To retrospectively investigate the prevalence and characteristics of intracranial vascular lesions in patients with acute severe headache with the use of CT angiography (CTA).

Methods

We systematically searched for neurologically intact patients with acute severe headache and normal unenhanced head CT. The study group consisted of 512 patients; 251 male; mean age 46.2?±?12.4 years. All patients underwent CTA between 1 day and 2 months after the headache attack. CTA images were interpreted by two experienced neuroradiologists for the presence of vascular lesions.

Results

Thirty-four (6.6 %) of the 512 patients had intracranial vascular lesions on CTA, including 33 aneurysms (2 patients had 2 aneurysms each), 2 moyamoya disease and 1 arterial dissection. No gender- or age-related differences were found. Aneurysms arose most commonly on the internal carotid artery (n?=?12), followed by the anterior communicating artery (n?=?7), and the middle cerebral artery (n?=?7). Maximal diameters ranged from 2.0 to 13.1 mm (mean, 3.9?±?2.6 mm).

Conclusions

CTA is a feasible tool for diagnosing intracranial vascular lesions in patients with acute severe headache. The prevalence of vascular lesions in our series was 6.6 %, which is higher than that predicted in the general population.

Key Points

? Unruptured cerebral aneurysms may be a cause of acute severe headache ? CTA assesses intracranial vascular lesions in patients with acute severe headache ? The prevalence of vascular lesions in our series of patients was 6.6 %     

Low-tube-voltage (80 kVp) CT aortography using 320-row volume CT with adaptive iterative reconstruction: lower contrast medium and radiation dose

Objectives

To evaluate CT aortography at reduced tube voltage and contrast medium dose while maintaining image quality through iterative reconstruction (IR).

Methods

The Institutional Review Board approved a prospective study of 48 patients who underwent follow-up CT aortography. We performed intra-individual comparisons of arterial phase images using 120 kVp (standard tube voltage) and 80 kVp (low tube voltage). Low-tube-voltage imaging was performed on a 320-detector CT with IR following injection of 40 ml of contrast medium. We assessed aortic attenuation, aortic attenuation gradient, image noise, contrast-to-noise ratio (CNR), volume CT dose index (CTDI_vol), and figure of merit (FOM) of image noise and CNR. Two readers assessed images for diagnostic quality, image noise, and artefacts.

Results

The low-tube-voltage protocol showed 23–31 % higher mean aortic attenuation and image noise (both P?<?0.01) than the standard-tube-voltage protocol, but no significant difference in the CNR and aortic attenuation gradients. The low-tube-voltage protocol showed a 48 % reduction in CTDI_vol and an 80 % increase in FOM of CNR. Subjective diagnostic quality was similar for both protocols, but low-tube-voltage images showed greater image noise (P?=?0.01).

Conclusions

Application of IR to an 80-kVp CT aortography protocol allows radiation dose and contrast medium reduction without affecting image quality.

Key Points

? CT aortography at 80 kVp allows a significant reduction in radiation dose. ? Addition of iterative reconstruction reduces image noise and improves image quality. ? The injected contrast medium dose can be substantially reduced at 80 kVp. ? Aortic enhancement is uniform despite a reduced volume of contrast medium.     

CT perfusion technique for assessment of early kidney allograft dysfunction: preliminary results

Objectives

To assess the benefit of quantitative computed tomography (CT) perfusion for differentiating acute tubular necrosis (ATN) and acute rejection (AR) in kidney allografts.

Methods

Twenty-two patients with acute kidney allograft dysfunction caused by either AR (n?=?6) or ATN (n?=?16) were retrospectively included in the study. All patients initially underwent a multiphase CT angiography (CTA) protocol (12 phases, one phase every 3.5 s) covering the whole graft to exclude acute postoperative complications. Multiphase CT dataset and dedicated software were used to calculate renal blood flow. Renal biopsy or clinical course of disease served as the standard of reference. Mean effective radiation dose and mean amount of contrast media were calculated.

Results

Renal blood flow values were significantly lower (P?=?0.001) in allografts undergoing AR (48.3?±?21 ml/100 ml/min) compared with those with ATN (77.5?±?21 ml/100 ml/min). No significant difference (P?=?0.71) was observed regarding creatinine level with 5.65?±?3.1 mg/dl in AR and 5.3?±?1.9 mg/dl in ATN. The mean effective radiation dose of the CT perfusion protocol was 13.6?±?5.2 mSv; the mean amount of contrast media applied was 34.5?±?5.1 ml. All examinations were performed without complications.

Conclusion

CT perfusion of kidney allografts may help to differentiate between ATN and rejection.

Key points

? Quantitative CT perfusion of renal transplants is feasible. ? CT perfusion could help to non-invasively differentiate AR from ATN. ? CT perfusion might make some renal biopsies unnecessary.     

Radiation dose reduction using 100-kVp and a sinogram-affirmed iterative reconstruction algorithm in adolescent head CT: Impact on grey–white matter contrast and image noise

Objectives

To retrospectively evaluate the image quality and radiation dose of 100-kVp scans with sinogram-affirmed iterative reconstruction (IR) for unenhanced head CT in adolescents.

Methods

Sixty-nine patients aged 12–17 years underwent head CT under 120- (n?=?34) or 100-kVp (n?=?35) protocols. The 120-kVp images were reconstructed with filtered back-projection (FBP), 100-kVp images with FBP (100-kVp-F) and sinogram-affirmed IR (100-kVp-S). We compared the effective dose (ED), grey–white matter (GM–WM) contrast, image noise, and contrast-to-noise ratio (CNR) between protocols in supratentorial (ST) and posterior fossa (PS). We also assessed GM–WM contrast, image noise, sharpness, artifacts, and overall image quality on a four-point scale.

Results

ED was 46% lower with 100- than 120-kVp (p?<?0.001). GM–WM contrast was higher, and image noise was lower, on 100-kVp-S than 120-kVp at ST (p?<?0.001). CNR of 100-kVp-S was higher than of 120-kVp (p?<?0.001). GM–WM contrast of 100-kVp-S was subjectively rated as better than of 120-kVp (p?<?0.001). There were no significant differences in the other criteria between 100-kVp-S and 120-kVp (p?=?0.072–0.966).

Conclusions

The 100-kVp with sinogram-affirmed IR facilitated dramatic radiation reduction and better GM–WM contrast without increasing image noise in adolescent head CT.

Key points

? 100-kVp head CT provides 46% radiation dose reduction compared with 120-kVp.? 100-kVp scanning improves subjective and objective GM–WM contrast.? Sinogram-affirmed IR decreases head CT image noise, especially in supratentorial region.? 100-kVp protocol with sinogram-affirmed IR is suited for adolescent head CT.

     

Volumetric low-tube-voltage CT imaging for evaluating hypervascular hepatocellular carcinoma; effects on radiation exposure, image quality, and diagnostic performance

Objectives

To assess the value of hepatic arterial-phase (HAP) imaging with a low tube voltage (80 kVp), using non-helical, volumetric acquisition with a 320-detector-rows area-detector CT (ADCT) scanner for evaluating hypervascular hepatocellular carcinoma (HCC) compared with routine 120-kVp HAP imaging.

Methods

This study enrolled 128 patients with 148 HCCs. Seventy-six patients with 79 HCCs underwent HAP imaging with 80 kVp obtained using a 320-detector-rows ADCT scanner. The remaining 52 patients with 69 HCCs underwent routine HAP imaging with 120 kVp obtained by 64-slice helical acquisition. Image noise and tumor to liver contrast-to-noise ratio (CNR) of the two sets of images were compared. Three radiologists evaluated both sets of images using receiver operating characteristic analyses.

Results

Although there was a two-fold increase in the mean image noise with 80 kVp over that with 120 kVp (p < 0.001), no significant differences were observed in CNR among the two sets. The mean area under the curve (Az value) and the sensitivity for detecting HCC with 80 kVp (0.980, 78/79, respectively) were higher than that of 120 kVp (0.892, 55/69, respectively).

Conclusions

HAP imaging with 80 kVp obtained by an ADCT scanner significantly improves the diagnostic performance for evaluating hypervascular HCC.     

A comparative study between arterial spin labeling and CT perfusion methods on hepatic portal venous flow

Purpose

The purpose of this study was to evaluate the feasibility and potential usefulness of unenhanced magnetic resonance (MR) hepatic portal perfusion using arterial spin labeling (ASL) among healthy volunteers and hepatocellular carcinoma patients.

Materials and methods

The five healthy volunteers underwent unenhanced MR perfusion with inversion time 2 (TI2) values at 500-ms intervals between 2,000 and 4,000 ms, and the 12 patients underwent unenhanced MR perfusion using ASL and computed tomography (CT) perfusion during superior mesenteric artery (SMA) portography. The regions of interest were placed in both the right and left lobes of the liver or both the right anterior and posterior segments of the liver and were placed over the tumor if a lesion was located within a particular perfusion study slice.

Results

In the healthy volunteer study, perfusion rate in hepatic parenchyma showed a peak at the TI2 value of 3,000 ms (254.3 ml/min/100 g ± 58.3). In patients, a fair correlation was observed between CT and MR perfusion (r = 0.795, P < 0.01).

Conclusion

Our results demonstrate a significant fair correlation between unenhanced MR hepatic portal perfusion imaging using ASL and CT perfusion during SMA portography.     

Diffusion-weighted MRI for distinguishing non-neoplastic cysts from solid masses in the mediastinum: problem-solving in mediastinal masses of indeterminate internal characteristics on CT

Objectives

To evaluate the usefulness of diffusion-weighted (DW) magnetic resonance images for distinguishing non-neoplastic cysts from solid masses of indeterminate internal characteristics on computed tomography (CT) in the mediastinum.

Methods

We enrolled 25 patients with pathologically proved mediastinal masses who underwent both thoracic CT and magnetic resonance imaging (MRI) including diffusion-weighted imaging (DWI). MRI was performed in patients with mediastinal masses of indeterminate internal characteristics on CT. Two thoracic radiologists evaluated the morphological features and quantitatively measured the net enhancement of the masses at CT. They also reviewed MR images including unenhanced T1- and T2-weighted images, gadolinium-enhanced images and DW images.

Results

The enrolled patients had 15 solid masses and ten non-neoplastic cysts. Although the morphological features and the extent of enhancement on CT did not differ significantly between solid and cystic masses in the mediastinum (P?>?0.05), non-neoplastic cysts were distinguishable from solid masses by showing signal suppression on high-b-value DW images or high apparent diffusion coefficient (ADC) values of more than 2.5?×?10^-3 mm²/s (P?<?0.001). ADC values of non-neoplastic cysts (3.67?±?0.87?×?10^-3 mm²/s) were significantly higher than that of solid masses (1.46?±?0.50?×?10^-3 mm²/s) (P?<?0.001).

Conclusions

DWI can help differentiate solid and cystic masses in the mediastinum, even when CT findings are questionable.

Key Points

? Non-invasive diagnosis of non-neoplastic cysts can save surgical biopsy or excision. ? Conventional CT or MRI findings cannot always provide a confident diagnosis. ? Mediastinal masses can be well-characterised with DWI. ? Non-neoplastic mediastinal cysts show significantly higher ADC values than cystic tumours. ? DWI is useful to determine treatment strategy.     

Triphasic CT in the diagnosis of acute mesenteric ischaemia

Objective

To evaluate the yield of each phase in a triphasic CT protocol used to diagnose acute mesenteric ischaemia (AMI).

Methods

Retrospective analysis of patients who underwent CT to exclude AMI was conducted. From 218 patients, 80 were randomly selected for analysis: 39 with proven AMI; 41 controls. Three readers evaluated the studies; two readers were provided with only portions of the examination to determine the yield of unenhanced CT (NECT) and CT angiography (CTA). The diagnostic accuracy of CT findings was calculated and compared between readers.

Results

The sensitivity and specificity of submucosal haemorrhage were 10 % and 98 %. Interobserver variability was poor (κ?=?0.17). All true-positive cases had other CT findings of AMI (n?=?4). There was no difference in the assessment of bowel enhancement between readers (P?<?0.05). There was no difference between readers (P?<?0.05) and interobserver variability was moderate to good when diagnosing arterial abnormalities without CTA. Sample size was small and errors occurred when using only the portal venous phase for this purpose.

Conclusion

NECT is not required for diagnosis of AMI. Splanchnic arterial abnormalities can be diagnosed without CTA although errors occur when using only the portal venous phase for this purpose.

Key points

? Triphasic CT is the current gold standard for diagnosing acute mesenteric ischaemia. ? Multiphase CT multiplies the radiation dose when compared to single phase CT. ? Each phase in a multiphase CT examination should be independently validated. ? Unenhanced CT is not required for diagnosis of acute mesenteric ischaemia. ? CT angiography should be performed for diagnosis of acute mesenteric ischaemia.     

Dual-energy CT with tin filter technology for the discrimination of renal lesion proxies containing blood, protein, and contrast-agent. An experimental phantom study

Purpose

To differentiate proxy renal cystic lesions containing protein, blood, iodine contrast or saline solutions using dual-energy CT (DECT) equipped with a new tin filter technology (TFT).

Materials and methods

70 proxies (saline, protein, blood and contrast agent) were placed in unenhanced and contrast-enhanced kidney phantoms. DECT was performed at 80/140 kV with and without tin filtering. Two readers measured the CT attenuation values in all proxies twice. An 80/140 kV ratio was calculated.

Results

All intra- and interobserver agreements were excellent (r?=?0.93–0.97; p?<?0.001). All CT attenuation values were significantly higher in the enhanced than in the unenhanced setting (p?<?0.05; average increase, 12.5?±?3.6HU), while the ratios remained similar (each, p?>?0.05). The CT attenuation of protein, blood and contrast agent solution differed significantly with tin filtering (p?<?0.01–0.05). Significant differences were found between the ratios of protein and blood compared to contrast medium solution (each, p?<?0.05) and between the ratios of protein and blood in both phantoms with tin filtering (each, p?<?0.05).

Conclusion

DECT allows discrimination between a proxy renal lesion containing contrast agent and lesions containing protein and blood through their different attenuation at 80 kV and 140 kV. Further discrimination between protein and blood containing proxies is possible when using a tin filter.     

The Image Quality and Radiation Dose of 100-kVp versus 120-kVp ECG-Gated 16-Slice CT Coronary Angiography

Objective

This study was conducted to assess the feasibility of performing 100-kVp electrocardiogram (ECG)-gated coronary CT angiography, as compared to 120-kVp ECG-gated coronary CT angiography.

Materials and Methods

We retrospectively evaluated one hundred eighty five gender- and body mass index-matched 16-slice coronary CT sets of data, which were obtained using either 100 kVp and 620 effective mAs or 120 kVp and 500 effective mAs. The density measurements (image noise, vessel density, signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) and the estimated radiation dose were calculated. As a preference test, two image readers were independently asked to choose one image from each pair of images. The results of both protocols were compared using the paired t-test or the Wilcoxon signed rank test.

Results

The 100-kVp images showed significantly more noise and a significantly higher vessel density than did the 120-kVp images. There were no significant differences in the SNR and CNR. The estimated reduction of the radiation dose for the 100-kVp protocol was 24%; 7.8 ± 0.4 mSV for 100-kVp and 10.1 ± 1.0 mSV for 120-kVp (p < 0.001). The readers preferred the 100-kVp images for reading (reader 1, p = 0.01; reader 2, p = 0.06), with their preferences being stronger when the subject''s body mass index was less than 25.

Conclusion

Reducing the tube kilovoltage from 120 to 100 kVp allows a significant reduction of the radiation dose without a significant change in the SNR and the CNR.