Evaluation of a novel reconstruction method based on the compressed sensing technique: Application to cervical spine MR imaging.

Compressed sensing-based reconstruction (CSR) is a new magnetic resonance (MR) image reconstruction method based on the compressed sensing (CS) technique. CSR suppresses ringing artifacts from truncated k-space sampling by estimating the high spatial frequency information required to support the acquired k-space data. CSR is intended to replace the existing zero-fill interpolation (ZIP) reconstruction. We investigated the usefulness of the CSR technique by obtaining sagittal T2-weighted images of the cervical spine and phantom images using CSR or ZIP. Our results indicated that the CSR technique reduces truncation artifacts compared to ZIP without prolonging the scan time or impairing image sharpness.

Clinical evaluation of CT radiation dose in whole-body 18F-FDG PET/CT in relation to scout imaging direction and arm position.

OBJECTIVE: Radiation exposure in CT is modulated by automatic exposure control (AEC) mainly based on scout images. We evaluated CT radiation dose in whole-body PET/CT in relation to scout imaging direction and arm position, and investigated the behavior of AEC. METHODS: Eighty adult patients who underwent whole-body 18F-FDG PET/CT were divided into groups A, B, C, and D. The posteroanterior scout image alone (PA scout) was used for AEC-based dose modulation in groups A and B, while the posteroanterior and lateral scout images (PA + Lat scout) were used in groups C and D. Patients in groups A and C were imaged with their arms beside the head, while those in groups B and D were imaged with their arms at the sides of the trunk. Dose-length product provided by the scanner was recorded. The tube current value, a determinant of radiation dose, for each slice was plotted against slice location to produce a tube current modulation curve. The scan range was divided into seven anatomical regions, and regional tube current was defined as average tube current for each region. Effective dose was calculated for each region and then summed together. RESULTS: Regional tube current was higher in the body trunk and proximal thigh using the PA scout than using the PA + Lat scout, resulting in higher dose-length product and effective dose using the PA scout. A marked dose increase was shown in the shoulder especially using the PA scout. Spike-like high current at the top of the head was often observed in tube current modulation curves using the PA scout but not using the PA + Lat scout. Raising the arms increased tube current in the head and neck and decreased it in the chest and abdomen. Although dose-length product did not differ significantly depending on arm position, raising the arms decreased effective dose significantly. CONCLUSIONS: AEC-based CT dose modulation in whole-body PET/CT is affected by scout imaging direction and arm position, which should be considered to determine an optimal imaging protocol for whole-body PET/CT.

Super-early images of brain perfusion SPECT using 123I-IMP for the assessment of hyperperfusion in stroke patients.

OBJECTIVE: With the advancement of reperfusion therapy in stroke patients, assessment of perfusion status after therapy is gaining importance. Hyperperfusion tends to be underestimated by the conventional early imaging of 123I-IMP brain perfusion SPECT. We evaluated the utility of super-early imaging as an adjunct to early imaging for the assessment of postischemic hyperperfusion in stroke patients. METHODS: Sixty-seven patients who underwent 123I-IMP brain perfusion SPECT within 14 days after the onset of cerebral infarction were retrospectively analyzed. Super-early (4-10 min) and early (15-45 min) images were acquired using a dual-headed gamma camera. Postischemic hyperperfusion was visually assessed using the early images alone and then using both the super-early and early images, and the frequency of postischemic hyperperfusion and the confidence level of the judgement were evaluated. For quantitative evaluation of image contrast, the contrast ratios (the count ratios of the hyperperfused to normal areas) were calculated. RESULTS: The frequency of postischemic hyperperfusion was significantly higher using both the super-early and early images (28/67 patients) than using the early images alone (17/67 patients, p < 0.001). In 56 patients in whom judgement regarding the presence or absence of postischemic hyperperfusion was unchanged, the confidence level was increased in 8 patients using both image sets. The addition of the super-early SPECT images was judged to be useful and marginally useful in 14 and 15 patients, respectively. The contrast ratio was significantly higher on the super-early images (1.48 ± 0.25) than on the early images (1.26 ± 0.18, p < 0.001). CONCLUSIONS: The addition of super-early imaging to the conventional early imaging aids assessment of postischemic hyperperfusion by 123I-IMP brain perfusion SPECT and may contribute to management of stroke patients in the era of reperfusion therapy.

Methods for optimizing the display conditions of brain magnetic resonance images.

PURPOSE: To investigate a method for optimizing the display conditions of brain magnetic resonance (MR) images. MATERIALS AND METHODS: We retrospectively analyzed brain MR images of 120 adults classified into screening, acute cerebral infarction, and brain tumor groups (n = 40 each). Two observers independently displayed the images on a monitor and optimized the display conditions using the W/L and U/L methods. In the W/L method, the observers manipulated the width and level of the display window, while in the U/L method they manipulated the upper and lower levels of the window. The times required were compared between the two methods. Additionally, the appropriateness of the determined window setting was evaluated visually by the respective observer to exclude the possibility that rough, suboptimal adjustment shortened the adjustment time. RESULTS: For both observers and all groups, the time required for optimization was significantly shorter for the U/L method than for the W/L method. The appropriateness of the window setting for the U/L method was equal to or better than that for the W/L method. CONCLUSION: Manipulating the upper and lower levels of the display window appears to improve the efficiency of interpreting brain MR images through rapid optimization of the display condition.

Methods of CT Dose Estimation in Whole-Body ¹8F-FDG PET/CT.

UNLABELLED: We evaluated the effective dose (ED) of the CT component of whole-body PET/CT using software dedicated to CT dose estimation and from dose-length product (DLP) values to establish practical methods of ED estimation. METHODS: Eighty adult patients who underwent (18)F-FDG whole-body PET/CT were divided into groups A and B, each consisting of 20 men and 20 women. In group A, ED of the CT component was calculated using CT-Expo for 6 anatomic regions separately, and whole-body ED was obtained by summing the regional EDs (CT-Expo method). DLP was calculated for each of the 6 regions and multiplied by a corresponding conversion factor described in International Commission on Radiological Protection publication 102 to obtain the ED for each region (regional DLP method). Whole-body ED was also calculated as the product of a whole-body DLP value provided by the scanner automatically and a conversion factor (simple DLP method). Moreover, the ED/DLP values were calculated using whole-body ED estimated by the CT-Expo method and the scanner-derived DLP, to optimize the conversion factor. In group B, the optimized conversion factor was applied for the estimation of ED by the simple DLP method. RESULTS: In group A, the regional DLP method allowed an accurate estimation of mean whole-body ED as a result of counterbalance of mild overestimation in men and mild underestimation in women, regarding the CT-Expo method as a standard. The simple DLP method using a conversion factor for the trunk (0.015 mSv/mGy/cm) caused overestimation. On the basis of the ED/DLP values in group A, a modified conversion factor of 0.013 mSv/mGy/cm and sex-specific conversion factors of 0.012 and 0.014 mSv/mGy/cm for men and women, respectively, were determined. In group B, the use of the modified conversion factor improved accuracy, and the use of sex-specific conversion factors eliminated sex-dependent residual errors. CONCLUSION: ED of the CT component of whole-body PET/CT can be assessed by multiplying the scanner-derived DLP by a conversion factor optimized for whole-body PET/CT.

Diffusion-weighted imaging of local recurrent prostate cancer after radiation therapy: comparison with 22-core three-dimensional prostate mapping biopsy.

Accurate localization of local recurrence within the prostate gland is important to perform focal salvage therapy effectively with minimal complications. The purpose of this study was to evaluate the usefulness of diffusion-weighted imaging (DWI) in the detection and localization of prostate cancer recurrence in patients with biochemical failure after definitive radiation therapy using 22-core three-dimensional prostate mapping biopsy (3D-PMB) as a standard reference. Ten patients who underwent magnetic resonance imaging and 22-core 3D-PMB were retrospectively analyzed. For visual assessment of DWI, the prostate was divided into 22 regions corresponding to 3D-PMB. Two diagnostic radiologists determined the presence of abnormal high signal intensity in each region on DWI, and the results of DWI were compared with those of 3D-PMB. Of the 220 regions, 16 regions in six patients were positive for cancer on 3D-PMB, and 30 regions in six patients were judged as positive on DWI. On a patient-by-patient basis, sensitivity and specificity were 100% (6/6) and 100% (4/4), respectively. On a region-by-region basis, sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 69% (11/16), 91% (185/204), 37% (11/30), 97% (185/190) and 89% (196/220), respectively. For discrepant localization between DWI and pathology, DWI-positive and pathology-positive regions tended to be adjacent to each other. In conclusion, DWI is a useful tool for the detection and localization of recurrent prostate cancer in patients with biochemical failure after radiation therapy and may be helpful in the planning of focal salvage therapy.

Imaging findings of pelvic tumor thrombosis extending from sacral bone metastasis of adrenocortical carcinoma.

We report the imaging findings of a patient with adrenocortical carcinoma who showed pelvic tumor thrombosis extending from sacral bone metastasis. Contrast-enhanced computed tomography demonstrated extensive intraluminal filling defects in the pelvic veins. A lytic lesion in the sacrum was also noted and continuity between the sacral lesion and the filling defect in the branch of pelvic veins was indicated. The filling defects showed increased uptake on positron emission tomography with (18)F-fluorodeoxyglucose and single-photon emission computed tomography with (131)I-iodomethylnorcholesterol, and fusion images with computed tomography aided the localization of the increased uptake areas. Multimodality imaging may be beneficial for the characterization and localization of lesions in patients suspected of having metastatic adrenocortical carcinoma.

Phase I clinical study of NMK36: a new PET tracer with the synthetic amino acid analogue anti-[18F]FACBC.

OBJECTIVE: NMK36 is a novel PET tracer containing a synthetic amino acid analogue anti-[(18)F]FACBC as the active ingredient, and is under development for the use of tumor diagnosis. A Phase I clinical study of NMK36 was conducted to evaluate its safety, biodistribution, and radiation dosimetry in healthy volunteers. METHODS: Six healthy volunteers (Japanese male) received a bolus injection of NMK36 (174.4-201.4 MBq) intravenously. The safety of NMK36 was evaluated by monitoring signs/symptoms, electrocardiography, recording vital signs, and laboratory examinations at baseline and several time points in 6 days after injection. A total of 11 whole-body PET-CT scans were acquired up to 4 h post-injection, and venous blood and urine samples were also collected for 6 and 24 h post-injection, respectively. Based on the results of the biodistribution study, absorbed radiation dose was estimated by the MIRD method. RESULTS: Although two adverse events occurred after the injection of NMK36, they were mild and disappeared without any specific treatment. NMK36 preferentially accumulated in the pancreas and liver early after injection, followed by rapid clearance from the pancreas. Persistent uptake was observed in the skeletal muscle. NMK36 showed low uptake in the brain, and its urinary excretion was limited (5.40 ± 1.43% of the injected dose at 24 h post-injection). The liver was the critical organ, with a mean absorbed dose of 40.6 µGy/MBq. The estimated effective dose of NMK36 was 13.8 µSv/MBq, which was similar to or lower than those of radiotracers approved for clinical use including [(18)F]FDG. CONCLUSIONS: The findings of this study indicate that NMK36 is well tolerated. NMK36 has favorable characteristics for imaging brain and pelvic tumors, such as low brain uptake, slow urinary excretion, and high in vivo stability.

Value of high-dose radiation therapy for isolated osseous metastasis in breast cancer in terms of oligo-recurrence.

BACKGROUND: For many years, patients with recurrent or distant metastatic cancer have been considered to be at the last stage of their lives because it was considered that the cancer had spread throughout the whole body. However, the development of methods for the early detection of recurrence or distant metastases allows the detection of limited site recurrence or single organ metastases, called oligometastases or oligo-recurrence. Additional local treatment for oligometastatic or oligo-recurrent lesions such as radiation therapy could be efficacious. The purpose of the current study was to evaluate radiation therapy for solitary osseous metastasis of breast cancer in terms of oligometastasis and oligo-recurrence. PATIENTS AND METHODS: One hundred and thirteen breast cancer patients were treated with radiation therapy for osseous metastases at Kitasato University Hospital, Japan between January 1998 and March 2003. Out of them, seven patients had solitary osseous metastases with primary and other sites controlled. These patients were registered in the current study, three had lumber spine metastases, three pelvic and one thoracic spine. The median time between the initial treatment of the primary lesions and diagnosis of the osseous metastases was 44 months (range: 10-95 months). The median total radiation dose was 46 Gy (30-50 Gy; BED: biological effective dose, 39-60 Gy10). RESULTS: The median follow-up time was 40 months (range: 11-80 months). All the patients were alive at the last follow-up. Only one patient relapsed in terms of pain from the osseous metastasis. This patient was treated with 30 Gy (BED 39 Gy10) irradiation, the lowest total dose among the seven patients. CONCLUSION: Radiation therapy for solitary osseous metastasis might be efficacious and moreover, high dose could be useful for long-term pain relief of osseous metastasis.