A relatively new CT technique, photon-counting CT, shows promise for reducing radiation dose by more than a third, researchers have found. They published their results June 24 in Academic Radiology.
The findings are good news for cancer patients, who often undergo many CT exams in the course of diagnosis and treatment, wrote a team led by Dr. Robin Wrazidlo of Eberhard-Karls University in Tübingen, Germany.
"In oncologic patients, who are repeatedly being referred to CT for treatment monitoring, dose accumulation during their medical history may become relevant," the group noted. "Hence, dose reduction in CT has gained increasing attention among radiologists and patients."
CT is the go-to modality for oncology imaging, and its advantages include widespread availability, short image acquisition times, relatively low cost, and high spatial resolution, the authors noted. But cancer patients have repeated CT exams, making it important to manage their radiation exposure.
That's where photon-counting CT could prove useful. The technique counts each individual x-ray photon as it passes through the patient, "converting incoming photons into electronic signals proportional to their deposited energy," the researchers wrote -- a quality that appears to translate into reduced radiation dose without affecting image quality. The U.S. Food and Drug Administration (FDA) cleared the first device in September 2021 (Naeotom Alpha, Siemens Healthineers).
"[The photon-counting CT] ... seems to be highly promising in terms of radiation dose reduction," the team explained.
Wradzidlo and colleagues compared image quality and radiation dose between a dual-energy CT (DECT) device and a photon-counting CT scanner. Their study included 70 patients who underwent abdominal, contrast-enhanced CT between November 2021 and February 2022. The patients had both a DECT exam and a follow-up exam with a photon-counting device (median time between the two scans was four months). The researchers assessed radiation dose between the two types of studies using the following metrics: CT dose index, dose length product, and size-specific dose estimation. Two radiologists scored the images for quality, particularly lesion visibility.
The group found that photon-counting CT reduced the size-specific dose estimation by 32%, without degrading image quality.
| Radiation dose comparison between dual energy CT and photon-counting CT | |||
| Measure | DECT | Photon-counting CT | p-value |
| CT dose index | 14.11 mGy | 7.98 mGy | < 0.001 |
| Dose length product | 693.6 mGy*cm | 393.1 mGy*cm | < 0.001 |
| Size-specific dose estimation | 14.63 mGy | 9.98 mGy | < 0.001 |
Additionally, the two readers rated lesion conspicuity higher on the photon-counting CT exams compared with the DECT exams, especially in the third quartile, the team noted.
Photon-counting CT shows real promise for a particular set of patients more vulnerable than most to radiation exposure, according to the authors.
"[Photon-counting CT] enables oncologic abdominal CT with a significantly reduced dose while retaining image quality similar to ... DECT," they concluded.
![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)
