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Note 3 - Fair Value Measurements (Tables) | 12 Months Ended
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Dec. 31, 2023
Notes Tables |
Fair Value, Assets Measured on Recurring Basis [Table Text Block] |
|  |  |  |  |  | Fair Value Measurements Using |
|  |  |  |  |  | Quoted |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Prices in |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Active |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Markets |  |  | Significant |  |  |  |  |
|  |  |  |  |  | for |  |  | Other |  |  | Significant |
|  | Balance at |  |  | Identical |  |  | Observable |  |  | Unobservable |
|  | December |  |  | Items |  |  | Inputs |  |  | Inputs |
|  | 31, 2023 |  |  | (Level 1) |  |  | (Level 2) |  |  | (Level 3) |
Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restricted cash held as a certificate of deposit |  | $ | 476 |  |  | $ | 476 |  |  | $ | — |  |  | $ | — |
Liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrant liability |  | $ | 334 |  |  | $ | — |  |  | $ | — |  |  | $ | 334 |
|  |  |  |  |  | Fair Value Measurements Using |
|  |  |  |  |  | Quoted |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Prices in |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Active |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Markets |  |  | Significant |  |  |  |  |
|  |  |  |  |  | for |  |  | Other |  |  | Significant |
|  | Balance at |  |  | Identical |  |  | Observable |  |  | Unobservable |
|  | December |  |  | Items |  |  | Inputs |  |  | Inputs |
|  | 31, 2022 |  |  | (Level 1) |  |  | (Level 2) |  |  | (Level 3) |
Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restricted cash held as a certificate of deposit |  | $ | 484 |  |  | $ | 484 |  |  | $ | — |  |  | $ | — |
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] |
|  | November 2021 Warrants |  |  | November 2021 Warrants |  |  | July 2020, November 2021 & September 2022 Warrants |  |  | July 2020, November 2021 & September 2022 Warrants |  |  | May 2023 Warrants |
Measurement event |  | Reporting date |  |  | Stockholder approval |  |  | Amendment and Issuance |  |  | Stockholder Approval |  |  | Issuance |
Date |  | December 31, 2021 |  |  | January 31. 2022 |  |  | September 9, 2022 |  |  | November 10, 2022 |  |  | May 1, 2023 |
Total Value |  | 9.6 million |  |  | 7.5 million |  |  | 5.2 million |  |  | 1.9 million |  |  | 1.6 million |
Gain |  | not applicable |  |  | 2.1 million |  |  | not applicable |  |  | 3.4 million |  |  | not applicable |
Assumptions: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price |  | $ | 18.55 |  |  | $ | 18.55 |  |  | $ | 6.30 |  |  | $ | 6.30 |  |  |  | 1.30 |
Market price |  | $ | 13.18 |  |  | $ | 10.50 |  |  | $ | 6.29 |  |  | $ | 2.80 |  |  | $ | 0.72 | (a)
Volatility |  |  | 87 | % |  |  | 91 | % |  |  | 79.6 | % |  |  | 79.5 | % |  |  | 80.1 | %
Risk-free rate |  |  | 1.31 | % |  |  | 1.65 | % |  |  | 3.58 | - | 3.43 | % |  |  | 3.93 | - | 4.15 | % |  |  | 3.60 | - | 4.04 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | % |  |  | 0.0 | % |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 6.0 |  |  |  | 6.0 |  |  |  | 3.4 | - | 6.0 |  |  |  | 3.2 | – | 5.8 |  |  |  | 2.1 | - | 5.1 | %
|  | May 2023 Warrants |  |  | December 2023 Warrants |  |  | December 2023 Warrants |
Measurement event |  | Stockholder Approval |  |  | Issuance |  |  | Reporting Date |
Date |  | June 9, 2023 |  |  | December 21, 2023 |  |  | December 31, 2023 |
Total Value |  | $1.4 million |  |  | $0.4 million |  |  | $0.3 million |
Gain |  | $0.2 million |  |  | not applicable |  |  | $56 thousand |
Assumptions: |  |  |  |  |  |  |  |  |  |  |  |
Exercise price |  | $ | 1.30 |  |  | $ | 0.25 |  |  | $ | 0.25 |
Market price |  | $ | 0.68 |  |  | $ | 0.23 |  |  | $ | 0.20 |
Volatility |  |  | 77.6 | % |  |  | 79.3 | % |  |  | 79.3 | %
Risk-free rate |  |  | 3.92 | – | 4.59 | % |  |  | 3.88 | % |  |  | 3.85 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 2.0 | - | 5.0 |  |  |  | 5.5 |  |  |  | 5.5 |
|  | July 2020 & November 2021 Warrants |
Measurement event |  | Prior to amendment |  |  | After amendment |
Date |  | September 9, 2022 |  |  | September 9, 2022 |
Total Value |  | $3.3 million |  |  | $5.2 million |
Loss |  | not applicable |  |  | $1.9 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 18.55 - 57.75 |  |  | $ | 6.30 |
Market price |  | $ | 6.29 |  |  | $ | 6.29 |
Volatility |  |  | 79.6 | % |  |  | 79.6 | %
Risk-free rate |  |  | 3.43 | - | 3.58 | % |  |  | 3.43 | - | 3.58 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 0.7 | – | 5.4 |  |  |  | 3.4 | – | 6.0 |
|  | July 2020, November 2021, September 2022 & November 2022 Warrants |
Measurement event |  | Prior to amendment |  |  | After amendment |
Date |  | April 27, 2023 |  |  | April 27, 2023 |
Total Value |  | $0.3 million |  |  | $0.5 million |
Loss |  | not applicable |  |  | $0.2 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 6.30 |  |  | $ | 1.50 |
Market price |  | $0.72 | (a) |  | $0.72 | (a)
Volatility |  |  | 80.1 | % |  |  | 80.1 | %
Risk-free rate |  |  | 3.59 | - | 4.73 | % |  |  | 3.59 | – | 4.73 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 1.1 | – | 5.6 |  |  |  | 1.1 | – | 5.6 |
|  | May 2023 Warrants |
Measurement event |  | Prior to amendment |  |  | After amendment |
Date |  | December 21, 2023 |  |  | December 21, 2023 |
Total Value |  | $56 thousand |  |  | $0.2 million |
Loss |  | not applicable |  |  | $0.1 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 1.30 |  |  | $ | 0.25 |
Market price |  | $ | 0.23 |  |  | $ | 0.23 |
Volatility |  |  | 79.3 | % |  |  | 79.3 | %
Risk-free rate |  |  | 3.92 | – | 4.62 | % |  |  | 3.92 | – | 4.62 |
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 1.5 | – | 4.5 |  |  |  | 1.5 | – | 4.5 |
|  | Series B |  |  | Series B & C |
Measurement event |  | Prior to amendment |  |  | After amendment |  |  | Prior to amendment |  |  | After amendment |
Date |  | September 9, 2022 |  |  | September 9, 2022 |  |  | April 27, 2023 |  |  | April 27, 2023 |
Total value (b) |  | $6.9 million |  |  | $12.5 million |  |  | $9.6 million |  |  | $11.6 million |
Deemed dividend |  | not applicable |  |  | $5.7 million |  |  | not applicable |  |  | $2.0 million |
Assumptions: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price |  | $ | 14.00 |  |  | $ | 6.30 |  |  | $ | 6.30 |  |  | $ | 1.30 |
Market price |  | $ | 6.29 |  |  | $ | 6.29 |  |  | $0.72 | (a) |  | $0.72 | (a)
Volatility |  |  | 79.6 | % |  |  | 79.6 | % |  |  | 80.1 | % |  |  | 80.1 | %
Risk-free rate |  |  | 3.64 | % |  |  | 3.64 | % |  |  | 4.91 | % |  |  | 4.91 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | % |  |  | 0.0 | % |  |  | 0.0 | %
Term (in years) |  |  | 1.3 |  |  |  | 1.3 |  |  |  | 0.8 |  |  |  | 0.8 |
|  | Series B & C |
Measurement event |  | Prior to amendment |  |  | After amendment |
Date |  | December 21, 2023 |  |  | December 21, 2023 |
Total value (b) |  | $1.7 million |  |  | $6.8 million |
Deemed dividend |  | not applicable |  |  | $5.1 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 1.30 |  |  | $ | 0.25 |
Market price |  | $ | 0.23 |  |  | $ | 0.23 |
Volatility |  |  | 79.3 | % |  |  | 79.3 | %
Risk-free rate |  |  | 5.43 | % |  |  | 5.43 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 0.3 |  |  |  | 0.3 |
|  | Secured Convertible Notes derivative |  |  | Secured Convertible Notes derivative |
Measurement event |  | Issuance |  |  | Shareholder approval |
Date |  | April 27, 2023 |  |  | June 9, 2023 |
Total value (b) |  | $0.2 million |  |  | $0.2 million |
Gain |  | not applicable |  |  | $40 thousand |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 1.30 |  |  | $ | 1.30 |
Market price |  | $ | 0.72 | (a) |  | $ | 0.75 |
Volatility |  |  | 80.1 | % |  |  | 76.9 | %
Risk-free rate |  |  | 4.88 | % |  |  | 5.41 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 0.8 |  |  |  | 0.7 |

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- Definition Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique for each separate class of asset and liability measured on recurring and nonrecurring basis. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb) -SubTopic 10 -Topic 820 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
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- Definition Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
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