SAN FRANCISCO - Iterative reconstruction helps tremendously when it comes to CT scanning, according to the experience of one U.K. facility. However, the real advancement in reconstruction is model-based iterative reconstruction (MBIR), which reduces dose to levels that could alter the way CT is used in the future.
Dr. Carl Roobottom from the Peninsula Radiology Academy in the U.K. presented his findings during the International Society for Computed Tomography (ISCT) meeting on Monday. During the same session, other presenters echoed Roobottom's sentiments regarding MBIR.
There are three types of reconstruction: filtered back projection (FBP), iterative reconstruction (IR), and MBIR. FBP has been a mainstay in the imaging community since the 1970s and makes computation simple, but also makes geometric assumptions, such as focusing on a particular point. In addition, FBP creates a noisy image.
The answer to a noisy image has been to turn the current up. "I suggest it's a little bit like having an old radio that you can't hear because of crackly noise, so you have to turn the volume up," Roobottom said. "The trouble with turning the volume up is the fact that because this is an inverse relationship, the less and less noise we want, the more and more tube current we have to give."
Iterative reconstruction on the other hand is insensitive to noise. And it produces images with incomplete datasets and also raw data. The data may also be postmanipulated so data can be blended afterward, Roobottom said. The problem is slice-based IR works through filtered back projection so it still has the inherent problems with FBP.
Model-based iterative reconstruction doesn't use FBP. It doesn't make any assumptions about the physics of the object, so it looks at the size of the focal spot, the voxel is a cubic voxel, and MBIR models all the different components of the imaging shape to reduce noise, he said.
"If we follow the analogy of the radio, FBP is like your old radio with noise. Slice-based or noise-based IR is like the good analog radio, and MBIR is more like you're DAB [digital auto broadcasting] radio or a good old British hi-fi," he said.
At the Peninsula Radiology Academy, clinicians used slice-based data and introduced a dose reduction by 40% across all their scans. There was very little difference in image quality compared with FBP. IR was used when images were inherently noisy. That means the technique was predominantly used with high-definition CT scanning of patients with a high body mass index.
Model-based iterative reconstruction is the same as adaptive statistical iterative reconstruction (ASIR) but provides dose reduction and resolution improvements. MBIR has the potential to move the goal post in a number of areas. For instance CT with MBIR can move into plain film doses, he said.
Other ISCT presenters shared Roobottom's enthusiasm for model-based iterative reconstruction.
Dr. Dominik Fleischmann from Stanford University in California said MBIR creates substantial improvement in image quality equating to the same or better image quality as FBP and IR, with at least 30% less dose.
Dr. Jeffrey Mendel, an assistant professor at Tufts University in Boston wonders why physicians are still using filtered back projection in the first place. After all, 1976, the year FBP was invented, is also the same year Microsoft was first trademarked, he noted.
![Examples of ultrasound findings and techniques. (A) Images in a 39-year-old male patient with a mass in the left thigh. The mass is heterogeneous on the B-mode US image (compared with the patient in D) and showed increased microvascularity (superb microvascular imaging [SMI]) and shear-wave elastography (SWE) values. Undifferentiated pleomorphic sarcoma was diagnosed at biopsy (with pleomorphic rhabdomyosarcoma in surgical specimen). (B) Images in an 18-year-old male patient with a mass in the left leg. The mass is hypoechoic on the B-mode image, with no other findings suggestive of malignancy. The lesion is in contact with the cortex of the tibia, which is slightly irregular. CT revealed a doubtful anteromedial tibial erosion. The microvascular study demonstrated high vascularization, suggestive of malignancy. Periosteal Ewing sarcoma was diagnosed with both histologic and immunohistochemical confirmation. (C) Images in a 69-year-old female patient with a lump growing on the outside of the left leg. Multiple SWE examinations were performed (please note the high values obtained in the measurements, whereas the color map highlights the stiffness relative to adjacent tissues). SMI showed areas of increased vascularization to target for sampling. Undifferentiated spindle cell sarcoma was diagnosed at biopsy, with residual leiomyosarcoma in the surgical specimen after neoadjuvant therapy. (D) Images in a 56-year-old female patient with a mass in the right thigh. The mass is heterogeneous at both B-mode ultrasound (similar to patient A) and MRI (coronal T2-weighted spectral attenuated inversion recovery [SPAIR]; T1-weighted pre-contrast and postcontrast imaging), which even shows uptake after the administration of paramagnetic contrast material, which is traditionally suggestive of malignancy. Low values at SMI and elastography are suggestive of benignity. Spindle cell lipoma was diagnosed at biopsy, with atypical spindle cell lipomatous tumor in the surgical specimen.](https://img.auntminnieeurope.com/mindful/smg/workspaces/default/uploads/2026/08/images-radiol250278fig2.APCFLSvX6p.jpg?auto=format%2Ccompress&fit=crop&h=100&q=70&w=100)
![Examples of ultrasound findings and techniques. (A) Images in a 39-year-old male patient with a mass in the left thigh. The mass is heterogeneous on the B-mode US image (compared with the patient in D) and showed increased microvascularity (superb microvascular imaging [SMI]) and shear-wave elastography (SWE) values. Undifferentiated pleomorphic sarcoma was diagnosed at biopsy (with pleomorphic rhabdomyosarcoma in surgical specimen). (B) Images in an 18-year-old male patient with a mass in the left leg. The mass is hypoechoic on the B-mode image, with no other findings suggestive of malignancy. The lesion is in contact with the cortex of the tibia, which is slightly irregular. CT revealed a doubtful anteromedial tibial erosion. The microvascular study demonstrated high vascularization, suggestive of malignancy. Periosteal Ewing sarcoma was diagnosed with both histologic and immunohistochemical confirmation. (C) Images in a 69-year-old female patient with a lump growing on the outside of the left leg. Multiple SWE examinations were performed (please note the high values obtained in the measurements, whereas the color map highlights the stiffness relative to adjacent tissues). SMI showed areas of increased vascularization to target for sampling. Undifferentiated spindle cell sarcoma was diagnosed at biopsy, with residual leiomyosarcoma in the surgical specimen after neoadjuvant therapy. (D) Images in a 56-year-old female patient with a mass in the right thigh. The mass is heterogeneous at both B-mode ultrasound (similar to patient A) and MRI (coronal T2-weighted spectral attenuated inversion recovery [SPAIR]; T1-weighted pre-contrast and postcontrast imaging), which even shows uptake after the administration of paramagnetic contrast material, which is traditionally suggestive of malignancy. Low values at SMI and elastography are suggestive of benignity. Spindle cell lipoma was diagnosed at biopsy, with atypical spindle cell lipomatous tumor in the surgical specimen.](https://img.auntminnieeurope.com/mindful/smg/workspaces/default/uploads/2026/08/images-radiol250278fig2.APCFLSvX6p.jpg?auto=format%2Ccompress&dpr=2&fit=crop&h=167&q=70&w=250)
