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Purpose <p>The aim of this study was to investigate the limits of diagnostics and therapy planning for patients with prostate cancer using non-time-of-flight <sup>18</sup>F/<sup>68</sup>Ga-PSMA PET/MRI under clinically challenging imaging conditions with small lesion sizes and low uptake. Lesion detectability and quantification accuracy were evaluated for different acquisition and reconstruction parameters in a systematic phantom study and subsequent on patient data.</p> Methods <p>PET/MRI measurements were performed using a small lesion NEMA phantom. PET data were acquired for nine different activity concentrations (AC). Data of a longer single-bed protocol in the pelvis or a shorter whole-body protocol were reconstructed using relative or absolute scatter correction (SC). PET images were analysed considering a ± 25% deviation range between imaged and true AC as acceptable. Thirteen PSMA-PET/MRI patients with primary lesions or lymph node metastasis &lt; 12&#xa0;mm in the pelvis were included in this study. The presence of the halo artefact was evaluated in six <sup>18</sup>F-PSMA and seven <sup>68</sup>Ga-PSMA PET/MRI patients. For 21 lesions (diameter 6.4–12.3&#xa0;mm) in total, the AC was quantified.</p> Results <p>For both radiotracers, the 9.7&#xa0;mm sphere was still visible at 0.16&#xa0;kBq/mL with emission times &gt; 40&#xa0;min. The 3.7&#xa0;mm sphere was only detectable at 22&#xa0;kBq/mL with emission times &gt; 4&#xa0;min. All spheres ≥ 6.5&#xa0;mm provide acceptable quantification at an AC of 1.32&#xa0;kBq/mL for <sup>18</sup>F PET/MRI protocols of ≥ 12&#xa0;min and 2.75&#xa0;kBq/mL for <sup>68</sup>Ga PET/MRI protocols. In phantom data, no halo artefact was observable and different SC methods had no impact on quantification. 4/6 <sup>18</sup>F-PSMA patients and 7/7 <sup>68</sup>Ga-PSMA patients showed a halo around the bladder using relative SC, which could be reduced in all patients using absolute SC. Comparing the minimum quantifiable AC (MQAC) from in the phantom study as a threshold to the patient data, all lesions provided acceptable quantification with values &gt; MQAC (AC 3.3–108.5&#xa0;kBq/mL) for equal reconstruction and acquisition parameters.</p> Conclusions <p>The results demonstrated that the detection of lesions in the sub-centimetre range and a reliable quantification of <sup>18</sup>F/<sup>68</sup>Ga-PSMA uptake using standard acquisition and reconstruction parameters within clinical PET/MRI protocols is possible. This allows for an individual assessment of potential therapy options for each patient.</p>

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Limitations in diagnostics and quantification of small lesions with low uptake in the clinical context of prostate 18F/68Ga-PSMA PET/MRI

  • 期刊论文

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  • 发表日期：

    2026年6月15日

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  • Maike E. Lindemann,
  • Walter Jentzen,
  • Alina Küper,
  • Pedro Fragoso Costa,
  • Marcel Gratz,
  • Lale Umutlu,
  • James Nagarajah,
  • Stephan G. Nekolla,
  • Ivo Rausch,
  • Ken Herrmann,
  • Harald H. Quick,
  • David Kersting

摘要

Purpose

The aim of this study was to investigate the limits of diagnostics and therapy planning for patients with prostate cancer using non-time-of-flight 18F/68Ga-PSMA PET/MRI under clinically challenging imaging conditions with small lesion sizes and low uptake. Lesion detectability and quantification accuracy were evaluated for different acquisition and reconstruction parameters in a systematic phantom study and subsequent on patient data.

Methods

PET/MRI measurements were performed using a small lesion NEMA phantom. PET data were acquired for nine different activity concentrations (AC). Data of a longer single-bed protocol in the pelvis or a shorter whole-body protocol were reconstructed using relative or absolute scatter correction (SC). PET images were analysed considering a ± 25% deviation range between imaged and true AC as acceptable. Thirteen PSMA-PET/MRI patients with primary lesions or lymph node metastasis < 12 mm in the pelvis were included in this study. The presence of the halo artefact was evaluated in six 18F-PSMA and seven 68Ga-PSMA PET/MRI patients. For 21 lesions (diameter 6.4–12.3 mm) in total, the AC was quantified.

Results

For both radiotracers, the 9.7 mm sphere was still visible at 0.16 kBq/mL with emission times > 40 min. The 3.7 mm sphere was only detectable at 22 kBq/mL with emission times > 4 min. All spheres ≥ 6.5 mm provide acceptable quantification at an AC of 1.32 kBq/mL for 18F PET/MRI protocols of ≥ 12 min and 2.75 kBq/mL for 68Ga PET/MRI protocols. In phantom data, no halo artefact was observable and different SC methods had no impact on quantification. 4/6 18F-PSMA patients and 7/7 68Ga-PSMA patients showed a halo around the bladder using relative SC, which could be reduced in all patients using absolute SC. Comparing the minimum quantifiable AC (MQAC) from in the phantom study as a threshold to the patient data, all lesions provided acceptable quantification with values > MQAC (AC 3.3–108.5 kBq/mL) for equal reconstruction and acquisition parameters.

Conclusions

The results demonstrated that the detection of lesions in the sub-centimetre range and a reliable quantification of 18F/68Ga-PSMA uptake using standard acquisition and reconstruction parameters within clinical PET/MRI protocols is possible. This allows for an individual assessment of potential therapy options for each patient.